Reverse chloride shift begins at the

Options

A. Venular end of pulmonary capillary
B. Arteriolar end of systemic capillary
C. Venular end of systemic capillary
D. Arteriolar end of pulmonary capillary

Answer

To solve the question "Reverse chloride shift begins at the", we need to understand the concept of the reverse chloride shift and where it occurs in the circulatory system. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Concept of Chloride Shift
- The chloride shift refers to the exchange of bicarbonate ions (HCO3-) and chloride ions (Cl-) across the membrane of red blood cells (RBCs).
- In tissues, carbon dioxide (CO2) is produced and enters the blood, leading to the formation of carbonic acid (H2CO3), which dissociates into bicarbonate ions and hydrogen ions.

**Hint for Step 1:** Remember that the chloride shift is crucial for maintaining the acid-base balance in the blood and occurs in the red blood cells.

### Step 2: Identify the Process of Reverse Chloride Shift
- The reverse chloride shift occurs when the blood passes through the lungs. Here, the level of carbon dioxide decreases as it is expelled from the blood into the alveoli.
- As the carbon dioxide level falls, bicarbonate ions (HCO3-) move out of the RBCs into the plasma, and chloride ions (Cl-) move into the RBCs to maintain electrical neutrality.

**Hint for Step 2:** Focus on the changes that occur in the blood as it travels from the tissues to the lungs, especially regarding the movement of bicarbonate and chloride ions.

### Step 3: Determine the Correct Location
- The question asks where the reverse chloride shift begins. It is important to note that this process starts at the arteriolar end of the pulmonary capillary, where blood is entering the lungs and carbon dioxide is being released.

**Hint for Step 3:** Recall that the reverse chloride shift is specifically linked to the exchange of gases in the pulmonary capillaries, where oxygen is taken in and carbon dioxide is expelled.

### Conclusion
Based on the understanding of the chloride shift and the reverse chloride shift, we conclude that the reverse chloride shift begins at the **arteriolar end of the pulmonary capillary**.

### Final Answer
The correct answer is: **Arteriolar end of pulmonary capillary**.