1. Chapter 6
Bone Tissue

2. Support of soft tissues and attachment of Tendons and skeletal muscle.
Function of Bone Tissue
Support of soft tissues and attachment of
Tendons and skeletal muscle.
2. Protection of internal organs
3. Movement (skeletal muscle contraction)
4. Mineral storage
5. Blood cell production in red marrow
6. Fat storage in yellow marrow

3. Structure of Bone-long bones
1. Diaphysis-bone shaft
2. Epiphysis-distal and proximal ends of bone
3. Metaphyses- regions where diaphysis joins epiphyses
(growing-epiphyseal plate)
4. Articular cartilage-hyaline cartilage covering epiphysis at
articulation
5. Periosteum-connective tissue sheath surrounding bone not
covered by articular cartilage-attached to bone
via perforating fibers
Medullary cavity-space within diaphysis containing
yellow marrow
7. Endosteum-thin membrane lining medullary cavity-contains
bone-forming cells

6. Types of cells in bone tissue
1. Osteogenic-stem cells from mesenchyme-only bone cells that
undergo cell division
2. Osteoblasts-synthesize and secrete collagen for the extracellular
matrix, initiate calcification
3. Osteocytes-mature bone cells, exchange nutrients and waste
with blood, maintain the bone tissue.
4. Osteoclasts-large cells, found in endosteum. Secretes
lysosomal enzymes for bone resorption, regulates blood Ca2+

7. Compact vs. Spongy Bone
Osteons vs. trabeculae (protect red marrow)
Strength vs. light weight
(although osteons and trabeculae are oriented
along stress lines)
3. Diaphyses vs short flat irregularly shaped
bones and epiphyses

8. Histology of Bone
Calcified extracellular matrix
Lacunae-small spaces

9. Histology of Spongy Bone
Spongy Bone trabeculae
Section of a trabeculae
Lacunae-small spaces contain osteocytes

10. and supply periosteum and outer part of compact bone
Blood Supply of Bone
1. Periosteal arteries-enter diaphysis through perforating canals
and supply periosteum and outer part of compact bone
Nutrient artery-passes through a hole in compact bone
(foramen)
Metaphyseal arteries-supply red marrow and metaphyses
Veins
1. Nutrient veins-run with nutrient artery in diaphysis
Epiphyseal veins and metaphyseal veins-run with their arteries
in the epiphyses
Periosteal veins-run with their artieries in the perosteum
Nerves run with blood supplies to transmit pain
especially in the periosteum (fractures, biopsy)

11. Blood and Nerve Supply of Bone

12. Intramembrane Ossification
Bone Formation
Ossification-process of bone formation
Two methods of ossification:
Intramembrane ossification-bone forms within mesenchyme
Endochondral ossification-bone forms within hyaline cartilage
Intramembrane Ossification
Ossification Center-mesenchyme (tissue from which
other tissues are derived) differentiates
2. Calcification-osteocytes extend processes into canaliculi
3. Formation of Trabeculae-extracellular matrix forms
spongy bone
4. Development of Periosteum-mesenchyme condenses

13. Intramembraneous Ossification
Mesenchyme differentiates (flat skull bones [fontanels] and mandible) 1 2 3 4

14. Endochondral Ossification
Replacement of cartilage by bone-most bones formed this way.
1. Development of Cartilage Model-hyaline cartilage
is surrounded by perichondrium membrane-chondroblasts
secrete extracellular matrix become buried-called chondrocytes).
Growth of the Cartilage Model-interstitial growth
(increases length-chondrocytes), appositional growth (increased
thickness-chondroblasts)
3. Development of Ossification Center-inward growth
from external surface
Development of medullary cavities-cavity formed
by osteoclasts
5. Development of secondary ossification centers-
proceeds outward from epiphysis center
6. Formation of articular cartilage/ephyseal plate-
hyaline cartilage covering epiphyses becomes articular cartilage

15. Endochondral Ossification
(replacement of cartilage with bone) 1 2 3
/medullary cavity 4 5

16. Bone Growth-length Epiphyseal plate
Zone of resting cartilage-nearest epiphysis, chondrocytes, anchors
epiphyseal plate to bone epiphysis.
Zone of proliferating cartilage-larger chondrocytes arranged in stacks,
divide to replace dead cells at diaphyseal side of epiphyseal plate.
Zone of hypertrophic cartilage-large chondrocytes arranged in columns
Zone of calcified cartilage-dead chondrocytes surrounded by calcified
extracellular matrix. Osteoclasts dissolve cartilage, area invaded by
osteoblasts and capillaries from the diaphysis and produce bone
extracellular matrix-becomes “new disphysis” cemented to disphysis of bone

17. Bone growth-epiphyseal plate

18. Bone growth-thickness
Periosteum differentiates into osteoblasts that secrete extracellular matrix and become osteocytes. Formation of bone ridges/grooves for periosteal blood supply.
The ridge/groove folds and fuses enclosing the blood vessels. Periosteum becomes endosteum.
Osteoblasts in endosteum deposit extracellular matrix forming concentric lamellae. Lamellae formation proceeds out-to-in (inward).
Osteoblasts deposit new outer cercumferential lamellae increasing bone thickness and enclosing additional blood vessels.
As new bone is deposited on the outer surface, the medullary cavity is being destroyed by osteoclasts-therefore the medullary cavity increases in size as the bone gets thicker.

19. Bone growth-thickness

20. Bone remodeling-replacement
of old tissue by new tissue. Processes
Involved are bone resorption
and deposition
Compact bone=4% per year
Spongy bone=20% per year
Why?
Weight stress=thicker bone
Shape can be altered based on need
(e.g. orthodontics).
Regulation
Minerals required
Vitamins: C (collagen synthesis),
K and B12 (protein synthesis), A (osteoblasts)
3. Hormones: IGF stimulated by hGH
(stimulates osteoblast division), Sex hormones (estrogen terminates
growth at epiphyseal plates).

21. Types of Bone Fractures
Open fracture-bone protrudes through skin
Comminuted-fragments between ends
Greenstick-only in children; bend/break
Impacted-one end inside other
Pott’s-distal end of lateral fibula, injury
to tibial articulation
Colles-distal end of radius with posterior
displacement

22. Bone fracture repair 1. 2.
+6h-3w
~3w 3. 4.
>3m 3m

23. Negative feedback for blood calcium
Blood calcium required for:
Nerve and muscle cell function
Blood clotting
Enzyme cofactor
Bone buffers Ca2+
Blood plasma Ca2+ (9-11mg/100ml)
Parathyroid Hormone (PTH)
increases blood Ca2+
2. Decrease in blood Ca2+ causes:
increase in cAMP which causes:
increase in PTH
increase in osteoclasts
retention of Ca2+ by kidneys

24. Osteoporosis Calcium depletion Bone resorption > Bone deposition
Result: depletion of bone mass leading to
fractures, height loss, hunched back, pain

25. Chapter 6
END