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Endocrinology semester 1 > calcium homeostasis > Flashcards

calcium homeostasis Flashcards

1
Q

why is calcium homeostasis important?

A

Ca2+ ion plays an important role in many biological processes.

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2
Q

what do Ca2+ ions play an important role in?

A
  • Excitation-contraction coupling
  • Excitation-secretion coupling
  • Excitability of nerves and muscle
  • Clotting of blood
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3
Q

what do muscle contractions require in terms of Ca2+ concentration?

A

an increase in intracellular Ca2+ ion concentration

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4
Q

what happens if there is an increase in Ca2+ ion concentration?

A

an increase in extracellular Ca2+ ion concentration decreases neuromuscular contractility and hence reduces likelihood of muscle contraction occurring.

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5
Q

what is normal plasma calcium level?

A

9-10 mg/dl (2.4±0.2 mmol/L)

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6
Q

what makes up total body calcium?

A
  • Bone - 99%
  • Intracellular in soft tissues - 0.9%
  • Extracellular fluid - 0.1%
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7
Q

which hormones control calcium homeostasis directly?

A

Parathyroid hormone or Parathormone (PTH)

Vitamin D metabolite (1,25-dihydroxyvitamin D3 or Calcitriol

Calcitonin

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8
Q

where is parathyroid hormone secreted from?

A

Chief cells of parathyroid glands (4 glands embedded in the back surface of thyroid gland)

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9
Q

where is PTH metabolised?

A

by the liver and kidney

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10
Q

what is the half-life of PTH?

A

2-5 minutes

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11
Q

what controls PTH secretion?

A

The concentration of Ca2+ in plasma regulates parathyroid gland secretion

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12
Q

what happens to PTH if there is low plasma Ca2+?

A

Low plasma Ca2+ cause increased secretion and high Ca2+ has an opposite effect

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13
Q

what does sustained hypocalcaemia result in?

A

hyperplasia and hypertrophy of the gland.

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14
Q

what is the primary function of PTH?

A

Maintain a normal level of Ca2+ in ECF

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15
Q

what organs does PTH target?

A
  • bone
  • kidney
  • intestine
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16
Q

what are the effects of PTH on the kidney?

A
  • Decrease Ca2+ excretion

- Increase PO43- excretion

17
Q

what are the effects of PTH on the intestine?

A
  • Increases absorption of both Ca2+ & PO43- by activation of Vitamin D
18
Q

what are the effects of PTH on the bone?

A
  • Fast Ca2+ efflux into the plasma from the bone fluid [Normal action]
  • Slow transfer of Ca2+ and PO43- by dissolution of bone itself [during chronic hypocalcaemia]
19
Q

what is the cause of PTH deficiency?

A

Most common cause: operative procedure on either thyroid or parathyroid gland

20
Q

what are the effects of PTH deficiency?

A

Hypocalcaemia

21
Q

what are the signs and symptoms of PTH deficiency?

A
  • Tetany of hands and feet with mechanical stimulation of peripheral nerves
  • With complete removal of the glands death occur due to asphyxiation due to tetany of respiratory muscle
  • Occasionally seizers can occur due to increased excitability in the brain
22
Q

what is the treatment for PTH deficiency?

A

Vitamin D and Calcium supplementation

23
Q

what causes excess PTH?

A

A tumour in one of the parathyroid glands

24
Q

what are the effects of excess PTH?

A

Hypercalcaemia & hypophosphataemia

25
Q

what are the effects of excess PTH on the bone?

A

Mild: no effect

Severe: extensive decalcification with large punched out areas of bone filled with osteoclasts

26
Q

what are the neuromuscular effects of excess PTH?

A 
muscle weakness
decreased mentation
poor memory
constipation, abdominal pain (groan)
peptic ulcer
depressed relaxation of heart during diastole
27
Q

what are the effects excess PTH on the kidney?

A

Increased tendency for formation of kidney stones

28
Q

what is the treatment for excess PTH?

A

surgical removal of tumour if possible

29
Q

what doe metabolite vitamin D enhance?

A

intestinal absorption of calcium and phosphate

the responsiveness of bone to PTH

30
Q

what does reduced calcium absorption lead to?

A

Reduced Calcium absorption leads to demineralisation of bone resulting from PTH action to maintain normal plasma Ca2+ level.

31
Q

what is osteoporosis?

A

a condition characterised by reduction in bone mass that result from bone resorption exceeding bone formation.

32
Q

what is calcitonin?

A

hypocalcaemic hormone, the effects generally opposite to those of PTH

33
Q

where is calcitonin produced?

A

by parafollicular cells or C cells of thyroid gland

34
Q

what stimulates the secretion of calcitonin?

A

stimulated by hypercalcaemia and inhibited by hypocalcaemia

35
Q

what is a therapeutic use of calcitonin?

A

To reduce hypercalcaemia, useful in disorders of increased skeletal remodeling such as Paget’s disease

Endocrinology semester 1 (10 decks)

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