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Diabetes & Endocrinology > Calcium homeostasis > Flashcards

Calcium homeostasis Flashcards

1
Q

5 important roles of calcium in the body

A 
signalling eg exocytosis, muscle contraction 
blood clotting 
apoptosis 
skeletal strength 
membrane excitability
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2
Q

What does calcium do to sodium permeability?

A

decrease it

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3
Q

What function of calcium is most important in the short term for homeostasis?

A

membrane excitability - sodium permeability

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4
Q

Hypocalcaemia - sodium permeability and the result

A

increases sodium permeability
hyperexcitation of the neurons
tetany - spread to larynx and strap muscles can cause asphyxiation

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5
Q

hypercalcaemia - sodium permeability and the result

A

decreases sodium permeability
decrease neuromuscular activity
can lead to arrhythmias

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6
Q

How much of calcium is stored in bone?

A

99%

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7
Q

Explain the remaining 1% of calcium in body

A
  1. 9% intracellular fluid stored in mitochondria and SR

0. 1% extracellular fluid although half is bound to carrier proteins

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8
Q

Is calcium in bone or ECF/ICF tightly regulated?

A

ICF/ECF

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9
Q

What % of calcium in the body is free? what is the result of this?

A

0.05%

physiologically active

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10
Q

How is calcium stored in bone and what does this mean?

A

hydroxyapatite - phosphate homeostasis important in calcium balance

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11
Q

Does calcium have a high or low affinity to proteins and why?

A

high

small positive charge to large negative charge

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12
Q

What happens to the plasma calcium ions neither bound to protein or free in solution?

A

bind to anions eg sulphate

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13
Q

Is calcium binding to plasma proteins increased under acidic or alkalotic conditions?

A

alkalotic

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14
Q

Explain what happens to calcium binding in hyperventilation

A

blow off more CO2
pH rises
more calcium bound to proteins
less plasma calcium = hypocalcaemic tetany

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15
Q

total body calcium =

A

calcium in (diet) - calcium out ( excreted at kidneys and faeces)

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16
Q

Is mechanical support or calcium balance more important in terms of the bones?

A

calcium balance

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17
Q

Osteoblasts

A

bone building, active

actively lay down collagen extracellular matric which can later calcify

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18
Q

Osteocytes

A

osteoblasts differentiate to form these, less active

regulate osteoblast and osteoclast activity

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19
Q

Osteoclasts

A

mobilise bone by secreting H+ (pH4) to dissolve calcium salts and also provide proteolytic enzymes to digest extracellular matrix

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20
Q

What are the 2 key endocrine hormones in calcium homeostasis?

A

PTH

calcitriol

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21
Q

What type of hormone is PTH and where is it released from?

A

polypeptide

parathyroid glands

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22
Q

What type of hormone is calcitriol? what is it the active form of? where is it produced?

A

steroid
vitamin D3
from vitamin D in liver and kidneys

23
Q

Where are parathyroid glands found and why are they important?

A

4 on posterior surface of thyroid gland - variable

essential for life so must know if they are elsewhere when removing thyroid gland

24
Q

What is PTH released in response to and what is its general action?

A

low plasma calcium

increase free calcium in the plasma

25
Q

What are some ways in which PTH works?

A

stimulate osteoclasts
inhibit osteoblasts
increase phosphate excretion
increase reabsorption of calcium from kidney tubules to reduce calcium in urine
stimulate kidney to synthesise calcitriol

26
Q

What does calcitriol promote?

A

kidney and gut absorption of calcium

27
Q

Does calcitriol complement or antagonise the action of PTH?

A

complement

28
Q

How is vitamin D activated?

A

dietary/precursors activated by sunlight

29
Q

How is calcitriol stimulated in pregnancy?

A

prolactin

30
Q

Explain the negative feedback loop of PTH and calcitriol

A

As plasma Ca rises this switches off PTH which then switches off calcitriol synthesis in the kidneys

31
Q

What does calcitriol bind to on target tissues?

A

nuclear receptors in intestine, bones, kidney

32
Q

How does calcitriol increase absorption of calcium from gut?

A

calcium from intestinal lumen to blood: calcitriol controls this active transport
low plasma calcium - increase PTH, increase calcitriol and increase intestinal absorption

33
Q

3 actions of calcitriol

A

increase intestinal absorption
facilitate renal absorption
mobilise calcium stores by stimulating osteoclasts

34
Q

Why does prolactin stimulate calcitriol synthesis?

A

increased demand for calcium for milk production in lactation

35
Q

Value of circulating vitamin D in deficiency

A

less than 20ng/ml

36
Q

Where is vitamin D extensively stored?

A

in fat

37
Q

Risk factors for vitamin D deficiency

A

age, lack of sunlight, diet

38
Q

What is the net effect of vitamin D?

A

increase plasma calcium and mineralisation of bone

39
Q

What happens to bones in vitamin D deficiency?

A

PTH works hard to release calcium

soft and weak bones

40
Q

Children and adults vitamin D deficiency presentation

A 
children = rickets 
adults = osteomalacia
41
Q

If you are vitamin D3 deficient what else will you be deficient in and why?

A

calcium and phosphate
intestinal malabsorption leads to decreased plasma calcium which increases PTH which promotes phosphate deficiency and aggravates calcium loss from bone

42
Q

Who is most at risk of vitamin D deficiency?

A

Asian and elderly

chapatti flour, pigmented skin

43
Q

What diseases is Vitamin D deficiency implicated in?

A

arthritis, MS, cancer and CVD

44
Q

What is the 1 key hormone acts to decrease plasma calcium

A

calcitonin

45
Q

What type of hormone is calcitonin and where is it produced from?

A

peptide hormone

thyroid gland

46
Q

How does calcitonin work?

A

increased calcium in plasma
binds osteoclasts and inhibits bone resorption
increase renal excretion and prevent further increase in calcium

47
Q

Why is calcitonin seen as unimportant?

A

in people with calcitonin tumours or not enough they still have stable calcium levels as PTH overrides it

48
Q

When may calcitonin be used in a clinical setting?

A

Pagets disease = overactive osteoclasts

49
Q

List 5 other endocrine hormones which alter calcium balance

A 
cortisol 
insulin 
oestrogen 
GH 
prolactin
50
Q

How does cortisol work to alter calcium balance?

A

inhibit osteoblasts and increase renal excretion of calcium and phosphate
reduce intestinal resorption
decrease plasma calcium which increases PTH and increases bone resorption
osteoporosis

51
Q

Insulin effect on calcium

A

increase bone formation and antagonise cortisol

diabetics have significant bone loss

52
Q

oestrogen effect on calcium

A

promotes bone formation via oestrogen receptors on osteoblasts. Post menopausal osteoporosis

53
Q

GH effect on calcium

A

constant stimulus for bone formation

54
Q

Prolactin effect on calcium

A

promotes calcium absorption from the gut by calcitriol synthesis

Diabetes & Endocrinology (24 decks)

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