**Question:** Following acute respiratory response to ascent to high altitude, there is normalization of blood pH. The mechanism is:

A. Increased carbon dioxide production
B. Decreased carbon dioxide production
C. Increased bicarbonate reabsorption in the kidneys
D. Increased bicarbonate secretion in the kidneys

**Core Concept:**
In response to altitude increase, the body undergoes an acute respiratory response to compensate for reduced atmospheric pressure and decreased oxygen availability. This leads to hypoxia, which triggers a series of physiological and biochemical changes to counteract the decreased oxygen saturation. One of the key reactions is the Hess's Law, which describes the relationship between the partial pressure of gases in the alveoli and arterial blood.

**Why the Correct Answer is Right:**
The correct answer (D) "Increased bicarbonate secretion in the kidneys" is related to the compensation for acidosis that occurs during high altitude exposure. As the body is exposed to lower oxygen levels, the acidic byproducts like carbon dioxide (CO2) accumulate in the blood. To counteract this, the kidneys increase the secretion of bicarbonate ions (HCO3-) in the urine, which helps to neutralize the excess acidic substances and restore the body's pH balance.

**Why Each Wrong Option is Incorrect:**

A. Increased carbon dioxide production (option A) is not correct because it would exacerbate the acidosis, not resolve it.

B. Decreased carbon dioxide production (option B) is incorrect as it would not effectively counteract the acidosis caused by hypoxia.

C. Increased bicarbonate reabsorption in the kidneys (option C) is not correct because reabsorption refers to the absorption of substances in the nephrons, not secretion. Secretion involves the movement of substances from the blood into the renal tubules, while reabsorption involves the movement of substances from the renal tubules back into the blood.

**Clinical Pearl:**
The body's response to hypoxia and acidosis during high altitude exposure is crucial to maintain homeostasis and prevent tissue damage. Acute mountain sickness (AMS) is a common condition that occurs when the body fails to adapt to the rapid ascent to high altitudes, and can lead to life-threatening complications if left untreated. It is essential for medical professionals to understand the physiological and biochemical adjustments made by the body during altitude exposure, as well as the potential risks associated with AMS.