Introduction of tissue - Epithelial tissue

Tissue- Definition
Type of Tissue
Epithelial tissue
Types of epithelial tissue

1. Chapter: 2
The Tissues
Part 1: Introduction and Epithelial tissue and
its types
By: BithikaBaidya
Content:
•Tissue:Definitionandbasicclassification
•EpithelialTissue:Definitionandcharacteristic
•EpithelialTissue:Classification(Structure,locationandfunction)

2. •Tissue: Definition
The word ‘Tissue’ comes from an old French verb meaning ‘to weave’
•Definition:
✓“Tissues are aggregates or groups of cells organized to perform one or more specific
functions.”
✓“Tissues are a group of cell that have similar structure, act together to perform specific
function and have same origin.”
✓“A tissue is a group of cells that usually have a common embryonic origin and function
together to carry out specialized activities.”

3. •Typesoftissues
Bodytissuescanbeclassifiedintofourbasictypesaccordingtostructureand
function:
1.Epithelialtissuecoversbodysurfacesandlinesholloworgans,bodycavities,
andducts.Italsoformsglands.(OriginEctoderm)
2.Connectivetissueprotectsandsupportsthebodyanditsorgans.Varioustypesof
connectivetissuebindorganstogether,storeenergyreservesasfat,andhelp
provideimmunitytodisease-causingorganisms.(OriginMesoderm)
3.Musculartissuegeneratesthephysicalforceneededtomakebodystructures
moveandgeneratesbodyheat.(origin)
4.Nervoustissuedetectschangesinavarietyofconditionsinsideandoutsidethe
bodyandrespondsbygeneratingactionpotentials(nerveimpulses)thatactivate
muscularcontractionsandglandularsecretions.(OriginEctoderm)

4. •EpithelialTissue:Definitionandcharacteristic
Anepithelialtissue(ep-i-THE¯-le¯-al)orepithelium(pluralisepithelia)consistsofcellsarrangedincontinuous
sheets,ineithersingleormultiplelayers.Epithelialtissueformscoveringsandliningsthroughoutthebody.
•Characteristic
✓Thecellsarecloselypackedandareheldtightlytogetherbymanycelljunctions.
✓Thereislittleintercellularspacebetweenadjacentplasmamembranes.
✓Itisnevercoveredbyanothertissue,soitalwayshasafreesurface.
✓Therearevarioussurfaces-Apicalsurfaceoftheepitheliumfacesthebodysurfaceorbodycavityanditmay
containciliaormicrovilli.Thelateralsurfacesofanepithelialcellfacetheadjacentcellsoneitherside.The
basalsurfaceofanepithelialcellisoppositetheapicalsurface,andthebasalsurfacesadheretobasement
membrane
✓Thebasementmembraneisathinextracellularthatfunctionsasapointofattachmentandsupportforthe
overlyingepithelialtissue.

5. •Types of epithelial tissue
•The bases for classifying epithelium tissue is
Cell shapes:
1.Squamous cellsarranged like floor tiles and are
thin.
2.Cuboidal cells are shaped like cubes or hexagon
3.Columnar cellsare much taller than they are wide,
like columns.
Arrangement of layers:
1.Simple:-single layer of cells present
2.Stratified:-multiple layers of cells are present

6. Combining the two characteristics (arrangements of layers
and cell shapes), the types of covering and lining epithelia
are as follows:
1. Simple epithelium
a)Simple squamous epithelium
b)Simple cuboidal epithelium
c)Simple columnar epithelium (nonciliated and ciliated)
d)Pseudostratified columnar epithelium (nonciliated and
ciliated)
2. Stratified epithelium
a)Stratified squamous epithelium
b)Stratified cuboidal epithelium
c)Stratified columnar epithelium
d)Transitional epithelium

7. 1. Simple epithelium
a)Simple squamous epithelium
Description:Single layer of flattened cells with disc-shaped centrally located nucleusand sparse cytoplasm; the simplest of the
epithelia.
Location: Lines heart, blood vessels, lymphatic vessels, air sacs of lungs, glomerular (Bowman’s) capsule of kidneys, and inner
surface of the tympanic membrane (eardrum); forms epithelial layer of serous membranes, such as the peritoneum, pericardium,
and pleura.
Function: Filtration, diffusion, osmosis, and secretion in serous membranes.
Nuclei of squamous
Epithelialcells
Air sacs of
lung tissue
Photomicrograph: Simple squamous epithelium
forming part of the alveolar (air sac) walls (125x).
Lungs

8. b) Simple cuboidal epithelium
Description: Single layer of cube-shaped cells; centrally located nucleus.
Location: Covers surface of ovary, lines anterior surface of capsule of the lens of the eye, forms the pigmented epithelium at
the posterior surface of the eye, lines kidney tubules and smaller ducts of many glands, and makes up the secreting portion of
some glands such as the thyroid gland and the ducts of some glands such as the pancreas.
Function: Secretion and absorption.
Simple cuboidal
Epithelialcells
Kidney tubules
Photomicrograph: Simple cuboidal
epithelium in kidney tubules (430x).

9. b) Simple columnar epithelium
Description:Singlelayeroftallcellswithroundtoovalnuclei;somecellsbearcilia;layermaycontainmucus-secreting
unicellularglands(gobletcells).
Location:(Ciliated)Coverssurfaceofovary,linesanteriorsurfaceofcapsuleofthelensoftheeye,formsthepigmented
epitheliumattheposteriorsurfaceoftheeye,lineskidneytubulesandsmallerductsofmanyglands,andmakesupthe
secretingportionofsomeglandssuchasthethyroidglandandtheductsofsomeglandssuchasthepancreas.
(Non-ciliated)Linesthegastrointestinaltract(fromthestomachtotheanus),ductsofmanyglands,andgallbladder
Function:Secretionandabsorption
Photomicrograph: Simple columnar epithelium
of the stomach mucosa (860X).
Simple columnar
Epithelialcell
Basement
membrane
gastrointestinal tract

10. d) Pseudostratified columnar epithelium:
Description: Not a true stratified tissue; nuclei of cells are at different levels; all cells are attached to basement membrane,
but not all reach the apical surface.
Location: Pseudostratified ciliated columnar epithelium lines the airways of most of upper respiratory tract;
pseudostratified non-ciliated columnar epithelium lines larger ducts of many glands, epididymis, and part of male urethra.
Function: Secretion and movement of mucus by ciliaryaction.
Photomicrograph: pseudostratified
columnar epithelium lining the human trachea (570x).
Pseudostratified
Epitheliallayer
Trachea
cilia

11. 2. Stratified epithelium
a) Stratified squamous epithelium:
Description: Several layers of cells; cuboidal to columnar shape in deep layers; squamous cells form the apical layer and
several layers deep to it; cells from the basal layer replace surface cells as they are lost.
Location: Keratinized variety forms superficial layer of skin; non-keratinized variety lines wet surfaces, such as lining of the
mouth, esophagus, part of larynx, part of pharynx, and vagina, and covers the tongue.
Function:Protects underlyingtissues in areas subjected to abrasion
Photomicrograph: Stratified squamous epithelium
lining the esophagus (285x).
Stratified
squamous
epithelium
Mouth, part of larynx,
pharynx

12. b) Stratified cuboidal epithelium (Rare)
Description: Two or more layers of cells in which the cells in the apical layer are cube-shaped.
Location: Ducts of adult sweat glands, salivary gland, mammary gland and part of male urethra.
Function: Protection and limited secretion and absorption.
Photomicrograph: Stratified cuboidal epithelium
Forming salivary gland duct
salivary gland
Stratified cuboidal
epithelium

13. c) Stratified columnar epithelium (Rare)
Description: Several layers of irregularly shaped cells; only the apical layer has columnar cells.
Location:Lines part of urethra, large excretory ducts of some glands, such as esophageal glands, small areas in anal
mucous membrane, and part of the conjunctiva of the eye.
Function: Protection and secretion
Photomicrograph: Stratified columnar epithelium
Lining male urethra
Stratified columnar
epithelium
male urethra

14. d)Transitionalepithelium
Description:Appearanceisvariable(transitional);shapeofcellsinapicallayerrangesfromsquamous
(whenstretched)tocuboidal(whenrelaxed).
Location:Linesurinarybladderandportionsofuretersandurethra.
Function: Stretches readily and permits distension of urinary organ
by contained urine.
urinary bladder
Photomicrograph: Transitional epithelium lining
the urinary bladder, relaxed state (360X);
Transitional
epithelium

15. Questions:
1.Define Tissue
2.Enlist the basic types of tissue found in the body.
3.Define: Epithelium tissue
4.What are the characteristics of epithelial tissues?
5.Enlist the various function of epithelial tissue.
6.What is the function of the basement membrane?
7.Write a note on Simple Epithelial tissue and its types.
8.Write a note on Stratified Epithelial tissue and its types.
References:
Principles of Anatomy and Physiology -12th Edition Gerard J. Tortoraand Bryan Derrickson
Essentials of Anatomy and Physiology (Pictures credit)
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