Bone histogenesis

Question 1

What bones form via intramembranous ossification?

Answer 1

Flat bones of the skull and face (e.g. mandible and clavicle)

Question 2

What is endochondral osteogenesis?

Answer 2

Cartilage provides a provisional matrix to be eroded and replaced with mature bone

Question 3

What are the steps of intramembranous bone formation?

Answer 3

1. Formation of well-vascularized connective tissue
2. Transformation of mesenchymal cells to basophilic osteoblasts (bone blastema)
   producing an eosinophilic osteoid matrix
3. Modeling/shaping of bone as fetus grows (osteoclasts/osteoblasts)

Question 4

How will bone stain?

Answer 4

Eosinophilic

Question 5

How will calcified cartilage stain?

Answer 5

Basophilic

Question 6

What are the 2 phases of bone formation?

Answer 6

1. Matrix (osteoid) formation

2. Mineralization

Question 7

What is the osteoid seam?

Answer 7

The layer between osteoblasts and mineralized matrix.

Question 8

What is the name of the first bone to appear? What replaces it?

Answer 8

Woven, primary bone.

Later replaced by lamellar, secondary bone.

Question 9

How does primary bone differ from secondary bone?

Answer 9

Less mineralized, more cellular than mature bone

Grows more rapidly

Question 10

What are the steps of endochondral bone formation?

Answer 10

1. Hypertrophy of chondrocytes in the central portion: matrix vesicles and type X collagen
2. Formation of the bone collar between the periosteum and the bone shaft
3. Calcification and condensing of cartilage matrix -> apoptosis of chondrocytes -> calcified cartilage
4. Invasion of blood vessels (periosteal/osteogenic bud) OPCs and HPCs form the primary ossification center
5. OPCs differentiate into osteoblasts, lay down bone matrix on calcified cartilage scaffoldC

Question 11

How do chondrocytes lead to their own death?

Answer 11

Secrete pyrophosphatase and alkaline phosphatase which increase overall posphate ions.

Question 12

What do matrix vesicles do?

Answer 12

Form mineral crystals in endochondral bone mineralization

Question 13

What does type X collagen do?

Answer 13

Binds mineral crystals together in endochondral bone mineralization.

Question 14

Can secondary centers of ossification occur?

Answer 14

Postnatally in long bones

Question 15

What is the epiphyseal plate?

Answer 15

The region of hyaline cartilage remaining between the primary and secondary centers.

Question 16

What is the diaphysis?

Answer 16

The long shaft of bone

Question 17

What is the epiphysis?

Answer 17

The ends of bone

Question 18

At the epiphyseal plate, endochondral bone is deposited on the _______ side of the plate.

Answer 18

Diaphysis

Question 19

What is a bone callus?

Answer 19

In healing bone the initial repair tissue is of greater diameter than the original bone shaft to compensate for the relative weakness of woven bone. It will be removed as the bone is remodeled to lamellar bone.

Question 20

What is a normal bone loss in men and women?

Answer 20

0.2-0.5% until up to 5% in menopausal women

Question 21

What is osteoporosis?

Answer 21

A condition where the body fails to form enough new bone or too much is resorbed by the body (or both).

Question 22

What causes osteoporosis?

Answer 22

Drop in estrogen and testosterone levels