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D&E Physiology > Endocrine Control of Calcium Balance > Flashcards

Endocrine Control of Calcium Balance Flashcards

1
Q

What are the rolls of calcium in the body?

A 
Signalling
Blood clotting
Apoptosis
Skeletal strength
Membrane excitability
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2
Q

What is the signalling role of Ca2+?

A

Exocytosis
Contraction of muscle fibres
Altering enzyme function

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3
Q

What is the blood clotting role of Ca2+?

A

Part of clotting cascade

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4
Q

What is the membrane excitability role of Ca2+?

A

Ca2+ decreases Na+ permeability

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5
Q

What effect does hypocalcaemia have?

A

Increased neuronal Na+ permeability causing hyper-excitations
- Tetany

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6
Q

What effect does hypercalcaemia have?

A

Decreased neuronal Na+ permeability
Reduced excitability
Depressed neuromuscular activity
Arrhythmias!!

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7
Q

What is the distribution of calcium in the body?

A

Bones 99%
Intracellular 0.9%
Extracellular fluid 0.1%

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8
Q

Where is intracellular calcium stored?

A

Inside mitochondria, sarcoplasmic reticulum

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9
Q

How is calcium stored in the extracellular fluid?

A

~50% bound

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10
Q

How much calcium in the body is free in solution?

A

0.05%

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11
Q

How much calcium is stored in bones? How is it stored?

A

99% - 1kg

Calcified extracellular matrix in hydroxyapatite with PO4

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12
Q

What other factor is also important in determining calcium balance?

A

Phosphate homeostasis

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13
Q

Calcium is stored with what in the bones?

A

Ca10(PO4)6(OH)2

Hydroxyapatite

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14
Q

What is the normal range of plasma Ca2+?

A

2.2-2.6mM in plasma

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15
Q

Calcium has a high affinity for what? Why?

A

Proteins

they have a large -ve charge

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16
Q

Which part of [Ca2+]plasma is physiologically active?

A

~50%, unbound, 1.2mM

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17
Q

What happens to the 10% of calcium ions not bound to plasma protein, nor free in solution?

A

Bound to plasma anions

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18
Q

What proteins, and to what proportion, is calcium bound?

A

Albumin - 80%

Globulin - 20%

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19
Q

Which anions is calcium typically bound to?

A 
HCO3
H2PO4
HPO4
Sulphate
Citrate
Lactate
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20
Q

What is the calcium distribution in blood?

A

40% protein bound
10% complexed
50% free

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21
Q

The binding capacity of Ca2+ is dependent on what?

A

pH

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22
Q

When is binding capacity increased?

A

Alkalotic conditions

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23
Q

What is the effect on plasma pH of hyperventilation?

A

Increased pH

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24
Q

How can hyperventilation precipitate hypocalcaemic tetany?

A

Decreased CO2
Increased pH
Increased bound [Ca2+]
Hypocalcaemia

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25
Q

What is the effect of acidosis on protein bound calcium?

A

Decreased pH increases plasma [H+] which displaces bound Ca2+, increasing free [Ca2+]

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26
Q

Total body calcium = ?

A

Calcium in - Calcium out

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27
Q

What is the most important role of bone?

A

Calcium balance maintenance

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28
Q

What are osteoblasts?

A

Bone building cells

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29
Q

How do osteoblasts work/

A

Highly active
Lay down collagen extracellular matrix which they then calcify
Differentiate into osteocytes in established bone

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30
Q

What do osteocytes do?

A

Regulate osteoblast/osteoclast activity

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31
Q

What is the function of osteoclasts?

A

Secrete H+ (pH 4) to dissolve calcium saltes

Provide proteolytic enzymes to digest extracellular matrix

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32
Q

Which hormones increase [Ca2+]plasma?

A

Parathyroid hormone

Calcitriol

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33
Q

What is parathyroid hormone?

A

Polypeptide hormone produced by the parathyroid gland

34
Q

What is calcitrol?

A

Active form of Vitamin D

Steroid hormone produced by liver and kidneys

35
Q

Where are the parathyroid glands located?

A

Lying on the posterior surface of the thyroid gland

36
Q

When is parathyroid hormone secreted?

A

Response to ↓[Ca2+]plasma

37
Q

How does parathyroid hormone increase [Ca2+]?

A
  1. Stimulate osteoclasts to resorb Ca and Phosphate
  2. Inhibit osteoblasts to reduce Ca deposition
  3. Increase reabsorption of Ca2 from kidney tubules
  4. Increase renal phosphate excretion
  5. Stimulate kidney calcitrol synthesis promoting calcium absorption
38
Q

How does increasing renal excretion of phosphate increased [Ca2+]?

A

Prevents Ca2+ from being deposited back into bone

39
Q

What is calcitriol?

A

Active vitamin D3

40
Q

What type of hormone is calcitriol?

A

Steroid hormone

41
Q

What also stimulates formation of calcitriol?

A

Prolactin (lactating women)

42
Q

How does sunlight form vitamin D3?

A

Action of UV light on the skin causing cholesterol –> vitamin D3

43
Q

What are the dietary sources of vitamin D3?

A

Fatty fish
Fish liver oils
Egg yolks

44
Q

How is calcitrol produced?

A

Vitamin D
Processed by liver, then kidneys
OR
Steroid precursors activated by UV light

45
Q

Which actions of calcitrol complement PTH?

A

Increased Ca2+ absorption in gut
Facilitates renal absorption of Ca2+
Mobilises calcium stores in bone

46
Q

How does calcitrol mobilise calcium stores in bone?

A

Stimulating osteoclast activity

47
Q

How does calcitriol control intestinal intake of Ca2+?

A

Controlling active transport system

48
Q

What is the effect of low plasma [Ca2+]?

A

↑ in PTH –> ↑calcitriol –> ↑intestinal Ca2+ absorption

49
Q

What is the effect of prolactin in relation to Calcium?

A

Stimulation of calcitriol synthesis by kidneys to supply increased demand

50
Q

What is the amount of dietary Ca2+ absorbed in a healthy individual?

A

30%

51
Q

What is the amount of dietary Ca2+ absorbed in a vitamin D deficient individual?

A

10-15%

52
Q

What is the amount of dietary Ca2+ absorbed in a pregnant/lactating/growing individual?

A

45-55%

53
Q

What is the amount of calcitriol in a vitamin D deficient individual?

A

Low

54
Q

What is the amount of calcitriol in a pregnant/lactating/growing individual?

A

High

55
Q

When is Vitamin D considered ‘deficient’?

A

Circulating vitamin D <20ng/ml

56
Q

What % of scots are vitamin D insufficient?

A

Summer - 75%

Winter - 92%

57
Q

When does Vitamin D deficiency become more prevalent?

A

> 65 years due to reduce absorption

58
Q

How does vitamin D deficiency present?

A

Children - Rickets

Adults - Osteomalacia

59
Q

If calcitriol causes Ca release from bone, how does it make bones stronger?

A

Greater effect on gut absorption/kidney reabsorption, which increases bone mineralization

60
Q

Vitamin D3 deficiency leads to what?

A

Ca2+ and Phosphate deficiency

61
Q

How does vitamin D3 deficiency lead to phosphate deficiency?

A

Intestinal malabsorption means low [Ca2+], this increases PTH
Increased PTH aggravated Ca loss from bone .’. loss of phosphate

62
Q

Why are asians at risk of Ca deficiency?

A

Chapatti flour contains phytate
Phytate binds dietary Ca2+
Pigmented skin less able to respond to UV light

63
Q

Vitamin D deficiency is implicated in what?

A

MS
Cancer
Arthritis
CVD

64
Q

Which hormone decreases [Ca2+]

A

Calcitonin

65
Q

What type of hormone is calcitonin?

A

Peptide hormone

66
Q

What stimulates calcitonin secretion?

A

↑ [Ca2+]

67
Q

Where is calcitonin produced?

A

Thyroid gland

68
Q

What are the main actions of calcitonin?

A

Bind to osteoclasts and inhibit bone resorption

Increase Ca2+ excretion by kidneys

69
Q

When is calcitonin used as a treatment?

A

Paget’s Disease

overactive osteoclasts

70
Q

What is the effect of Cortisol on Ca2+ balance?

A

Inhibit osteoblasts
Increase Ca2+ and phosphate
Reduce intestinal absorption
Increase PTH .’. ↑bone resorption

71
Q

What can increased cortisol lead to over time?

A

Osteoporosis

72
Q

What is the effect of insulin on Ca2+ balance?

A

Inhibit cortisol

Increase bone formation

73
Q

What is the effect of oestrogen on Ca2+ balance?

A

Promote bone formation via oestrogen receptors on osteoblasts

74
Q

What is the effect of growth hormone on Ca2+ balance?

A

Constant stimulus for bone formation

75
Q

What is the effect of prolactin on Ca2+ balance?

A

Promotes calcium absorption by the gut, stimulating synthesis of calcitriol

76
Q

When are osteoclasts stimulated?

A

When calcium is low

77
Q

Where is Calcitriol activated?

A

Kidneys

78
Q

What causes the inhibition of PTH?

A

Increased plasma [Ca2+]

79
Q

Calcitriol binds to what?

A

Target tissue nuclear receptors
Intestine
Bone
Kidney

80
Q

What is the primary action of vitamin D?

A

Get calcium out of the gut

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