Ossification and Bone disease

Question 1

How do long bones develop?

Answer 1

Endochondral ossification

Question 2

What is endochondral ossification?

Answer 2

Replacement of a hyaline cartilage template with bone

Question 3

Outline the process of endochondral ossification:

Answer 3

Begins at primary growth site
Collar of periosteal bone
Medulla then ossifies, becoming cancellous bone
Secondary centres develop in epiphyses
Growth plates (calcified cartilage) move apart
Bone lengthens
In adults, the plates close

Question 4

What is intramembranous ossification?

Answer 4

Mesenchymal tissue

Condensation of

Question 5

What bones develop via intramembranous ossification?

Answer 5

Flat bones

e.g skull, pelvis, clavicle

Question 6

What is the effect of GH on bone before puberty?

Answer 6

Excess GH causes gigantism, promotes growth at epiphyseal growth plates
Insufficiency leads to pituitary dwarfism

Question 7

What are the effects of GH on bone in adults?

Answer 7

Excess causes bone thickening (not lengthening as growth plates have closed) so causes acromegaly

Question 8

What is rickets?

Answer 8

Childhood disease
Vit. D def
So low calcium so low rigidity
Bones become soft and malformed

Question 9

What is osteomalacia?

Answer 9

Adult equivalent of rickets
Lo Ca or Vit D
Bone pain, back pain
Leads to pathological fx e.g. NoF, pubic ramus, spine, ribs

Question 10

What is achrodroplasia?

Answer 10

Common form of short limb dwarfism
Autosomal dominant
FGRF3 point mutation
Decreased endochondral ossification
So short limbs, enlarged skull, normal length trunk
Homozygous condition is fatal

Question 11

What is osteoporosis?

Answer 11

Enhanced bone reabsobtion compared to formation

So bone no longer provide adequate mechanical support

Question 12

Explain T1 and T2 osteoporosis:

Answer 12

T1 = PM womon
Oestrogen withdrawal
Inc. osteoclast number

T2= senile, both sexes >70 yo.
Attenuated osteoblast function

Question 13

What are some risk factors of osteoporosis?

Answer 13

Genetic
Insufficient Ca intake (PM women should achieve 800mg pd.)
Insufficient Ca absorption, low renal activation of Vit. D
Lack of exercise
Smoking

Question 14

What is osteogenesis imperfecta?

Answer 14

Autosomal dominant
Mut. in Type 1 collagen gene
“Brittle bone disease”

T1 = hearing loss, Fx due to thin/curved/delicate bone, blue (thin) sclerae

T2 = fatal, almost all bones fx during labour

Can be confused with abuse