Describe the renal handling of bicarbonate and the changes in urine pH along the nephron. (80% of marks)

How is this affected by hypoventilation? (20% of marks)

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College Answer

This question sought knowledge of an important and basic area of physiology that applies to many
circumstances encountered in daily intensive care practice. For a good answer candidates were
expected to mention that bicarbonate is freely filtered, it’s fate along the nephron and that it is not
normally found in the urine. Mechanisms by how it is reabsorbed and generated along the different
segments of the nephron were expected to be described in some detail. The last part of this
question relating to hypoventilation was poorly answered. For a good answer candidates were
expected to mention that Hypoventilation results in an increase in arterial PCO2 that readily
diffuses into tubular cells resulting in increased intracellular H2CO3 and subsequently bicarbonate,
that is reabsorbed, and H+ that is secreted.
Syllabus: D1 Renal Physiology, 2e, 2k
References: Ganong, Review of Medical Physiology, Ch 39 and 40