Secretion of aldosterone in birds, man, and other mammals is stimulated by

Options

A. Fall In concentration of `Na^(+)` in blood plasma
B. Rise in concentration of `K^(+)` in blood plasma
C. Both (1) & (2)
D. Fall in `ca^(++)` concentration in blood plasma

Answer

### Step-by-Step Solution:

1. **Understanding Aldosterone**: Aldosterone is a steroid hormone secreted by the adrenal cortex of the adrenal glands. Its primary role is in osmoregulation, which involves maintaining blood pressure and electrolyte balance in the body.

2. **Functions of Aldosterone**:
- Aldosterone promotes the reabsorption of sodium ions (Na+) in the renal tubules, which increases sodium concentration in the blood.
- It also facilitates the excretion of potassium ions (K+) from the body, thereby decreasing potassium concentration in the blood.

3. **Stimuli for Aldosterone Secretion**:
- The secretion of aldosterone can be stimulated by:
- A **fall in sodium concentration** in the blood plasma. When sodium levels drop, aldosterone is secreted to help increase sodium levels back to normal.
- A **rise in potassium concentration** in the blood plasma. Elevated potassium levels trigger the secretion of aldosterone to promote potassium excretion and restore balance.

4. **Evaluating the Options**:
- **Option 1**: Fall in concentration of sodium in blood plasma - This is a correct stimulus for aldosterone secretion.
- **Option 2**: Rise in concentration of potassium in blood plasma - This is also a correct stimulus for aldosterone secretion.
- **Option 3**: Fall in calcium concentration in blood plasma - This is incorrect as it pertains to the action of parathyroid hormone, not aldosterone.

5. **Conclusion**: Since both the first and second options are correct, the answer to the question is that the secretion of aldosterone in birds, man, and other mammals is stimulated by both a fall in sodium concentration and a rise in potassium concentration.

### Final Answer:
The secretion of aldosterone in birds, man, and other mammals is stimulated by **both a fall in concentration of sodium in blood plasma and a rise in concentration of potassium in blood plasma**.