Among the options provided, which blood vessel in mammals contains the minimal quantity of urea?
Hepatic portal vein
Hepatic vein
Dorsal aorta
Renal vein
The renal vein, which carries blood away from the kidneys, contains the least amount of urea among the given options. This is because the kidneys are responsible for filtering waste products, including urea from the blood. As the filtration and reabsorption processes occur in the kidneys, water and essential nutrients are reabsorbed while waste products like urea remain in the tubular fluid. Consequently, the remaining fluid, known as urine, flows out of the kidneys and into the renal vein. Compared to other blood vessels involved in filtration, such as the hepatic portal vein and hepatic vein, the renal vein has a lower concentration of urea. Thus, the renal vein contains the minimal quantity of urea.Hence, the correct answer is option 4.