Question

Which one of the following blood vessel in mammals contains the least amount of urea
A. Hepatic Portal Vein
B. Hepatic vein
C. Dorsal aorta
D. Renal vein

Answer 1

Urea is secreted in the thin ascending limb of the Henle loop, so significant amounts of urea reach the distal nephron. In the collecting ducts, urea is reabsorbed together with water. Movement of huge amounts of urea across cell membranes is carried out by urea transporter proteins

Complete answer:
The renal vein contains less amount of urea. The renal artery enters the kidney as an afferent arteriole. It carries blood which is loaded with urea and then moves into the glomerulus of the kidney. The blood is then filtered by the glomerulus, then moving into the bowman's capsule and then the filtrate runs parallel to the Loop of Henle. The urea is absorbed in the nephric filtrate by the process of tubular secretion in the loop of Henle, distal convoluted tubule, and collecting duct. This process of tubular secretion helps to secrete urea from the blood to collect duct which is then excreted in form of urine. The pureblood comes from the kidney through the renal vein which has the blood with the least amount of urea. Thus the renal vein contains the least amount of urea.
So, the right answer is Option D ( Renal vein).

Additional Information:
The renal vein is formed by the union of two-to-three renal parenchymal veins in the renal sinus. It arises from the renal hilum anterior and moves to the renal artery and drains into the inferior vena cava. The renal vein is an asymmetrically paired blood vessel that carries the deoxygenated blood from the kidney to the inferior vena cava. Both left and right veins move to the anterior side of their corresponding arteries. The right renal vein receives tributaries only from the kidney, while the left renal vein receives several types of blood vessels from other organs, including the left gonadal (ovarian/testicular) vein, left inferior phrenic vein, and left adrenal veins. These all the vessels bring deoxygenated blood from different organs to the kidney for filtration.

Note: Wastes such as urea, ammonia, uric acid are generally excreted in the urine. The potassium, sodium, and calcium ions are also excreted out of the body in the urine. Humans are called as ureotelic as the major component in urine is urea.