Final answer:
Respiratory acidosis is caused by B. Under elimination of H+, which results from the body's inability to expel enough CO2, leading to excess carbonic acid. Conditions like pneumonia, emphysema, and congestive heart failure can lead to this imbalance.
Step-by-step explanation:
The cause of respiratory acidosis is B. Under elimination of H+. This condition arises when the body is unable to excrete enough carbon dioxide (CO2) through respiration, leading to an excess of carbonic acid in the bloodstream. Situations such as pneumonia, emphysema, or congestive heart failure can impair the lungs' ability to remove CO2, consequently increasing the levels of carbonic acid and thus resulting in respiratory acidosis. The increase in carbonic acid lowers the pH of the blood, making it more acidic.
In the early stages, bicarbonate (HCO3−) levels may be normal; however, as the body attempts to compensate, these levels may rise. It's important to distinguish this from other conditions, such as respiratory alkalosis, which is caused by a deficiency in carbonic acid and occurs when the body expels too much CO2 from the lungs.