Which of the following has least regeneration

Options

A. Nervous system
B. Excretory system
C. Reproduction system
D. Digestive system

Explanation

To determine which of the following systems has the least regeneration, we need to analyze the options provided: nervous system, excretory system, digestive system, and reproductive system.

### Step-by-Step Solution:

1. **Understanding Regeneration**: Regeneration is the process by which organisms replace or restore lost or damaged tissues or organs. Different systems in the body have varying capacities for regeneration.

2. **Analyzing the Nervous System**:
- The nervous system is primarily composed of neurons (nerve cells).
- Neurons are often in a phase called the G0 phase, which is a resting phase where cells do not actively divide or repair themselves.
- This means that the nervous system has a very limited ability to regenerate after injury.

3. **Examining Other Systems**:
- **Excretory System**: This system includes organs like the kidneys, which can regenerate to some extent.
- **Digestive System**: The liver, a part of the digestive system, is known for its significant regenerative abilities. It can regenerate after partial removal or damage.
- **Reproductive System**: Certain cells in the reproductive system can also regenerate, especially in females where the ovaries can produce new eggs.

4. **Conclusion**: Among the options provided, the nervous system has the least capacity for regeneration due to the nature of its cells (neurons) being in a non-dividing state most of the time.

5. **Final Answer**: Therefore, the correct answer is the **nervous system**.