S8 Bone Formation And Repair

Question 1

What are the two types of bone?

Answer 1

Cortical and cancellous

Question 2

What is the structure of cancellous bone?

Answer 2

Avascular

Made up of trabeculae with bone marrow in the spaces

Question 3

What is the structure of cortical bone?

Answer 3

Vascular (Haversian and Vaulkmann’s canals)

Made up of osteons which are made up of lamallae, caniculi and lacuna (containing osteocytes) surrounded by periosteum

Question 4

What are the cell types in bone?

Answer 4

1. Osteoprogenitor cells - produce osteoblasts
2. Osteocytes - mature osteoblasts (embedded in bone matrix)
3. Osteoblasts - make bone (lay down osteoid)
4. Osteoclasts - break down bone

Question 5

What are the 3 sections of bone called?

Answer 5

Epiphysis, metaphysis, diaphysis

Question 6

What is the precursor model for bones growing by endochondral ossification?

Answer 6

Hyaline cartilage

Question 7

Where does hyaline cartilage grow from and by what sort of growth?

Answer 7

Grows from pericondrium but appositional growth

Question 8

What are the organic and inorganic compositions of bone?

Answer 8

1. Inorganic (65%) - Ca2+, Mg2+ and Al3- (helps to resist bending and compression)
2. Organic (35%) - collagen 1, GAGs (help to resist pulling and tension)

Question 9

Describe the process of endochondral ossification (5 steps)

Answer 9

1. Hyaline cartilage model and collar of periosteal bone
2. The central cartilage calcifies, a nutrient artery penetrates (providing osteogenic cells and forming the primary ossification centre)
3. The medulla becomes cancellous bone, the cartilage forms epiphyseal growth plates. Secondary ossification centres develop in epiphyses
4. Epiphyses ossify and the growth plates move apart (lengthening the bone)
5. Epiphyseal growth plates are replaced by bone and hyaline articular cartilage (at ends of bone) remains

Question 10

What is the importance of vitamin D in bones?

Answer 10

Vitamin D provides bone stability, it produces calcitriol which is used for Ca2+ absorption.
A deficiency in vitamin D leads to rickets/osteomalacia.

Question 11

Describe the process of bone repair after a fracture (6 steps)

Answer 11

1. Haematoma formation
2. Inflammation (e.g. macrophages, neutrophils, etc.) to remove dead tissue
3. Granulation, fibroblasts lay down collagen,
4. Chondroblasts lay down hyaline cartilage forming soft callus
5. Ossification occurs (hard callus formation)
6. Bone remodelling

Question 12

What are the two steps in bone remodelling?

Answer 12

1. Osteoclasts make a wide tunnel in the bone (cutting cone)

2. Osteoblasts make a smaller tunnel of cortical bone (closing cone)

Question 13

What is osteomalacia?

Answer 13

Adult version of rickets.

Vitamin D deficiency - there’s less Ca2+ resorption so less mineralisation/osteoid.

Soft bones, easy fracturing, muscle weakness.

Question 14

What is rickets?

Answer 14

Vitamin D deficiency - poor calcium mobilisation so ineffective mineralisation.

Short stature, weakened bones, soft bones, painful to walk, bowed legs

Question 15

What is primary osteoporosis?

Answer 15

Type 1 and type 2

1. Post-menopausal women, increased osteoclast number due to loss of oestrogen
2. Older men and women, decreased osteoblast number due to loss of both oestrogen and androgen

Question 16

What is secondary osteoporosis?

Answer 16

1. A result of drug therapy

2. Processes affecting bone remodelling 3. Metabolic bone diseases - metastatic cancer, hyperparathyroidism

Question 17

What does osteoporosis result in?

Answer 17

Gaps in cancellous bone

Incomplete filling of osteoclast resorption bays

Question 18

What are modifiable risk factors for osteoporosis?

Answer 18

1. Increase calcium intake
2. Exercise
3. Don’t smoke cigarettes

Question 19

What is osteogenesis imperfecta?

Answer 19

Brittle bone disease.

A mutation of the COL1A gene results in incorrect collagen 1 production.

Blue sclera, short stature, weakened bones.

Question 20

What is achondroplasia?

Answer 20

Mutation in FGF3 receptor gene.

Endochondral ossification occurs from cartilage, however this mutation prevents cartilage forming bone. But intramembranous ossification occurs as normal.

Short stature, normal sized head and torso.