A portal system is one in which

Options

A. A vein start from an organ and end up in heart
B. A vein starts from an organ and ends up in another organ
C. A vein starts from heart and ends up in lungs
D. None of these

Answer

To answer the question "A portal system is one in which", we need to analyze the options provided and understand what a portal system entails.

### Step-by-Step Solution:

1. **Understanding the Portal System**: A portal system is a specific type of blood circulation where blood flows from one organ to another organ through a vein, without first passing through the heart.

2. **Evaluating the Options**:
- **Option 1**: A vein starts from an organ and ends up in the heart.
- This describes a typical venous return system, not a portal system.
- **Option 2**: A vein starts from an organ and ends up in another organ.
- This is characteristic of a portal system, as it involves blood moving from one organ (like the intestines) to another organ (like the liver) via a portal vein.
- **Option 3**: A vein starts from the heart and ends up in the lungs.
- This describes the pulmonary circulation, not a portal system.
- **Option 4**: None of these.
- This option is incorrect since we have identified a valid description in option 2.

3. **Conclusion**: Based on the analysis, the correct answer is **Option 2**: "A vein starts from an organ and ends up in another organ."

### Final Answer:
A portal system is one in which a vein starts from an organ and ends up in another organ.

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