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Musculoskeletal system > Calcium homeostasis > Flashcards

Calcium homeostasis Flashcards

1
Q

Is vitamin D a vitamin?

A

No, it is a hormone

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2
Q

Where does the synthesis of vitamin D begin?

A

Keratinocytes in skin

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3
Q

What is vitamin D synthesised from?

A

Cholesterol

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4
Q

What is essential for cholesterol to be synthesised to vitamin D?

A

UV B radiation

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5
Q

Where is vitamin D converted to calcidiol?

A

Liver

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6
Q

Where is calcidiol converted to calcitriol?

A

Kidneys

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7
Q

What is vitamin D converted to?

A

Calcidiol

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8
Q

What is calcidiol converted to?

A

Calcitriol

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9
Q

Which enzyme catalyses to conversion of calcidiol to calcitriol?

A

1-alphahydroxylase

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10
Q

What does calcitriol do?

A

Stimulates GI tract to absorb calcium

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11
Q

Flow chart for synthesis of calcitriol

A

Cholesterol -(UV B)-> vitamin D -> bloodstream -> liver -> calcidiol -> kidneys -(1-alphahydroxylase)->calcitriol

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12
Q

Which hormone stimulates production of 1-alphahydroxylase?

A

PTH

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13
Q

What impact does PTH have on bone?

A

Increases resorption - increases movement of calcium from bone fluid to plasma

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14
Q

What impact does PTH have on kidneys?

A

Stimulates production of 1-alphahydroxylase for conversion of calcidiol to calcitriol

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15
Q

Which three hormones are responsible for regulating calcium concentration?

A

Vitamin D, calcitonin, PTH

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16
Q

What impact does calcitonin have on osteoclasts?

A

Inhibits activity

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17
Q

What are the main causes of calcium metabolism disorders?

A

Too much/little PTH or vitamin D deficiency

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18
Q

What is hypocalcemia?

A

Total calcium <2.2

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19
Q

What is hypercalcemia?

A

Total calcium >2.6

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20
Q

Causes of hypocalcemia

A

Hypoparathyroidism, kidney disease, hyperventilation

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21
Q

Effects of hypocalcemia

A

Muscle spasms, paraesthesia, arrthymias

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22
Q

Causes of hypercalcemia

A

Hyperparathyroidism, malignancy

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23
Q

Effects of hypercalcemia

A 
Stones - kidney stones
Bones - osteoporosis
Groans - GI symptoms - constipation etc
Moans - malaise, fatigue
Thrones - constipation
Psychiatric overtones - effects on CNS e.g. confusion
24
Q

What happens when calcium concentration gets too high?

A

C cells in thyroid produce calcitonin
Increases bone deposition
Increases calcium excretion in kidneys
Calcium levels fall

25
Q

What happens when calcium concentration gets too low?

A

Parathyroids produce PTH
Increases bone resorption
Acts on kidneys to produce vitamin D to increase Ca absorption in GI tract
Calcium levels rise

26
Q

What impact does calcitonin have on osteoclasts?

A

Binds to receptor on them to inhibit activity

27
Q

How does PTH stimulate osteoclasts?

A

PTH binds to receptors on osteoblasts
Secretes hormone called RANKL
Osteoclasts have receptor for RANKL
RANKL binds to osteoclasts and stimulates them to dissolve bone

28
Q

Why must phosphate be excreted?

A

Equal ratio of calcium and phosphate means that bone forms

29
Q

What impact does PTH have on the kidney?

A

Excrete phosphate, reabsorb calcium

30
Q

What impact does PTH have on the distal convoluted tubule?

A

Remove phosphate ions

31
Q

What impact does PTH have on proximal convoluted tubule?

A

Reabsorb calcium ions

32
Q

How does PTH create calcitriol?

A

Stimulates production of 1-alphahydroxylase in kidneys to convert calcidiol to calcitriol

33
Q

What does calcitriol do?

A

Increases uptake of calcium from GI tract into plasma

34
Q

What is the normal range of calcium concentration in the plasma?

A

2.2-2.6 mmol/l

35
Q

How much of the calcium in the plasma is in active form?

A

About half

36
Q

Where is calcium found?

A

Skeleton
Teeth
Cells
Extracellular fluid

37
Q

How much calcium is stored in the skeleton?

A

99%

38
Q

How much calcium is stored in cells?

A

0.9%

39
Q

How much calcium is stored in extracellular fluid?

A

0.1%

40
Q

Function of calcium in bones

A

Hydroxyapatite crystals = strength

41
Q

Function of calcium in blood

A

Clotting cascade

42
Q

Function of calcium in endocrine system

A

Stimulus secretion coupling

Movement from extracellular fluid into cells releases hormones

43
Q

Function of calcium in muscle contraction

A

Excitation contraction coupling

Low calcium = less heart contraction = muscle failure

44
Q

Function of calcium in nervous system

A

Stimulus secretion coupling

Release of neurotransmitters from presynaptic neurones is triggered by calcium moving from fluid

45
Q

Function of calcium in secondary messenger

A

Extracellular signalling

46
Q

Function of calcium in tight junctions

A

Found between cells - the blood/brain barrier

47
Q

Roughly how much calcium do we ingest each day?

A

1000 mg

48
Q

Which two substances are the only ones whose reserves have a function in their own right?

A

Calcium and glucose

49
Q

Impacts of hypocalcaemia

A

Heart slows down or beats too rapidly
Muscles go into spasm
Confusion and coma

50
Q

Impacts of hypercalcaemia

A

Depression of nervous system
Muscle weakness
Fatigue/lethargy

51
Q

Which ethnicity has highest bone density?

A

African-americans

52
Q

What is pituitary dwarfism?

A

Under-secretion of growth hormone

53
Q

What does PTH do?

A

Increases blood calcium levels
Stimulates osteoclastic bone reabsorption in response to lower ca2+ in plasma
Stimulates renal production of 1,25dihyroxyvitamin D
This helps reabsorb calcium from gut

54
Q

Where is 1,25dihydroxyvitamin D made?

A

Kidney

55
Q

What does 1,25dihydroxyvitamin D do?

A

Helps reabsorb calcium from gut

56
Q

What does calcitonin do?

A

Decreases blood calcium levels by inhibiting osteoclastic activity

57
Q

What does 1,25 hydroxyvitamin D do?

A

Increases synthesis of 1 alpha hydroxylase

Musculoskeletal system (24 decks)

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