Bone Development & Growth

Bone Growth Video Segment

Hyaline Cartilage – the most common cartilage

Chondrocytes = cartilage cells

Lacunae = pockets that house chondrocytes

Cartilage is avascular (without a blood supply)

The Early Embryonic Skeleton

• First skeleton composed of cartilage• Replaced with bone (ossification); starting 6 weeks

after fertilization• More than 300 bones at birth → fuse to 206

Bonedevelopslater →

Bone Growth2 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

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

Bone Nutrition

• Minerals – 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

Homeostatic Imbalances

Rickets

Homeostatic Imbalance: Rickets

• Disease of children due to lack of vitamin D

• Calcium is not deposited in bones

• Bones become soft & deformed

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

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

Homeostatic ImbalancesAnother Example of Homeostatic Imbalance:

Osteoporosis

• 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

Osteoporosis

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

Steps in the Repair of a

Fracture

Fig. 6.9