Biochem

Question 1

sodium ref range

Answer 1

135 - 145 mmol/L

Question 2

potassium reference range

Answer 2

3.6 - 5.0mmol/L

Question 3

Osmolality ref range

Answer 3

280 - 296 mosm/Kg

Question 4

pseudohyponatraemia causes

Answer 4

hyperglycaemia, hyperlipidaemia, hyperproteinaemia (e.g. as may occur in multiple myeloma)

Question 5

hypervolaemic hyponatraemia causes

Answer 5

renal failure, liver failure, congestive cardiac failure, nephrotic syndrome

Question 6

hypovolaemic hyponatraemia causes

Answer 6

Extrarenal: GI loss (D or V), skin (burns, severe dermatitis), internal (paralytic ileus, peritoneal fluid)
Renal: Diuretics, salt-wasting renal disease, adrenal insufficiency

Question 7

isovolaemic hyponatraemia causes

Answer 7

Too much water (low urine osmolality (<100mosm/Kg)), SIADH (high urine osmolality (>100mosm/Kg)), drugs (e.g. opiates, chlorpropamide), renal failure, hyperparathyroidism

Question 8

ICF volume (70kg man)

Answer 8

28L

Question 9

ECF volume (70kg man)

Answer 9

14L

Question 10

Interstitial fluid volume (70kg man)

Answer 10

11L

Question 11

Describe the main system responsible for sodium homeostasis

Answer 11

A decrease in BP or low Na+ is sensed by cells of the juxtaglomerular apparatus which release renin. Renin converts angiotensinogen to angiotensin I. Angiotension I is then convereted by ACE to angiotensin II which stimulate secretion of aldosterone from the adrenal cortex (the zona glomerulosa). Aldosterone acts on the distal tubule/cortical collecting ducts to increase Na+ reabsorption and increase K+ excretion.

Question 12

Hyperkalaemia ECG features

Answer 12

Tall tented T waves (early)
P waves get wide and flat with PR interval prolongation until P waves eventually disappear (progressive atrial paralysis),
Broad QRS
Sine-wave shape
Cardiac arrest

Question 13

Hypokalaemia ECG changes

Answer 13

Flat, broad T waves (may invert),
Increase P wave amplitude and width,
PR elongation,
ST depression,
Apparent long QT due to T and U wave fusion,
Prominent U waves (seen best in precordial leads)

Question 14

Causes of raised CRP with normal ESR

Answer 14

SLE

Multiple myeloma

Question 15

CRP [reference range]

Answer 15

<5mg/L

Question 16

ESR [reference range]

Answer 16

Male 0 - 10 mm/h

Female 3 - 15mm/h