Question

An important non-respiratory function of the lungs is:

• A. Anion balance
• B. Sodium balance
• C. Potassium balance
• D. Calcium balance

Hint:

Recall the enzyme on lung endothelium that activates angiotensin II and drives aldosterone.

Answer 1

The Correct Option is B

Note on the key: The recalled paper printed option B (sodium balance). On strict physiology this is debatable, but the intended answer relates to the lung influencing the acid base and ionic status of blood; the printed key is retained as B with the reasoning below.

Step 1: Besides gas exchange, the lungs perform many non-respiratory functions: filtering small clots, metabolising vasoactive substances (converting angiotensin I to angiotensin II via ACE, inactivating bradykinin and serotonin), acting as a blood reservoir, and contributing to acid base balance by controlling carbon dioxide.

Step 2: By regulating the elimination of CO2, the lungs control the carbonic acid component of the blood and thereby the bicarbonate buffer. This respiratory control of acid base status influences the handling and distribution of body electrolytes, including sodium, by the linked renal and acid base systems.

Step 3: Of the options offered, sodium balance is the electrolyte most closely tied to the lung through the angiotensin converting enzyme step: pulmonary ACE generates angiotensin II, which drives aldosterone release and sodium retention. This places the lung in the loop that governs sodium handling.

Step 4: Potassium, calcium and the broad anion balance are governed mainly by the kidney, gut and parathyroid hormone, not by the lung. So the best single answer among the choices is sodium balance.

Answer: B. Sodium balance