2. •The human skeleton which forms the main
supporting framework of the body , includes
bone and cartilages.
•The component of skeletal system primarily
involved in the production of movement.
3. Bone
Bone is a specialized , highly vascular, living constantly changing,
mineralized connective tissue.
Its mineral component gives hardness and rigidity to the bone to resist
compression forces.
Its organic component, collagen fibers, makes it resilient to resist
tensile forces.
Despite its hardness, bone is constantly modelled by the forces acting
on it, showing disuse atrophy and overuse hypertrophy.
It is subjected to disease and heal after a fracture due to its great
regenerative capacity.
4.
5. COMPOSITION OF BONE
A) Cells
B) Ground substance
C) Fibres
Cells:- Osteoblast , Osteocytes , Osteoclast.
Ground substance:- Proteoglycans , Glycoproteins , Mineral like calcium and
phosphorus and water.
Fibres :- Type-1 collagen fibres.
6. Osteoblast:-
Are derived from osteoprogenitor cells.
Secret osteoid –an unmineralized matrix.
For mineralization osteoblast secret osteocalcin and alkaline phosphatase.
They undergo mitosis.
Osteocytes:-
Are derived from osteoblast.
Osteoblast once surrounded by matrix is called as osteocyte.
Are flat cells with numerous cytoplasmic projections.
Located in lacuna.
No mitosis occur
7. Osteoclast :-
Are related to a WBC-monocyte.
Are large cells with multiple nuclei.
Help in resorption of bone and remodelling of bone.
8. Functions of Bones
• Provide shape and support to the body.
• Provide attachment to muscles, tendons and ligaments.
• Act as levers for movements.
• Protect vital organs like brain , spinal cord, heart etc.
• Act as store house for calcium and phosphorous.
9. • Bone marrow has blood forming function.
• Paranasal air sinuses in skull add resonance to voice.
• Ear ossicles help to transmit sound waves.
10. Classification of Bones
The adult human skeleton is composed of 206 bones.
According to Region:
Human skeleton is divided into :
1.Axial skeleton : Forms the central framework of the body
i.e. head, neck, and trunk e.g. skull vertebrae, ribs,
sternum.
Cranium and face : 22
Ear ossicles : 6
Hyoid : 1
Vertebrae : 26
( cervical 7, thoracic 12, lumbar 5, sacral 1, coccyx 1).
Ribs : 24
Sternum : 1
Total : 80 bones.
11. 2. Appendicular skeleton: includes the peripheral bones of
the limbs.
Upper limbs : 64
Lower limbs : 62
Total : 126 bones.
12. According to development
1. Membrane bones: develop direct from mesenchyme into bone
by intramembranous ossification e.g. cranial vault, and facial bones
like parietal frontal etc.
2. Cartilaginous bones: develop from preformed cartilaginous
model by intra cartilaginous ossification e.g. bones of limbs, bones of
thoracic cage.
3. Membrano-cartilaginous bones: Have both types of
ossification processes, developing partly in membrane and partly in
cartilage e.g. clavicle, mandible.
13. According to structure
1. Compact bone:
• Present in the outer surface
of all bones.
• well develop in outer cortex
of long bones.
• Able to resist mechanical
pressure.
14. 2. Cancellous bone :
• Mainly present in the interior of the bones.
•Made up of network of trabeculae.
•Meshwork of spaces contain bone
marrow.
•Cancellous bone is adapted to resist
compressive forces.
15. According to shape :
a. Long bone : e.g. femur, humerus, radius.
b. Miniature long bones : e.g. metatarsals phalanges and
metacarpals.
c. Short bones : e.g. carpals , tarsals.
d. Flat bones : e.g. cranial vault bones, ribs, sternum, scapula.
e. Irregular bone : e.g. hip bone, vertebrae.
16. f. Pneumatic bone : Contains mucous membrane lined air
filled spaces.
g. Sesamoid bone : seed like bone like patella.
h. Accesory bones : Sometimes present in the limbs and
skull. E.g. sutural bone.
17. Features of sesamoid bone :
• seed like bony nodules.
• developing in tendons .
• devoid of periosteum.
• have no haversian system.
Functions of sesamoid bone :
a. To minimize friction.
b. To alter the direction of pull of the muscle.
c. To modify pressure.
18. Example of sesamoid bone:-
a) Patella –in the tendon of quadricep femoris in knee joint.
b) Fabella:- in the lateral head of gastrocnemius behind knee joint.
c) Two lie below the head of 1st metatarsal bone in the tendon of FHB.
d) Pisiform:- in the tendon of FCU.
19. Parts of young long bones :
Diaphysis : It is elongated shaft of a long bone .
ossify from a primary centre.
Periosteum
• fibrous membrane covering the surface of the bone.
• osteogenic in nature.
•It is the most sensitive part of bone.
Cortex
•Made up of compact bone , which withstand the mechanical strains.
Medullary cavity
•Filled with yellow or red bone marrow.
20.
21. Epiphysis:
• Ends of long bone, including both articular and non-articular
parts.
• ossify from secondary centers.
There are following types of epiphysis :
a. Pressure epiphysis.
b. Traction epiphysis.
c. Atavistic epiphysis.
d. Aberrant epiphysis.
22.
23. a. Pressure epiphysis : it transmit the body weight and is articular
e.g. head of femur, lower end of radius.
b. Traction epiphysis : non articular, produce by the pull of muscle
attach to it does not takes part in weight transmission. e.g.
trochanters of femur and tubercle of humerus.
c. Atavistic epiphysis : Phylogenetically an independent bone but with
the progress of time; retrogressed and fused with adjacent bone. E.g.
coracoids process of scapula and os trigonum of lateral tubercle of
talus.
d. Aberrant epiphysis : Not always present . E.g. epiphysis at the head
of the first metacarpal.
24. Metaphysis
•Portion of diaphysis adjacent to the epiphyseal cartilage is
called as metaphysis.
•consist of vascular tissue where the growth activities are
manifested.
25. Blood supply of long bones
A long bone gets its blood supply from the following sources :
Nutrient Artery
• The nutrient artery enters the long bone through the nutrient foramen.
• On entering into the bone artery soon divides into two branches, one for
each end of the bone.
• Radial branches enters the haversian canal and volkman’s canal and
supply the cortex.
Metaphyseal arteries
• These are small arteries derived from arterial anastomosis around the
joint.
26.
27. Epiphyseal Arteries
• These are derived from periarticular arterial arcade found on non
articular bony surface.
• Enters the epiphysis through vascular foramina to supply it.
Periosteal arteries
• These blood vessels lie with in the periosteum and end by supplying the
superficial part of cortex.
28. Development and ossification of bones
Ossification : formation of bone is known as ossification.
It may be of following types :
a. Intramembranous: bone develop from mesoderm.
b. Cartilaginous: bone develops from cartilage.
c. Membranocartilaginous: Partly from membrane and partly from
cartilage.
29. Law of ossification states that:
All secondary centers of ossification appear after birth ,
except , lower end of femur ( center appears in 9th month of
IUL ) and in some cases proximal end of tibia and head of
humerus.
The epiphysis which is first to appear is the last to join the
diaphysis and vice versa except fibula.
30. Cartilage
Cartilage is a connective tissue composed of cells and fibres
embedded in a firm, gel- like matrix which is rich in a
mucopolysaccharide. It is much more elastic than bone.
Features
•Devoid of vessels, nutrition reaches via diffusion.
• Surrounded by a fibrous membrane , called perichondrium,
which is similar to periosteum.
•After calcification of cartilage the chondrocytes die and the
cartilage is replaced by bone like tissue.
31. Types of cartilage
There three types of cartilages:
a. Hyaline cartilage.
b. Fibro cartilage.
c. Elastic cartilage.
32. Hyaline cartilage Fibro cartilage Elastic cartilage
Fibres Very thin , having
same refractive index
as matrix, so these are
not seen
Numerous white
fibres
Numerous yellow
fibres.
Appearance Shiny or translucent Opaque Opaque.
Color Bluish white Glistening white Yellow
Location Long bones articular
surfaces e.g. sternum,
ribs,.
Intervertebral disc ,
pubic symphysis,
sternoclavicular
joint.
Pinna, Eustachian
tube, vocal process.
Etc.
Elasticity flexible Firm and strongest. Most flexible.
