Chapter 7: Bone Development & Growth

Question 1

In what two ways do bones form when replacing existing bone tissue?

Answer 1

1. Intramembranous
2. Endochondral

Question 2

What bones form from intramembranous ossification?

Answer 2

1. Flat skull bones
2. Clavicles
3. Sternum
4. Some facial bones

Question 3

What bones form from endochondral ossification?

Answer 3

1. Long bones
2. And most of skeleton

Question 4

What is intramembranous ossification?

Answer 4

The process of replacing embryonic connective tissue.

Question 5

What is the process of intramembranous ossification?

Answer 5

1. Mesenchymal cells differentiate into osteoblasts.
2. They deposit bone matrix around them until they are surrounded by matrix and become osteocytes in lacunae.
3. Spongy bones forms.
4. The mesenchyme on the outside condenses to form the periosteum.
5. Osteocytes on the inside of the forming periosteum deposit compact bone.

Question 6

What is endochondral ossification?

Answer 6

The process of replacing hyaline cartilage.

Question 7

What is the process of endochondral ossification?

Answer 7

1. Starts as a hyaline cartilage model.
2. Cartilage tissue breaks down and periosteum forms.
3. Blood vessels and osteoblasts from the periosteum invade the disintegrating tissue and form spongy bone.
4. Osteoblasts then deposit compact bone and become osteocytes when surrounded by bone matrix.

Question 8

What region of the bone is responsible for growing in length?

Answer 8

Epiphysial plate

Question 9

Where is the epiphysial plate located?

Answer 9

Between the epiphysis and the diaphysis.

Question 10

There are four zone of the epiphysial plate, what are they?

Answer 10

1. Zone of Resting Cartilage
2. Zone of Proliferating Cartilage
3. Zone of Hypertrophic Cartilage
4. Zone of Calcified Cartilage

Question 11

What is the zone of resting cartilage?

Answer 11

This is the layer closest to the epiphysial plate; it anchors the epiphysial plate to the epiphysis.

Question 12

What is the zone of proliferating cartilage?

Answer 12

Layer with young cells undergoing mitosis.

Question 13

What is the zone of hypertrophic cartilage?

Answer 13

Rows of older cells are left behind when new cells appear (lengthening the bone). The older cells begin to calcify (die).

Question 14

What is the zone of calcified cartilage?

Answer 14

A row of calcified cells.

Question 15

What is the role of osteoclasts?

Answer 15

Break down bone cells (Bone Resorption).

Question 16

What is the role of osteoblasts?

Answer 16

Make bone cells (Bone Deposition).

Question 17

How much bone is replaced every year?

Answer 17

10-20%

Question 18

What factors affect bone growth and repair?

Answer 18

1. Vitamins D, A, & C
2. Hormones
3. Physical Stress

Question 19

What does vitamin D do?

Answer 19

Helps with calcium absorption; deficiencies can cause rickets and osteomalacia.

Question 20

What does vitamin A do?

Answer 20

Helps with osteoblast/clast activity; deficiencies can retard bone development.

Question 21

What does vitamin C do?

Answer 21

Helps with collagen synthesis; deficiencies will result in slender, fragile bones.

Question 22

What hormones affect bone growth and repair?

Answer 22

1. Thyroid Hormone
2. Parathyroid Hormone (PTH)
3. Sex Hormones

Question 23

What does the thyroid hormone do?

Answer 23

Causes replacement of cartilage with bone in epiphyseal plate, osteoblast activity.

Question 24

What does the parathyroid hormone do?

Answer 24

Stimulates osteoclasts.

Question 25

What do the sex hormones do?

Answer 25

Promotes bone formation;
stimulate ossification of epiphyseal plates.