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Endocrinology > Control of Calcium Balance > Flashcards

Control of Calcium Balance Flashcards

1
Q

What are the functions of calcium in the body?

A 
Signalling 
Blood clotting 
Apoptosis 
Skeletal strength 
Membrane excitability
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2
Q

How does calcium affect membrane excitability?

A

Ca2+ decreases Na+ permeability

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3
Q

What is the effect of hypocalcaemia on membrane excitability?

A

Increases neuronal Na+ permeability

Hyper excitation of neurons

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4
Q

What can extreme cases of hypocalcaemia cause?

A

Tetany

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5
Q

What can happen if tetany spreads to the larynx and respiratory muscles?

A

Asphyxiation

Suffocating

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6
Q

What is the effect of hypercalcaemia on membrane excitability?

A

Decreases neuronal Na+ permeability
Reduces excitability
Depress neuromuscular activity

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7
Q

What is the distribution of calcium in the body?

A

Bones 99%
Intracellular fluid - 0.9%
Extracellular fluid - 01.%

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8
Q

Where is the vast majority of calcium found in our bodies?

A

In our bones

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9
Q

What % of calcium is found in our cells?

A

0.9%

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10
Q

What is calcium in our bones mostly in the form of?

A

Hydroxyapatite

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11
Q

What does calcium require to lay it down in the bones?

A

Phosphate homeostasis

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12
Q

What is the calcium level in the plasma?

A

2.2-2.6mM

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13
Q

What does calcium have a high affinity for?

A

Proteins

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14
Q

What % of calcium is bound to plasma proteins?

A

40%

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15
Q

In what form is calcium physiologically active?

A

Unbound calcium is active

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16
Q

How does Ca2+ binding change with pH?

A

Binding capacity increases under alkalotic conditions

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17
Q

What happens to calcium binding in hyperventillation?

A

Plasma pH rises
Binding capacity increase
Casing plasma Ca2++ to fall and therefore precipitate hypocalcaemic tetany

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18
Q

What happens to calcium binding in hypoventilation?

A

Acidosis occurs

Binding capacity reduces and free Ca2+ in plasma rises

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19
Q

Where does all the calcium that enters our body come from?

A

Diet

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20
Q

What happens if calcium levels are disrupted in the body?

A

The bone will release calcium at the expense of bone strength

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21
Q

What are osteoblasts?

A

Bone building cells

Highly active cells which lay down collagen extracellular matrix which then calcify

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22
Q

What do osteoblasts differentiate to form?

A

Osteocytes

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23
Q

What do osteoclasts do?

A

Cells that breakdown bones

Cells that are responsible for mobilizing bone

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24
Q

What 2 hormones control calcium homeostasis?

A

Parathyroid Hormone

Calcitriol

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25
Q

Where is PTH produced?

A

Parathyroid glands

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26
Q

Where is calcitriol produced?

A

Vitamin D by the liver and kidneys

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27
Q

How many parathyroid glands are there?

28
Q

What is the most important hormone for controlling calcium?

29
Q

Where are the parathyroid glands found?

A

On the posterior surface of the thyroid gland

30
Q

When is PTH secreted?

A

In response to decreased calcium conc. in the plasma

31
Q

How do PTH increase free Ca conc.?

A

Stimulate oesteoclasts to release Ca2+ from bones

Inhibit osteoblasts from laying down more bone

Increase reabsorption of Ca2+ from kidneys

Increases renal secretion of phosphate

Stimulates the kidneys to synthesis calcitriol from vitamin D which promotes calcium absorption at the gut and kidneys

Increase calcium absorption from the gut

32
Q

What is calcitriol?

A

Secondary hormone in terms of maintaining calcium levels

33
Q

What does calcitriol complement the action of?

A

the action of PTH to increase plasma Ca2+

34
Q

What type of hormone is calcitriol?

A

Steroid hormones

35
Q

How is calcitriol produced?

A

In 2 steps

From dietary vitamin D

36
Q

How is the formation of calcitriol stimulated?

A

By hormone prolactin in lactating women

37
Q

How is active vitamin D3 formed?

A

From cholesterol derivatives by the action of UV light on the skin
Gained from the diet also

38
Q

How does the conversion to the active form of calcitriol come bout?

A

Via the release of PTH

39
Q

What is the most important action of calcitriol?

A

Increase absorption of Ca2+ from the gut.

- That’s its most important action

40
Q

What is the active transport system that moves Ca2+ from the intestinal lumen to the blood under the control of?

A

Calcitriol

41
Q

In a situation of low Ca2+ plasma what happens to PTH and calcitriol?

A

Increase in PTH leads to increase in calcitriol leads to increase in Ca2+ absorption

42
Q

What is the result of increased plasma Ca2+?

A

Inhibition of PTH causing a greater osteoblast deposition and less osteoclast resorption

43
Q

What are all the actions of calcitriol?

A

Binds to nucleur receptors in target tissue to increase absorption of Ca2+ from the gut
Facilitate the renal absorption of Ca2+
Mobilisecalcium stores in bone by stimulating osteoclast activity

44
Q

What circulating molecule controls the proportion of dietary calcium absorbed from the gut?

A

1,25(OH)2D

45
Q

What is classed as vitamin D deficiency?

A

Circulating levels less than 20ng/ml

46
Q

What things add to the problem of lack of sunlight?

A

UVB sunscreen

clothing diet

47
Q

What is the effect of GH on bones?

A

Constant stimulus for bone formation

48
Q

What is the effect of plasma pH on hperventillation?

A

Increase in plasma pH

49
Q

What is the effect of hypoventillation on plasma pH?

A

Decrease in plasma pH

50
Q

What is 1,25 dihydroxycholecalciferol (1,25(OH)2D3) another name for?

A

Vitamin D3

51
Q

What is the effect of vitamin D3 deficiency?

A

intestinal malabsorption of Ca2+ , this decreases [Ca2+ ] plasma which increases PTH which then promotes phosphate deficiency – aggravates Ca2+ loss from bone.

52
Q

What is the hormone which acts to decrease Ca2+?

A

Calcitonin

53
Q

What type of hormone is calcitonin?

A

Peptide hormone

54
Q

Where is calcitonin released?

A

Thyroid gland

55
Q

What is calcitonin secretion stimulated by?

A

Increase Ca2+ plasma conc.

56
Q

What is the main actions of calcitonin?

A

Bind to osteoclasts to inhibit bone breakdown as well as increase renal excretion
To decrease Ca2+

57
Q

Is there much evidence that calcitonin is important in humans?

A

No very little

Patients with no calcitonin have normal Ca2+ levels

58
Q

What is the direct effect of Vit D3?

A

To release Ca2+ from the bone

59
Q

What is the net effect of Vitamin D3 on calcium?

A

Increase plasma Ca2+ conc.

60
Q

What is calcitriol the active form of?

A

Vitamin D3

61
Q

What is the effect of cortisol on calcium?

A

Inhibits osteoblasts
Increase renal excretion of Ca2+
Thus decreasing intestinal absorption of Ca2+
Decreases plasma Ca2+

62
Q

What is the effect of insulin on calcium?

A

Increases bone formation

Antagonises the action of cortisol

63
Q

What is the effect of oestrogen on calcium?

A

Promotes bone formation

64
Q

What is the effect of prolactin on calcium?

A

Promotes calcium absorption of the gut by stimulating the synthesis of calcitriol

65
Q

What happens in Vitamin D deficiency?

A

PTH has to work hard to maintain plasma Ca2+
In doing so continually breaks down bone
Can lead to osteomalacia

Endocrinology (19 decks)

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