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Endocrinology > Regulation of Calcium and Phosphate > Flashcards

Regulation of Calcium and Phosphate Flashcards

1
Q

What are the hormones that increase serum calcium and phosphate

A

Parathyroid hormone

Vitamin D

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2
Q

What are the hormones that decrease serum calcium and phosphate

A

Calcitonin

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3
Q

What is the most abundant metal in the body

A

Calcium

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4
Q

Whast is a good source of Vitamin D

A

Oily fish

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5
Q

What is the calcium distribution in the body

A

99% resides in skeleton and teeth

Extracellular calcium is tightly regulated

‘Unbound’ ionised calcium is the most biologically active compound

Bound Ca is to plasma proteins (albumin) or anions

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6
Q

What are the two sources of Vitamin D

A

Diet - ergocalciferol D2

Skin synthesis - sunshine - cholecalciferol D3

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7
Q

Which light shines on the skin

A

UVB

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8
Q

Show the synthesis of Vitamin D3 in the skin

A
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9
Q

What happens to Vitamin D when it enters the bloodstream

A

Has to undergo two hydroxylation reactions

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10
Q

Why do you not measure calcitriol

A

It is unstable in the body

Instead measures 25(OH) cholecalciferol as body stores

1,25 (OH)2 cholecalciferol regulates own synthesis to 1 alpha- hydroxylase

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11
Q

What are the effects of calcitriol

A

Increase Ca reabsorption

Increase Ca reabsorption from kidney

Increases Ca and PO4 absorption from gut

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12
Q

Where are the parathyroid glands

A
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13
Q

How are parathyroid hormones secreted

A

From chief cells

Secreted as a large precursor (pre-pro-PTH) and cleaved to PTH

G-protein coupled calcium sening receptor change in circulating calcium

PTH secretion is invesly proportional to serum calcium

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14
Q

Actions of the parathyroid hormone

A

Increase Ca reabsorption

Increase Ca bone reabsorptuion

Increase PO4 excretion

Increase 1 - alpha - hydroxylase activity

This increases calcitriol synthesis

This increase Ca and PO4

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15
Q

PTH action in bone

A

PTH receptor activates osteoblast (builds bone)

Makes osteoclast activating factors (RANKL which is the receptor activator of nuclear factor kappa-B ligand)

Osteoclast is activated

Bone resorption

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16
Q

How does osteoclast release enzymes

A

Through the ruffled border

17
Q

Calcitriol action in bone

A

LOW serum calcium - Calcitriol increases calcium reabsorption from bone osteclasts > osteoblasts

NORMAL serum calcium - calcitriol works to increas ebone fomration osteoblasts > osteoclasts

18
Q

PTH regulation

A

Negative feedback on calcium receptors on the parathyroid hormones

Vitamin D receptors as well on the chief cells

19
Q

What does calcitonin do

A

Thryoid glands secreted from parafollicular cells

Reduces serum calcium

Removal of thyroid gland does not affect serum calcium

20
Q

How does calcitonin regulate calcium

A

Increase in plasma Ca

Kidney Ca excretion

Decrease in osteoclast activity

21
Q

Regulation of serum phosphate by FIbroblast Growth Factor 23 (FGF23)

A

It reduces phosphate

This inhibitors sodium-phosphate cotransporter

Inhibits calcitriol production - less PO4 reabsoprtion from the gut

22
Q

What does high extracellular calcium indicate (HYPERcalcaemia)

A

Less membrane excitability

Ca blocks Na influx

23
Q

What does LOW extracellular calcium (HYPOcalcaemia) indicate

A

Greater Na influx so more membrane excitability

24
Q

Symptoms of hypocalcaemia

A

Parasthesia - tingling

Convulsions

Arrhythmias - irregular heartbeat

Tetany - muscle contract but not relax

25
Q

How to test for hypocalcaemia

A

Tap facial nerve just below zygomatic arch

Positive response - twitching of facial muscles

Inflation of BP cuff for several minutes which induces carpopedal spasm

indicates neuromuscular irritability

26
Q

What are the causes of hypocalcaemia

A

Low PTH levels - hypoparathyrodisim

Surgery

Auto-immune

Magnesium deficiency - need it to make PTH

Congenital

Vitamin D deficiency

27
Q

Causes of Vitamin D deficiency

A

Malabsoprtion or dietary insufficency

Inadequate sun exposure

Liver disease

Renal disease

Vitamin D receptor defects (rare)

28
Q

What are the conseuqneces of Vitamin D deficiency

A

Lack of bone mineralisations

Children - rickets.- bowing of bones

Adults - osteomalacia (fractures, proximal myopathy) - adult bone more developed

29
Q

What are the symptoms in the hypercalcaemia

A

Stones - nephrocalcinosis - kidney stones

Abdominal - anorexia, nausea, dyspepsia, constipation, pa

Psychic groans - tiredness, low mood, coma, fatigue, depression

30
Q

Causes of hypercalcaemia

A

Priamry hyperparathyroidism

Usually due to parathyroid gland adenoma

No negative feedback

Malignancy - tumours produce factors to activate osteoclasts

Vitamin D excess- tablet overdose

Endocrinology (10 decks)

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