Clinical chemistry

Question 1

Normal conc of Na

Answer 1

135-145

Diffuses down concentration gradient into cells but pumped out by ATPas

Question 2

Which 2 systems regulate Na?

Answer 2

ADH - increased plasma osmalality sensed by chemoRs in hypothalamus - stimulates thirst and release of ADH from post pit - renal h2o absorption

RAAS - leads to release of aldosterone which causes reuptake of Na in distal tubule

Question 3

Causes of hypernatremia

Answer 3

Na retention in excess of water - low water intake (most common), primary hyperaldonsteronism (Conn’s) or cushing’s disease

Water loss in excess of Na - diarrhoea, vomiting, burns + haemorrhage. DI

Artefactual - contamination of sample with IV saline

Question 4

Conn’s syndrome?

Answer 4

Excessive production of aldosterone –> resulting in low renin (usually caused by hyperplasia or tumour of adrenal glands)

Question 5

Diabetes insipidus

Answer 5

Common cause of hyper Na.
pituitary doesn’t produce ADH (central DI) or kidney doesn’t response to ADH (nephrogenic DI)

Sx = polyuria + thirst
Dx = water deprivation test + serum Na + osmalality measurements

Question 6

Causes of hyponatremia

Answer 6

Water retention in excess of Na - oedematous states, excessive drinking, SIADH

Na loss in excess of water - DKA/HONK, diuretic stage of renal failure, diuretic use, hypocortolism e.g. addisons, diarrhoea, vomit, burns

Question 7

SIADH

Answer 7

Inappropriate ADH secretion. Causes include: CNS disease, pulmonary disease, porphyria or drugs e.g. SSRIs, carbamazepine, amitryptline
Dx: exclusion - pt must be euvolemic

Question 8

How to treat hyponatremia

Answer 8

very slow infusion of 0.9% saline to avoid central pontine myelinolysis

Question 9

Normal serum concentration of potassium

Answer 9

3.5 - 5.3 mmol/L (extracellular) - majority of K is intracellular