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Regulation of calcium and phosphate Flashcards

1
Q

What is the most abundant metal in the body?

A

Calcium

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2
Q

What meets all requirements for calcium?

A

Diet

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3
Q

What percentage of calcium is found in skeleton and teeth?

A

99%

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4
Q

What form is calcium in in bone?

A

Calcium hydroxyapatite crystals

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5
Q

Is extracellular calcium tightly regulated?

A

Yes

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6
Q

What is the biologically active component of calcium?

A

‘Unbound’ ionised calcium

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7
Q

What percentage of calcium is intracellular?

A

1%

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8
Q

What percentage of calcium is extracellular?

A

0.1%

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9
Q

What hormones increase serum calcium?

A

Parathyroid hormone
Vitamin D

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10
Q

What hormones decrease serum calcium?

A

Calcitonin- can reduce calcium if injected, but generally in body has not overall effect

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11
Q

What are the names of the two types of vitamin D?

A

Ergocalciferol-
Cholecalciferol-

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12
Q

Where is Ergocalciferol derived from?

A

UV irradiation of plants

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13
Q

Where is Cholecalciferol derived from?

A

UV irradiation of skin (animals and humans) and certain foods (oily fish, egg yolks)

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14
Q

What is calcitriol?

A

The active form of vitamin D

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15
Q

What is the major role of calcitriol?

A

↑ Ca2+ and
PO43- reabsorption from the GUT

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16
Q

What cells secrete PTH?

A

Chief cells in parathyroid gland

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17
Q

What is PTH secreted as?

A

large precursor (pre-pro-PTH) & cleaved to PTH

18
Q

What does the G-protein coupled calcium sensing receptor on chief cells do?

A

detects change in circulating calcium concentration

19
Q

What is the relationship between PTH secretion and serum calcium?

A

Inversely proportional

20
Q

Why does low extracellular calcium cause release of PTH?

A

Less calcium binds to receptors on parathyroid cells

21
Q

Does PTH increase or decrease bone re-absorption?

A

Increase

22
Q

How does PTH lead to bone resoprtion?

A

Binds to PTH receptor on osteoblasts, activating osteoclast activating factors (OAFs)

23
Q

How does cacitriol affect bone when serum calcium is low?

A

calcitriol works with PTH to increase calcium reabsorption from bone
osteoclasts > osteoblasts

24
Q

How does cacitriol affect bone when serum calcium is normal?

A

calcitriol promotes bone formation
osteoblasts > osteoclasts

25
Q

What is calcitonin?

A

A hormone

26
Q

Where is calcitonin secreted from?

A

parafollicular (C) cells of the thyroid gland

27
Q

What does calcitonin do?

A

Reduces serum calcium

28
Q

Does removal of the thyroid gland affect serum calcium?

A

No

29
Q

What are the effects of calcitonin?

A
  1. Decreased osteoclast activity
  2. Increased calcium excretion in kidneys
  3. ↓ plasma Ca2+
30
Q

Describe the affects of hypercalcaemia on membrane excitability

A

Ca2+ blocks Na+ influx, so LESS membrane excitability

31
Q

Describe the affects of hypocalcaemia on membrane excitability

A

enables GREATER Na+ influx, so MORE membrane excitability

32
Q

What are the symptoms of hypocalcaemia?

A

1.Paraesthesia (hands, mouth, feet , lips)
2. Convulsions
3. Arrhythmias
4. Tetany

Mnemonic - [CATs go numb]

33
Q

What is Chvostek’s sign?

A

Tap facial nerve just below zygomatic arch
Positive response = twitching of facial muscles
Indicates neuromuscular irritability due to hypocalcaemia

34
Q

What is Trousseau’s sign?

A

Inflation of BP cuff for several minutes induces carpopedal spasm = neuromuscular irritability due to hypocalcaemia

35
Q

What are the two causes of hypocalcaemia?

A

Low PTH levels = hypoparathyroidism

Vitamin D deficiency

36
Q

What are the causes of hypoparathyroidism?

A

Surgical – neck surgery
Auto-immune
Magnesium deficiency
Congenital (agenesis, rare)

37
Q

What are the causes of vitamin D deficiency?

A
  1. Inadequate sun exposure
  2. Malabsorption or dietary insufficiency leads to lack of ergocalciferol
  3. Liver disease
  4. Renal disease
  5. Vit D receptor defects
38
Q

What are the consequences of vitamin D deficiency?

A

Lack of bone mineralisation = ‘soft’ bones

In children – rickets (bowing of bones)
In adults – osteomalacia (fractures, proximal myopathy)

39
Q

What are the symptoms of hypercalcaemia?

A

‘Stones, abdominal moans and psychic groans’

Reduced neuronal excitability – atonal muscles

Stones – renal effects
Nephrocalcinosis – kidney stones, renal colic

Abdominal moans - GI effects
Anorexia, nausea, dyspepsia, constipation, pancreatitis

Psychic groans - CNS effects
Fatigue, depression, impaired concentration, altered mentation, coma (usually >3mmol/L)

40
Q

What are the 3 causes of hypercalcaemia?

A

Primary hyperparathyroidism

Malignancy

Vitamin D excess (rare)

41
Q

What are the causes of Primary hyperparathyroidism

A

Too much PTH
Usually due to a parathyroid gland adenoma
No negative feedback - high PTH, but high calcium

42
Q

How does malignancy cause hypercalcaemia?

A

Bony metastases produce local factors to activate osteoclasts, increasing calcium reabsorption from bone

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