Calcium dysregulation Flashcards
(40 cards)
which hormones act to increase serum calcium
What tissues do these act on
vitamin D (calcitriol)
parathyroid hormone
Main regulators of calcium (& phosphate) homeostasis via actions on kidney, bone and gut
which hormones act to decrease serum calcium
Calcitonin
Can reduce calcium acutely, but no negative effect if parafollicular cells are removed eg thyroidectomy
what are the sources of calcitriol?
synthesised in skin, diet
what are the sources of parathyroid hormone
parathyroid gland
what are the sources of calcitonin
thyroid parafollicular cells
what are the main sources of calcium in the body?
bones, gut, kidney
what is the difference between vitamin D2 and D3
D2 from diet (ergo)
D3 from skin (chole)
which enzymes are essential for vitamin D synthesis
25-hydroxylase (liver)
1-a-hydroxylase (kidney)
Vitamin D metabolism
What do we measure to determine body vitamin D status?
Serum 25-OH vitamin D
How does 1,25(OH)2 vitamin D (calcitriol) regulate its own synthesis?
decreasing transcription of 1 alpha hydroxylase
name all the physiological effects of calcitriol
increases calcium and phosphate reabsorption in kidneys
increases calcium and phosphate absorption in gut
increases osteoblast activity
name all the physiological effects of PTH
increased calcium reabsorption in kidney, increased excretion of phosphate, increased 1ah action (vit D synthesis)
increases calcium and phosphate absorption in the gut
increases osteoclast activity
Via what transporter does phosphate reabsorption occur in the kidneys? What effect reabsorption this have on serum phosphate and urinary sodium?
How is this affected by hyperparathyroidism?
Phosphate is reabsorbed via sodium phosphate transporter cells. In the kidney, reabsorption of phosphate via these transporters results in less sodium excretion in the urine. Reabsorption increases serum phosphate levels.
PTH inhibits renal phosphate reabsorption by inhibiting these transporters – so in primary hyperparathyroidism, serum phosphate is low due to increased urine phoshate excretion.
where is FGF23 made
by osteocytes
what is the main role of FGF23
prevents kidney reabsorption of phosphate
inhibits Vit D synthesis (via reduced activity of 1-a-hydroxylase)
what is FGF23s MOA
inhibits Na/PO4 transporter in proximal tubule of kidney (more excretion of PO4)
inhibits calcitriol synthesis (for less PO4 absorption in gut)
what are the two signs of hypocalcaemia
Chvosteks sign (facial paresthesia)
Trousseaus sign (carpopedal spasm)
what are the symptoms of hypocalcaemia
Hypocalcemia sensitizes excitable tissue
CATs go numb
convulsions, arrhythmias, tetany, paraesthesia
what are the two major causes of hypocalcaemia
due to low PTH
due to low Vit D
what are some causes of low PTH causing hypocalcaemia
neck surgery
autoimmunity
magnesium deficiency
congenital agenesis of Pt gland (rare)
what are some causes of low calcitriol causing hypocalcaemia?
deficiency due to diet, lack of UV (darker skin more prone), malabsorption, impaired production (renal failure)
what are the signs and symptoms of hypercalcaemia
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)
what is the most common cause of hypercalcaemia
primary hyperparathyroidism, usually a parathyroid gland adenoma
