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Year 2- Endocrine System > Endocrine Control Of Calcium Balance > Flashcards

Endocrine Control Of Calcium Balance Flashcards

1
Q

What is the role of calcium in the body?

A
  1. Cell signalling
  2. Blood clotting
  3. Apoptosis
  4. Skeletal strength
  5. Membrane excitability
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2
Q

What role does calcium play in cell singalling?

A

Plays a role in the exocytosis of synaptic vesicles e.g. neurotransmitters/hormones.
Contraction of muscle fibres
Alters enzyme function

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3
Q

What would happen is calcium was removed from the plasma?

A

Blood would stop clotting

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4
Q

RECAP- what is apoptosis?

A

Programmed cell death

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5
Q

What % of calcium in the body is in the skeleton?

A

99%

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6
Q

What happens if we are deficient in calcium?

A

Bones weaken

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7
Q

What role does calcium play in membrane excitability?

A

Decreases sodium permeability

->this is more critical in short term homeostasis

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8
Q

Hypocalcaemia?

A

Low levels of calcium in the blood

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9
Q

What does hypocalcaemia lead to in terms of sodium permeability?

A

Increased sodium permeability leading to hyperexcitation of neurons.

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10
Q

In extreme cases of hypocalcaemia, the hyperexcitation of neurons can causes what to happen?

A

Tetany (involuntary muscle contraction).

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11
Q

If there is tetany, which ion is low in the blood?

A

Calcium

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12
Q

How can low calcium levels lead to asphyxiation (being deprived of oxygen, ultimately leading to death)?

A

The increased sodium permeability causes hyperexcitation of neurons and tetany, as previously discussed.

If this involuntary muscle contraction spreads to the larynx and respiratory muscles, it can cause asphyxiation.

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13
Q

What can hypercalcaemia cause to happen?

A

Decreases neuronal sodium permeability which reduces excitability.
This depresses neuromuscular activity.

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14
Q

The depressed neuromuscular activity associated with hypercalcaemia can cause what to happen?

A

Can trigger cardiac arrhythmias

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15
Q

What % of calcium in the body is intracellular?

A

0.9%

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16
Q

What % of calcium in the body is in the extracellular fluid?

A

0.1%

-> 99% in bone, 0.9% intracellular, 0.1% in ECF

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17
Q

So, there’s 0.1% of body calcium found in the ECF. Half of these is bound to protein. Therefore, what % of calcium in the body is physiologically active?

A

0.05%

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18
Q

What form is calcium in the bone found as?

A

Hydroxyapatite

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19
Q

Which type of homeostasis is important in determining calcium balance?

A

Phosphate homeostasis

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20
Q

What does calcium has a high affinity for?

A

Protein

-> in plasma, around 40% of calcium in bound to plasma proteins

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21
Q

How many mM of calcium is found in the plasma?

A

2.2-2.6 mM

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22
Q

In the plasma, there is 0.1% of our calcium. Explain, in %, what this calcium is found as.

A

0.1%

40% bound to plasma protein
50% free/ionised, physiologically active
10% in complexes e.g. bicarbonate etc.

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23
Q

What effects the binding of calcium to plasma proteins?

A

pH

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24
Q

Is binding capacity increased under acidic or alkaline conditions?

A

Alkaline

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25
Q

If you hyperventilate, what happens to pH?

A

Blow of CO2, lower hydrogen ions and increase pH, making it more alkaline

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26
Q

If more calcium binds to plasma proteins, the calcium concentration in the plasma would fall. What can this cause again?

A

Hypo calcaemic tetany

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27
Q

RECAP 1ST YEAR : If you were retaining CO2, if this acidosis or alkalosis:?

A

Acidosis

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28
Q

If the pH of plasma is more alkaline, what happens?

A

More calcium becomes bound to plasma proteins

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29
Q

What is the total amount of calcium in the body determined by?

A

The about of calcium in via the diet and the amount out via excretion

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30
Q

99% of calcium in stored in bones. However, this can fluctuate. Why?

A

The body can use the stores of calcium in the bones if required

-> calcium needed to provide skeletal strength but it’s role in maintaining calcium balance takes priority

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31
Q

There is continuous turnover of bone, it is continually deposited and resorbed.
What do osteoblasts do?

A

Bone-building cells, lay down a collagen extracellular matrix which they then calcify

-> think Blasts= Bone-Building

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32
Q

What do osteoclasts do?

A

Responsible for mobilising bone and dissolve the calcium salts.
They provide proteolytic enzymes to digest the extracellular matrix.

->basically, osteoclasts breakdown bone, osteoblasts build back bone

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33
Q

Which two hormones act to increase calcium levels?

A

Parathyroid hormone
Calcitriol

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34
Q

What is parathyroid hormone and where is it produced?

A

Polypeptide hormone produced by parathyroid glands

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35
Q

What is calcitriol the active form of?

A

Vitamin D

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36
Q

What is calcitriol and where is it produced?

A

Steroid hormone produced from vitamin D in the liver and kidneys

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37
Q

Which hormone increases calcium levels and is a polypeptide hormone?

A

Parathyroid hormone

38
Q

Which hormone increases calcium levels and is a steroid hormone?

A

Calcitriol

39
Q

Name the hormone which acts to decrease calcium levels in the plasma.

A

Calcitonin

40
Q

What type of hormone is calcitonin?

A

Peptide hormone

41
Q

Where is calcitonin released from?

A

Parafollicular cells of the thyroid gland

42
Q

Where are the parathyroid glands?

A

Posterior surface of thyroid gland

43
Q

How many parathyroid glands do we have?

A

4

->not all required for survival, can live with one or two. In surgery for removal of thyroid, always tried to keep some of them

44
Q

When is parathyroid hormone released?

A

In response to low levels of calcium

45
Q

How does parathyroid hormone act to increase free calcium levels in the plasma regarding bones?

A

Stimulates osteoclasts to increase release/resorption of calcium and phosphate in bone
Inhibits osteoblasts which reduce calcium deposition

46
Q

How else does parathyroid hormone act to increase free calcium levels in the plasma?

A

Increases reabsorption of calcium from the kidney tubules which decreases it’s secretion in urine
Increases renal excretion of phosphate as prevents calcium being deposited back into bone as this process requires phosphate

47
Q

Calcium and phosphate are both required to get calcium into bones via hydroxyapatite . Therefore, when there are low plasma levels of calcium, what happens to phosphate?

A

In order to increase calcium levels in the plasma, phosphate needs to be excreted

48
Q

How does parathyroid hormone use calcitriol to increase levels of plasma calcium?

A

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

49
Q

Calcitriol complements the actions of which other hormone?

A

Parathyroid hormone

50
Q

RECAP- what are all steroid hormones, like calcitriol, derived from?

A

Cholesterol

51
Q

Calcitriol is produced in two steps from vitamin D. Where does:
a. Step 1 take place
b. Step 2 take place?

A

a. Liver
b. Kidneys

52
Q

What is the name of inactive vitamin D?

A

Cholecalciferol

53
Q

How do we get cholecalciferol (inactive vitamin D)

A

Via diet or sunlight

54
Q

Name some food sources of vitamin D.

YAY

A

Oily fish, liver, oils, egg yolks.

->Fat soluble vitamin so good dietary sources are fatty.

55
Q

When is the formation of calcitriol from cholecalciferol enhanced?

A

Enhanced in lactating women by the hormone prolactin

56
Q

Which hormone is the only hormone which can increase calcium absorption from the gut?

A

Calcitriol

57
Q

Since calcitriol is a steroid hormone, it binds to intracellular nuclear receptors in the target tissues. What are the target tissues?

A

Intestine, bone and kidney

58
Q

What happens when calcitriol binds to the target tissues?

A

Increases the absorption of calcium from the gut

-> unlike potassium and sodium, which are completely absorbed from the gut, a lot of calcium in the diet is excreted.
Calcitriol controls a system which moves calcium from the intestinal lumen into the blood

59
Q

If there is low levels of calcium in the plasma, what happens in terms of hormones?

A

Increases in parathyroid hormones, increase in calcitriol which increases the intestinal absorption of calcium

60
Q

If there are high levels of calcium in the plasma, what happens in terms of hormones?

A

Inhibits the release of PTH (negative feedback)
Greater osteoblast deposition and less osteoclast resorption so we can store the excess calcium in bone

61
Q

How can calcitriol act on the kidneys in order to increase plasma calcium?

A

Similar to PTH
Increases calcium absorption from the gut and facilitates renal absorption of calcium

62
Q

What does vitamin D promote the reabsorption of?

A

Phosphate

63
Q

Therefore, if you are deficient in vitamin D, what happens?

A

Weak bones

64
Q

What % of calcium consumed through the diet is absorbed?

A

30%

65
Q

What % of calcium consumed through the diet is absorbed if the individual is deficient in vitamin D?

A

10-15%

66
Q

What % of calcium consumed through the diet is absorbed if the individual is pregnant/lactating/having a growth spurt?

A

45-55%

67
Q

Below what level does vitamin D levels need to fall below in order to be classed as deficient?

A

Below 20ng/ml

68
Q

In which groups of people is vitamin D deficiency more prevalent?

A

-Those living in northern hemisphere due to lack of sunlight
-Those over 65yrs due to reduced gut absorption

69
Q

What can vitamin D deficiency lead to in children?

A

Rickets

70
Q

What can vitamin D deficiency lead to in adults?

A

Osteomalacia

71
Q

What is the direct effect of vitamin D?

A

To release calcium from bones and increase plasma calcium

72
Q

What is the net effect of vitamin D?

A

While increasing calcium in plasma, plasma phosphate levels also increase which means there is an increase in bone strength

73
Q

Therefore, why do we get weak bones if we are deficient in vitamin D?

A

PTH works to maintain calcium levels but also excretes phosphorus so calcium cannot join to it and be laid back into bone.

Therefore, weaker bones

74
Q

What happens in rickets?

A

Bones bend

75
Q

What happens in osteomalacia?

A

Bones are more likely to fracture

76
Q

So in turn, a deficiency in vitamin D leads to which other deficiencies?

A

Calcium and phosphate deficiencies

77
Q

Which populations are at greater risk of vitamin D, calcium and phosphate deficiency?

A

Asian and Elderly populations

-> this is because chapatti flour contains phytate which binds to dietary calcium, there may be a dietary deficiency and pigmented skin is less able to make vitamin D in response to UV light

78
Q

In which conditions if vitamin D deficiency more common?

A

MS, cancer, arthritis and CVD

79
Q

What type of hormone is calcitonin?

A

Peptide hormone

80
Q

Where is calcitonin produced from?

A

Thyroid gland

81
Q

When is the secretion of calcitonin increased?

A

When there is increased calcium levels in the plasma

-> just wanted to say out of interest that there’s little evidence to suggest that humans need calcitonin

82
Q

How does calcitonin reduce calcium plasma levels?

A

Binds to osteoclasts and inhibits bone resorption.
Increases renal excretion.

83
Q

Any effects of excess calcitonin is overridden by what?

A

PTH

84
Q

Which condition can calcitonin be useful in and help in the treatment of?

A

Paget’s disease

85
Q

What happens in Paget’s disease?

A

Overactive osteoclasts which break down bone, leading to soft bone

86
Q

How does cortisol alter calcium balance?

A

Inhibits osteoblasts and increases renal excretion of calcium.
Over time, this can lead to osteoporosis

87
Q

How does insulin alter calcium balance?

A

Increases bone formation and antagonises the action of cortisol

88
Q

Therefore, those with diabetes can have what effect on bone?

A

Significant bone loss as lack of insulin which aids in bone formation

89
Q

How does oestrogen alter calcium balance?

A

Promotes bone formation via oestrogen receptors on osteoblasts.

-> Post-menopausal osteoporosis is a major problem

90
Q

How does GH alter calcium balance?

A

Acts as a constant stimulus for bone formation

91
Q

How does prolactin alter calcium balance?

A

Promotes calcium absorption form gut by stimulating the synthesis of calcitriol

Year 2- Endocrine System (27 decks)

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