**Core Concept**
Metabolic alkalosis is a condition characterized by an increase in blood pH above the normal range, typically due to an imbalance in the body's acid-base regulation. This occurs when the body loses hydrogen ions (H+) or gains bicarbonate (HCO3-) through various mechanisms such as vomiting, diarrhea, or excessive use of diuretics.

**Why the Correct Answer is Right**
Metabolic alkalosis is often associated with an increase in plasma bicarbonate levels. The kidneys compensate for this by excreting more bicarbonate in the urine to maintain acid-base balance. However, in the presence of metabolic alkalosis, the kidneys are unable to adequately excrete bicarbonate, leading to its accumulation in the blood. This results in an elevation of blood pH and a decrease in hydrogen ion concentration.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe the pathophysiology of metabolic alkalosis. In metabolic alkalosis, there is an increase in plasma bicarbonate, not a decrease.
**Option B:** This option is incorrect as it refers to respiratory alkalosis, which is a different condition characterized by an increase in blood pH due to hyperventilation.
**Option C:** This option is incorrect as it refers to a normal physiological process and does not accurately describe the pathophysiology of metabolic alkalosis.

**Clinical Pearl / High-Yield Fact**
It is essential to note that metabolic alkalosis can be caused by various factors, including vomiting, diarrhea, and excessive use of diuretics. The kidneys play a crucial role in compensating for this condition by adjusting bicarbonate excretion.

**Correct Answer: D**