Ca, Mg homeostasis Flashcards
what is the distribution of total body calcium
about 1 kg
99% in bone
1 intracellular
0.1 extracellular (2.2- 2.6 mmol/L)
what is the equation to calculate total Ca
ionised ca
bound ca
complexed ca
where is phosphate predominantly in the body and what is it for
intracellular
signalling, and glycolysis, backbone of DNA
what is the total body distribution of phosphate
700g 85% in bine 14 intracellular 1 extracellular 70% organic covalently bound 30% inorganic
what are the two controlling factors for Ca homeostasis
PTH and Vit D
what happens in response to low blood ca
Mg allows release of PTH
act on bone for Ca reabsorption and act on kidney to increase Ca reuptake and increase phosphate excretion
what two molecular stimuli causes release of PTH
high serum phosphate
low serum calcium
how can we get Vit D
from diet such as oily fish
synthesised in skin from cholesterol precursor by UVb which are passed through the liver for hydroxylation then kidney for the same to make active form vit D
how does PTH affect VIT d conc
acts on kidney to increase activity of hydrating enzyme for activating VIT d
how does vit d affect the intestine
increase absorption of calcium and phosphate
what factors affect level of vit D
season, clothing, skin tone, age (decreased vit d with age), diet, bmi (stored in adipose)
other than PTH and VIT D what other regulators affect calcium and phosphate homeostasis
Klotho/FGF23 - secreted by osteocytes suppress hydroxylation of vit D - negative feedback and less Ca
calcitonin - secreted by C cells in thyroid - inhibit bone reabsorption to decrease Ca release
oestrogen - antiresportive properties ie high oestrogen = low Ca
what are the signs and symptoms of hypocalcaemia
tetany - muscular spasms, ca deficiency
what is chvosteks sign or trousseaus sign
hypocalcaemia - tapping over facial nerve = facial spasm
trousseaus sign - spasms of wrist and hand
what are two causes of hypocalcaemia
vit D deficiency - dietary and malabsorption
inadequate dietary calcium - hypoproteinaemia and hypoparathyroidism
what are the signs and symptoms of high Ca ie hypercalcaemia
stones, bones, moans, groans
stones - renal colic and kidney stones
bones - bone pain - osteoporosis
moans - lethargy, fatigue
groans (GIT) - abdominal pain, nausea, vomiting
why do you get dehydration in hypercalcaemia
ca in kidneys causes renal resistance to ADH = polyuria
what are the causes of hypercalcamia
hyperparathyroidism - parathyroid adenoma
malignancy - osteoclast activators, PTH secreting tumours
medications
vit D excess - supplementation and diet
what are the symptoms of phosphate deficiency
haematological problems - severe muscle weakness, respiratory failure - chronic causes rickets
what are the causes of phosphate deficiency
malnutrition, alcohol
excess loss
refeeding syndrome - malnutrition to over feeding = severe depletion
alkalosis
what are the symptoms and causes of hyperphosphataemia
usually due to hypocalcaemia
renal failure or vit d toxicity
spurious causes
why do we need Mg and what is the distribution
cofactor of ATP - nueuromuscular, regulates ion channel
total 1.1 mol
54% bone
45% intracellular, 1% extracellular
what is the normal range of Mg
0.7-1 mmol/L
how is homestasis of Mg maintained
mainly by kidneys
partly by PTH as release stimulated by low Mg but severe low Mg inhibits PTH
what are the signs and symptoms of hypomagnesaemia
tremor, tetany, muscle weakness, psychosis
ECG cognates and arrhythmia
nausea and anorexia
what are the causes of hypomagnesaemia
malnutrition, malabsorption
renal loss - niurteic through tubular necrosis
hypercalcaemic states
drugs - gentamicin and cisplatin
why is hypermagnesemia rare
kidneys can excrete large amounts of Mg
