How many time dose a molecule of urea have to pass through the heart in its journey from liver to kidney ?

Options

A. 0
B. 1
C. 2
D. 4

Answer

To determine how many times a molecule of urea passes through the heart during its journey from the liver to the kidney, we can break down the process step by step:

### Step-by-Step Solution:

1. **Urea Production in the Liver**:
- Urea is produced in the liver as a result of the urea cycle, which detoxifies ammonia (a byproduct of protein metabolism).

2. **First Passage to the Heart**:
- Once urea is synthesized in the liver, it enters the bloodstream. The blood from the liver is carried to the heart via the hepatic veins. This is the first time the urea molecule passes through the heart.

3. **Transport from the Heart to the Kidneys**:
- After passing through the heart, the urea is then transported through the systemic circulation to the kidneys. However, before reaching the kidneys, the urea molecule may also pass through the heart again if we consider the overall circulation of blood.

4. **Second Passage to the Heart**:
- As the blood returns from the systemic circulation to the heart, it can be considered that the urea molecule passes through the heart a second time before being directed to the kidneys.

5. **Final Destination - Kidneys**:
- After passing through the heart for the second time, the urea is then transported to the kidneys, where it is filtered out of the blood and excreted from the body.

### Conclusion:
- In total, a molecule of urea passes through the heart **twice** during its journey from the liver to the kidneys.

### Final Answer:
- The answer is **2 times**.