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Endocrinology > Regulation Of Calcium > Flashcards

Regulation Of Calcium Flashcards

1
Q

Distribution of calcium in the body?

A

99% skeleton
1% intracellular
0.1% extracellular - (Plasma ~2.5mmol/L)

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2
Q

What state is calcium in the plasma in?

A

45% ionised (free) the rest is bound Ca2+

Ca2+ either bound to plasma proteins such as albumin or anions e.g. phosphate, lactate

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3
Q

What hormones increase and decrease calcium ( and phosphate?)

A 
Increase:
Vit D
Parathyroid hormone
Both = major 
Decrease:
Calcitonin - not major regulatory role
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4
Q

What are sources of vitamin D?

A

Vitamin D2 = ergocalciferol from diet e.g. oily fish

Vit D3 from sunshine (UVB) =cholecalciferol

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5
Q

How is vitamin D metabolised?

A

UVB (sunlight) shines on skin
-> 7-dehydrocholestrol ->pre vit D3 -> vit D3 -> taken by blood supply to liver
The fit D2 from diet -> vet D3 and also taken to liver

-> 25 hydroxylase hydroxylses vit D3 ( precursor), vit D3 still not activated = 25(OH)cholecalciferol -> kidney-> 1 alpha hydroxylase activates it by making 1, 25 dihydroxycholecalciferol = vit D= CALCITRIOL

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6
Q

How does vitamin D regulate its own synthesis

A

by decreasing transcription (negative feedback) of 1 alpha- hydroxylase

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7
Q

Effects of calcitriol?

A

Works in bones - increases calcium absorption from bone, kidney, increases calcium absorption from gut
Also increases phosphate absorption

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8
Q

Where is PTH released from?

A

Chief cells in Parathyroid gland

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9
Q

How is PTH secreted?

A

Secreted as a large precursor, (pre-pro -PTH) …

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10
Q

What is PTH secretion inversely proportional to?

A

Serum calcium

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11
Q

What happens when calcium is high I’m ECF?

A

Binds to receptors on parathyroid cells (chief)

PTH secretion inhibited

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12
Q

What happens when there’s low Calcium in ECF?

A

Less Ca2+ binds to receptors

PTH increases

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13
Q

What are the effects of PTH?

A

Increases calcium reabsorption from bone
Increases calcium from kidney
Increases action of 1 alpha hydroxylase -> increases calcitriol and so indirectly effects gut.

Kidney - increased secretion of phosphate but calcitriol - increases phosphate from gut so has conflicting effects on phosphate

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14
Q

What cells build bones?

A

osteoBlasts

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15
Q

What cells dissolve bones.

A

Osteoclasts (calcium reabsorption)

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16
Q

How does PTH act on the bone

A

PTH binds to PTH receptors on osteoblasts, activates osteoclasts activating factors, activates osteoclasts - calcium reabsorption from bone

17
Q

What is calcitriol s action on the bone?

A

Same as PTH but effects depend on serum calcium

18
Q

What does calcitriol do when there is low serum calcium

A

Calcitriol increases calcium reabsorption from bone

19
Q

If vit d is important in bone formation, why does it cause absorb calcium from bone?

A

If serum calcium is low (blood) , it’s more imp to get that back to normal first

20
Q

What happens in normal serum levels of calcium in terms of vit d?

A

Osteoblasts preferred

21
Q

Where is calcitonin secreted from

A

From parafollicular cells, around follicular cells in thyroid

22
Q

What is the function of calcitonin?

A

Reduces serum calcium acutely

23
Q

If thyroid gland removed, what happens to regulation of calcium?

A

Not affected, calcitonin doesn’t play major role

24
Q

What does calcitonin do?

A

Lowers serum plasma calcium / EC ca

Reduces osteoclasts
Promotes calcium excretion from kidney

25
Q

What is a hormone that’s important for phosphate regulation

A

Fibroblast Growth factor 23 (FGF23)

26
Q

What happens to phosphate in the proximal tube?

A

—-

27
Q

What does FGF23 do to phosphate

A
  • secretion in urine bc it inhibits cotransporter so can’t be reabsorped
  • can inhibit calcitriol - decreases intestinal phosphate absorption
28
Q

What is the effect Of hypo/hypercalcaemia ?

A

Blocks Na+ influx in nerves/skeletal muscles, less excitability

29
Q

Describe what happens in hypocalcaemia and it’s signs and symptoms

A

Sensitises excitable tissue, muscle cramps, tetany - muscles can contract but not relax ?., tingling (parasthesea)

30
Q

What is Chvosteks sign?

A

When you tap the facial nerve below zygomatic arch:

Twitching of facial muscles would indicate hypocalcaemia

31
Q

What is trousseau sign?

A

Induce tetany.

Hypocalcaemia

32
Q

Causes of hypocalcaemia

A

Low PTH (hypo parathyroidism):
- surgical ( damage during neck surgery)
- auto-immune
-magnesium deficiency (need it to make PTH)
-congenital (rare but no parathyroid gland’
MAIN CAUSE = VIT D deficiency

33
Q

What are causes of vit D deficiency?

A 
Malabsorption (Celiac) / dietary insufficiency
Inadequate sun exposure
Liver disease ( 1st hydroxylation step)
Kidney disease (2nd hydroxylation step)
Receptor issues - can’t recognise it
34
Q

Consequences of Vit D deficiency

A

Lack of bone mineralisation = soft bonds
In children = rickets (bowing of bones)
In adults:

35
Q

Signs and symptoms of hypercalcaemia

A

Reduces neuronal excitability
Stones, abdominal moans, psychic groans
Stones : renal effects
- nephrocalcinosis = kidney stones, renal colic

Abdominal moans - GI effects
Anorexia, nausea, dyspepsia,…

36
Q

Causes of hypercalcaemia

A

Primary hyper parathyroidism
- too much PTH
Usually due to parathyroid gland adenoma
No negative feedback - high PTH but high calcium

Malignancy

Excess Vit D (rare)

37
Q

Why is calcium important?

A 
Neuromuscular excitability 
Muscle contraction & bone strength
Intracellular 2nd messenger
Intracellular co enzyme
Hormone /neurotransmitter stimulus - secretion coupling
38
Q

What is the biologically active form of calcium?

A

The ionised / free

39
Q

Where do Vit D and PTH act to regulate calcium?

A

Kidney, bone and gut

Endocrinology (8 decks)

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