Ossification And Bone Disease

Question 0

Where does intramembranous ossification take place and what does it form?

Answer 0

Withing condensations of mesenchymal tissue

Forms flat bones e.g. Skull, maxilla, mandible, pelvis, clavical

Question 1

Describe intramembranous ossification as related to bone growth

Answer 1

1) starts as highly vascularised connective tissue
2) focus of activity is at primary centre of ossification
3) mesenchymal cells differentiate into osteoblasts, surrounded by collagen fibres and ground substance
4) osteoblasts secrete uncalcified matrix (osteoid) which later calcifies
5) osteoblasts become osteocytes (entombed in osteoid)

Question 2

Describe the process of endochondral ossification

Answer 2

Hyaline cartilage acts as trmplate, it is reabsorbed s d replaced by bone
Begins as primary centre for ossification in the diaphysis shaft and later at secondary centres at each end (ephysis)
Growth in diameter by deposition of bone at periphery of shaft
Growth in length occurs at cartilaginous ephysial growth plates

Question 3

Where does endochondrial ossification occur and what does it form?

Answer 3

In hyaline cartilage within bones at growth regions

Most bones develop like this

Question 4

Describe osteogenesis imperfecta

Answer 4

Rare genetic disorder
Affects type 1 synthesis of collagen during ossification
Bones are brittle and prone to fractures
Legal importance - confusion with abuse

Question 5

Describe rickets (children) and osteomalacia (adults)

Answer 5

Absence of vitamin D causes poorly minrealaised, pliable matrix to form(osteoid)
Unable to support bodyweight - bend and fracture (rickets)
Back and bone ache (osteomalacia)

Question 6

Describe osteoporosis

Answer 6

Loss of bone matrix, structural density and demineralaisation
Increases risk of fractures
Easily detected by dexa bone density scan
Risk factors - age, menopause, gonad deficiency, lack of activity

Question 7

Describe achondroplasia

Answer 7

Autosomal dominant point mutation in FGFQ3 gene
Results in gain of function of FGFQ3 gene which decreases endochondrial ossification, cellular hypertrophy and production of cartilage matrix & increases proliferationof chondrocytes
Results in short limbs, normal trunk

Question 8

Describe effect if hormonal abnormalaties on bone

Answer 8

Affect bone development in years of growth
Lack of GH -> ephysial cartilage -> pituatary dwarfism
Excess GH -> gigantism, acromegaly
Lack of gonads -> osteoporosis

Question 9

What lifestyle factor increases risk of osteomalacia?

Answer 9

Inadequate dietary intake of calcium, vitamin D and phosphate

Question 10

What lifestyle factor increases risk of osteoporosis?

Answer 10

Lack of physical excercise

Question 11

What lifestyle factor increases risk of rickets?

Answer 11

Inadequate vitamin D ( stay indoors too much)

Question 12

Describe the radiological and histological changes in osteoporosis

Answer 12

Reduced bone density, increases risk of fractures
Collagen framework and deposited minerals broken down faster than formed
Osteoclast activity> osteoblast activity
Medullary canals in the centre of bone become enlarged and gaps develop in lamellae making the bone fragile

Question 13

List common risk factors for osteoporosis

Answer 13

Middle age onwards - bone thinner and more porus
Post menopause - falling oestrogen (osteoclasts not inhibited)
Poor diet
Insufficient excercise