15. Bone Growth & Growth Hormone

What are the two processes bones use to grow during childhood?

1. Interstitial growth, 2. Appositional growth

Where does interstitial growth occur?

At epiphyseal plates

What type of bone growth results from interstitial growth?

Growth in length of bones

What occurs during appositional growth?

Adds layers of matrix to the external surface

What type of bone growth results from appositional growth?

Growth in diameter

What are the 5 zones of interstitial growth?

1. Zone of resting cartilage, 2. Zone of proliferation, 3. Zone of hypertrophy, 4. Zone of calcification, 5. Zone of ossification

Where is the zone of resting cartilage located?

Closest to epiphysis

What is the function of the zone of resting cartilage?

Attaches epiphyseal plate to epiphysis

What process occurs in the zone of proliferation?

Rapid mitotic division of chondrocytes

What effect does the zone of proliferation have on the layer?

Increase thickness of layer

What happens to chondrocytes in the zone of hypertrophy?

Chondrocytes stop dividing and greatly enlarge

How many chondrocyte layers are in the zone of calcification?

2-3 layers of chondrocytes

What happens in the zone of calcification?

Minerals begin to deposit and chondrocytes begin to die

What cells form osteoblasts in the zone of ossification?

Osteoprogenitor cells

What do osteoblasts create in the zone of ossification?

Create bone matrix

What two actions result in overall interstitial growth?

Forming new cartilage and new bone

What causes interstitial growth to stop?

As bone formation speeds up, entire plate becomes bone

Where do osteoblasts create new bone during appositional growth?

Between periosteum and bone surface

What formation begins appositional bone growth?

Formation of circumferential lamellae

What do circumferential lamellae eventually remodel into during appositional growth?

Osteons

What gland makes human growth hormone (hGH)?

Anterior pituitary gland

What are the three ways hGH causes bone growth?

1. Increased mitosis in chondrocytes, 2. Increased activity in osteoprogenitor cells, 3. Stimulates osteoblasts

What causes gigantism?

Excessive hGH secretion before closure of epiphyseal plates

What growth types are excessive in gigantism?

Excessive interstitial and appositional growth

What causes acromegaly?

Excessive hGH secretion after closure of epiphyseal plates

Which bones become enlarged in acromegaly?

Bones of face, hands, feet

What type of tissue growth occurs in acromegaly besides enlarged bones?

Soft tissue growth