Bone

Question 0

What is the composition of bone?

Answer 0

Calcium hydroxyapatite crystals
Type 1 collagen
Water
Non-collagen proteins

Question 1

What do Haversian and Volksmann canals do?

Answer 1

Carry blood vessels, lymph vessels and nerves

Question 2

Give the four main stages of fracture repair

Answer 2

1. Haematoma formation
2. Fibrocartilaginous callus forms
3. Bony callus formation
4. Bone remodelling

Question 3

What are the functions of bone?

Answer 3

Support
Protection
Mineral storage
Haemopoiesis

Question 4

What is the marrow cavity lined with?

Answer 4

Endosteum

Question 5

How is calcium concentration in the blood maintained?

Answer 5

When low: parathyroid hormone stimulates osteoclasts to reabsorbed bone matrix -> higher calcium in the blood

When high: calcitonin inhibits osteoclast activity and decreases bone reabsorption

Question 6

Describe what happens in the first stage of fracture repair

Answer 6

Haematoma forms in which granulation tissue arises.

Question 7

Describe what happens in the second stage (fibrocartilaginous callus formation)

Answer 7

The procallus of granulation tissue is replaced by a fibrocartilaginous callus in which bony trabeculae develop.

Question 8

Describe what happens in the third stage of fracture repair,

Answer 8

Endochondral and intramembranous ossification give rise to a bony callus of spongy/cancellous bone

Question 9

Describe what happens in the fourth stage of fracture repair

Answer 9

Cancellous bone is replaced by compact cortical bone until remodelling is complete

Question 10

Describe the process of endochondral ossification.

Answer 10

Cartilage is reabsorbed and replaced with bone.
This begins at the primary centre of the shaft - diaphysis - and continues at the epiphysis.
Growth in length is at the epiphyseal growth plates.

Question 11

Describe the process of intramembranous ossification.

Answer 11

Bone begins as highly vascularised connective tissue.
Mesenchymal cells differentiate into osteoblasts surrounded by collagen fibres and ground substance
They secrete uncalcified matrix (osteoid) and become osteocytes.

Question 12

Describe growth of long bone by endochondral ossification.

Answer 12

Begins as hyaline cartilage
Collar of periosteal bone appears in the shaft

Central cartilage calcifies
Nutrient artery penetrates - supplying osteogenic cells
Primary ossification centre is formed

Medulla becomes cancellous bone
Cartilage forms epiphyseal growth plates
Epiphyses develop secondary ossification centre

Epiphyses ossify and growth plates continue to move apart, lengthening bone

Epiphyseal growth plates are replaced by bone.

Question 13

Which type of bones develop by intramembranous ossification?

Answer 13

Flat bones

Question 14

How is osteogenesis imperfecta inherited?

Answer 14

Autosomal dominant

Question 15

What is osteogenesis imperfecta caused by?

Answer 15

A mutation in the gene for type I collagen so abnormal collagen synthesis by osteoblasts and fibroblasts

Question 16

What can osteogenesis imperfecta lead to?

Answer 16

Where it is not fatal before birth (Type II), bones are thin, delicate and abnormally curved.
Multiple fractures of long bone which leads to deformities because they don’t heal correctly.
Also affects ears, teeth, sclerae, ligaments, skin and joints.

Question 17

What effects can growth hormone have on bones before puberty?

Answer 17

Excessive - promotion of epiphyseal growth plate activity leads to gigantism

Insufficient - effect epiphyseal cartilage and cause pituitary dwarfism

Question 18

What does excessive growth hormone cause in adults and how?

Answer 18

Acromegaly

Increase in bone width by promoting periosteal growth

Question 19

What effect can a deficiency in thyroid hormone have on newborns?

Answer 19

Cretinism - neurological and intellectual damage, and short stature

Question 20

List some risk factors for osteoporosis

Answer 20

Genetics
Gender
Age
Insufficient calcium intake
Insufficient calcium absorption and vitamin D
Lack of exercise
Smoking

Question 21

What happens in osteoporosis?

Answer 21

Bone density reduced to a point where there is a risk of fractures
Collagen framework and deposited minerals are broken down faster than they are being replaced
Medullary canals become enlarged, gaps develop in lamellae, bones become more fragile

Question 22

How is achondroplasia inherited?

Answer 22

Autosomal dominant

Question 23

What does achondroplasia result in?

Answer 23

Decreased endochondral ossification
Inhibited proliferation of chondrocytes in growth plate cartilage
Decreased cellular hyper trophy
Decreased cartilage matrix production

Question 24

Describe the features of bones affected by rickets

Answer 24

Bone matrix fails to calcify properly - osteoid
Epiphyseal plate becomes distorted by body weight
Bones grow slowly and deformed
Bones are prone to fractures

Question 25

Describe what happens to a bone affected by osteomalacia

Answer 25

Deficient calcification of recently formed bone results in bone softening

Question 26

What is osteomalacia caused by?

Answer 26

A calcium deficiency

Question 27

Which bone disease has medicolegal significance?

Answer 27

Osteogenesis imperfecta

Question 28

What does a deficiency in vitamin d cause and why?

Answer 28

Rickets and osteomalacia

It is involved in absorption of calcium from the small intestine. Without calcium, the bone matrix cannot mineralise.