calcium dysregulation

Question 1

what increases and decreases serum calcium

Answer 1

increase
-Vit D- synthesised in skin/diet.
-parathyroid hormone.
- homeostasis via actions on kidney, bone, gut.

decrease
calcitonin- secreted by parafollicular cells

Question 2

vit D metabolism

Answer 2

25-hydroxylase (25-OH) in liver. indicator of body vit D status

1 alpha-hydroxylase in kidney.

1,25(OH)2 cholecalciferol (inactive form)
calcitriol=active form of vit D
-regulates own synthesis by decreasing transcription of 1-alpha-hydroxylase

Question 3

VIT D2/D3?

Answer 3

vit D2=from diet
vit D3=from UVB

Question 4

effects of calcitriol

Answer 4

increase osteoblast activity

increase Ca2+ and and (PO4)3- absorption and reabsorption in kidneys

Question 5

effects of PTH

Answer 5

increase calcium resorption from bone (osteoclast activity)

kidney:
increase calcium reabsorption,
increase phosphate excretion,
increase 1-a-hydroxyalse activity—-> increase vit D synthesis

in turn:
increase calcium and phosphate absorption in gut

overall increase plasma calcium

Question 6

what regulates serum phosphate

Answer 6

FGF23 -from bone –
inhibits phosphate reabsorption in the kidneys
by inhibiting sodium phosphate co-transporter.
Also inhibits calcitriol synthesis=less gut phosphate absorption.
—–less sodium and phosphate excretion in the urine.

PTH inhibits renal phosphate reabsorption by inhibiting these transporters –

primary hyperparathyroidism, serum phosphate is low due to increased urine phosphate excretion.

Question 7

hypocalcaemia signs and symptoms

Answer 7

CATs go numb
convulsion
arrhythmias
tetany- involuntary muscle contraction
paraesthesia (mouth, lips, hand, feet)

Chvosteks’ sign- facial paresthesia
Trousseau’s sign-carpopedal spasm

Question 8

facial paresthesia

Answer 8

Chvosteks’ sign

Question 9

carpopedal spasm

Answer 9

Trousseau’s sign
-involuntary muscle contraction with pain

Question 10

cause of hypocalcaemia

Answer 10

-low PTH=hypoparathyroidism
surgery/autoimmune/magnesium deficiency

-Low vit D
deficiency= poor diet/malabsorption, lack of UV light-
renal failure=impaired production

Question 11

signs and symptoms of hypercalcaemia

Answer 11

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)

Question 12

cause of hypercalcaemia

Answer 12

-primary hyperparathyroidism
parathyroid gland adenoma
but no negative feedback loop

-malignancy (bony metastases/certain cancer (squamous cell carcinoma)secrete PTH related peptide

-excess vit D (rare)

Question 13

relationship between PTH and calcium

Answer 13

as PTH increases, calcium decreases and vice versa

Question 14

treatment for secondary hyperparathyroidism

Answer 14

replace vit D
normal renal function: give 25 hydroxy vit D
-ergocalciferol
-cholecalciferol

renal failure give:
-alfacalcidol

Question 15

treatment for hypercalcaemia of malignancy

Answer 15

bisphosphonate

inhibit osteoclast
stop bone absorption(consumption)
lowers calcium