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B5W1 > BONE METABOLISM AND METABOLIC BONE DISEASE > Flashcards

BONE METABOLISM AND METABOLIC BONE DISEASE Flashcards

1
Q

what are the 4 main functions of bone?

A

mechanical support
protection of vital organs
haematopoiesis
calcium storage

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2
Q

what are the 2 compartments of bone?

A

a collagen matrix and organic cells (osteoblast, osteoclasts and osteocytes)

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3
Q

outline bone remodelling?

A

Osteoclasts first excavate a cavity within the bone
After a few weeks, osteoblasts begin to produce osteoid and the osteoclasts enter programmed cell death
Within three months the newly formed osteoid is then mineralised, forming new bone

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4
Q

at what age is bone mass at its peak?

A

around 30

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5
Q

after 30 why do humans get a slow but steady loss of bone mass?

A

trabeculae become thinner and the bone becomes more porous

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6
Q

describe what happens to bone mass when women reach menopause?

A

they rapidly lose bone mass in response to a reduction in oestrogen that decreases osteoblast and increases osteoclast activity

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7
Q

how is most of calcium and phosphorous stored?

A

in the bones as hydroxyapatite crystals

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8
Q

what promotes calcium absorption from the gut into the serum?

A

vitamin D

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9
Q

what promotes calcium resorption in the kidneys?

A

parathyroid hormone

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10
Q

what promotes gut absorption of phosphorous?

A

vitamin D

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11
Q

what promotes excretion of phosphorous by the kidney?

A

Parathyroid hormone

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12
Q

how do we get vitamin D?

A

diet and the action of sunlight on skin

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13
Q

what is vitamin D3? what is vitamin D2?

A

cholecalciferol

ergocalciferol

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14
Q

what is the inactive form of vitamin D called?

what is the active form of vitamin D called?

A

25-hydroxyvitamin D

1,25-hydroxyvitamin D

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15
Q

how do we produce 1,25-hydroxyvitamin D?

A

vitamin D2 and D3 undergo hydroxylation in the liver to produce 25-hydroxyvitamin D which then undergoes further hydroxylation and activation in the kidneys (catalysed by PTH) to form 1,25-hydroxyvitamin D

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16
Q

what catalyses the activation of vitamin D?

A

parathyroid hormone

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17
Q

what is the aim of 1,25-hydroxyvitamin D?

A

to increase serum calcium and phosphate levels

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18
Q

how does 1,25-hydroxyvitamin D increase serum calcium and phosphate levels?

A

Increase calcium and phosphate absorption from the intestine

Induces bone marrow monocytes to differentiate into osteoclasts to stimulate bone resorption

Targets the PCT in nephrons to stimulate the reabsorption of phosphate and calcium

19
Q

what inhibits the parathyroid gland?

A

1,25-hydroxyvitamin D

20
Q

where is parathyroid hormone secreted from?

A

the 4 parathyroid glands on the thyroid gland

21
Q

when does parathyroid hormone get secreted?

A

at low serum calcium levels

22
Q

how does parathyroid hormone increase calcium and phosphate serum levels?

A

Break down bone to release calcium and phosphate into the plasma

Stimulates cells in DCT in nephrons to reabsorb calcium
Targets 1 alpha hydroxylase which activates vitamin D (1,25 (OH)2 vitamin D3)

increased calcium & phosphate absorption from intestine, via 1,25 (OH)2 vitamin D3- =Indirect effect

23
Q

what does calcitonin do?

A

lowers serum calcium and phosphate levels

24
Q

where is calcitonin released from?

A

the parafollicular cells of the thyroid in response to high serum calcium levels

25
Q

what is the mechanism of calcitonin?

A

to reduce bone resorption by activating calcitonin receptors expressed by osteoclasts

26
Q

what expresses oestrogen receptors?

A

oestoblasts and osteoclasts

27
Q

how does oestrogen maintain bone mass?

A

it inhibits osteoclast formation and function- reduces bone resorption
it lowers serum calcium and phosphate levels- increases bone levels of them

28
Q

what are androgens?

A

male sex hormones but are also present in females. e.g. testosterone

29
Q

how do androgens decrease bone resorption?

A

by inhibits osteoclasts

30
Q

what is the cause of osteoporosis?

A

excess osteoclast and reduced osteoblast activity causes trabecular bone becomes fragile and bone density is reduced, resulting in an increased risk of fracture

31
Q

what are risk factors for osteoporosis?

A

age, being female, early menopause, hyperthyroidism, glucocorticoid therapy, chronic diseases, low BMI, anorexia, family history of hip fractures, smoking, alcohol, low testosterone

32
Q

how can osteoporosis present?

A

Back pain, caused by a fractured or collapsed vertebra.
Loss of height over time.
A stooped posture.
A bone that breaks much more easily than expected

33
Q

what is DEXA?

A

an X-ray that measures bone mineral density and bone loss- normally taken on hip, spine and wrist)

34
Q

what is osteopenia?

A

low bone mineral density but not at osteoporosis levels

35
Q

what is the treatment for osteoporosis?

A

minimise risk factors ; fall reduction; diet; weight-bearing exercise; calcium and vit D; bisphosphonates

36
Q

what are bisphosphonates?

what are the main side effects?

A

drugs that inhibit osteoclastic activity to prevent the loss of bone density- has GI side effects

37
Q

what is osteomalacia?

A

vitamin D deficiency in adults- causes a failure of bone mineralisation causing a structural change in the bone matrix

38
Q

what is rickets?

A

vitamin D deficiency in children- causes a failure of bone mineralisation causing a structural change in the bone matrix

39
Q

how many adults in the UK have a vitamin D deficiency?

A

50%

40
Q

causes of vitamin D deficiency?

A

inadequate diet, lack of sunlight, malabsorption, liver or kidney disease, drugs, calcium deficiency, rare genetic conditions

41
Q

how can we prevent osteomalacia?

A

dietary supplements
sunlight exposure
education

42
Q

how does osteomalacia present?

A

asymptomatic, bone and muscle pain, muscle weakness, paraesthesia, fractures and deformities

43
Q

how do we diagnose osteomalacia?

A

a blood test

44
Q

what is the treatment for osteomalacia?

A

vitamin D supplements

B5W1 (9 decks)

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