1. Bone Histology and Movement
Module #4

2. Characteristics of Bone Tissue
Called Osseous tissue
Is a type of connective tissue
Two types :
1. Compact – strength
2. Spongy – lighter weight

3. Characteristics of compact bone tissue:
 Composed of:
1. Hydroxyapatite - ionic compound
composed of calcium and phosphorus.
Ca10(PO4)6(OH)2
2. Ground substance (water and other
proteins)
3. Collagen

4. The characteristics of compact bone:
 Hydroxyapatite and other minerals
give bone its hardness and compressive
strength
Collagen (protein) fibers give bone its
flexibility.

5. Compact bone - Functional unit
called an osteon.
Osteon

6. Osseous Tissue
Bone contains 4 types of cells:
1. Osteogenic
2. Osteoblasts
3. Osteocytes
4. Osteoclasts

7. 1. Osteogenic cells
 Osteogenic cells are stem cells that
divide to produce osteoblasts.
 Assist in repairing bone fractures.
 Overproduction causes osteogenic
sarcoma (cancer).

8. Osteogenic Sarcoma

9. 2. Osteoblast cells
 Osteoblasts are immature bone cells
that secrete the matrix
 When osteoblasts are surrounded by
bone, they mature and become
osteocytes.

10. 3. Osteocyte cells
 Osteocytes are mature bone cells
that maintain the bone matrix.
 Each osteocyte lives in a lacuna.
 Canaliculithrough the lamellae allow
osteocytes to obtain necessary
nutrients.

11. 3. Osteocyte cells continued
 Osteocytes do not divide.
 The main functions of osteocytes are:
1. to maintain the protein and mineral
content of the matrix.
2. to help repair damaged bone.

12. Osteocyte
Osteocyte

13. 4. Osteoclast cells
 Osteoclasts
are very large cells that
remodel bone.(break down old bone)
Note:
 Bone building and bone recycling must
be kept in balance. When osteoclasts
break down bone faster than osteocytes
build bone, bones become weak.

14. Osteoclast
Osteoclast

15. Note:
 Wolff'slaw : Bones get stronger
with exercise, stress causes
osteocytes to build more bone.
 Bone remodeling: Bone is broken
down because it deteriorates over
time and must be replaced. Also
minerals are released that the body
needs.

17. Osseous Tissue

18. Structure of compact bone
 Osteon –basic unit.
 Osteocytes are arranged in
concentric circles (concentric lamella)
around a central canal called the
Haversian canal
which contains the
blood vessels.

20. Structure of compact bone
 Connecting the central canal is
the perforating canals called the
canaliculi carry nutrients to the
osteocytes
 Lacunae – spaces in the rings where
osteocytes are found

21. Structure of compact bone
 In between the osteons is interstitial
lamellae or “packing material”

22. Structure of compact bone:
Circumferential lamallae - A bony
layer that underlies the periosteum
or endosteum.

23. Structure of compact bone
 Perforating canal – canals in the bone
that blood vessels pass sideways between
Haversian canals

26. Structure of compact bone
 All osteons in long bones run
the length of the bone,
strengthening the bone in that
direction.

27. Structure of compact bone
 All osteons in long bones run
the length of the bone,
strengthening the bone in that
direction.

28. Spongy bone
Found in the
center of bones
and on the ends
Light weight

29. Structure of spongy bone
Spongy bone
does not have
osteons. Its
matrix forms an
open network of
trabeculae.

30. Structure of spongy bone
 no blood vessels
 Spacesare filled
with red bone
marrow which has
blood vessels and
supplies nutrients to
the osteocytes.

31. Structure of spongy bone
 Red bone marrow
is red because it
forms red blood
cells.
 In other bones,
spongy bone may
hold yellow bone
marrow, which is
yellow because it
stores fat.

32. Bone formation
 Human bones grow until about age
25.
 The process of replacing cartilage
tissue with bone is called
ossification.

33. Growth in length of long bone
Epiphyseal plate is the site of
growth in the long bone. Located
between epiphysis and diaphysis.
Epiphyseal plate is composed of
hyaline cartilage with chondrocytes
(reproductive).

34. Growth in long bone:
1.At epiphyseal plate chondrocytes
will reproduce.
2.New chondrocytes are laid down on
the epiphysis end of bone
3.Old chondrocytes on the diaphysis
end will elongate the lacunae.
4.Calcium salts will be laid down
around elongated lacunae.
5.Chondrocyte is cut off from nutrients
and will die.

35. Growth in long bone:
6.Blood vessels will grow in lacunae
of dead chondrocytes and bring
osteoblasts.
7.Osteoblasts will produce and
maintain bone matrix and mature to
osteocytes.
8.Therefore, spongy bone will of
epiphysis is remodeled into compact
bone and diaphysis increases in
length.

36. Growth in long bone
NOTE: Epiphysis can grow in the
same way except from the articular
cartilage at the end of bone.

37. Growth in long bone
Appositional bone growth –
growth in width of the bone.
Osteoblast lay down new matrix
on top of old matrix expanding
diameter.

38. Bone Remodeling
Old bone broken down by osteoclast
and rebuilt by osteoblast.
Reasons:
1.Change spongy bone to compact
2.Increase/decease mass of bones
3.Repair damaged
4.Replace worn out collagen

39. Bone Remodeling
How:
Osteoclasts secrete acids and
proteolytic enzymes that break down
and dissolve bone salts and digest
proteins (collagen).
Osteoblast brought in by damaged
blood vessels to lay down new
matrix.

40. Diseases of the bone:
1. Rickets – low calcium and
phosphorous levels in the blood
leading to a lack of hydroxyapatite in
the bones resulting in the bones
becoming rubbery.
Cause: lack of Vitamin D in the
diet which regulates Ca and P

42. Diseases of the bone:
2. Brittle Bone Disease Osteogenesis imperfecta –
Result of decreased amount of
collagen making the bones brittle.
Cause – genetic

43. Fractures
Fractures are repaired in 4 steps:
Step 1. Hematoma forms
Bleeding produces a clot called
the fracture hematoma
Bone cells in the area die.

44. Fractures
 Fractures are repaired in 4 steps:
Step 2. Callus forms
A callus (mass of tissue that connects
the ends of broken bone) is formed.
Internal callus forms new bone tissue
and is found between the breaks
External callus stabilizes the bone while
it begins to heal and is found around the
outside of the bone

45. Fractures
Fractures are repaired in 4 steps:
Step 3 Callus is ossified
Osteoblasts replace the
central cartilage of the
external callus with spongy
bone.

46. Fractures
Fractures are repaired in 4 steps:
Step 4. External callus
removed and remodeled
Osteoblasts and osteocytes
continue to remodel the
fracture for up to a year,
reducing the bone calluses.