Acid-Base and Water Balance MCQs

125 MCQs with clinical pearls · MBBS Biochemistry · Prof Jariya

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Topics covered (13)

ABG Interpretation — 19 MCQs
Anion Gap and Delta Ratio — 19 MCQs
Metabolic Acidosis — 18 MCQs
Metabolic Alkalosis — 11 MCQs
Buffer Systems — 10 MCQs
Mixed Disorders and Compensation — 10 MCQs
pH and Henderson-Hasselbalch — 9 MCQs
Respiratory Acidosis — 8 MCQs
Renal Acid Handling — 5 MCQs
Lines of Defence — 5 MCQs
Respiratory Alkalosis — 5 MCQs
Electrolyte and Calcium Effects — 4 MCQs
Bioenergetics — 2 MCQs

Sample MCQs with clinical pearls

Which of the following is seen in acidosis?

A) Hypercalcemia

B) Hyperkalemia ✔

C) Hypermagnesemia [5th]

D) Hyperphosphatemia

E) Hypernatremia

In ACIDOSIS, hydrogen ions enter cells and are buffered by intracellular protein, and POTASSIUM moves out to preserve electroneutrality - so serum potassium RISES. The shift is marked in MINERAL acidosis such as renal failure or diarrhoea, and much weaker in ORGANIC acidoses like ketoacidosis, where the anion enters the cell with the hydrogen ion. Beware the trap: total body potassium may be DEPLETED even while serum potassium is high. MEMORY: 'Hydrogen in, potassium out.'

The most important extracellular buffer in the body is:

A) Ammonia buffer [5th]

B) Bicarbonate buffer ✔

C) Hemoglobin buffer system

D) Phosphate buffer

E) Protein buffer

The BICARBONATE system is the most important EXTRACELLULAR buffer, despite a pKa of 6.1 that is far from blood pH - which should make it a poor buffer. Its power comes from being an OPEN system: carbon dioxide is continuously removed by the lungs and bicarbonate regenerated by the kidneys, so neither component is exhausted. MEMORY: 'A mediocre buffer made excellent by having both ends open.'

Which of the following is the principal buffer in interstitial fluid?

A) Bicarbonate buffer system [5th] ✔

B) H2PO4

C) Other proteins

D) Phosphate buffer

E) Carbonic acid

BICARBONATE is also the principal buffer of INTERSTITIAL fluid, which is essentially plasma without the proteins - so the protein buffering available in plasma is absent and bicarbonate dominates even more completely. Interstitial fluid is the largest extracellular compartment, making this quantitatively important. MEMORY: 'No protein in the interstitium, so bicarbonate does the work alone.'

These are three of 125 MCQs in this section. Every question carries a clinical pearl explaining the reasoning.

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