2. Bone Development & Growth Bone Growth Video Segment

3. Hyaline Cartilage – the most common cartilage
Chondrocytes = cartilage cells
Lacunae = pockets that house chondrocytes
Cartilage is avascular (without a blood supply)

4. The Early Embryonic Skeleton
Bone
develops
later →
First skeleton composed of cartilage
Replaced with bone (ossification); starting 6 weeks after fertilization
More than 300 bones at birth → fuse to 206

5. Bone Growth 2 types: Interstitial – in length
at epiphyseal plate; when growth ceases, bone shows epiphyseal lines
Appositional – in width;
new bone is added to the outer surface by osteoblasts from periosteum

6. Bone Remodeling = replacement of old bone by new
bone is very metabolically (chemically) active
bone is remodeled along the lines of mechanical stress (remember to exercise; exercise increases bone mass)
different rates in different regions
distal head of the femur is replaced ~ every 4 months

7. Bone Nutrition Minerals Vitamins
Calcium (dairy, leafy vegetables, tofu; the most abundant mineral in the human body)
Phosphorus (dairy, lean meat, fish)
Vitamins
A – stimulates osteoblasts
C – needed for collagen synthesis
D – needed to make calcitriol (hormone that increases intestinal absorption of Ca++)
B12 & K – needed for synthesis of bone proteins

8. Homeostatic Imbalance: Rickets
Homeostatic Imbalances
Disease of children due to lack of vitamin D
Calcium is not deposited in bones
Bones become soft & deformed
Rickets

9. Hormonal Regulation Growth hormone
responsible for general growth of all body tissues
Sex hormones (testosterone and estrogen) stimulate osteoblasts
Calcitonin & parathyroid hormone regulate Ca++ level
(calcitonin ↓ [Ca++ ] while parathyroid hormone ↑ [Ca++ ] in the blood)
Calcitriol ↑ Ca++ level

10. Calcium Homeostasis
Bone serves as a “buffer” to prevent sudden changes in blood Ca++ levels
too much blood Ca++ (hypercalcemia) or too little (hypocalcemia) can cause the heart to stop working

11. Another Example of Homeostatic Imbalance: Osteoporosis
Homeostatic Imbalances
Decline in bone density
Increased risk of fracture
Possible causes:
Lack of estrogen in women
Lack of exercise to stress the bones
Inadequate intake of calcium and phosphorus
Abnormalities of vitamin D metabolism
Loss of muscle mass

12. Osteoporosis

13. Bone Fractures Fracture = break of the bone Repair of bone:
Spongy bone forms in first few days
Blood vessels regrow and spongy bone hardens
Full healing takes 1-2 months

14. Steps in the Repair of a Fracture
Fig. 6.9