General osteology

Presentation general anatomy

1. General osteology
DR. JAMIL ANWAR

2. Plan of the lecture
1.General concepts about skeleton
2.Bone as an organ
3.Functions of the skeleton
4.Classification of bones
5.Types of bone ossification
6.Development of bones

3. The Skeletal System!
Our First System
Cells (Osteocytes)
Tissues (Osseous Tissue)
Organs (Bones)
Systems (Skeletal)

4. THE LOCOMOTOR APPARATUS – ITS
COMPONENTS AND FUNCTIONAL ROLE
The skeleton is a complex of hard
structures that is of mesenchymal origin
and possesses a mechanical significance.
The term skeleton comes from a Greek word
meaning “dried up”.
NB: All the bones and articulations of the
body make up the passive part of the
locomotor apparatus.

5. The skeleton
The science concerned
with the study of bones is
termed osteology.
The skeletal system of an
adult is composed of
approximately 206 bones.
Each bone is an organ of
the skeletal system.
For the convenience of
study, the skeleton is
divided into axial and
appendicular parts.

6. The axial skeleton
The axial skeleton
consists of 80 bones that
form the axis of the body
and which supports and
protects the organs of the
head, neck, and trunk.
Skull
Auditory ossicles
Hyoid bone
Vertebral column
Thoracic cage

7. The appendicular
skeleton
The appendicular skeleton is composed of 126
bones of the upper and lower limbs and the
bony girdles, which anchor the appendages
to the axial skeleton.
The shoulder girdle (the scapula
and clavicle)
The upper limb (the humerus,
ulna, radius and bones of the hand)
The pelvic girdle (the hip bone)
The lower limb (the femur, tibia,
fibula and bones of the foot)

8. BONE AS AN ORGAN
STRUCTURE OF A BONE AND STRUCTURE OF THE
PERIOSTEUM
Bone (osis) is one of the hardest structures of
the body. It possesses also a certain degree of
toughness and elasticity. Its color, in a fresh
state, is pinkish-white externally, and red
within.

9. Types of bone tissue
There are two types of bone tissue:
a)compact bony tissue
b)spongy bony tissue
The names imply that the two types differ in density, or how tightly the
tissue is packed together.
There are three types of cells that contribute to bone homeostasis.
a)osteoblasts are bone-forming cell
b)osteoclasts resorb or break down the bone
c)osteocytes are mature bone cells.
An equilibrium between osteoblasts and osteoclasts maintains the bone tissue.

10. OSSIFICATION
OSTEOBLASTS
FORM NEW BONE
MATRIX
COLLAGEN
STERNGTH
CALCIUM DEPOSITION
OSTEOCYTES
MAINTAIN BONE
OSTEOCLASTS
MAINTAIN SHAPE

11. Structure of bone
On examining a cross section of
any bone, it is composed of two
kinds of bony tissue:
Compact tissue, it is dense in
texture and it is always placed
on the exterior of the bone.
Cancellous tissue consists of
slender fibers and lamellae,
which join to form a reticular
structure and it is placed in the
interior of the bone

12. Macromicroscopic
structure of bone
The morphofunctional unit of
the bone is the osteon, or
Haversian system.
The osteon consists of a
system of bony lamellae
arranged concentrically around
a canal, which is called
Haversian canal and this canal
contains nerves and vessels.
The bone lamellae consist of
osteocytes, their lacunae, and
interconnecting canaliculi and
matrix.

14. The spongy bone tissue
Spongy (cancellous) bone
is lighter and less dense
than compact bone.
Spongy bone consists of
plates (trabeculae) and bars
of bone adjacent to small,
irregular cavities that
contain red bone marrow.
The canaliculi connect to
the adjacent cavities,
instead of a central
haversian canal, to receive
their blood supply.

15. The spongy bone tissue
It may appear that the
trabeculae are arranged in a
haphazard manner, but
they are organized to
provide maximum strength
similar to braces that are
used to support a building.
The trabeculae of spongy
bone follow the lines of
stress and can realign if the
direction of stress changes.

16. The periosteum
Externally bone is covered by
periosteum (except articular
surfaces). The periosteum
adheres to the surface of the
bones.
It consists of two layers closely
united together:
a)The outer layer fibrous
layer
b)The inner layer or bone-
forming layer (cambial)

17. Structure of
the periosteum
The periosteum is rich in
vessels and nerves, and it
contributes to the nutrition
and growth of the bone in
thickness. Nutrients are
conveyed by blood vessels
penetrating in great number
the outer (cortical) layer of
the bone from the
periosteum through
numerous vascular
openings (foramina
nutricia).

18. The interior of
each long tubular
bone of the limbs
presents a
cylindrical cavity
named marrow
cavity and it is
lined with the
medullary
membrane called
endosteum.

19. Chemical Composition of Bone

20. Functions of the skeletal system
1. Support - framework for the body
2. Protection - skull, vertebrae, ribcage
3. Leverage - bones are levers, joints are
fulcrums
4. Mineral storage – (calcium)
5. Lipid Storage – (yellow marrow)
6. Blood cell formation - hematopoiesis

21. Functions of the skeleton
Biological functions
Mechanical functions

22. Biological functions of the skeleton
a)Haemopoiesis
b)Mineral storage.

23. Bone marrow
The bony compartments contain bony marrow,
medulla ossium. Two types of bone marrow can be
distinguished:
red bone marrow
white bone marrow
The white or yellow marrow fills up the medullary
cavities of the shafts of the long tubular bones.
The red marrow is located within the cancellous
tissue and extends into the larger bony canals
(Haversian canals) that contain blood vessels.

24. Haemopoiesis function
The bone marrow provides
haemopoiesis function and biological
protection of the organism. It takes
part in nutrition, development and
growth of the bone. The red marrow
concerned with haemopoiesis and bone
formation, has an active role in the
healing of fractures. Red marrow
predominates in infants and in
children, with growth of child the red
marrow is gradually replaced by
yellow marrow.
NB: The
bones of the
embryo and
new-born
contain only
red marrow.

25. Haemopoiesis function
The red bone marrow of an adult produces white
blood cells, red blood cells, and platelets.
In an infant, the spleen and liver produce red blood
cells, but as the bones mature, the bone marrow
performs this task.
It is estimated that an average of 1 million blood
cells are produced every second by the bone marrow
to replace those that are worn out and destroyed by
the liver.

26. Mineral storage
The inorganic matrix of bone is
composed primarily of minerals
calcium and phosphorus. These
minerals give bone rigidity and
account for approximately two-
thirds of the weight of bone.
About 95% of the calcium and 90%
of the phosphorus, within the body,
are stored in the bones and teeth.
In addition to calcium and
phosphorus, lesser amounts of
magnesium and sodium salts are
stored in bones.

27. Mechanical functions of the skeleton
a)Support
b)Protection
c)Body movement

28. Support (weight bearing)
The skeleton forms a
rigid framework to
which are attached the
soft tissues and organs
of the body.

29. Protection
function
Protection is assured by the
property of the bones to form
body cavities which protects the
vital important organs.
The skull and vertebral column
enclose the central nervous system.
The thoracic cage protects the heart,
lungs, great vessels, liver and
spleen.
The pelvic cavity supports and
protects pelvic organs.
Even the site where blood cells are
produced is protected within the
central portion of certain bones.

30. Body movement
Bones serve as anchoring
attachments for most
skeletal muscles. In this
capacity, the bones act as
levers, with the joints
functioning as pivots, when
muscles, which are
regulated by the nervous
system, contract to cause
the movement.

31. Classification of bones by shape
Tubular bones
a) Long tubular bones
humerus,
radius, ulna,
femur,
tibia, fibula
b) Short tubular bones
metacarpal,
metatarsal bones and phalanges

32. Classification of bones
Spongy bones
a) Long spongy bones
sternum,
ribs, etc
b) Short spongy bones
carpal and tarsal bones
c) Sesamoid bones
knee-cap
pisiform bone, etc.

33. Classification of bones
Flat bones
Skull bones
Bones of the vault of the
skull
Girdle bones
The scapula
The hip bone, etc.

34. Classification of bones
Mixed bones
The vertebrae are mixed, or
irregular bones (their bodies
are referred to spongy
bones, but their arches and
processes are referred to flat
bones).

35. Bone formation (osteogenesis)
Osteogenesis occurs throughout life but in different
ways
1. embryo responsible for laying down of bony
skeleton (ossification well started by 8
th
week)
2. bone growth continues until early adulthood
3. remodeling & repair continues for life
•Ossification - The process of replacing other
tissues with bone (endochondral and
intramembranous)
Calcification - The process of depositing calcium
salts
Occurs during bone ossification and in other
tissues

36. 2 types of ossification
1. Intramembranous (dermal ossification)
Formation of most of the flat bones of the skull and the
clavicles from a fibrous membrane
Fibrous connective tissue membranes are formed by
mesenchymal cells
2. Endochondral
Formation of bone in hyaline cartilage
Both lead to the same type of bone
Both begin with migration of mesenchymal cells from c.t. to
areas of bone formation
No blood supply chondroblasts
Blood supplyosteoblasts

37. Intramembranous Ossification: Step 1
Mesenchymal cells
aggregate:
differentiate into
osteoblasts
begin ossification
at the ossification
center
develop
projections called
spicules

38. Intramembranous Ossification: Step 2
Blood vessels grow
into the area:
to supply the
osteoblasts
Spicules connect:
trapping blood
vessels inside bone

39. Intramembranous Ossification: Step 3
Spongy bone develops and
is remodeled into:
osteons of compact bone
periosteum
or marrow cavities

40. Endochondral Ossification
Begins in the second month of
development
Uses hyaline cartilage “bones” as models
for bone construction
Requires breakdown of hyaline cartilage
prior to ossification

41. Endochondral Ossification: Step 1
Chondrocytes in the
center of hyaline
cartilage:
enlarge
form struts and calcify
die, leaving cavities in
cartilage

42. Endochondral Ossification: Step 2
Blood vessels grow
around the edges of the
cartilage
Cells in the
perichondrium change
to osteoblasts:
producing a layer of
superficial bone around
the shaft which will
continue to grow and
become compact bone .

43. Endochondral Ossification: Step 3
Blood vessels enter the
cartilage:
bringing fibroblasts that
become osteoblasts
spongy bone develops at
the primary ossification
center

44. Endochondral Ossification: Step 4
Remodeling creates a
marrow cavity:
bone replaces cartilage
at the metaphyses

45. Endochondral Ossification: Step 5
Capillaries and
osteoblasts enter the
epiphyses:
creating secondary
ossification centers

46. Endochondral Ossification: Step 6
Epiphyses fill with
spongy bone:
cartilage within the
joint cavity is
articulation cartilage
cartilage at the
metaphysis is
epiphyseal cartilage

47. Primary centers of ossification
In the second month of the
intrauterine life, the
primary points of
ossification appear first, in
the shafts, or diaphyses of
tubular bones, and in the
metaphyses.
They ossify by
perichondral and
enchondral osteogenesis.

48. Secondary and accessory
points of ossification
The secondary points of
ossification appear shortly
before birth or during the
first years after birth and
they develop by encondral
osteogenesis.
The accessory points of
ossification appear in
children, adolescents, and
even adults in the
appophyses of bones (e.g.
tubercles, trochanters, the
accessory processes of the
lumbar vertebrae).

49. Blood Supply of Mature Bones
3 sets of blood vessels develop
Nutrient artery and vein:
a single pair of large blood
vessels enters the diaphysis
through the nutrient foramen
Metaphyseal vessels:
supply the epiphyseal cartilage
where bone growth occurs
Periosteal vessels provide:
blood to superficial osteons
secondary ossification centers

50. Effects of Hormones and Nutrition on Bone
1. Growth hormone
Single most important stimulus to the
epiphyseal plate (dwarfism/gigantism)
2. Thyroid hormone
Moderates growth hormone to insure proper
proportions of growth
3. Sex hormones (estrogens & androgens)
A great ‘rush’ at puberty = growth spurt
Lead to a breakdown of cartilage that leads
to a closure of plates …steroids!
4. Calcitriol
Made in kidneys; synthesis requires cholecalciferol
Helps absorb calcium & phosphorus from GI tract

51. Additional dietary regulators
Need adequate calcium, phophorus, magnesium,
flouride, iron, & manganese
Calcium is necessary for:
Transmission of nerve impulses
Muscle contraction
Blood coagulation
Secretion by glands and nerve cells
Cell division
Vitamin D – absorption of calcium from GI
Vitamin C – formation of collagen
Vitamin A – stimulates osteoblast activity
Vitamins K and B
12
- help synthesize bone proteins

52. Bone Fractures (Breaks)
Bone fractures are classified by:
The position of the bone ends after fracture
The completeness of the break
The orientation of the bone to the long axis
Whether or not the bones ends penetrate the skin

53. Types of Bone Fractures
Nondisplaced – bone ends retain their normal position
Displaced – bone ends are out of normal alignment
Complete – bone is broken all the way through
Incomplete – bone is not broken all the way through
Linear – the fracture is parallel to the long axis of the bone
Transverse – the fracture is perpendicular to the long axis of the bone
Compound (open) – bone ends penetrate the skin
Simple (closed) – bone ends do not penetrate the skin
Comminuted – bone fragments into three or more pieces; common in the
elderly
Spiral – ragged break when bone is excessively twisted; common sports
injury
Depressed – broken bone portion pressed inward; typical skull fracture
Compression – bone is crushed; common in porous bones
Epiphyseal – epiphysis separates from diaphysis along epiphyseal line;
occurs where cartilage cells are dying
Greenstick – incomplete fracture where one side of the bone breaks and
the other side bends; common in children

54. The Major Types of Fractures

55. The Major Types of Fractures

56. Fracture Repair: Step 1
Bleeding:
produces a clot
(fracture hematoma)
establishes a fibrous
network
Bone cells in the area
die

57. Fracture Repair: Step 2
Cells of the endosteum
and periosteum:
Divide and migrate into
fracture zone
Calluses stabilize the
break:
external callus of
cartilage and bone
surrounds break
internal callus develops
in marrow cavity

58. Fracture Repair: Step 3
Osteoblasts:
replace central
cartilage of
external callus
with spongy bone

59. Fracture Repair: Step 4
Osteoblasts and
osteocytes remodel the
fracture for up to a year:
reducing bone
calluses

60. Osteoporosis
Bone reabsorption>bone
production
Osteopenia begins between
ages 30 and 40
Women lose 8% of bone mass
per decade, men 3%
Decrease in bone
massincrease fracture risk
Decreased levels of estrogen
primarily
Most important cause of fracture
in women>50
35% of bone mass may be gone
by age 70
Vertebrae & femur neck are
most affected
Risk Factors
Body build – short
women have less bone
mass
Weight – thinner at
greater risk
Smoking – decreases
estrogen levels
Lack of dietary calcium
Exercise – decrease rate
of absorption
Drugs – alcohol,
cortisone, tetracycline
Premature menopause

61. Osteopenia
Figure 6–19 The Effects of Osteoporosis on Spongy Bone.

62. Homeostatic Imbalances
Osteomalacia
Bones are inadequately mineralized causing softened,
weakened bones
Main symptom is pain when weight is put on the affected
bone
Caused by insufficient calcium in the diet, or by vitamin D
deficiency
Rickets
Bones of children are inadequately mineralized causing
softened, weakened bones
Bowed legs and deformities of the pelvis, skull, and rib cage
are common
Caused by insufficient calcium in the diet, or by vitamin D
deficiency

63. Developmental Aspects of Bones
The embryonic skeleton ossifies in a predictable
timetable that allows fetal age to be easily determined
from sonograms
At birth, most long bones are well ossified (except for
their epiphyses)
By age 25, nearly all bones are completely ossified
In old age, bone resorption predominates
A single gene that codes for vitamin D docking
determines both the tendency to accumulate bone mass
early in life, and the risk for osteoporosis later in life

64. THE END