Calcium dysregulation Flashcards
which hormones act to increase serum calcium
vitamin D (calcitriol) parathyroid hormone
which hormones act to decrease serum calcium
Calcitonin
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)
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
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
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
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 of hypercalcaemia
stones, (abominal) moans and psychic groans
Nephrocalcinosis; anorexia, nausea, dyspepsia, constipation and pancreatitis; fatigue, depression and impaired concentration
what are the symptoms of hypercalcaemia
nephrocalcinosis, kidney stones, renal colic
anorexia, nausea, dyspepsia, constipation, pancreatitis
fatigue, depression, impaired concentration, altered mentation, coma
what is the most common cause of hypercalcaemia
parathyroid gland adenoma
what are the main causes of hypercalcaemia
primary hyperparathyroidism
malignancy
vit D excess
how can malignancy cause hypercalcaemia?
bony metastases produce local factors to activate osteoclasts
or certain cancers secrete PTH-related peptide which acts on PTH receptors
what would be the blood results for primary hyperparathyroidism
high calcium, low phosphate, high PTH
what is the cause of primary hyperparathyroidism?
parathyroid adenoma - autonomous secretion of PTH
how do you treat primary hyperparathyroidism?
parathyroidectomy
what are the long term risks of primary hyperparathyroidism?
osteoporosis
renal calculi
mental and mood deficits
what is secondary hyperparathyroidism?
normal physiological response to chronically low calcium
what are the blood results for secondary hyperparathyroidism?
low/norm Ca2+
high PTH
what is the most common cause of secondary hyperparathyroidism?
Vit D/calcitriol deficiency
what are the causes of secondary hyperparathyroidism?
Vit D deficiency by diet or reduced sunlight
renal failure
how do you treat someone with secondary parathyroidism who has normal renal function?
vitamin D replacements - usually D3
how do you treat someone with secondary hyperparathyroidism in renal failure?
give Alfacalcidiol - 1-a-hydroxycholecalciferol
why do treatments differ for 2o hyperparathyroidism depending on renal function?
renal failure patients have inadequate 1a-hydroxylation so can’t activate 25hydroxy vit D preparations like those with normal renal function
what is tertiary hyperparathyroidism?
chronically low Ca2+ in the context of chronic renal failure and prolonged calcitriol deficiency, where one gland produces PTH independent of any other factors
what are the consequences of tertiary hyperparathyroidism?
PTH increases, PT gland enlarges (hyperplasia)
autonomous PTH secretion causes hypercalcaemia
how is tertiary hyperparathyroidism treated?
parathyroidectomy
how does high calcium affect the nerves
Calcium ions block sodium ion influx so there is less membrane excitability
how does low calcium affect the nerves
low Ca2+ allows more sodium ion influx so there is increased membrane excitability
