Vasopressin influences :

Options

A. electrolyte efflux
B. nerve excitability
C. water reabsorption
D. all of these

Answer

To solve the question "Vasopressin influences:", we need to analyze the options provided and understand the role of vasopressin (also known as antidiuretic hormone or ADH) in the body.

### Step-by-Step Solution:

1. **Identify the Source of Vasopressin**:
- Vasopressin is produced in the hypothalamus and released from the posterior pituitary gland.

2. **Understand the Function of Vasopressin**:
- The primary function of vasopressin is to regulate water balance in the body. It does this by promoting water reabsorption in the kidneys.

3. **Evaluate Each Option**:
- **Option 1: Electrolyte efflux**: This option is incorrect. Electrolyte balance is primarily regulated by hormones like aldosterone, not vasopressin.
- **Option 2: Nerve excitability**: This option is also incorrect. Nerve excitability is influenced by hormones such as adrenaline, which are involved in the fight-or-flight response.
- **Option 3: Water reabsorption**: This option is correct. Vasopressin directly influences water reabsorption in the kidneys, leading to concentrated urine and reduced water loss.
- **Option 4: All of these**: This option is incorrect since not all the previous statements are true.

4. **Conclusion**:
- Based on the evaluation, the correct answer is that vasopressin influences water reabsorption.

### Final Answer:
Vasopressin influences water reabsorption.