2. BONE (syn – Os; Osteon)
Osseous tissue, a specialised form of dense connective
tissue consisting of bone cells (osteocytes)
Embedded in a matrix of calcified intercelluar
substance
Bone matrix contains collagen fibres and the minerals
calcium phosphate and calcium carbonate
3. Functions of Bones
Bones serve several vital functions:
Mechanical
Bones provide a frame to support the body. Muscles,
tendons, and ligaments attach to bones. Without
anchoring to bones, muscles could not move the body.
Some bones protect the body's internal organs. For
instance, the skull protects the brain, and the ribs
protect the heart and lungs.
Synthesizing
Cancellous bone produces red blood cells, platelets, and
white blood cells. Also, defective and old red blood cells
are destroyed in bone marrow.
4. Metabolic
Storing minerals: Bones act as a reserve for minerals, particularly calcium
and phosphorous.
They also store some growth factors, such as insulin-like growth factor.
Fat storage: Fatty acids can be stored in the bone marrow adipose tissue.
pH balance: Bones can release or absorb alkaline salts, helping blood to
stay at the right pH level.
Detoxification: Bones can absorb heavy metals and other toxic elements
from the blood.
Endocrine function: Bones release hormones that act on the kidneys and
influence blood sugar regulation and fat deposition.
Calcium balance: Bones can raise or reduce calcium in the blood by
forming bone, or breaking it down in a process called resorption.
5. SKELETAL ORGANIZATION
• The actual number of bones in the human skeleton
varies from person to person
• Typically there are about 206 bones
• For convenience the skeleton is divided into the:
• Axial skeleton
• Appendicular skeleton
7. CLASSIFICATION OF BONES BY SHAPE
Long bones
Short bones
Flat bones
Irregular bones
Pneumatized
bones
Sesamoid bones
(Short bones include sesmoid bones)
8. LONG BONES
Diaphysis – shaft
Epiphysis – expanded
ends
Shaft – 3 surfaces, 3
borders, medullary
cavity and a nutrient
foramen directed away
from the growing end
Ex – humerus, radius,
ulna, femur, etc
9. SHORT BONES
Are small and thick
Their shape is usually
cuboid, cuneifrom,
trapezoid or scaphoid
Ex – carpal and tarsal
bones
10. FLAT BONES
Are thin with parallel surfaces.
Are found in the skull, sternum,
ribs and scapula
Form boundaries of certain body
cavities
Resembles a sandwich of
spongy bone between 2 layers of
compact bone
11. PNEUMATIC BONES
Certain irregular bones contain large air spaces lined
by epithelium
Make the skull light in weight, help in resonance of
voice, and act as air conditioning chambers for
inspired air
Ex – maxilla, sphenoid, ethmoid, etc
12. SESAMOID BONES
Resembling a grain of
sesame in size or shape
Bony nodules found
embedded in the tendons or
joint capsules
No periosteum and ossify
after birth
Related to an articular or
nonarticular bony surface
Ex – patella, pisiform,
fabella, etc
Functions
16. Membrane (dermal) bones
Ossify in membrane (intramembranous of
mesenchymal)
Derived from mesenchymal condensations
Ex – bones of the vault of skull and facial bones
Defect – cleidocranial dysostosis
17. Cartilaginous bones
Ossify in cartilage (intracartilagenous or
endochondral)
Derived from preformed cartilaginous models
Ex – bones of limbs, vertebral column and thoracic
cage
Defect – common type of dwarfism called
achondroplasia
20. BONE CELLS
ELEMENTS COMPRISING BONE TISSUE
1. It consists of bone cells or osteocytes – separated by
intercellular substance
2.Osteoblasts – bone producing cells
3. Osteoclasts – bone removing cells
4.Osteoproginator cells – from which osteoblasts and
osteoclasts derived
22. OSTEOPROGENITOR CELLS
Mesenchymal stem cells
that divide to produce
osteoblasts
•Are located in inner,
cellular layer of
periosteum
(endosteum)
•Assist in fracture repair
23. OSTEOBLASTS
Immature bone cells that
secrete matrix compounds
(osteogenesis)
Osteoid
•Matrix produced by
osteoblasts, but not yet
calcified to form bone
•Osteoblasts surrounded
by bone become
osteocytes
24. OSTEOCYTE
Mature bone cells that
maintain the bone matrix
• Live in lacunae
• Are between layers
(lamellae) of matrix
• Connect by cytoplasmic
extensions through
canaliculi in lamellae
• Do not divide
25. OSTEOCLAST
•Secrete acids and protein
digesting enzymes
•Giant, mutlinucleate cells
•Dissolve bone matrix and
release stored minerals
(osteolysis)
•Are derived from stem cells
that produce macrophages
29. PERIOSTEUM
External surface of any bone covered by a membrane –
periosteum
Two layer
Outer – fibrous membrane, inner – cellular
In young bones – inner layer – numerous osteoblasts –
osteogenitic layer
In adults – osteoblasts are not conspicuous, but
osteoprogeniter cells present here can form osteoblasts
when need arises
31. FUNCTIONS
Medium through which mucles, tendons and
ligaments are attached
Forms a nutritive function
Can form bone when required
Forms a limiting membrane that prevents bone tissue
from ‘spilling out’ into neighbouring tissues
32. CORTEX
Is made up of a compact bone which gives the
desired strength
Can withstand all possible mechanical strains
33. ENDOSTEUM
• An incomplete cellular layer:
– lines the marrow cavity
– covers trabeculae of spongy
bone
– lines central canals
• Contains osteoblasts,
osteoprogenitor cells, and
osteoclasts
• Is active in bone growth and
repair
34. MEDULLARY CAVITY
Filled with red or yellow bone marrow
1.Red – at birth – haemopoiesis
2.Yellow – as age advance – atrophies – fatty
3.Red marrow persists in the cancellous ends of
long bones
35.
36. PARTS OF YOUNG BONE
It ossifies in 3parts
The twoends from thesecondarycenters
Intervening shaft from a primary center
37. EPIPHYSIS
(Gr., a growing upon)
The ends of a bone which ossify from secondary
centers:
1. Pressure epiphysis – transmission of the weight. Ex-
head of femur, etc
2. Traction epiphysis – provides attachment to one or
more tendons which exerts a traction on the
epiphysis. Ex- trochanters of femur, etc.
38. 3. Atavistic epiphysis – phylogenitically an independent
bone , which fuses to another bone.
Example- coracoid process of scapula, etc.
4. Aberrant epiphysis – not always present.
Example- head of the 1st metacarpal and base of
other metcarpal.
39. DIAPHYSIS
(Gr., a growing through)
It is the elongated shaft of a long bone which ossifies
from a primary center
Made of thick cortical bone
Filled with bone marrow
40. METAPHYSIS
(Gr. meta, after, beyond, + phyein, to grow)
Epiphysial ends of adiaphysis
Zone of activegrowth
Typically made of cancellousbone
Hair pin bends of endarteries
41. EPIPHYSIAL PLATE OF CARTILAGE
It separates epiphysis from the metaphysis.
Proliferation – responsible for lengthwise growth of
the long bone
Epiphysial fusion – can no longer grow
Nourished by both epiphysial and metaphysial arteries
43. Nutrient artery
1. Enters through the nutrient foramen
2.Divides into ascending and descending branches in the
medullary cavity
3.Branch divides – small parallel channels – terminate in
adult metaphysis.
4.Anastomosing with the epiphysial, metaphysial and
periosteal arteries
5.Supplies the medullary cavity , inner 2/3 of the cortex
and metaphysis
6.Nutrient foramen is directed away from the growing
end of the bone
44.
45. Periosteal arteries
1. Numerous beneath the
muscular and ligamentous
attachments
2.Ramify beneath the
periosteum and enter the
volkmann’s canals to supply
the outer 1/3 of the cortex
46.
47. Epiphysial arteries
1. Derieved from periarticular vascular arcades
(circulus vasculosus)
2.Out of the numerus vascular foramina in this region
– few admit arteries and rest venous exits
3. Number size – idea of the relative vascularity of the
two ends of long bone
48. Metaphysial arteries
1. Derived from the neighbouring systemic vessels
2.Pass directly into the metphysis and reinforce the
metaphysial branches from the primary nutrient
artery
49.
50.
51. CARTILAGE (L.-cartilago – gristle)
It is a connective tissue composed of cells
(chondrocytes) and fibres (collagen) in matrix, rich in
mucopolysaccarides
Groung substance – chemically GAG
Core protein – aggrecan
Collagen – type 2
Fibrocartilage and perichondrium – type 1
52. General features
Has no blood vessels or lymphatics
Nutrition is by diffusion through matrix
No nerves – insensitive
Surrounded by a fibrous membrane – perichondrium
Articular cartilage has no perichondrium –
regeneration after injury inadequate
When calcifies – chondrocytes die – replaced by bone
55. HYALINE CARTILAGE
(G. hyalos - transparent stone)
Bluish white and transparent due to very fine collagen
fibres
Abundantly distributed – tendency to calcify after
40yrs of age
All cartilage bones are preformed in hyaline cartilage
Ex – articular cartilage, costal cartilage
56.
57.
58. FIBROCARTILAGE
White and opaque due to abundance of dense collagen
fibres
Whenever fibres tissue is subjected to great pressure –
replaced by fibrocartilage
Tough, strong and resilient
Ex – intervertebral disc, intraarticular disc
60. ELASTIC CARTILAGE
Made of numerous cells and
Rich network of yellow elastic fibres pervading the
matrix – so that it is more pliable
Cartilage in the external ear, auditory tube
