Blood of which vessel in mammals carries least percentage of urea ?

Options

A. (a) Renal vein
B. (b) Aorta
C. (c) Renal artery
D. (d) Vena cava

Answer

To determine which blood vessel in mammals carries the least percentage of urea, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of Urea**: Urea is a waste product formed from the breakdown of proteins. It is primarily excreted by the kidneys.

2. **Function of the Kidneys**: The kidneys filter the blood to remove waste products, including urea. This process occurs in the nephrons, the functional units of the kidneys.

3. **Blood Flow Through the Kidneys**: Blood enters the kidneys through the renal artery, where it is filtered. The filtered blood, which has had urea and other waste products removed, exits the kidneys.

4. **Identify the Blood Vessel After Filtration**: After the filtration process, the blood leaves the kidneys through the renal vein. This blood is now low in urea because the kidneys have already removed it.

5. **Comparison with Other Blood Vessels**: Other blood vessels, such as the aorta or pulmonary artery, carry blood that has not been filtered by the kidneys and therefore contains higher levels of urea.

6. **Conclusion**: Since the renal vein carries blood that has been filtered and has the least amount of urea, we conclude that the blood vessel in mammals that carries the least percentage of urea is the **renal vein**.

### Final Answer:
The blood of the **renal vein** carries the least percentage of urea in mammals.

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