TOB Session 7 Flashcards Preview

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Flashcards in TOB Session 7 Deck (28)
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1
Q

What is Endochondral Ossification?

A

When bone forms from cartilage. Cartilage is reabsorbed and replaced by bone.

2
Q

Where does Endochondral Ossification begin?

A

Endochondral ossification begins at the diaphysis in the primary centre of the bone, and then the secondary centres form at each end (epiphysis).

3
Q

How does diameter of the bone increase?

A

Bone is deposited at the periphery of the shaft.

4
Q

How does length of the bone increase?

A

It grows from the growth (epiphyseal) plates at the end of the bone.

5
Q

What is intramembranous ossification?

A

ossification from a sheet of mesenchyme or loose connective tissue. Bone development starts in a highly vascularised connective tissue.

6
Q

Into what do mesenchymal cells differentiate?

A

Osteoblasts. They are surrounded by collagen fibres and ground substance.

7
Q

What do osteoblasts secrete?

A

Uncalcified matrix (osteoid) which later becomes calcified)

8
Q

Where do osteocytes come from?

A

They are formed from osteoblasts.

9
Q

Where does compact bone come from?

A

It is formed from spongy bone.

10
Q

What is the name of the process by which bone structure is constantly changing?

A

Bone remodelling

11
Q

Describe the symptoms and causes of Osteogenesis Imperfecta.

A

The bones are very fragile and brittle and so fractures are very common. Deformity of joints and bones is also prevalent. Multiple fractures are usually present at or before birth. It is caused by a mutation in the genes coding for type I collagen (no glycine).

12
Q

Describe Osteoporosis.

A

The bones become thinner and more porous as the levels of sex hormones begin to fall with age. Bone density is reduced and so fractures become more common. Bones reabsorption exceeds bone formation.

13
Q

What are the risk factors of Osteoporosis?

A

Genetic predisposition, Iinsufficient calcium intake, insufficient calcium absorption and vitamin D, immobilization of bone (lack of exercise or prolonged bed rest) and cigarette smoking.

14
Q

What is Achondroplasia and what is it caused by?

A

Short limb Dwarfism. It is caused by an autosomal dominant point mutation in the fibroblast growth factor receptor-3 gene (FGFR3). This causes decreased endochondral ossification amongst other things.

15
Q

What are the characteristics of achondroplasia?

A

The limbs are very short, the torso is of normal length and the vault of the skull is enlarged with a small face. Intelligence is entirely normal.

16
Q

Why is Vitamin D important in normal bone development?

A

Vitamin D undergoes hydroxylation in the liver to form 1,25 dihydroxyvitamin D3. This increases calcium absorption by the small bowel and promotes mineralisation of bone.

17
Q

What is Rickets?

A

It is a childhood disease in which the bones do not harden due to a Vitamin D deficiency. Bones become solft and malformed as there is insufficient calcium deposition for adequate bone rigidity. The bone matrix does not calcify properly and the epiphyseal plate becomes distorted.

18
Q

What is osteomalacia?

A

It is the adult version of rickets, caused by a significant calcium deficiency. Symptoms include bone pain, back ache and muscle weakness. The deficiency in calcification of recently formed bone causes fragility and increases risk of fractures.

19
Q

What can Osteogenesis Imperfecta often be confused with?

A

Child abuse

20
Q

How do dietary and behavioural factors influence rickets and osteomalacia?

A

Osteomalacia and Rickets can both be a consequence of inadequate calcium or vitamin D intake in the diet. Low sun exposure can also cause vitamin D deficiency.

21
Q

Describe how osteoblast and osteoclast activity differs in a patient with osteoporosis compared to a healthy person.

A

In someone with osteoporosis, osteoclast activity exceeds osteoblast activity and so bone becomes fragile.

22
Q

How do the medullary canals change in someone with osteoporosis?

A

They become enlarged and gaps develop in the lamellae.

23
Q

Explain the importance of osteoporosis as a risk factor for fractures in the elderly

A

Elderly people with osteoporosis are more likely to suffer fractures from falling down.

24
Q

How do abnormal levels of Growth Hormone (GH) affect bone development?

A

Lack of growht hormone affects the epiphyseal cartilage causing pituitary dwarfism. Excessive GH can cause gigantism through promotion of epiphyseal growth plate activity in children.

25
Q

Why can excessive amounts of growth hormone not cause gigantism in adults? What happens instead?

A

Because there are no longer epiphyseal growth plates. Excessive GH in adults can cause acromegaly due to periosteal growth.

26
Q

How do sex hormones affect bone development?

A

Sex hormones influence the time of appearance and development of ossification centres. Precocious sexual maturity stunts growth due to premature fusion of epiphyses. Deficiencies of sex hormones can lead to delayed fusion of epiphyses causing excessive growth.

27
Q

What does Thyroid hormone deficiency cause (relating to bone development)?

A

Cretinism (stunted physical and mental development).

28
Q

How can decreased thyroid hormone production in a newborn be reversed (to prevent cretinism)?

A

By administration of thyroxine