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Metabolism and Homeostasis > Ca2+ homeostasis > Flashcards

Ca2+ homeostasis Flashcards

1
Q

What hormone regulates Ca2+

A

Parathyroid hormone from parathyroid gland

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2
Q

What is the function of Ca2+

A

Structural integrity of skeleton and tooth enamel
Neurotransmitter release.
Blood coagulation

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3
Q

What is hypocalcaemic tetany?

A

Extracellular Ca2+ falls below normal, nervous system becomes progressively more excitable due to increased permeability of Na+ - this causes tetanic contraction

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4
Q

What are the 3 ways in which calcium exists?

A

Ionised (free Ca2+), anion complex (CaCO3), bound to albumin or globulins

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5
Q

What happens to calcium absorbed into the gut through the diet?

A

80% excreted in the faeces. 35% absorbed by the extracellular fluid, 15% secreted back into the gut from the extracellular fluid

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6
Q

What happens to ca2+ absorbed into the extracellular fluid?

A

Some secreted back into gut, the rest is excreted in the urine

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7
Q

What is the rapidly exchangeable pool?

A

Ca2+ on the surface of the skeleton, they are always being exchanged

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8
Q

What occurs to Ca2+ in the rapidly exchangeable pool?

A

Bone formation - from pool to bone.

Bone resorption - from bone to pool

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9
Q

What are the 3 major target organs of Ca2+?

A

Intestine
Kidney
Bone

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10
Q

How is calcium absorbed from the intestine passively?

A

Across layer of epithelium, down the concentration gradient, between cells = paracellular pathway. This occurs in the ileum

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11
Q

What is the transcellular pathway of absorption in the intestine?

A

Calcium ions taken up into the cell by diffusion and bind to calcium binding proteins to maintain concentration gradient, at the other end calcium gets released and is pumped out of the cell against the concentration gradient using ATP. This occurs in the duodenum and jejunum

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12
Q

How is Ca2+ reabsorbed in the proximal tube in the kidneys?

A

Transcellular pathway

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13
Q

How is Ca2+ reabsorbed int he loop of Henle in the kidneys?

A

Paracellular pathway

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14
Q

How is Ca2+ absorbed in the distal tubule of the kidneys?

A

Transcellular pathway

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15
Q

Why is the transcellualr pathway in the distal tubular important?

A

Ca2+ uptake can be regulated by parathyroid hormone

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16
Q

What is bone remodelling?

A

The constant formation and resorption of bone

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17
Q

In which area of bone does bone remodelling occur?

A

Trabecular bone

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18
Q

What are the areas of bone?

A

Trabecular and compact

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19
Q

Why does calcium exchange occur on the trabecular bone?

A

Greater SA as it is spongy

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20
Q

What is the function of osteoblasts?

A

Bone forming cells that secrete organic bone matrix (osteoid) on which mineralisation occurs

21
Q

What is the function of osteocytes?

A

Mature bone cells enclosed in bone matrix. They are connected to other cells via cannaliculi to allow for nutrient and ion exchange

22
Q

What is the function of osteoclasts?

A

Large multinucleate cells that resorb bone

23
Q

From what cell type are osteoclasts derived?

A

Monocytes

24
Q

What 3 hormones function in Ca2+ homeostasis?

A

Parathyroid hormone (PTH)
1,25 DHCC
Calcitonin

25
Q

Where is PTH synthesised and secreted?

A

Parathyroid gland (behind thyroid gland)

26
Q

What cells int he parathyroid Galen are the site of PTH synthesis?

A

Chief cells

27
Q

How does pTH become active?

A

It is first formed as a pre-prohormone which is cleaves to form PTH

28
Q

What is the main effect of PTH on Ca2+ concentration?

A

Increases plasma Ca2+

29
Q

When is PTH stimulated for release?

A

low levels of Ca2+ in blood

30
Q

What is the mechanism of action of PTH on bone?

A

Increases the number of osteoclasts and increases osteoclast activity to increase bone resorption. Decreases bone formation by decreasing collagen synthesis by osteoblasts

31
Q

What is the mechanism of action of PTH on the kidneys?

A

Acts to increase Ca2+ resorption in the distal tubule by increasing ca2+ uptake into cells.
Stimulates 1-alpha-hydroxylase which catalyses the formation of 1,25DHCC

32
Q

What is the mechanism of action of PTH on the intestine?

A

indirect action by stimulating 1,25DHCC

33
Q

How is 1,25DHCC formed?

A

From vitamin D to the liver where is is converted to 25 HCC, to kidney where PTH stimulates 1-alpha-hydroxylase which converted 25HCC to 1,25DHCC

34
Q

What is the mechanism of action of 1,25 DHCC?

A

Main affect on the intestine to increase Ca2+ absorption from the intestine by increasing number of calcium binding proteins.

35
Q

What is the mechanism of action of 1,25 DHCC on the kidney?

A

Increases tubular reabrotpion of CA2+ = minor affect

36
Q

What is the mechanism of action fo 1,25 DHCC on bone?

A

Promotes the actions of PTH = bone resorption

37
Q

PTH promotes the synthesis of 1,25DHCC and 1,25 DHCC promotes the effects of PTH. How is this controlled?

A

1,25 DHCC inhibits the production of PTH

38
Q

What is the effect of calcitonin?

A

Decrease plasma Ca2+ levels

39
Q

Where is calcitonin synthesised and secreted?

A

Parafollicular cells of the thyroid gland

40
Q

What is the main target cell of calcitonin?

A

Osteoclasts

41
Q

What is the affect of calcitonin on bone?

A

Inhibit osteoclast motility and cell shape to inactivate them so bone respotion can’t occur

42
Q

What is the effect of calcitonin on kidneys?

A

Decrease tubular reabsorption oF CA2+ but this is a weak affect

43
Q

Why does excess calcitonin not produce hypocalcaemia?

A

PTH and 1,25 DHCC dominate

44
Q

What is osteoporosis?

A

Reduced bone mass and density

45
Q

What causes osteoporosis?

A

Uncoupling of the equilibrium of bone formation dn resorption

46
Q

In osteoporosis does bone formation exceed bone resorption?

A

No, other way around

47
Q

Is bone present in osteoporosis biochemically normal?

A

Yes

48
Q

What causes rickets?

A

Inadequate mineralisation of bone matrix

49
Q

What causes hypercalcaemia?

A

Excess PTH or 1,25DHCC

Metabolism and Homeostasis (13 decks)

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