7.5- Bone growth and remodeling

Question 1

What are the five zone of interstitial growth from epiphysis to diaphysis?

Answer 1

1) Zone of resting cartilage. - Resembles hyaline cartilage
2) Zone of proliferating cartilage- Chondrocytes do mitotic cell division and stack lacunae to look like columns which are parallel to the diaphysis.
3) Zone of hypertrophic cartilage- Chondrocytes stop dividing and start to hypertrophy- walls of lacunae become thin as chondrocytes a resorping.
4) Zone of calcified cartilage- two or three layers of chondrocytes- Minerals deposited in matrix between columns of lacunae. Mineral deposition (calcification) kills chondrocyte and makes columns appear opaque.
5) Zone of ossification- Walls break down between lacunae forming channels perpendicular to diaphysis.
These channels are invaded by vessels and osteoprogenitor cells from the medullary cavity. New bone matrix is deposited on the remaining calcified cartilage matrix.

Question 2

Which zones of interstitial growth cause bone lengthening?

Answer 2

Zone two- of proliferation

Zone three- of hypertrophy

Question 3

Where does appositional growth occur?- How does it work?

Answer 3

Periosteum- osteoblast on thinner most layer of the periosteum deposit bone matrix that becomes circumferential lamellae and increases the bone diameter. While this happens osteoclast from the medullary cavity resorb the interior portion of the bone matrix resulting in a larger medullary cavity.

Question 4

What is bone remodeling?

Answer 4

The constant building and respiration of bone. This depends on mechanical stress and hormones.

Question 5

Growth hormone

Answer 5

Stimulates the liver to produce IGF which causes cartilage proliferation and causes bone elongation.- Produces by anterior pituitary gland.

Question 6

Thyroid hormone

Answer 6

Stimulates bone growth by stimulating the metabolic rate of osteoblasts.
Secreted by thyroid gland.

Question 7

Calcitonin

Answer 7

Promotes calcium deposition in neon and inhibits osteoclast activity.

Question 8

Calcitriol

Answer 8

Stimulates absorption of calcium ions from the small intestine into the blood.

Question 9

Parathyroid hormone

Answer 9

Increases blood calcium levels by encouraging bone resorption by osteoclasts.

Question 10

Sex hormones (estrogen and testosterone)

Answer 10

Stimulate osteoblasts: promote epiphyseal growth and closure.

Question 11

Glucocorticoids

Answer 11

Increase bone loss, and in children impair bone growth when there are chronically high levels of glucocorticoids.
Released by adrenal cortex.

Question 12

Serotonin

Answer 12

Inhibits osteoprogenitor cells from differentiating into osteoblasts when there are chronically high levels of serotonin.

Question 13

What are the types of fractures?

Answer 13

Transverse- straight perpendicular to diaphysis
Linear- perpendicular to diaphysis
Oblique Non-displaced- angled to diaphysis- no displacement
Oblique displace- angled to diaphysis- displaced
Spiral- spiraling up/down the diaphysis of the bone
Green Stick- fractured on one side (more common in kids)
Comminuted- crushed between two ends of bone

Question 14

What are the four steps of bone repair?

Answer 14

1) Hematoma Formation- Mass of clotted blood, bone cells die, inflammation, pain, loss of function
2) Fibrocarilagenous callus formation- Phagocytic cells remove debris, fibroblasts and osteoblast invade area, collagen spans break, cartilage matrix secreted, spongy bone begins to form
3) Boney Callus formation- trabeculae begin to form, fibrocartilagenous callus turned to bony callus (spongy bone)
4) Bone Remodeling- excess material removed, compact bone formed.