Ca, Mg homeostasis

Question 1

what is the distribution of total body calcium

Answer 1

about 1 kg
99% in bone
1 intracellular
0.1 extracellular (2.2- 2.6 mmol/L)

Question 2

what is the equation to calculate total Ca

Answer 2

ionised ca
bound ca
complexed ca

Question 3

where is phosphate predominantly in the body and what is it for

Answer 3

intracellular

signalling, and glycolysis, backbone of DNA

Question 4

what is the total body distribution of phosphate

Answer 4

700g 
85% in bine 
14 intracellular 
1 extracellular 
70% organic covalently bound 
30%  inorganic

Question 5

what are the two controlling factors for Ca homeostasis

Answer 5

PTH and Vit D

Question 6

what happens in response to low blood ca

Answer 6

Mg allows release of PTH

act on bone for Ca reabsorption and act on kidney to increase Ca reuptake and increase phosphate excretion

Question 7

what two molecular stimuli causes release of PTH

Answer 7

high serum phosphate

low serum calcium

Question 8

how can we get Vit D

Answer 8

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

Question 9

how does PTH affect VIT d conc

Answer 9

acts on kidney to increase activity of hydrating enzyme for activating VIT d

Question 10

how does vit d affect the intestine

Answer 10

increase absorption of calcium and phosphate

Question 11

what factors affect level of vit D

Answer 11

season, clothing, skin tone, age (decreased vit d with age), diet, bmi (stored in adipose)

Question 12

other than PTH and VIT D what other regulators affect calcium and phosphate homeostasis

Answer 12

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

Question 13

what are the signs and symptoms of hypocalcaemia

Answer 13

tetany - muscular spasms, ca deficiency

Question 14

what is chvosteks sign or trousseaus sign

Answer 14

hypocalcaemia - tapping over facial nerve = facial spasm

trousseaus sign - spasms of wrist and hand

Question 15

what are two causes of hypocalcaemia

Answer 15

vit D deficiency - dietary and malabsorption

inadequate dietary calcium - hypoproteinaemia and hypoparathyroidism

Question 16

what are the signs and symptoms of high Ca ie hypercalcaemia

Answer 16

stones, bones, moans, groans

stones - renal colic and kidney stones
bones - bone pain - osteoporosis
moans - lethargy, fatigue
groans (GIT) - abdominal pain, nausea, vomiting

Question 17

why do you get dehydration in hypercalcaemia

Answer 17

ca in kidneys causes renal resistance to ADH = polyuria

Question 18

what are the causes of hypercalcamia

Answer 18

hyperparathyroidism - parathyroid adenoma
malignancy - osteoclast activators, PTH secreting tumours
medications
vit D excess - supplementation and diet

Question 19

what are the symptoms of phosphate deficiency

Answer 19

haematological problems - severe muscle weakness, respiratory failure - chronic causes rickets

Question 20

what are the causes of phosphate deficiency

Answer 20

malnutrition, alcohol
excess loss
refeeding syndrome - malnutrition to over feeding = severe depletion
alkalosis

Question 21

what are the symptoms and causes of hyperphosphataemia

Answer 21

usually due to hypocalcaemia
renal failure or vit d toxicity
spurious causes

Question 22

why do we need Mg and what is the distribution

Answer 22

cofactor of ATP - nueuromuscular, regulates ion channel
total 1.1 mol
54% bone
45% intracellular, 1% extracellular

Question 23

what is the normal range of Mg

Answer 23

0.7-1 mmol/L

Question 24

how is homestasis of Mg maintained

Answer 24

mainly by kidneys

partly by PTH as release stimulated by low Mg but severe low Mg inhibits PTH

Question 25

what are the signs and symptoms of hypomagnesaemia

Answer 25

tremor, tetany, muscle weakness, psychosis
ECG cognates and arrhythmia
nausea and anorexia

Question 26

what are the causes of hypomagnesaemia

Answer 26

malnutrition, malabsorption

renal loss - niurteic through tubular necrosis
hypercalcaemic states
drugs - gentamicin and cisplatin

Question 27

why is hypermagnesemia rare

Answer 27

kidneys can excrete large amounts of Mg