General Histology for Medicine is awesome

General Histology

Yekatit 12 Hospital Medical Collage
Prepared by:
Tsegaye M.(BSc, MSc, Ass. professor of Human Anatomy)

1
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Objectives
At the end of this session students will be able to
Define histology
Describe microscopy
Function
Types
Parts
Using (focusing)
List histological Techniques
List dawn component of cell

2 Tsegaye Mehare(BSc, MSc, Ass. professor of Human Anatomy)

Introduction to histology
The study of cells and tissues of the body and how
these are arranged to constitute organs.

Named because most tissues are webs of
interwoven cells, filaments and fibers, both cellular
& noncellular.
Histology involves all aspects of tissue biology, with
the focus on how cells' structure and arrangement
optimize functions specific to each organ.

Cont.…..
Tissues are made of two interacting components: cells
and intercellular substance called extracellular matrix
(ECM).

The ECM consists of many kinds of molecules, most of
which are highly organized and form complex
structures, such as collagen fibrils and basement membranes.

The main functions once attributed to the ECM were
I.Furnish mechanical support for the cells
II.Transport nutrients to the cells
III. Carry away catabolites and secretory products.

4
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
Although the cells produce the ECM, they are also influenced
and sometimes controlled by molecules of the matrix, thus,
there is an intense interaction between cells and matrix.

The small size of cells and matrix components makes histology
dependent on the use of microscopes.

This chapter reviews several of the more common methods
used to study cells and tissues and the principles involved in
these methods
5
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Introduction to MICROSCOPE
“Micro”- means very small
“Scope”- means to look at
The Microscope:
•is an optical instrument that uses a lens or a
combination of lenses to magnify and resolve the
fine details of an object.
•Microscopy is the science of investigating small
objects using microscopes.
•Microscopic means invisible to the eye unless
aided by a microscope.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

History
Many scholars contributed to the invention of
microscopes

The Greeks & Romans used “lenses” to magnify
objects over 1000 years ago

The first microscope was huge and 6 feet long!!!

7
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

History….
•Hans and Zacharias Janssen of Holland
created the “first” compound
microscope
Zacharias Jansen
1588-1631
The “First” Microscope
8
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

History….
•Anthony van Leeuwenhoek and Robert
Hooke made improvements by working on
the lenses.

Anthony van Leeuwenhoek
1632-1723
Robert Hooke
1635-1703
Hooke
Microscope
9
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Types of microscopes
1.Based on what interacts with the
sample/object to generate the image:
a. Light (optical) microscopes
b. Electrons (electron) microscopes:
SEM and TEM

2. Based on their capacity to analyze the
sample via a scanning point:
a. confocal optical microscopes
b. scanning electron microscopes
10
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
3. Based on the ability to analyze the sample all at
once:
a. Wide field optical microscope
b. Transmission electron microscopes
Light Microscopy
a. Simple Microscope: has only one lens
e.g. Hand lens
b. Compound Microscope:
– has two or more lenses
e.g. Cpd. Light Microscope
(what we use most often)
11
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
1.Simple
Microscope
•Similar to a
magnifying glass and
has only one lens
e.g. hand lens

12
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
2. Compound
Light Microscope
•Lets light pass
through an
object and then
through two or
more lenses.

13
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Components and light path of a bright-field compound light
microscope.
14
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
Parts of a Compound LM
I. Optical System
II. Mechanical System
I. Optical/Lens System
a. Illuminator: artificial light, usually supplied by a light bulb,
to illuminate the specimen.
•Transmitted Illumination: when the light is directed up
through the specimen from the base.
•Vertical or Reflected Illumination: when the light comes
from above and reflects off the specimen.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
B. Condenser: lens system under the microscope stage that
collects and focuses the illumination to produce a cone of
light that focuses onto the specimen.
C. Objective Lens:
The lens closest to the specimen; usually several objectives
are mounted on a revolving nosepiece.
Enlarges and projects the illuminated image of the object in
the direction of the ocular lens.
D. Eyepiece or Ocular Lens:
The lens closest to the eye which further magnifies this
image and projects it into the viewer’s retina or a
photographic plate.

16
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
Compound microscope can be divided into two
based on the number of eyepiece lens
I.Monocular: a microscope having only one
eyepiece.
II.Binocular: a microscope having two eyepieces.
•has of a beam splitter in the body tube

17
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
Mechanical parts:
•Body tube
•Revolving nose piece
•Arm
•Coarse and fine adjustments
•Stage and stage clips
•Mirror or electrical lamp
•Metal base
•Metal bar
•Movable(rack) frame of objective lenses

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Eyepiece
Body Tube
Revolving Nosepiece
Arm
Objective Lens
Stage
Stage Clips
Coarse Focus
Fine Focus
Base
Diaphragm
Light
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

1. Eye piece (ocular lens)
•is the top part of
the microscope
•is the lens you
look through to
see your specimen
•Magnifies the
specimen image

20
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

•Eyepiece
Lense
•Usually has a
power of 10x
maginification

21
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

2. Body Tube
•Connects the
eyepiece to the
objective
lenses
•Holds the
objective
lenses and the
ocular lens at
the proper
distance
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

3. Revolving Nose Piece /Turret
•holds the objective lenses and can be
turned or rotated to change the
magnification
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

4. Objective Lenses
•The Objective Lenses increase
magnification (usually from 4x to 100x)
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

- Most microscopes have
2, 3, 4, or more lenses
that magnify at different
powers
- Always start with the
lowest power and work
your way up to the
strongest when
examining a specimen.
- The shortest objective is
usually the lowest
power

25
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

5. Stage
•Is where the sample slide or specimen is placed
for examination.

26
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

6. Stage Clips
•These are usually two clips hold the slide or
specimen in place on the stage
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

7. Iris-Diaphragm
•Is what allows you to control the amount
of light on the specimen/slide that comes
through the stage (through the aperture).
Turn to let more
light in or to make
dimmer
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

8. Aperture
•is the hole in
the stage that
allows light to
pass through
for better
viewing of the
specimen
29
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

9. Light Source
•Projects light upwards through the diaphragm,
the specimen and the lenses
•It can be a bulb or a mirror, and is usually
found near the base of the microscope shining
up through the stage.
•light source (110 volts)
Light
source
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

10.Coarse Adjustment Knob
•Moves the stage up and down (quickly) for
focusing your image roughly
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Coarse adjustment
•Is the larger of the two
knobs on the side of a
microscope
•Is used to focus on the
specimen; it may move
either the stage or the
upper part of the
microscope (in a relative
up and down motion).
•Always focus with the
coarse knob first.

CA
32
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

11. Fine Adjustment Knob
•Is the smaller round knob on the side of the
microscope used to fine-tune the focus of your
specimen after using the coarse adjustment knob
•This knob moves the stage SLIGHTLY to sharpen the
image
33
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

12. Arm
•Used to support the microscope when carried.
•Holds the body tube, nose piece and the
objectives
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

13. Base
•Supports and carry the microscope
•The bottom, or foot of the microscope, used
for support
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Body Tube
Nose Piece
Objective
Lenses
Stage
Clips
Diaphragm
Light Source
Ocular Lens
Arm
Stage
Coarse Adj.
Fine Adjustment
Base
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
Function (quality) of microscopes
A.Magnification: apparent enlargement of an object.
e.g. a magnification of "100x" means that the image is
100 times bigger than the actual object.

B. Resolution: clarity, sharpness of a microscope to show
two very close points separately.
 Defines how easily you can define two adjacent
objects from each other & is adjusted by the aperture
of the objective lens.

37
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
Magnification
It is the increase in the linear dimensions of an object
without resulting in any optical defects.

Calculated as the ratio between one parameter of the
image and its corresponding parameter in the object.

Total Magnification= Eyepiece Lens X Objective Lens

38
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
Total magnification of an object seen with the L.M.=
magnifying power of eyepice X magnifying power of objective.
Ocular 10x Objective 40x:10 x 40 = 400
Objective Lens have
their magnification
written on them
Ocular lenses usually
magnifies by 10x
So the image is 400 times “larger" than the object
39
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
Resolution
It is the power of the microscope to distinguish
fine details
The magnification is valued only when
accompanied by high resolution.
Limit of resolution:
The shortest distance between two details below
which they appear as one. or
The smallest diameter of an object below which it
can not be seen at all with the microscope.

The power of resolution therefore increases as the limit of
resolution decreases.

Cont.…

Numerical Aperture (NA) of a lens : It is a measure of the
amount of light entering the lens.
Factors affecting Resolving power of LM
–Numerical aperture (N.A.) of the objective lenses.
–Objective lenses magnification
–Wave length of the light used λ

Quality of the image – its clarity and richness of detail depends
on the microscope’s resolving power.
Maximal resolving power of the L.M. is around 0.2 um. This
permits good images magnified 1000-1500 times.
Objects smaller or thinner than 0.2µm (such as a
ribosome, a membrane, or actin filament) cannot be
distinguished with this instrument.

41
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.….
Likewise, two objects such as mitochondria will be
seen as only one object if they are separated by less
than 0.2µm.
The resolving power of a microscope depends mainly
on the quality of its objective lens.
The eyepiece lens enlarges only the image obtained by
the objective; it does not improve resolution.
For this reason, when comparing objectives of
different magnifications, those that provide higher
magnification also have higher resolving power.

42
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Factors affecting limit of resolution:
- It is directly proportional to wave
length of the light used (λ) and
- indirectly proportional to the
numerical aperture (NA) of the
objective lens.
K= Constant =0.61
L.r.= K X λ ⁄ NA
Cont.….
43
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…
 The light microscope can not distinguish two
close details unless they are at least 0.2 µm
apart and can not distinguish any structure
less than 0.2 µm in diameter.
- i.e. L.r. of light microscope is 0.2 µm

The limit of resolution of the human eye is 0.1mm
(100 µm).
44
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cont.…

•1 mm = 1000 µm
•1 um = 1000 nm The minimum useful magnification:
An object will be clearly seen in the light
microscope only when it has been magnified to
reach the limit of resolution of the eye.
Q. For an object to bee seen under a light
microscope it should be magnified at least to the
size of _______µm.

45
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

How a Microscope Works
Convex Lenses are
curved glass used to
make microscopes
(and glasses etc.)
Convex Lenses
bend light and
focus it in one
spot.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

How a light microscope Works
Ocular Lens
(Magnifies
Image)
Objective Lens
(Gathers Light,
Magnifies
And Focuses
Image Inside
Body Tube)
Body Tube
(Image
Focuses)
•Bending Light: The objective (bottom) convex lens
magnifies and focuses (bends) the image inside the
body tube and the ocular convex (top) lens of a
microscope magnifies it (again)
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Components
and light path
of a bright-field
microscope.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Tissue appearance with bright-field light
Microscope: collagen fibers appear red, along with
thin dark elastic fibers and cell nuclei
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

•Place slide on stage making sure
object to be viewed is centered over
the hole in the stage.
•Use Stage Clips
•Click Nosepiece to the lowest
(shortest) setting
•Look into the Eyepiece
•Use the Coarse Focus
•Don’t use the coarse adjustment
knob on high magnification…you’ll
break the slide!!!
•Use the fine Focus
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Four adjustments to be made when using a
microscope
Focus – adjust if the
image is blurry or
well defined by
using the focus
knobs
Brightness – controls
how light or dark the
image is using the
illumination

Resolution – defines how
easily you can define two
adjacent objects from
each other and is
adjusted by the aperture
of the objective lens
Contrast – which is the
difference in lighting
between two areas
- This can be adjusted by
changing the intensity of
the light and the pinhole
aperture.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

•Follow steps to focus using low power
•Click the nosepiece to the longest objective
•Do NOT use the Coarse Focusing Knob
•Use the Fine Focus Knob to bring the slide
What can you find on your
slide? 52
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

3. Electron Microscopes
•They are based on the
interaction of electrons &
tissue components
•There are two types: Scanning
and transmission E.M.
•Uses a magnetic field to bend
beams of electrons; instead of
using lenses to bend beams of
light.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Electron Microscopy
•The wavelength in the electron beam is much shorter
than of light, allowing a 1000-fold increase in resolution.
Transmission Electron Microscopy (TEM)
•TEM is an imaging system that permits resolution
around 3 nm.
•This high resolution allows magnifications of up to
400,000 times to be viewed with details.
•Unfortunately, this level of magnification applies only to
isolated molecules or particles.
•Very thin tissue sections can be observed with details at
magnifications of up to about 120,000 times.
54
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Scanning Electron Microscopy (SEM)
•SEM permits pseudo–three-dimensional views of
the surfaces of cells, tissues, and organs.

•Like the TEM this microscope produces and
focuses a very narrow beam of electrons, but in
this instrument the beam does not pass through
the specimen.

•Instead the surface of the specimen is first dried
and coated with a very thin layer of metal atoms
through which electrons do not pass readily.

55
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

SEM….
• When the beam is scanned from point to
point across the specimen it interacts with the
metal atoms and produces reflected electrons
or secondary electrons emitted from the
metal.
•These are captured by a detector and the
resulting signal is processed to produce a
black-and-white image on a monitor.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

E.M. L.M.
High resolving power (1) Resolving power improves with
shortening of light wave length
Minimal useful magnification
400,000 (T.E.M.)
(2) Maximum magnification=1500
ultrathin sections (50nm) (3)Thin sections (3-6µm)
Glass or diamond knives (4) Microtome metal knives
5nm (Scanning E.M.), 3nm (T.E.M.) (11) Resolution limit 0.20 - 0.24µm
Use fixed and sectioned or
metal coated specimen
(12) Living and prepared specimen
with inherent and applied fluorescent
properties
57
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Microtechniques

It is the preparation of tissues or organs to be ready for
microscopic examination
Four different approaches for microtechniques
1-Fresh preparation e.g., smear (blood, sperm, cheek
cell), connective tissue spread.
2-Fixed preparation e.g., paraffin, celloidin
3-Frozen preparation e.g., frozen section
4-Special techniques e.g., tissue culture, cell fractionation
, radioautography and in situ hybridization.

Gross specimen examination
59
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Main steps of fixed preparation techniques
1-Fixation: using fixatives e.g., 10 % Formalin, Bouin, Sausa,
Zenker.
2-Dehydration: by using different ascending concentration
of alcohol (gradual dehydration) to prevent shrinkage of
tissue. 3-Clearing: in xylol/xylene or benzene.
4-Embedding: in paraffin or celloidin.
5-Sectioning: Cutting by microtome and spreading on hot
plate.
6-Paraffin removal: by using xylol/xylene
7-Rehydration: by using descending concentration of
alcohol.
8-Staining: by using the suitable stains
9-Dehydration, Clearing in xylol, Mounting in Canada
balsam or DPX & Covering by cover slip.

60
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

61
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

62
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

CELL STRUCTURE AND FUNCTION
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

•Definition of cell
•Components of cellular organism
•Anatomical division of cell
•What is cell membrane & its structural components
• What is cytoplasm & its structural components
•What is nucleus & its structural components

64
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

65
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

CELLS

 Cells are the basic structural and functional unit of the
living organism showing a variety of functional
specializations which perform all the activities necessary
for the survival, growth and reproduction of the
organism.

Cells are the smallest entities capable of independent
life.

66
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Activity 1:
1. Enumerate as many human body cells as you can.

Cells are diverse in
Number (around 100 trillion (10
12
) cells
Type (more than 250 named cell types)
Shape (round, oval, columnar, multipolar, polygonal,
cylindrical, fusiform, pyramidal, pyriform, etc.)
Size (3µm - 120µm in diameter)
Function

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

a. A micrograph of ovarian cortex shows several primordial follicles (PF) and their
flattened follicles cells (arrows), and two unilaminar primary follicles (UF) in which
the follicles cells or granulosa cells (G) form a single cuboidal layer around the large
primary oocyte (O). Micrograph b was taken at the same magnification and shows a
larger multilayered primary follicle. Granulosa cells (G) have now proliferated to
form several layers.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

72
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

250
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

74
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cellular Functions Specialized Cell(s)
1.Movement Muscle & other contractile cells
2. Form adhesive and tight junctions
between cells to form membranes
Epithelial cells
3. Synthesize & secrete components of the
ECM
Fibroblasts, cells of bone and
cartilage
4. Convert physical & chemical stimuli into
action potentials
Neurons and sensory cells
5. Synthesis & secretion of enzymes Cells of digestive glands
6. Synthesis & secretion of mucous
substances
Mucous-gland cells, goblet cells
7. Synthesis & secretion of steroids adrenal cortex, testis, & ovary
8. Ion transport
Cells of the kidney & salivary gland
ducts, stomach parietal cells
9. Intracellular digestion Macrophages & some WBC
10. Lipid storage Fat cells
11. Metabolite absorption Cells lining the intestine 75
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Organization of the Cell
•A typical cell, as seen by the light microscope has two major
parts: the nucleus and cytoplasm.

•Nucleus is separated from cytoplasm by a nuclear
membrane, and cytoplasm is separated from the
extracellular environment by a cell membrane, also called
the plasma membrane.
•Different substances that make up the cell are collectively
called protoplasm.

•Protoplasm is composed mainly of six basic substances:
water, electrolytes (ions), proteins, lipids, carbohydrates,
and nucleic acids.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PROTOPLASM
nucleus
Cytoplasm
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Water
Is the principal fluid medium of the cell, present in
most cells, except for fat cells, in a concentration of 70
to 85%.

many cellular chemicals are dissolved in the water.
Others are suspended in the water as solid
particulates.

Chemical reactions take place among the dissolved
chemicals or at the surfaces of the suspended particles
or membranes.

78
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Ions
Most important ions in the cell are potassium,
magnesium, phosphate, sulfate, bicarbonate, and
smaller quantities of sodium, chloride, and calcium.
Ions provide inorganic chemicals for cellular reactions.
Necessary for operation of some of the cellular
control mechanisms.
For instance, ions acting at the cell membrane are
required for transmission of electrochemical impulses
in nerve and muscle fibers.

79
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Proteins

After water, the most abundant substances in most
cells are proteins, which normally constitute 10 to
20% of the cell mass. These can be divided into two
types: structural proteins and functional proteins.

Structural proteins:
They are present in the cell mainly in the form of
long filaments that themselves are polymers of many
individual protein molecules.

80
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Structural protein….
Prominent use of such intracellular filaments is to form
microtubules that provide the "cytoskeletons" of such
cellular organelles as cilia, nerve axons, the mitotic
spindles of mitosing cells, and a tangled mass of thin
filamentous tubules that hold the parts of the cytoplasm
and nucleoplasm together in their respective
compartments.

Extracellularly, fibrillar proteins are found especially in
the collagen and elastin fibers of connective tissue and in
blood vessel walls, tendons, ligaments, and so forth.

81
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Functional proteins
• They are an entirely different type of protein, usually
composed of combinations of a few molecules in
tubular-globular form.

•Mainly the enzymes of the cell and, in contrast to the
fibrillar proteins, are often mobile in the cell fluid.

•Many of them are adherent to membranous structures
inside the cell.

82
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Functional proteins….
Enzymes come into direct contact with other
substances in the cell fluid and thereby catalyze
specific intracellular chemical reactions.

For instance, the chemical reactions that split glucose
into its component parts and then combine these
with oxygen to form carbon dioxide and water while
simultaneously providing energy for cellular function
are all catalyzed by a series of protein enzymes.

83
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Lipids
Lipids are several types of substances that are grouped
together because of their common property of being
soluble in fat solvents.

Especially important lipids are phospholipids and
cholesterol, which together constitute only about 2% of
the total cell mass.

The significance of phospholipids and cholesterol is
that they are mainly insoluble in water and, therefore,
are used to form the cell membrane and intracellular
membrane barriers that separate the different cell
compartments.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Lipids….
In addition to phospholipids and cholesterol, some
cells contain large quantities of triglycerides, also
called neutral fat.

In the fat cells, triglycerides often account for as much
as 95% of the cell mass.

Fat stored in these cells represents the body's main
storehouse of energy-giving nutrients that can later be
dissoluted and used to provide energy wherever in
the body it is needed.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Carbohydrates
Have little structural function in the cell except as parts of
glycoprotein molecules, but they play a major role in
nutrition of the cell.

Most human cells do not maintain large stores of
carbohydrates; the amount usually averages about
1% of
their total mass but increases to as much as 3% in muscle
cells and, occasionally, 6% in liver cells.

However, carbohydrate in the form of dissolved
glucose is always present in the surrounding
extracellular fluid so that it is readily available to the
cell.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Carbohydrates ….
Small amount of carbohydrate is virtually always
stored in the cells in the form of glycogen, which is an
insoluble polymer of glucose that can be
depolymerized and used rapidly to supply the cells'
energy needs.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Physical structure of cell

 Cell is not merely a bag of fluid, enzymes, and
chemicals; it also contains highly organized physical
structures, called intracellular organelles, cytoskeletal
elements, and cytoplasmic inclusions.

The physical nature of each organelle is as important
as the cell's chemical constituents for cell function.

For instance, without one of the organelles, the
mitochondria, more than 95% of the cell's energy
release from nutrients would cease immediately.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Parts of cell as seen by EM
1. Plasma membrane/
Plasmalemma – outer
limiting membrane
that serves as a
selective barrier

2. Cytoplasm –
protoplasm outside of
the nucleus which
contains different
organelles and
inclusions of the cells

3. Nucleus – contains the
genetic material of
cell
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Human Anatomy)

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Plasma membrane
Also known as the plasmalemma or cell membrane
About 7.5 nm thick, & exhibits a trilaminar structure
(called the unit membrane) under transmission EM
microscope.

Envelope the cell & aids in maintaining its structural &
functional integrity

Both plasma membrane and other membranes of the
different organelles are composed of a lipid bilayer &
associated proteins &carbohydrates (Oligosaccharide
chains).

PM….
 Functions as a semi-permeable membrane between
cytoplasm and extracellular environment

Also a sensory device that permits the cell to recognize
(and recognized by) other cells and macromolecules

Composed of an inner leaflet (facing the
cytoplasm)and an outer leaflet (facing the
extracellular mellu).

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
Ultrastucture of PM
Pertains to the outer
trilaminar-appearing
membrane surrounding
the cell.

A phospholipid bilayer
about 7.5nm thick

A selective barrier that
regulates the entrance
and exit of substances
into and out of the cell.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
Fluid mosaic model of plasma membrane
A.Lipid Bilayer
Is freely permeable to small nonpolar lipid-soluble
molecules but is impermeable to charged ions.
a. Molecular structure of lipid bilayer
is composed of phospholipids, glycolipids, & cholesterol
1. Phospholipids (60-70% of the membrane lipids)
Are amphipathic, meaning that they possess a polar
(hydrophilic) head and two nonpolar (hydrophobic) fatty
acid tails.
Polar head of each phospholipid molecule faces membrane
surface, where as the two hydrophobic tails projects into
the interior of the membrane.

Model of Plasma membrane
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
Consist of a bilayer of
phospholipid molecules
which are amphipathic i.e.
have a polar hydrophilic
head and two non-polar
hydrophobic fatty acid
tails
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
 Polar head consists of nitrogenous cpd, phosphate
bridge, & glycerol.
Four types of phospholipids: phosphatidylcholine
(lecithin), phosphatidylserine, phosphatidylethanol amine
(cephalin), and sphingomyelin.

Lipid composition of each half of the bilayer is different (i.e.
the two leaflets are asymmetrical).
For example, in RBC (erythrocytes), phosphatidylcholine
and sphingomyelin are more abundant in the outer leaflet,
whereas phosphatidylserine and phosphatidylethanol
amine are more concentrated in the inner leaflet.
Tails of the phospholipids in the inner and outer leaflets
form weak bonds that attach the leaflets to one another.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
B. Glycolipids & other lipids (5-10%)
Are about one tenth of the membrane lipid
molecules.
Present in the outer leaflet only and thus, contribute
to lipid asymmetry.

Have polar carbohydrate residues containing
oligosaccharide chains (their "glyco" portions) which
invariably protrude to the outside of the cell, dangling
outward from the cell surface into the extracellular
space, forming part of the glycocalyx.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
C. Cholesterol (20-30%)
Found in both leaflets of the plasma membrane
Assists in maintaining the structural integrity of the plasma
membrane.
Its steroid nucleus is highly fat soluble & are dissolved in
the bilayer of membrane.
Its amount determines the fluidity of the membrane, high
cholesterol content decrease its fluidity.
Mainly help determine the degree of permeability (or
impermeability) of the bilayer to water-soluble
constituents of body fluids.
Cholesterol controls much of the fluidity of the membrane
as well.

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Human Anatomy)

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cholesterol
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
2. Membrane Proteins
Are the molecular and functional components of
membranes (~50% w/w in the plasma membrane)

Synthesized in the rough endoplasm reticulum, are
modified and completed in the Golgi apparatus, and
transported in vesicles to the cell surface.

Function as transport proteins (ion channels or
carriers proteins that bind ions and other molecules),
enzymes, or receptors (for hormones, drugs, etc)
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Human Anatomy)

PM….
Membrane Proteins can be divided into two groups:
I. Integral proteins- directly incorporated within the lipid
bilayer itself
II. peripheral proteins- which exhibit a looser association with
one of the two membrane surfaces.
Some integral proteins span the membrane one or more
times, from one side to the other and ccordingly, they are
called one-pass or multipass transmembrane proteins.
Loosely bound peripheral proteins can be easily extracted from
cell membranes with inorganic salt solutions, whereas integral
proteins can be extracted only by drastic methods using
detergents to disrupt the lipids.

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Human Anatomy)

PM….
Many integral and peripheral proteins that function as
components of large enzyme complexes are located in
specialized patches of membrane having higher
concentrations of cholesterol.
Within these regions called lipid rafts membrane fluidity is
reduced, allowing the associated proteins to remain in closer
proximity and interact more efficiently.

Some transport proteins are simple aqueous ion channels,
though many of these have special features that make them
effective for a given substance such as Ca
2+
or, in the case of
aquaporins, for water.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
 Many transport proteins are continuously open, but
the rate at which they transport ions can be varied; that
is, they are gated.

Some are gated by alterations in membrane potential
(voltage-gated), whereas others are opened or closed
when they bind a ligand (ligand-gated).

Ligand is often external (eg, a neurotransmitter or a
hormone) however, it can also be internal; intracellular
Ca
2+
, cAMP, lipids, or one of the G proteins produced in
cells can bind directly to channels and activate them.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
Some channels are also opened by mechanical stretch, and
these mechanosensitive channels play an important role in
cell movement.
Typical voltage-gated channels are the Na
+
& Ca
2+
channels,
and a typical ligand-gated channel is the acetylcholine
receptor.

Other transport proteins are carriers that bind ions and
other molecules and then change their configuration,
moving the bound molecule from one side of the cell
membrane to the other.
Molecules move from areas of high concentration to areas
of low concentration (down their chemical gradient), &
cations move to negatively charged areas whereas anions
move to positively charged areas (down their electrical
gradient).

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Human Anatomy)

PM….
When carrier proteins move substances in the direction of their
chemical or electrical gradients, no energy input is required and
the process is called facilitated diffusion.

A typical example is glucose transport by the glucose transporter,
which moves glucose down its concentration gradient from the
ECF to the cytoplasm of the cell.
Other carriers transport substances against their electrical and
chemical gradients. This form of transport requires energy and is
called active transport.

In animal cells, the energy is provided almost exclusively by
hydrolysis of ATP. Not surprisingly, therefore, the carrier
molecules are ATPases, enzymes that catalyze the hydrolysis of
ATP.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
One of these ATPases is sodium–potassium-activated
adenosine triphosphatase (Na
+
–K
+
ATPase), which is
also known as the Na
+
–K
+
pump.

There are also H
+
–K
+
ATPases in the gastric mucosa and
the renal tubules.

Ca
2+
ATPase pumps Ca
2+
out of cells. Proton ATPases acidify many intracellular organelles,
including parts of the Golgi complex and lysosomes.

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Human Anatomy)

PM….
Some of the transport proteins are called uniports,
because they transport only one substance.

Others are called symports, because transport requires
the binding of more than one substance to the transport
protein and the substances are transported across the
membrane together.

An example is the symport in the intestinal mucosa that
is responsible for the cotransport by facilitated diffusion
of Na
+
and glucose from the intestinal lumen into
mucosal cells.

Other transporters are called antiports because they
exchange one substance for another.

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Human Anatomy)

PM….
 As with lipids, the distribution of membrane proteins
is different in the two surfaces of the cell membranes.
Therefore, all membranes in the cell are asymmetric.
3. Oligosaccharide chains
They are on the external surface of the plasmalemma
form the carbohydrate moieties of the glycoproteins
and glycolipids.
•Important components of specific molecules called
receptors that participate in important interactions
such as cell adhesion, recognition, and response to
protein hormones.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

“Fluid Mosaic Model”

Membrane proteins are
globular and float like
iceberg in a sea of lipid
The more acceptable
model
Explains that membrane
is in a dynamic state
PM….
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Fluidity of lipid bilayer
Crucial to such cellular activities as exocytosis,
endocytosis, membrane trafficking (flip-flop), &
membrane biogenesis.

Increased by a rise in temperature and by greater
unsaturation of the hydrocarbon (fatty acyl) tails.

Decreased by an increase in the membrane’s
cholesterol content.

PM….

PM…..
Support of the cell membrane
Strengthened and supported by framework of proteins (such
as spectrin, actin & other attachment proteins) attached to
membrane via transmembrane proteins
Spectrin
Actin in
junctional
complex
attachment proteins
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Human Anatomy)

PM….
Glycocalyx (sugarcoat)
Are glycoprotein & glycolipid
polysaccharides covering of the
external surface of the cell
membrane.
Sometimes wrongly named cell
coat.
Found on the external
surface/leaflet only
Imparts a special identity to each
cell type, therefore, plays an
important role in histocompatibility
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Glycocalyx
Electron micrograph of the apical region of an intestinal epithelial cell. An
extracellular cell coat (glycocalyx) is bound to the plasmalemma of the microvilli.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
Functions of glycocalyx
1.Glycocalyx protects cell surface from mechanical and
chemical damage also lubricates surface (by adsorbing
water).
2.Aiding in cellular attachment to extracellular matrix.
3.Binding of antigens and enzymes to the cell surface.
4.The glycocalyx of some cells attaches to the glycocalyx of
other cells, thus attaching cells to one another (Facilitating
cell-to-cell recognition & interaction e.g. sperm-egg
adhesion)
5.Many of them have a negative electrical charge, which gives
most cells an overall negative surface charge that repels
other negative objects.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

PM….
6. Many of the carbohydrates act as receptor substances for
binding hormones, such as insulin; when bound, this
combination activates attached internal proteins that, in turn,
activate a cascade of intracellular enzymes.
7. Some carbohydrate moieties enter into immune reactions.
Major functions of plasma membrane
1.Serves as a barrier, while maintaining integrity of cell contents,
2.Allows for selective transport of molecules across it…into and
out of cell for purpose of ingestion and excretion and allowing
important electrolytes in and out.
3.Play a major role in cell to cell communication as receptors are
bound externally here on hormones and specialized white blood
cells etc.

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Human Anatomy)

What permeates membrane easily?
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Size of Hydrated Ions and Other Substances of Biological Interest.
Substance Atomic or Molecular
Weight
Radius (nm)
Cl
-
35 0.12
K
+
39 0.12
H
2O 18 0.12
Ca
2+
40 0.15
Na
+
23 0.18
Urea 60 0.23
Li
+
7 0.24
Glucose 180 0.38
Sucrose 342 0.48
Inulin 5000 0.75
Albumin 69,000 7.50
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Human Anatomy)

PM….
FUNCTIONS OF CELL SURFACE

1. Filtration barrier
2. Receptor site for
hormones & enzymes
3. Cell recognition
(GLYCOCALYX)
4. Transport across the cell
membrane (diffusion of
gases, endocytosis,
exocytosis, etc)

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Human Anatomy)

PHAGOCYTOSIS
EXOCYTOSIS
PINOCYTOSIS
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Endocytosis
Is a process in which cell takes in material from the
extracellular fluid using dynamic movements and fusion of
cell membrane to form cytoplasmic, membrane-enclosed
structures containing the material.

Such cytoplasmic structures formed during endocytosis fall
into the general category of vesicles or vacuoles.

Endocytosis occurs as:
(a): Phagocytosis involves the extension from cell of large folds
called pseudopodia which engulf large particles, for example
bacteria, and then internalize this material into a cytoplasmic
vacuole or phagosome.
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Human Anatomy)

Endocytosis….
(b): In pinocytosis the cell membrane invaginates (dimples
inward) to form a pit containing a drop of small particles
in solution. The pit pinches off inside the cell when the
cell membrane fuses and forms a pinocytotic vesicle
containing the fluid.

(c): Receptor-mediated endocytosis includes membrane
proteins called receptors which bind specific molecules
(ligands).
When many such receptors are bound by their ligands,
they aggregate in one membrane region which then
invaginates and pinches off to create vesicle or endosome
containing both the receptors and the bound ligands.

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Human Anatomy)

Exocytosis
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Human Anatomy)

Components of the cell
lysosome
mitochondrion
peroxisome
Golgi
apparatus
endoplasmic
reticulum
nuclear
envelope
vesicle
cytosol
plasma
membrane
nucleus
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Human Anatomy)

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Liver cells (hepatocytes) with large, well-stained nuclei
located in the center of the cytoplasm
nucleus
Cytoplasm
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Body fluids
Extracellular Fluid-The "Internal Environment"
About 60% of the adult human body is fluid, mainly a
water solution of ions and other substances.

Although most of this fluid is inside the cells and is
called intracellular fluid, about one third is in spaces
outside the cells and is called extracellular fluid.

Extracellular fluid is in constant motion throughout the
body, also called internal environment of the body, or
milieu intérieur.
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Human Anatomy)

Body fluids….
Cells are capable of living, growing, and performing
their special functions as long as the proper
concentrations of oxygen, glucose, different ions,
amino acids, fatty substances, and other constituents
are available in this internal environment.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Body fluids….
Differences Between Extracellular and Intracellular Fluids
Intracellular fluid differs significantly from the extracellular fluid
by containing large amounts of
K
+
, Mg
2+
& PO
4
-3 ions instead of the Na
+
& Cl
-
ions found in the
extracellular fluid.
Special mechanisms for transporting ions through the cell membranes
maintain the ion concentration differences between extracellular and
intracellular fluids.
Extracellular fluid contains large amounts of
Na
+
, Cl
-
& bicarbonate ions plus nutrients for the cells, such as oxygen,
glucose, fatty acids, & amino acids.
 Carbon dioxide that is being transported from cells to lungs to be
excreted, plus other cellular waste products that are being transported to
kidneys for excretion.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Objectives
At the end of this session students will be able to :
Define cytoplasm, contents of cytoplasm?
Describe nucleus
List dawn types of human tissue
 List dawn specific characteristics of each tissue
Enumerate division of epithelial tissue

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cytoplasm
Cytoplasm is composed of:
1- ORGANELLES: Specialized
structures, ESSENTIAL for vital
processes of the cell.
2- Inclusions: They are not
essential for vitality of cells,
may be present or absent.
Examples are lipids, glycogen
and pigments like melanin.
3.Cytoskeleton (microtubules,
intermediate filaments and
microfilaments).
4.Cytosol: fluid portion 136
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cytoplasm….
Cytosol
•Cell contents excluding organelles
•Largest single compartment in
most cells
•Viscous aqueous solution (gel) due
to concentration of large and
small molecules
•Site of many chemical reactions
 initial stages in metabolic
breakdown of nutrients
 protein manufacture - ribosomes
Adapted from ECB Fig 1-24
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cytoplasm….
1.Ribosomes
2. Endoplasmic
reticulum: RER & SER
3. Mitochondria
4. Golgi Complex
5. Lysosomes
6. Peroxisomes(microbodies)
7. Centrioles /centrosome
8. Coated vesicles
9. Annulate lamellae

Cytoplasmic organelles
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cytoplasm….
•
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cytoplasm….

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Ribosome
12 nm wide & 25 nm long
Contain ribosomal RNA( rRNA) and several ribosomal
proteins
Function
 Are site of protein synthesis( mRNA is translated in to
protein)
Found in 2 forms
I. Free Ribosomes
Float in the cytosol; have no attachments to other
organelles
Synthesize proteins for use inside the cell

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Human Anatomy)

.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

II. Attached Ribosomes
Attached to endoplasmic reticulum( rough) or outer nuclear
membrane
Involved in the synthesis of proteins intended for insertion in
the plasma membrane or for export from the cell.

Endoplasmic reticulum(ER)
Consist of an anastomosing network of
intercommunicating channels and sacs formed by a
continuous membrane
Is a network of membranes in the form of sacs or tubules
Continuous with outer nuclear membrane.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Function
Provides surface area for chemical reaction
Transportation of cellular products from one portion of cell to
another portion.
Based on its association with ribosome's, the ER is
divided in to 2 types
Rough (granular)Endoplasmic Reticulum(RER)
Is continuous with the nuclear membrane and usually is folded
in to a series of flattened sacs
is the site where proteins are synthesized
has receptors( ribophorins) in its membrane to which the large
ribosomal subunits binds
Delivery of the packaged protein: the packaged proteins are
pinched off from the rough endoplasmic reticulum, and then
travel through the cytoplasm as transfer vesicles to fuse with
the Golgi apparatus.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Endoplasmic Reticulum…
Smooth( agranular) Endoplasmic Reticulum (SER)
With no ribosome’s on its surface( thus appearing
smooth)
Appear as branching anastomosing tubule or vesicles
Function
Synthesizes fatty acids and steroid hormone
(estrogen and testosterone )
Drug detoxification - in hepatocytes
Muscle contraction & relaxation - sarcoplasmic
reticulum, because it stores calcium ion.

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Human Anatomy)

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Endoplasmic Reticulum…
FUNCTIONS of SER
•In striated muscle: as
sarcoplasmic reticulum
•In endocrine cells:
biosynthesis of steroid
hormone
•In intestinal villi: synthesis of
neutral fats
•In parietal cells of the
stomach: formation of HCl
acid
•In hepatocytes, drug
detoxification

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Mitochondria
Rod shaped (7 µ m long & 0.2 µ m wide )
Consists of 2 membranes( similar in structure to
plasma membrane)
Outer membrane - bounds the organelle, smooth
Inner membrane - invaginate ( folds) to form cristae
2 compartments
Intermembrane compartment ( between the 2
membrane)
Inner matrix compartment ( enclosed by inner
membrane and cristae)

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Mitochondria…

Function
Generate ATP (power house of a cell)
Heat production in brown fat cell
Unique Properties
–Possess their own genetic apparatus.
–Proliferate by division (fission) of pre
existing mitochondria.

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Golgi complex (apparatus)

Highly dynamic organelle, which completes posttranslational
modifications and then packages and addresses proteins
synthesized in the RER.
Consists of several disk-shaped cisternae (saccules) arranged in a
stack.
Function
Processing of proteins synthesized in the RER
membrane retrieval, recycling & redistribution
Lysosomes
Are dense, membrane- bounded vesicles (0.2-0.5µm)
Contains more than 40 powerful enzymes( hydrolases) which are
synthesized in RER
These enzymes breakdown a wide variety of molecules, bacteria &
other substances

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Peroxisomes
Similar in structure to Lysosomes but smaller
(0.15-0.25µm).
contain oxidative enzymes & other enzymes
Function
Oxidation of fatty acids
Detoxification of harmful substances(e.g.
ethanol)

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Centriole
 Pairs of cylindrical rods (0.2µm wide and 0.5µm
long).
Located in centrosome (dense area of cytoplasm
near nucleus).
Function: center for organizing microtubules (in non
dividing cells) and mitotic spindle (during cell
division).

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Human Anatomy)

Inclusions
Are ‘lifeless’ accumulations of materials that are not
metabolically active.
usually present in cytosol only temporarily.
not bounded by membrane
Examples
Fat
 Glycogen
 Proteins
 Crystals
 Granules
 Pigments

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Cytoskeleton
Fibrillar elements of cytoplasm
Complex network of protein structures & includes
(1) Microtubules
(2) Microfilaments
(3) Intermediate filaments
Functions
Support the cell & facilitate cell attachment
Determine the cell shape & are involved in all cell
shape changes such as those during endocytosis,
exocytosis, and cell locomotion,
Play an important role in the movements of
organelles and cytoplasmic vesicles, and also allow
the movement of entire cells
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cytoskeleton
Microfilaments microtubules
intermediate
filaments
Adapted from ECB Fig 1-27
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Human Anatomy)

Cytoskeleton….
Filaments
 There are 2 Categories of filaments:
A.Microfilaments: diameter measure less than about 8 nm
Most are contractile acting to promote cell shape or motility
(myofilaments).
B. Intermediate filaments /Tonofilaments :diameter range from 8-
12 nm
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•
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Cytoskeleton….
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Actin filaments (red) are most concentrated at the cell
periphery, forming prominent circumferential bundles from
which finer filaments project into the transient cellular
extensions at the edge of the cell and push against the cell
membrane.

Such an arrangement of actin filaments forms a dynamic
network important for cell shape changes such as those
during cell division, locomotion, and formation of cellular
processes, folds, pseudopodia, lamellipodia, veils, microvilli,
etc. which serve to change a cell's surface area or give
direction to a cell's crawling movements.
Cytoskeleton….
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Human Anatomy)

Microtubules (green/yellow) are present throughout the cytoplasm and are oriented in
arrays which generally extend from the area around the nucleus into the most
peripheral extensions.
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Human Anatomy)

A large number of actin-binding proteins with different
activities have been demonstrated and include:
Actin motor proteins such as the myosins, which carry
other molecules or vesicles along microfilaments,
Actin-capping proteins such as tropomyosin, which bind
the free end and stabilize microfilaments,
Actin filament-severing proteins such as gelsolin, which
break microfilaments into short pieces,
Actin-bundling proteins such as fimbrin, villin, and -
actinin, which crosslink microfilaments,
Actin-branching proteins such as formin, which produce
branch points along a microfilament.
Cytoskeleton….
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Human Anatomy)

Intermediate Filaments
Intermediate in size between the other two cytoskeletal
components and with a more variable diameter averaging 8–12
nm.
 In comparison with microtubules and actin filaments,
intermediate filaments are much more stable and vary in their
protein subunit structure in different cell types.
A dozen or more heterogeneous protein classes that form such
filaments have been identified and localized
immunocytochemically.
Main function is to provide mechanical strength
All are essentially rod-like rather than globular proteins that form
coiled tetramers which self-assemble into large cable-like arrays
stabilized by further interactions laterally.
Cytoskeleton….
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Human Anatomy)

Table. Examples of intermediate filaments found in eukaryotic cells.
Filament Type Cell Type Examples
Cytokeratins Epithelium
Both keratinizing and
nonkeratinizing epithelia
Vimentin Mesenchymal
Fibroblasts,
cells
chondroblasts,
macrophages,
endothelial cells,
vascular smooth muscle
Desmin Muscle
Striated and smooth
muscle (except vascular
smooth muscle)
Glial fibrillary acidic proteins Glial cells
Astrocytes
Neurofilaments Neurons
Nerve cell body and
processes 163
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Human Anatomy)

Cytoskeleton….
Tonofilaments
Bundles of
cytokeratins
Not known to be
contractile and
appear to serve
exclusively in a
supportive role.

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Human Anatomy)

TONOFILAMENTS
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Human Anatomy)

Cytoskeleton….
FUNCTIONS
1.Provide resiliency to forces tending to alter that shape;
prominent in cytoplasm of “wear & tear” epithelia
•I.e. maintain cellular shape

2. Regular component, together with microtubules; in
nerve cells.

3. Found in the sites of adhesions between adjacent cells
of epithelial systems important as supportive
intracellular network and in transmission of forces
among adherent cells.
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Human Anatomy)

Microtubules
Are tiny, but rigid tubular structures which assemble
from heterodimers of α and β tubulin subunits.

Also found centrioles, basal bodies, & in cytoplasmic
processes called cilia and flagella.

Have an outer diameter of 24 nm and a hollow lumen
14 nm wide, with a dense wall 5 nm thick .
Tubulin molecules are arranged to form 13
protofilaments
Cytoskeleton….
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Cytoskeleton….
The specific orientation of the tubulin dimers results in
structural polarity of the microtubule.

Elongate or rapidly shorten by the addition or removal
of tubulin at the ends of individual protofilaments.

The lengths and locations of cytoplasmic microtubules
vary greatly during different phases of cell activity, with
assembly dependent on shifting balances between
polymerized and unpolymerized tubulin and other
factors in "dynamic instability."

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Human Anatomy)

Occasionally, two or more microtubules are linked by
protein arms or bridges, which are particularly
important in cilia & flagella
X/S: appear as a circle composed of 13 globular subunits

Besides serving to stabilize cell shape, microtubules
form the tracks for kinesin-based transport of vesicles
& organelles into the cell periphery & dynein-based
transport toward the cell nucleus.
Cytoskeleton….
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•
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Human Anatomy)

Cytoskeleton….
Structures formed of microtubules
Cilia:
•Hair-like striations on the free surface
of some cells.
•Function: movement of particles or fluids in one direction.
Flagella:
•Longer and larger than cilia.
•Form the tails of sperms.
•Function: important for movement of
the sperms.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Microtubules
Electron micrograph of the apical portion of a ciliated epithelial cell. Cilia are
seen in longitudinal section. Each cilium has a basal body (B) from which it grows.
Microvilli (MV) are shown. x59,000. Inset: Cilia in cross section. The 9 + 2 array of
microtubules in each cilium is evident. x80,000.
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Human Anatomy)

Cytoskeleton….
Functions of microtubules
1.Are an important element of the spindle
apparatus in dividing cells; they form the
mitotic spindle.
2.They form the cores of cilia & flagella of sperm
cells– nine doublets around 2 centrally located
microtubules.
3.Play a role in maintaining diverse cell shape.
4.Provide substrate for axoplasmic streaming in
axons of neurons.
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Human Anatomy)

Nucleus

The largest structure and spherical or oval in shape
(varies in shape)
varies in number
Uni- in most cells
Bi- in parietal cells, one/two cardiac muscle cells, hepatocytes
Multi- in osteoclasts, skeletal muscle cells, megakaryocytes.
Absent in mature RBCs and platelets
Double membrane; nuclear envelope separate it from the
cytoplasm
Within it there are nucleolus, nucleoplasm and chromatin
Contains genetic apparatus which control cellular structure
and direct many cellular activities

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Human Anatomy)

Nuclear envelope
Surrounds nuclear material
Consists of 2 parallel membrane separated from each
other by a narrow perinuclear cistern
Perforated at intervals by openings called nuclear pores
allows most ions and water soluble molecules to
shuttle between nucleus and cytoplasm.

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Human Anatomy)

Cont’d
Nucleolus
Well-defined, not membrane bounded nuclear inclusion
rather it is a cluster of protein, DNA, and RNA
It may be one or more
involved in synthesis of rRNA
Nucleoplasm
Is the portion of protoplasm surrounded by nuclear
envelope.
Consists of matrix and various particles.
Chromatin
The substance that forms chromosomes and contains
DNA, RNA and various proteins

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Human Anatomy)

Tissues

TISSUES OF HUMAN BODY

The cells of the human body do not operate
independently of one another.
Related cells live and work together in cell communities
called tissue.
A tissue is a group cells of similar structure that usually
have a common origin and function.
The science that deals with the study of tissues is
termed as histology.
Classification of tissues
Body tissues can be classified into 4 principal types
according to their function and structure.

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Human Anatomy)

 All organs are built of these four tissues, which have
consistent characteristics and arrangements from
organ to organ.
Epithelial tissue (covering)
Connective tissue(support)
Muscle tissue(movement)
Nervous tissue(control)

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Human Anatomy)

Table. Main Characteristics of the Four Basic Types of Tissues
Tissue Cells Extracellular
Matrix
Main Functions
Nervous Intertwining
(linked)
elongated
processes
None Transmission of
nervous
impulses
Epithelial Aggregated
polyhedral cells
Very small
amount
Lining of surface
or body cavities,
glandular
secretion
Muscle Elongated
contractile cells
Moderate
amount
Movement
Connective Several types of
fixed and
wandering cells
Abundant
amount
Support and
protection 182
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Human Anatomy)

Sheet of cells that covers a body surface or lines
body cavity
With minor exceptions, all of the outer and
inner surfaces of the body are covered by
epithelia. E.g. skin, inner lining of all hollow
viscera such as stomach, respiratory tube &
lining of all blood vessels.

Epithelial tissue

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Functions of epithelium

1.Transportation of molecules from one epithelial surface to
another-simple squamous epithelium in walls of
capillaries and air sacs(alveola) in the lung.
2. Absorption simple epithelia tissue -cuboidal and columnar
3. Secretion

4. Selective permeability- (e.g., intestinal epithelium)

5. Protection-stratified epithelia
6. Sensory reception (e.g., gustatory and olfactory
neuroepithelium)

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Human Anatomy)

Special characteristics of epithelia
Composed almost entirely of cells.
These cells are separated by a minimal amount of
extracellular material- cellularity.
Supported by connective tissue.
Avascular but innervated
Have a high regenerative ability
Originates from all germ layers (mesoderm,
endoderm & ectoderm)

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Human Anatomy)

Classification of epithelial tissue
1. Based on number of cell layers
Three types
I. simple epithelium
 If the cells arranged in a single layer
 Found in areas of minimal wear & tear
II. stratified epithelium
 If the cells arranged in several layers
 Found in areas of high wear and tear
III. Pseudo stratified epithelium
•Has only one layer of cells, but some of the
cells do not reach the surface ,which give the
tissue a multi layered or stratified appearance
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Human Anatomy)

First name of tissue indicates number of layers
•Simple – one layer of cells

•Pseudo stratified epithelium
- Some cells are tall and reach the
surface and some are short not
reaching the surface
one layer of cells
•Stratified ≥ two layers of cells
Classifications of Epithelia
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Human Anatomy)

Classifications of Epithelia
•Last name of tissue describes shape of cells
a). Squamous – cells wider than
tall (plate or “scale” like)

b).Cuboidal – cells are as wide as
tall, as in cubes

c). Columnar – cells are taller than
they are wide, like columns
d). Transitional cells radialy change shape .
 It found where there is a great degree of
distention (stretching) in the body
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Human Anatomy)

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Human Anatomy)

Cont’d
 Each epithelium is given two name
The first name indicates the number of cell layers and the last
name describes the shape of cells
E.g. simple squamous epithelium
Stratified squamous epithelium
 Based on the presence or absence of epithelial
specialization & keratin
a. Cilia- whiplike, highly motile extension of the apical surface
membranes of certain epithelia cell.
 ciliated (have cilia)
 non ciliated (have no cilia)
b.
keratin-a tough fibrous protein that gives the epidermis its
protective properties.
 keratinized
 Non -keratinized

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Human Anatomy)

Simple Squamous Epithelium
•Description
–The simplest epithelium
–Single layer of flat cells with disc-shaped nuclei
•Sites of Locations
–Endothelium (inner covering)
•slick lining of hollow organs
–Parietal layer of Bowman’s capsule, thin limbs of
Henle
–Alveoli of the lungs
–Mesothelium (middle covering)
•Lines peritoneal, pleural, and pericardial cavities
•Covers visceral organs of those cavities

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Human Anatomy)

Simple Squamous Epithelium
•Function
–Passage of materials by passive diffusion and
filtration
–Secretes lubricating substances in serous
membranes.
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Human Anatomy)

Simple Squamous Epithelium

Simple squamous
lining the walls of
the capillary
If it’s from a
mesothelial lining
Function
Passage of materials by passive diffusion and filtration
Secretes lubricating substances in serous membranes.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Simple Cuboidal Epithelium
A single layer of square or round cells
Centrally-placed spherical nuclei
Apical layer often has microvilli
–Microvilli are small extensions of the cell membrane
that increase the surface area of the cell.
–to be efficient, cell needs to have more surface area
when involved with secretion or absorption.
Found in most kidney tubules, exocrine pancreas, thyroid,
salivary, and most other glands, bronchioles (small tubes
within the lungs) & Liver.

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Human Anatomy)

Simple Cuboidal Epithelium
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Human Anatomy)

Simple Columnar Epithelium
•Description
•single layer of column-shaped (rectangular) cells
with oval nuclei, vertically-oriented, usually located
in the basal half of the cell.
–May contain goblet cells
–Microvilli is common.
–Some bear cilia at their apical surface: Cilia are hair-
like extensions of the cell membrane that can move
and sweep material across the cell surface
•Function
Absorption; secretion of mucus, enzymes, and other
substances
Ciliated type propels mucus or reproductive cells by
ciliary action
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Human Anatomy)

Simple Columnar Epithelium
Tall and column-shaped.
The nuclei are oval and basal.
Types & Sites:
1.Non ciliated line gall bladder may
changed its shape into squamous
when it was distended.
2.Ciliated lining the uterus, small
bronchi.
3.Striated: the cells have striated or
brush border, found in the intestine.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Simple Columnar Epithelium
•Locations:
–Inner lining of
stomach,
intestines, and
rectum.
–Inner lining of
gallbladder
–Inner lining of
uterus and
uterine tubes
Non-ciliated Simple columnar epithelium
lining the lumen of the gallbladder.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Simple Columnar Epithelium
Functions:
–Absorption & secretion
•Columnar cells in small intestine
have microvilli to increase the
available surface area for the
absorption of nutrients.
–Movement of egg and
embryo in uterine tube.
•Hence the presence of cilia.
–Secretion of mucus.
•Lots of goblet cells in the
large intestine so as to
lubricate it and ease the
passage of feces.
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Pseudostratified Columnar Epithelium:
All the cells rest on the basal lamina but they
do not all reach the surface.
Some cells are tall and reach the surface and
some are short not reaching the surface.
The nuclei appear to lie in various levels
giving false appearance of being stratified.
Two kinds are found
a- Pseudostratified Columnar Ciliated:
found In the trachea, respiratory tract
b- Pseudostratified Columnar non-ciliated:
large ducts of glands and male genital
ducts such as epididymis & vas deferense.
Non-ciliated
ciliated
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Pseudostratified Columnar Epithelium
Functions:
•In the respiratory tract
there are lots of mucus-
secreting goblet cells.
•The mucus traps dust and
bacteria
•Cilia “sweep” the bacteria-
loaded mucus up the
respiratory tract towards
the pharynx where it can
be swallowed.
•Smoking paralyzes cilia –
smokers have to cough
violently to expel their
mucus.
Then they die!
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Stratified Epithelia
Primary function- protection
Formed of two or more layers of cells
The basal cells are columnar or cuboidal
Cells present in the middle are polyhedral
Are named according to the shape of cells at apical layer
Only the deepest layer of cells rest on basal lamina.
According the morphology of superficial cells this type is
classified into:
1.Stratified Squamous Epithelium:
A. Non-keratinized.
B.Keratinized.
2.Stratified Cuboidal Epithelium.
3. Stratified Columnar Epithelium.
4. Transitional Epithelium.

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Human Anatomy)

Stratified Squamous Epithelium
•Description
–Many layers of cells – squamous in shape
–Deeper layers of cells appear cuboidal or
columnar
–Thickest epithelial tissue – adapted for protection
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Human Anatomy)

Stratified Squamous Epithelium
Specific types
1.Keratinized – contain the protective protein keratin
 Surface cells are dead and full of keratin
2.Non-keratinized – forms moist lining of body openings
Functions _ Protection!
Keratinized version (a.k.a. dry epithelium)
- Protects against mechanical abrasion, water loss, and pathogen
entry.
- Keratin is very strong, waterproof, and is bacteriostatic (prevents
bacteria from reproducing).
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Human Anatomy)

Stratified Squamous Epithelium….
Non-keratinized version (a.k.a., wet epithelium)
 Protects from mechanical abrasion.
Eating food, swallowing, sexual intercourse, birth,
defecation.
Location
Keratinized – forms epidermis
Non-keratinized – forms lining of esophagus, mouth,
vagina
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

•
Non-keratinized keratinized
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Human Anatomy)

Stratified Cuboidal Epithelium
•Description
–2 or more layers of cells.
–Surface layers are square or round (cuboidal).
•Function
–Protection
–Contributes to sweat secretion.
–Secretion of ovarian hormones
(e.g., estrogens)
•Location
–Forms largest ducts of sweat glands
–Ovarian follicle
•Cells that surround the developing egg
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Human Anatomy)

Stratified Columnar Epithelium
•Description
•several layers; basal cells
usually cuboidal
_ superficial cells elongated columnar.
•Function
–protection and secretion
•Location
–Rare tissue type
–Found in male urethra and, largest ducts of salivary
glands
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Transitional Epithelium
•Description
–Basal cells usually cuboidal or columnar
–Superficial cells dome-shaped or squamous
•Function
–stretches and permits distension of urinary
bladder
•Location
–Lines ureters, urinary bladder and part of urethra
209
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Transitional Epithelium
Relaxed state
Stretched state
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Human Anatomy)

Glands

Single or group of epithelial cells specialized for secretions
Synthesize and release specific secretions
Most are derived from the surface epithelium
Classification of glands
I. Three types of glands based on the site of secretion
where they release their secretion
1. Exocrine-release secretions through ducts.
2. Endocrine-ductless glands, release secretions to the
circulatory system and it takes to the target organ.
3. Paracrine –similar with endocrine glands, they are ductless
and they release their secretions directly to the target organ.
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Human Anatomy)

Glands….

Classification of exocrine glands
I. Based on number of cells
A. Unicellular Exocrine glands e.g. goblet cell secret
mucin. Mucin + water = mucus
Mucus covers, protects and lubricates many internal body
surfaces. E.g. intestine and respiratory tubes.
Composed of a single cell
B. Multicellular exocrine glands- has two basic parts: an
epithelium walled duct and a secretory unit consisting
of secretory epithelium.
Many celled glands

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Glands….
II. Based on the type of secretion
A. Serous glands-produce thin watery fluid
Contain proteins and enzymes
e.g. parotid gland, lacrimal gland
B. Mucous glands-produce (secrete) viscous material that
protects or lubricates cell Surface
Free of enzymes
e.g. palatine glands
C. Mixed glands-secretory part consists of both serous and
mucous glands
E.g. - Submandibular –seromucous
- Sublingual-mucoserous

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Human Anatomy)

III. According the mode of secretion (the way
secretions leave the cell)can be classified into:
1.Merocrine: no parts of the cells are
released with the secretion.
Most exocrine glands are Merocrine
E.g. salivary glands, pancreas, parotid

2. Apocrine: the apical cytoplasm is released
with the secretion.
E.g. mammary glands

3. Holocrine: the whole cells are released
with the secretion.
E.g. sebaceous gland
Glands….

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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Objectives
At the end of this session students will be able to :
Enumerate division of connective tissue
List dawn division of muscle tissues
 Describe nerve tissue

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Human Anatomy)

Connective tissue
 A really diverse group of tissues!
Most abundant, widely distributed, and histologically
variable of the 4 primary tissue types.

Consists of cells that are typically widely separated by lots
of extracellular material – referred to as the extracellular
matrix.
Most cells are not in contact with each other but are
distributed throughout the extracellular matrix.

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Human Anatomy)

Connective tissue….
Connective tissues do far more than just connect the tissues
and organs of the body together.

Form the basis of the skeleton, store and carry nutrients,
surround all the blood vessels and nerves of the body, and
lead the body’s ﬁght against infection.
Provides structural support for organs and cells.
Protects and insulates internal organs
compartmentalizes structures.
Serves as a medium for exchange of materials
Provide site for fat storage.

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Human Anatomy)

Special characteristics of CT.
1.Relatively few cells, lots of ECM.
2.ECM composed of ground substance and fibers.
3. Common embryonic origin –mesenchyme with exception in
the neck region.
Any connective tissue is made up of three elements
1.Fibers: they proteins (collagen, reticular, and elastic fibers)
2. Ground substance: is a highly hydrophilic, macromolecules
(glycosaminoglycans , proteoglycans) and multiadhesive
glycoproteins (laminin, fibronectin, and others) that
stabilizes the ECM by binding to receptor proteins (integrins)
on the surface of cells and to the other matrix components.
3.Cells

Connective tissue….
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Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

• Four main classes of connective tissue are
1.Connective tissue (CT) proper
2.Cartilage
3.bone tissue
4. blood.

Connective tissue….
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Human Anatomy)

Fibrous connective tissue(Connective tissue proper)
Based on the relative abundance of fibers, there are
two types of fibrous connective tissue:
1. Loose Connective Tissue
•Lots of ground substance and cells.
•Fewer fibers.
•Leaves lots of empty space in tissue sections.
•Contains fibroblasts, defense cells (macrophages, plasma
cells, mast cells) and fat cells.(white and brown adipose
tissue)

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Connective tissue….
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Connective tissue ….
•Loose connective tissues are well vascularized,
flexible, not very resistant to stress.
•More abundant than dense connective tissue.
Function
support and bind other tissue
 holding body fluids
defending body against infection
storing nutrient as fat.

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Connective tissue….
 Loose connective tissue has three subdivisions
1.Areolar tissue :
•Is a very common type of CT that supports many
structures which are normally under some pressure
and low friction.
•Usually supports epithelial tissue, forms a layer
around small blood and lymphatic vessels, and fills
the spaces between muscle and nerve fibers.

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Connective tissue….
2.Adipose tissues:
•Are connective tissue cells that have specialization for
storage of neutral fats or for the production of heat.
•Often called fat cells, they have considerable metabolic
significance
•Contain huge droplets of lipids for storage.

3. Reticular tissue:
•Spongelike structure within which cells and fluids are
freely mobile .
•They present in basement membrane, lung, liver, &
hematopoietic organs (lymph nodes, tonsils, thymus,
spleen, and bone marrow).

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Connective tissue….
2.Dense connective tissue
•Fibers occupy the most space.
•Much lower number of cells and less ground
substance.
•Appears closely packed in tissue sections.
•Dense connective tissue is adapted to offer
resistance and protection.
•Dense connective tissue is less flexible and far
more resistant to stress than is loose connective
tissue.

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Connective tissue….
Dense connective tissue has three sub divisions
1. Irregular CT:
•Fibers run in different planes, allowing this tissue to
resist tensions from different direction.
•Localization: reticular layer of dermis; periosteum,
perichondrium

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Connective tissue….
2. Regular CT:
•Fibers usually run in the same direction, parallel to the
direction of pull.
•Localization: tendons, ligaments, capsules, fasciae, and
fibrous membranes
3. Elastic CT:
•Undergo considerable expansion or stretching & return to
the original shape or size (highly flexible)
•Localization: present in large arteries, larynx and trachea,
ligamentum nuchae, epiglottis and framework of the
spleen, lung, outer ear, etc.

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Cartilage
A firm but flexible tissue
Cartilage is characterized by an extracellular matrix (ECM)
enriched with GAGs and proteoglycans, macromolecules
that interact with collagen and elastic fibers.
Collagen, hyaluronic acid, proteoglycans, and small amounts
of several glycoproteins are the principal macromolecules
present in all types of cartilage matrix.
Avascular & no nerve supply

Connective tissue….
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Cells of mature cartilage are called chondrocytes, which
occur singly or in groups within a space called lacunae in
the matrix.
Special form of connective tissue that supports soft tissue.
Content:
•Cell- chondrocytes, chondroblasts
•Fibres- collagen fibers, elastic fibers
• Ground substance : GAGs + core protein
Qualities
•Tensile strength
• Structural support
•Flexibility with out distortion

Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Connective tissue….

Classification
Based on the types and amount of fibers present in
the matrix, cartilage is classified into three types.
A.Hyaline cartilage
B.Elastic cartilage
C.Fibrocartilage
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A. Hyaline cartilage
It is most common type of cartilage, and is
avascular.
In embryo- it is skeletal model (replaced by bone
by endochondral ossification).
In adult- it is found in the:
 articular surface of bones
 end of ribs (costal cartilage)
 nose
 larynx (with some exceptions)
 trachea
 bronchi

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 Embryonic cartilage:
 Perichondrium is very thin and cellular.
Its matrix is scanty and smooth in appearance.
The cells are numerous, small, round chondrocytes
are housed in small spaces in the matrix known as
lacunae.
Adult hyaline cartilage:
 Perichondrium has two layers:
1.Outer fibrous layer, which contains collagen and fibroblasts
2.Inner chondrogenic cells and chondroblasts

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B. Elastic cartilage
Elastic cartilage is essentially very similar to hyaline cartilage
except that it contains an abundant network of fine elastic
fibers in addition to collagen type II fibrils.
Fresh elastic cartilage has a yellowish color owing to the
presence of elastin in the elastic fibers.
Elastic cartilage is found in the:
Auricle of the ear
Walls of the external auditory canals
Auditory (eustachian) tubes
 Epiglottis
Cuneiform cartilage in the larynx

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Elastic cartilage is frequently found to be gradually
continuous with hyaline cartilage.

Like hyaline cartilage, elastic cartilage possesses a
perichondrium.

The cells are chondrocytes, chondroblasts and
chondrogenic cells as in hyaline cartilage.

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C. Fibrocartilage
Fibrocartilage is a tissue intermediate between hyaline
and elastic cartilage.
Its fibers oriented in direction of functional stress.
Fibrocartilage is found:
Intervertebral discs
Symphysis pubis
Certain joints (mensci)

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Human Anatomy)

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Perichondrium is usually absent in fibrocartilage.
The ground substance of the matrix is very scanty.
Many thick collagen bundles are located between
parallel rows of chondrocytes.

Chondrocytes in fibrocartilage are smaller than those in
hyaline or elastic cartilage and they are arranged in
parallel longitudinal rows between bundles of thick
collagen fibers.
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Connective tissue….
Bone tissue
Bone is the hard tissue in the body rich in calcium and
phosphorus
Four types of cells are present in bone tissue:
Osteogenic/osteprogenitor cells: unspecialized stem cells
Osteoblasts:- Bone building cells
Osteocytes: Mature bone cells
Osteoclasts: bone resorbing cells

Function
 Support soft tissues
 Protects delicate structures
 Stores Ca & Phosphorus
 Houses red and yellow marrow
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Bone
Bone is special form of connective tissue.
It has mineral (calcium phosphate) deposition in the
matrix.
Functions
• Bear weight
•Site of attachment for muscles and organs
•Protection
skull ≈ brain
thorax ≈ heart, lungs
pelvis ≈ urinary organs, reproductive organs
•Site of hemopoiesis (blood cell formation)
• Reservoir of minerals such as calcium, phosphate etc.

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There are two membrane which cover the bone both
internally and externally
1. Endosteum:
•Lining of marrow cavity and central canals of osteons
•Is osteogenic- bone producing
 Containing bone depositing cells and bone destroying cells
2. Periosteum :
•Tough membrane covering bone but not the cartilage
•Richly supplied by nerves and blood vessels
•Secured to the underlying by perforating fibers called
sharpey’s fiber
•Has two layer
1.Fibrous layer = dense irregular CT
2.Osteogenic layer = bone cells

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Human Anatomy)

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Bone (osseous) tissue
Consists of widely separated cells surrounded by large
amounts of extracellular matrix.
Has both organic and inorganic components.

Chemical composition
Healthy bone is half as strong as steel in resisting
compression and equally strong in resisting tension.

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Bone is composed of organic and inorganic components:
Organic components(35%)
• Cells, fibers, and ground substance
•Organic substance particularly collagen contribute flexibility
and tensile strength that allow bone resists stretching and
twisting.
Inorganic components(65%)
•Minerals (mostly calcium phosphate and calcium carbonate)
•Provides bones hardness
•Bone is not completely solid since it has small spaces for
vessels and bone marrow
Spongy bone has many such spaces
Compact bone has very few such spaces
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Human Anatomy)

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Based on gross observation bone has two different
structures:
1. Compact
•Dense outer layer that looks smooth and solid to the naked eye.
Outer layer provides strength.
Looks like solid hard layer of bone.
Makes up the shaft of long bones and the external layer
of all bones
Resists stresses produced by weight and movement

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2. Spongy (cancellous)
•Consists of trabeculae (a honeycomb of small needle
like), containing marrow for blood cell production or
fat storage.
•Forms most of the structure of short, flat, and
irregular bones, and the epiphyses of long bones.
•Spongy bone tissue is light thus, supports and
protects the bone marrow.

Connective tissue….
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Microscopic structure of bone
Compact bone is arranged in units called osteons or
Haversian systems
It is a group of concentric tubes that in cross-section
appear as rings.
They are made up of lamella (layer of bone matrix
with collagen running in one direction).
Osteons contain blood vessels, lymphatic vessels,
nerves, and osteocytes along with the calcified
matrix.

Connective tissue….

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Circular lamella is called concentric or circumferential
and interstitial lamella is an incomplete lamella b/n
osteons.

Within the lamella is a network of osteocytes embedded
in lacunae and connected by canaliculi (little canals).

These cells are maintained alive by nutrients and oxygen
provided by blood vessels passing through the center of
the osteon called the central or harvasian canal and the
volkman’s canal (transverse to diaphysis) .

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249
Cells of bone
Osteoprogenitor cells:
•Are flattened, undifferentiated-appearing cells.
•Located in the cellular layer of the periosteum, in endosteum
,and lining the haversian canals.
•They give rise to osteoblasts.
Osteoblasts:
•Are cuboidal to low-columnar cells responsible for the
synthesis of bone matrix.
•As they elaborate bone matrix, they become surrounded by
the matrix and then become osteocytes.
•Bone matrix is calcified due to seeding of the matrix via matrix
vesicles, derived from osteoblasts.

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Human Anatomy)

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Osteocytes:
•Are flattened, discoid cells located in lacunae.
•They are responsible for the maintenance of bone.
•Their cytoplasmic processes contact and form gap junctions
with processes of other osteocytes within canaliculi.
Osteoclasts:
•Are multinucleated cells derived from monocytes.
•Osteoclasts are located in Howship’s lacunae along resorptive
surfaces of bone.
• They are responsible for the resorption of bone.
•Cooperation between osteoclasts and osteoblasts is
responsible not only for the formation, remodeling and
repair but also for the long-term maintenance of calcium and
phosphate homeostasis of the body.

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252
Osteoid, noncalcified bone matrix, is interposed
between the cells of bone and the calcified tissue.

Vascular supply
Blood vessels are found in the periosteum, in the
marrow cavity and in the haversian canals of osteons.
Haversian canals are connected to each other by
Volkmann’s canals

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Bone formation
Bone is formed via:
1.Intermembranous ossification
2.Endochondral ossification
1.Intramembranous ossification
•Ossification centers: centers of ossification are vascularized
area of mesenchymal connective tissue where mesenchymal
cells probably differentiate into osteoprogenitor cells, which
differentiate into osteoblasts.

Connective tissue….

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2. Endochondral ossification
•Primary ossification center:
Perichondrium of diaphysis of the cartilage template
becomes vascularized, followed by hypertrophy of
centrally located chondrocytes confluence contiguous
lacunae, calcification of the cartilage remnants and
subsequent
chondrocytic death.
Concomitant with these events, chondrogenic cells of the
perichondrium become osteoprogenitor cells which in
turn, differentiate into osteoblasts.
Osteoblasts form the subperiosteal bone collar, thus
converting the overlying perichondrium into a
periosteum.

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•,
Osteogenesis of long bones by endochondral ossification.

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Human Anatomy)

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257
•Primary ossification center…
A periosteal bud invades the diaphysis, entering the
confluent lacunae left empty by the death of
chondrocytes.

Osteogenic cells give rise to osteoblasts, which elaborate
bone on the
trabeculae of calcified cartilage.

Hemopoiesis begins in the primitive medullary cavity;
osteoclasts/chondroclasts develop, which resorb the
bone-covered trabeculae of calcified cartilage as the
subperiosteal bone collar becomes thicker and elongated.

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•Secondary ossification center:
Epiphyseal (secondary) center of ossification is limited
somewhat after birth.

It begins in the center of epiphysis and proceeds radially
from that point by leaving cartilage (hyaline) only at the articular surface and at the interface between epiphysis
and diaphysis, the future epiphyseal plate.

Epiphyseal plate: is responsible for the future
lengthening of a long bone.
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Human Anatomy)

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 Epiphyseal plate is divided into five zones:
I.Zone of reserve cartilage, a region of randomly arranged
chondrocytes.
II.Zone of cell proliferation, where chondrocytes are arranged in
rows whose longitudinal axis parallels that of the growing bone.
III.Zone of cell maturation and hypertrophy, where cells enlarge and
the matrix between adjoining cells becomes very thin.
IV. Zone of calcifying cartilage, where lacunae become confluent and
the matrix between adjacent rows of chondrocytes becomes
calcified, causing subsequent chondrocytic death. V.Zone of provisional ossification where osteoblasts deposit bone
on the calcified cartilage remnants between the adjacent rows.
Osteoclasts resorb the calcified complex.

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Blood
Blood is a connective tissue circulating in a regular
unidirectional movement within closed system of
vessels.
It is traditionally classified as a form of connective
tissue in which the intercellular substance is a fluid.
•This is because it is derived from reticular connective
tissue of bone marrow that in turn originates from the
mesenchyme.
Blood and the interstitial fluid provide the means by
which essential substances are delivered to the cells
and materials not needed are removed from the cells.
•It acts as universal means of transportation and
distribution in the body and enabling the body to function
as a
unified whole.

Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Connective tissue….

Blood tissue & hematopoiesis
Blood is a specialized connective tissue in which cells, i.e.
blood cells/formed elements are suspended in fluid or
extracellular material called plasma.

Adult human has about
5 liters of blood, which is roughly 7-
8% of the total body weight.
A typical sample of blood is 45% formed elements and 55%
plasma by volume.
Formed elements include erythrocytes (red blood cells),
leukocytes (white blood cells) and platelets

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•
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Human Anatomy)

Functions of blood
It functions principally as a vehicle for the transport of
gases (oxygen & carbon dioxide), nutrients, metabolic
waste products, cells, & hormones through out the body

Provides tissues and cells with nutrients and oxygen.
It carries waste products such as carbon dioxide

It transports hormones, drugs, elements and cells that
protects the body from infections and foreign bodies.
It has a homeostatic role based on its thermoregulatory
and buffering capacity.

Connective tissue….

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Composition of whole blood.

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Human Anatomy)

Plasma
A protein-rich intercellular aqueous solution (pH 7.4)
that convey blood its fluid properties.

Contains substances of low or high molecular weight
that make up 8–10% of its volume.

Plasma proteins account for approximately 7% of the
dissolved components, with the remainder including
nutrients, nitrogenous waste products, hormones,
and many inorganic ions collectively called
electrolytes.
Connective tissue….

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Connective tissue….

 Through the capillary walls, low-molecular-weight
components of plasma are in equilibrium with the
interstitial fluid of the tissues.

The composition of plasma is usually an indicator of the
mean composition of the extracellular fluids in tissues.

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Human Anatomy)

Plasma
A straw-
coloured
liquid that
carries the
cells and the
platelets
which help
blood clot.
• carbon dioxide
• glucose
• amino acids
• proteins
• minerals
• vitamins
• hormones
• waste materials
like urea.
It also contains
useful things like;
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Major plasma proteins
Albumin, the most abundant plasma protein, is made
in the liver and serves primarily in maintaining the
osmotic pressure of the blood.

α- and β-globulins, made by liver and other cells,
include transferrin and other transport factors;
fibronectin; prothrombin & other coagulation/clotting
factors.

Connective tissue….
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Connective tissue….

 γ-globulins, which are immunoglobulins (antibodies)
secreted by plasma cells in many locations.
Complement proteins, a system of factors important
in inflammation and destruction of microorganisms.

Fibrinogen, the largest plasma protein (340 kD), also
made in the liver, which during clotting polymerizes as
insoluble, cross-linked fibers (Fibrin) which block
blood loss from small vessels.
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Human Anatomy)

Functions of plasma
Maintaining optimal blood pressure and volume
Supplying critical proteins for blood clotting and immunity.
A medium for exchange of vital minerals such as Na
+
, K
+
, Ca
++
, &
phosphorus to maintain proper ionic balance.

Nutrients, such as glucose, proteins, lipids, and hormones are
carried from site of absorption or synthesis and distributed to
various areas of the body by blood plasma.

Moreover, plasma transports nitrogenous wastes (such as urea,
uric acid & creatinine), excess salt & water to be removed from
the blood by the kidneys.
Connective tissue….
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Blood cells
•Erythrocytes (RBC)

•Leukocytes (WBC)

•Platelets
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Membranes

The combination of an epithelial layer and an
underlying connective tissue layer
I. Mucous membrane(mucosa)
•Lines body cavity that opens directly to the exterior.
•Digestive, respiratory, reproductive and urinary tracts.
•The epithelial layer of a mucosa is a barrier against microbes
and certain cells
• Secrete mucus and enzymes.
•Connective tissue layer of a mucosa is called lamina propria.
•It binds the epithelium to underlying structures and holds
blood vessels in place.

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Human Anatomy)

Membrane ….
II. Serous membrane (serosa)
Lines the body cavity that does not open directly to the
exterior, and covers the organs that lie within the cavity.
Composed of two portions
1.Parietal portion -the part attached to the cavity wall.
2.Visceral portion - the part that covers and attaches to
the organ inside the cavities.
•Pleura - the serous membrane lining the thoracic
cavity and covering the lungs.
•Pericardium- lines the heart cavity and covers the
heart.
•Peritoneum- lines the abdominal cavity and covers the
abdominal organs and some pelvic organs.
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Human Anatomy)

The epithelial layers of serosa secrete a lubricating
fluid, called serous fluid that allows the organ to
glide easily against one another or against the walls
of the cavities
III. Cutaneous membrane
Is the skin covering the outer surface of the body.
It is a dry membrane.
Its outer epithelium is the thick epidermis and the
inner connective tissue is the dense dermis.
Membrane ….

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Muscle tissue is composed of cells differentiated for
optimal cell property termed contractility.
Microfilaments and associated proteins together
generate the forces necessary for cellular contraction,
which drives movement within certain organs and the
body as a whole.

Muscle cells are long and narrow, so they are called
‘muscle fibers’
Muscle cells are mesodermal in origin (with few
exception)
Muscle tissue
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Human Anatomy)

Muscle tissues….
Functions of muscle tissues
1.Production of movement
•Movement of body parts
•Movement of blood through the heart and
the circulatory vessels.
•Movement of lymph through the lymphatic
vessels
•Movement of food (and, subsequently,
food waste) through the GI tract
•Movement of bile out of the gallbladder
and into the digestive tract
•Movement of urine in the urinary tract
•Movement of semen through the male
reproductive tract and female reproductive
tract
•Movement of newborn through birth canal

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Human Anatomy)

2.Maintenance of posture
•Muscle contraction is
constantly allowing us to
remain upright.
•The muscles of your neck are
keeping your head up right
now. 3.Thermogenesis
•Generation of heat.
•Occurs via shaking – involuntary
contraction of skeletal muscle.
Muscle tissues….
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Human Anatomy)

4. Stabilization of
joints
•Muscles keep the
tendons that cross
the joint nice and
taut. This does a
wonderful job of
maintaining the
integrity of the joint.

All the things muscles do fall under one of these 4 categories.
Muscle tissues….
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Human Anatomy)

Muscle tissue….
Special characteristics of muscle tissue
1. Excitability/Irritability
The ability to receive and respond to a stimulus
•In skeletal muscle, the stimulus is a neurotransmitter (chemical
signal) release by a neuron (nerve cell).
•In smooth muscle, the stimulus could be a neurotransmitter, a
hormone, stretch, pH, Pco
2, or Po
2.
•In cardiac muscle, the stimulus could be a neurotransmitter, a
hormone, or stretch.

The response is the generation of an electrical impulse that
travels along the plasma membrane of the muscle cell.
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2.Contractility
•The ability to shorten forcibly when adequately
stimulated.
•This is the definite property of muscle tissue.
3.Extensibility
•The ability to be stretched
4.Elasticity
•The ability to recoil and resume original length & shape after
being stretched.
Muscle tissues….
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Human Anatomy)

Three types of muscle tissues can be
distinguished on the basis of morphologic and
functional characteristics and the structure of
each type is adapted to its physiologic role.
Types
1.Skeletal muscle tissue
2.Cardiac muscle tissue
3.Smooth muscle tissue
Muscle tissues….
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Human Anatomy)

Muscle tissue….
Skeletal muscle tissue
Contraction is caused by the interaction of thin actin filaments
& thick myosin filaments whose molecular configuration allows
them to slide upon one another.
 The forces necessary for sliding are generated by weak
interactions in the bridges between actin & myosin.

Characteristics
–Long, cylindrical cells
–Multinucleate
–Obvious striations
•Function
–Voluntary movement
–Manipulation of environment
–Facial expression
•Location
–Skeletal muscles attached to bones (occasionally to skin)
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Human Anatomy)

Muscle tissue….
Cardiac muscle tissue
Function
•Contracts to propel blood into circulatory system
Characteristics
•Nuclei of cardiac cells are located at the center of
the cell that helps to distinguish them from
multinucleated skeletal muscle fibers
•Intercalated discs
: It is structures that joined cardiac
muscle cells.
•Branching cells
•Uninucleate/binucleated
Location
•Occurs only in walls of heart
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Human Anatomy)

Muscle tissue….
Injury and repair cardiac muscle
Mature cardiac muscle cells do not divide
•Repair is through the formation of fibrous connective
tissue with consequent loss of cardiac function at the site
of injury

•Pattern of injury and repair in non-fatal leads myocardial
infarction (heart attack)

•Scar tissue build up due to repeated small myocardial
infarctions can be as dangerous as the damage from a
single large infarction.

285
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Muscle tissue….
Smooth muscle tissue
Characteristics
•Spindle-shaped cells with central nuclei
•Smooth muscle tissue is innervated by the autonomic nervous
system unlike skeletal muscle which is innervated by the somatic
nervous system (over which you have voluntary control)
•Arranged closely to form sheets
•No striations
Function
•Propels substances along internal
passageways
•Involuntary control
Location
•Mostly walls of hollow organs

286
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Muscle tissue….
Smooth muscle is always maintaining a normal level of
activity – creating muscle tone.

Smooth muscle can respond to stimuli by altering this
tone in either direction.
–Smooth muscle can be inhibited and relax
–Smooth muscle can be excited and contract

Possible stimuli include neurotransmitters, hormones,
pH, Pco
2, Po
2, metabolites (such as lactic acid) or
even stretch.
287
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Skeletal muscle Cardiac muscle Smooth muscle
Attached to the
skeleton, in
tongue, pharynx,
esophagus
Found in the
myocardium of
the heart
Found in the
blood vessels &
viscera
Striated Striated Non-striated
Voluntary

Involuntary Involuntary

Muscular Tissues
288
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

290
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

291
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

292
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue
293
Like the CPU of a computer, the nervous system is the
master controlling system of the body.
It is designed to constantly and rapidly adjust and respond to
stimuli the body receives.
Includes the brain, cranial nerves, spinal cord, and associated
peripheral nerves.
Human nervous system is by far the most complex system in the
body histologically and physiologically and is formed by a network
of many billion nerve cells (neurons), all assisted by many more
supporting glial cells.
•Each neuron has hundreds of interconnections with other
neurons, forming a very complex system for processing
information and generating responses.

Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue….
294
Properties of Neurons
Extreme longevity: can live and function for a
lifetime
Do not divide (amitotic): fetal neurons lose their
ability to undergo mitosis; neural stem cells are an
exception
High metabolic rate: require abundant oxygen and
glucose
Conductivity: respond to stimuli by initiating
electrical signals that travel quickly to other cells at
distant locations.

Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue….
295
Organization of the Nervous System
Two main divisions:
1. Central Nervous System (CNS)
- Consists of the brain and spinal cord
with tracts and nuclei
 Nucleus = a collection of nerve
cell bodies in the CNS.
 Tract = bundle of nerve fibers
within the CNS
2. Peripheral Nervous System (PNS)
- Consists of ganglia, cranial nerves,
spinal nerves and peripheral
receptors
 Ganglia = a collection of nerve cell
bodies in the PNS
 Nerve = bundle of nerve fibers in
the PNS
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue ….
296
Two distinct cell types form nervous tissue .
Neurons
which are excitable cells that initiate and transmit nerve
impulses.
are the functional and structural units of nervous tissue.
are terminally differentiated cells that are mitotically
inactive, i.e. can not divide.
Glial cells(neurogelia)(Supporting cells)
which are non-excitable cells.
support and protect neurons, and participate in neural
activity, neural nutrition, and defense of cells in the
central nervous system.
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue….
Supporting cells
•Six types of supporting cells
–Four in the CNS
–Two in the PNS
•Provide supportive functions for neurons
•Cover nonsynaptic regions of the neurons
Make up half the mass of the brain & can divide
throughout life

297
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue….
Neuroglia in the CNS
1. Astrocytes are the most abundant glial cell type
–Extract blood sugar from capillaries for energy
–Take up and release ions in order to control
environment around neurons
•Involved in synapse formation in developing
neural tissue
2.Microglia – smallest and least abundant glial cell
–Phagocytes – the macrophages
of the CNS
–Engulf invading microorganisms and dead neurons
–Derive from blood cells called monocytes

298
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Figure 12.12a 299
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

3.Ependymal cells
•Line the central cavity of the spinal cord and brain
•Bear cilia – help circulate the cerebrospinal fluid
4.Oligodendrocytes – have few branches
•Wrap their cell processes around axons in CNS
–Produce myelin sheaths
Nervous tissue….
300
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue ….
Neuroglia in the PNS
5.Satellite cells – surround neuron cell bodies within ganglia
6.Schwann cells (neurolemmocytes) – surround axons in
the PNS
–Form myelin sheath around axons of the PNS
Figure 12.13 301
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue….
Myelin Sheaths
Segmented structures composed of the lipoprotein
myelin
Surround thicker axons
Form an insulating layer
–Prevent leakage of electrical impulse
Increase the speed of impulse conduction
Myelin Sheaths in the PNS
Formed by Schwann cells(neurolemmocytes)
Develop during fetal period and in the first year of postnatal life
Schwann cells Cover the axon in a tightly packed coil of
membranes

302
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Figure 12.15a
Myelin Sheaths in the PNS
Nodes of Ranvier – gaps along axon
Thick axons are myelinated
Thin axons are unmyelinated
Conduct impulses more slowly
Nervous tissue….
303
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue….
Myelin Sheaths in the CNS
•Oligodendrocytes form the myelin sheaths in the CNS
–Have multiple processes
–Coil around several different axons
Figure 12.15b 304
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue….
305
Neuron structure
Neurons come in all shapes and sizes, but all neurons share
certain basic structural features.
Despite great variation in size and shape in different parts of the
nervous system, all neurons have the same basic structure
A typical neuron has a cell body, dendrites, and axon.
Neuronal cell body (perikaryon)
Contains the usual cellular organelles
Synthesis & metabolism occurs primarily in the soma
The outer cell membrane contains the receptors for incoming
information (stimuli)
Most cell bodies are located within the CNS
Clusters of neuron cell bodies in the CNS are called nuclei
Clusters of neuron cell bodies in the PNS are called ganglia

Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Neuronal processes…
306
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

307
Dendrites
Short, tapering, highly branched processes or extensions
from soma which have not myelination.
The location for some cell organelles
sites of receptive or input regions & transfer information to
the cell body
Posses a cytoplasm similar to that in the cell body except GA
(absent/few)
Posses dendritic spine- for contact formation

Nervous tissue….
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue ….
308
Axons
A long thin cylindrical cytoplasmic projection
Starts at a cone-shaped region – the axon hillock
Modified ER and GA are absent starting from the axon
hillock, and lacks ribsomes…
May be long (1 meter) or short (1 mm) to null but long axon
is called a nerve fiber
Transmit information away from the soma & ends in many
branches known as axonal terminals
•May be 10,000 on one nerve
•Form synapses (junctions) with neighboring neurons or with
effector cells (muscles or glands)
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

309
Axon filled with axoplasm and surrounded by an axolemma
Action potentials start at the axon hillock (trigger zone);
travel along the axon to the axon terminal
Axon terminal has the secretory component
•Action potential (nerve impulse) arrival causes the release of
stored neurotransmitters
•Neurotransmitters transfer the message across a synapse to
the next neuron or to an effectors
•Neurotransmitters can excite or inhibit the action of the next
cell in the pathway

Nervous tissue….
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Neuronal processes…
310
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Nervous tissue….
311
Classifications of neurons
Neurons vary widely in morphology and location.
They can be classified according to either their
structure or their function.
Neurons can be classified according to structure(the
number of processes extending from the cell body)
•Multipolar – possess more than two processes
Numerous dendrites and one axon, most neurons in
brain and spinal cord
•Bipolar – possess two processes
Rare neurons – found in some special sensory organs,
Retina of eye
•Unipolar (pseudounipolar) – possess one short, single
process
Start as bipolar neurons during development, located in
posterior root ganglia or sensory root of spinal nerves
and ganglia of cranial nerves

Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Classification…
312
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

Classification…
313
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

314
Tsegaye Mehare(BSc, MSc, Ass. professor of
Human Anatomy)

General Histology for Medicine is awesome

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