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endocrine > endocrine control of calcium balance > Flashcards

endocrine control of calcium balance Flashcards

1
Q

What are the roles of calcium in the body

A

Signalling - exocytosis of synaptic vesicles

Blood clotting - component of the clotting cascade

Apoptosis

Skeletal strength - the majority of calcium is in bone where it gives strength to the skeleton

Membrane excitability - calcium decreases sodium permability

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2
Q

What is the effect of hypocalcaemia on membrane excitability

A

Increases sodium permeability and leads to hyper excitation of neurons which can cause tetany

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3
Q

What is tetany

A

Involuntary contraction of muscles caused by low calcium levels

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4
Q

What is the effect of hypercalcaemia on membrane excitability

A

Decreases sodium permability which reduces excitability of neurons and depresses neuromuscular activities

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5
Q

What is the calcium in bone stored as and why is phosphateimportant

A

It is stored as hydroxyapatite (Ca10(PO4)6(OH)2) - contains phosphate in it

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6
Q

how much calcium is found in the plasma

A

2.2-2.6 mM

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7
Q

How much of the plasma calcium is bound to plasma proteins

A

40 % due to the high affinity due to charges

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8
Q

how much calcium is physiologically active (free and unbound)

A

1.2mM (50% of plasma calcium)

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9
Q

What 3 forms does plasma calcium exist as

A

40% protein bound
50% free
10% complexed

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10
Q

What is the effect of PH on the binding of proteins to calcium

A

Increased pH (alkaline) causes increased binding - proteins are deprotonated and the negative charge in the proteins allows calcium to bind

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11
Q

What are osteoblasts and what do they do

A

They are bone building cells - highly active cells which lay down a collagen extracellular matrix which then calcifies

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12
Q

What do differentiated osteoblasts form

A

Osteocytes - regulate the activity of osteoblasts and osteoclasts

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13
Q

What are osteoclasts and what do they do

A

Bone breaking cells - secrete protons to dissolve the calcium salts and provide proteolytic enzymes to digest the extracellular matrix

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14
Q

What are the two hormones which increase calcium in the plasma

A

PTH - parathyroid hormone

Calcitrol - active form of vitamin D produced by liver and kidney

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15
Q

What hormone decreases calcium in the plasma

A

Calcitonin - peptide hormone released from the clear cells of the thyroid cells

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16
Q

Where are the parathyroid glands located

A

usually 4 present posterior to the thyroid gland

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17
Q

What causes increased secretion of PTH

A

Decreasee in free plasma calcium

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18
Q

How does PTH increase plasma calcium levels

A

Stimulates osteoclasts to increase resorption of calcium from bone and inhibiting osteoblasts so that they can not deposit into the bone

It also increases resorption of calcium from the kidney tubules which decreases it’s excretion

PTH excretes more phosphate so that there is less deposits being put back into the bone

19
Q

What is the effect of vitamin D on calcium

A

It causes calcium absorption

20
Q

What in lactating in women can enhance production

A

prolactin

21
Q

Where does Vitamin D become activated

A

Kidney and liver where it becomes calcitriol in the presence of PTH

22
Q

What is the action of calcitriol on calcium absorption at the gut

A

Calcitriol controls the active transport system which moves calcium from the intestinal lumen to the blood

23
Q

What are the actions of calcitriol

A

Increases absorption of calcium in the gut

Facilitates renal absorption calcium

Stimulates osteoclasts

24
Q

What is the correlation between prolactin and calcitriol

A

Prolactin stimulates calcitriol synthesis with increased demands for calcium

25
Q

What is hypocalcaemic tetany

A

voluntary twitching caused by hypocalcaemia

26
Q

What inhibits PTH

A

increased plasma concentration of calcium

27
Q

What is the effect of vitamin D3

A

Increase plasma calcium concentration and mineralization of bone

28
Q

What happens in Vit D3 deficiency

A

The PTH works extra hard to control plasma and continually activates osteoclasts which results in easily fractured bones

29
Q

What is the condition were bones become soft and easily fractured in adults

A

Osteomalacia

30
Q

What is the condition where bones are soft and if still growing become bent in children

A

rickets

31
Q

What is the effect of vitamin D defficiency

A

Intestinal malabsorption of calcium therefore decreased plasma calcium which activates PTH and that actives osteoclasts which aggravates calcium loss from bone

32
Q

What population are at most risk of vitamin D3 defficiency

A

Asian and elderly populations

33
Q

What hormone acts to decrease calcium levels

A

calcitonin and maybe cortisol

34
Q

What produces calcitonin

A

thyroid gland

35
Q

What stimulates secretion of calcitonin

A

Increased plasma calcium

36
Q

What are the main functions of calcitonin

A

Bind to osteoclasts and inhibit bone resorption and increases calcium excretion - therefore reduces plasma calcium

37
Q

What happens if there is excess calcitonin in the body

A

PTH overrides the effects

38
Q

What is paget’s disease and what can help to treat it

A

Overactive osteoclasts breaking down bone - calcitonin can rarely be used to treat Paget’s disease

39
Q

What is the effect of cortisol on calcium balance

A

Inhibits osteoblasts and increases renal excretion of calcium and phosphate excretion which decreases calcium in the plasma which stimulates bone resorption to increase the levels

40
Q

What is the effect of insulin on calcium balance

A

Increases bone formation - diabetics can have slight bone loss due to low insulin and antagonises action of cortisol

41
Q

What is effect of testosterone and oestrogen

A

Activate osteoblasts

42
Q

What is the effect of growth hormone on calcium balance

A

Constant stimulus for bone formation

43
Q

What is the effect of prolactin on calcium balance

A

Promotes calcium absorption from the the gut by stimulating calcitriol

44
Q
A

endocrine (30 decks)

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