Which one of the following blood vessels in mammals would normally carry the largest amount of urea

Options

A. Dorsal Aorta
B. Hepatic Vein
C. Hepatic Portal Vein
D. Renal Vein

Answer

To determine which blood vessel in mammals carries the largest amount of urea, we can analyze the options provided:

1. **Dorsal Aorta**: This is a major artery that carries oxygenated blood from the heart to the rest of the body. It does not specifically carry urea, as its primary function is to distribute oxygen-rich blood.

2. **Hepatic Vein**: This vein carries blood away from the liver. Since urea is produced in the liver as a waste product of protein metabolism, the hepatic vein would carry a significant amount of urea from the liver to the heart.

3. **Hepatic Portal Vein**: This vein carries blood from the gastrointestinal tract and spleen to the liver. While it does transport nutrients and some waste products, it does not carry the largest amount of urea, as it is primarily involved in nutrient transport to the liver for processing.

4. **Renal Vein**: This vein carries blood away from the kidneys. While the kidneys filter urea from the blood, the renal vein does not carry the highest concentration of urea compared to the hepatic vein.

Based on this analysis, the blood vessel that normally carries the largest amount of urea in mammals is the **Hepatic Vein**.

### Final Answer:
**Hepatic Vein**