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Endocrine System > Calcium Homeostasis COPY COPY > Flashcards

Calcium Homeostasis COPY COPY Flashcards

1
Q

What are the roles of calcium in the body?

A
  1. Signalling
  2. Blood clotting
  3. Apoptosis
  4. Skeletal support
  5. Membrane excitatability
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2
Q

What is the role of calcium in signalling?

A

Exocytosis of synaptic vessels

  • Sarcoplasmic reticulum = contraction of muscle fibres
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3
Q
A
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4
Q

How does calcium mediate membrane excitatability?

A

Calcium decreases sodium permeability of the membrane

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5
Q

What happens to membrane excitatability during hypocalcaemia?

A
  • Neuronal Na+ permeability is increased
  • Hyperexcitation of neurones occurs
  • In extreme cases, hypocalcaemia causes tetany and asphyxiation
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6
Q

What happens to membrane excitatability during hypercalcaemia?

A
  • High calcium decreases neuronal Na+ permeability
  • Reduces excitatability
  • Depresses neuromuscular activity
  • Hypercalcaemia can cause cardiac arrhythmias
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7
Q

How is calcium distributed in the body?

A

99% in bones

0.9% ICF

0.1% ECF - only physiologically active

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8
Q

How is calcium stored in bone?

A

Stored as hydroxyapatite (contains phosphates so phosphate homeostasis is important in calcium storage)

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9
Q

Where is calcium stored in the ICF?

A

Mitochondria/sarcoplasmic reticulum

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10
Q

How is calcium found in the ECF?

A

40% is bound to proteins

50% free

10% complexed

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11
Q

What are normal values of [Ca2+]plasma

A

2.2 - 2.6mM

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12
Q

What is the effect of alkalosis on calcium protein binding?

A

Increased

  • Therefore hyperventilation (alkalosis) can lead to hypocalcaemic tetany
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13
Q

What is the effect of acidosis on calcium binding?

A

Reduced

  • H+ ions displace protein bound calcium
  • Can lead to arrhythmia
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14
Q

What is the primary and secondary role of bone stored calcium?

A

Primary = maintaining plasma calcium levels

Secondary = structural support

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15
Q

What is the role of osteoblasts and how do they achieve it?

A

Build up bone

  • Lay down collagen matrix that they then calcify
  • They then differentiate into osteocytes
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16
Q

What is the role of osteoclasts and how do they do it?

A

Break down bone and release calcium

  • Secrete H+ ions into the bone to dissolve calcium and release it
17
Q

What two hormones increase [Ca2+]plasma?

A
  1. Parathyroid hormone
  2. Calcitriol
18
Q

What type of hormone is parathyroid hormone (PTH)?

19
Q

When and by what is parathyroid secreted?

A
  • Low [Ca2+]plasma
  • Secreted by parathyroid glands
20
Q

In what ways does PTH increase [Ca2+]plasma?

A
  1. Stimulates osteoclasts
  2. Inhibits osteoblasts
  3. Increases reabsorption of Ca2+ in kidney tubules
  4. Increase renal excretion of phosphates (inhibitis formation of hydroxyapatite)
  5. Stimulates kidneys to synthesise calcitriol
21
Q

What type of hormone is calcitriol?

22
Q

What is calcitriol made from?

A

It is the activated form of vitamin D3

23
Q

What is the 2 step production of calcitriol?

A
  1. Dietary and sunlight Vit D used
  2. Converted to 25 hydroxycholecalciferol in the liver
  3. Then converted to calcitriol in the kidney by the action of PTH
24
Q

How does calcitriol increase [Ca2+]plasma?

A
  • Stimulates osteoclasts
  • Increases renal absorption of calcium
  • Increases calcium uptake in the gut
25
Q

How is calcium absorbed in the gut?

A

Requires active transport

  • This requires calcitriol to occur
26
Q

What are rickets and osteomalacia?

A

Rickets = bone bending during growing in children from Vit D def.

Osteomalacia = same but in adults

27
Q

What type of hormone is calcitonin?

A

Peptide hormone

28
Q

Where is calcitonin released from and when is it released?

A

C cells in the thyroid gland

  • Released in response to high [Ca2+]plasma
29
Q

What is the function of calcitonin and how does it achieve this?

A

Decreases [Ca2+]plasma

  • Binds to osteoclasts to prevent bone reabsorption
30
Q

Is calcitonin very important in humans?

A

No

Full thyroidectomies don’t usually have any effect on [Ca2+]plasma

31
Q

What effect does cortisol have on [Ca2+]plasma?

A
  • Mixed effect
  • Inhibits osteoblasts so may increase
  • BUT
  • Increases renal excretion and
  • Reduces intestinal reabsorption
32
Q

What effect do Insulin and Oestrogen have on [Ca2+]plasma?

A
  • Both increase bone formation therefore lower
  • Insulin at high levels during growth spurts to increase this bone formation
33
Q

What effects does prolactin have on body calcium stores?

A
  • Promotes calcium absorption by stimulating the secretion of calcitriol

Endocrine System (90 decks)

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