Question

Arrange the following statements in proper sequence:

(A). Hyperventilation and removal of excess \(\text{CO}_2\) from ECF
(B). Restoration of pH and bicarbonate to carbonic acid ratio
(C). Decrease in pH and bicarbonate to carbonic acid ratio
(D). Decrease in partial pressure of \(\text{CO}_2\)
(E). Stimulation of respiratory centre

Choose the correct answer from the options given below:

• A. (E), (A), (D), (C), (B).
• B. (C), (E), (A), (D), (B).
• C. (E), (A), (B), (D), (C).
• D. (C), (B), (D), (A), (E).

Hint:

To solve sequencing questions, identify the cause and effect:
Acidosis (C) is the initial cause of the disturbance, and the ultimate goal is the homeostatic restoration of pH (B).
Thus, the sequence must begin with "C" and end with "B".

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
When metabolic changes alter systemic pH, the respiratory system acts as a rapid physiological buffer by adjusting the rate and depth of ventilation to stabilize carbon dioxide levels.

Step 2: Detailed Explanation:
Let us establish the logical sequence of respiratory compensation during metabolic acidosis:
1. Initial disturbance (C): A metabolic disturbance causes a accumulation of acid, leading to a decrease in pH and the bicarbonate to carbonic acid ratio.
2. Detection (E): The excess hydrogen ions (\(\text{H}^+\)) stimulate peripheral and central chemoreceptors, leading to stimulation of the respiratory center in the brainstem.
3. Action (A): The activated respiratory center increases breathing rate and depth, causing hyperventilation and the active elimination of excess \(\text{CO}_2\) from the extracellular fluid (ECF).
4. Effect (D): This increased expiration of \(\text{CO}_2\) leads to a decrease in the partial pressure of \(\text{CO}_2\) (\(\text{pCO}_2\)) in the blood.
5. Recovery (B): The reduction in carbonic acid levels restores the blood pH and the bicarbonate-to-carbonic acid ratio back toward normal physiological limits (\(20:1\)).
Therefore, the correct chronological sequence is: (C) \(\rightarrow\) (E) \(\rightarrow\) (A) \(\rightarrow\) (D) \(\rightarrow\) (B).

Step 3: Final Answer:
The correct option is 2, which corresponds to (C), (E), (A), (D), (B).