Urea production and transport after protein meal

Steps:

• Protein-rich meal digested to amino acids, absorbed into hepatic portal vein.
• Amino acids reach liver, where deamination produces ammonia converted to urea via urea cycle.
• Urea released from liver into hepatic vein, enters systemic circulation via inferior vena cava.
• Systemic blood with elevated urea reaches renal artery, supplying kidneys for filtration.

Why B is correct:

• Renal artery carries systemic blood with peak urea concentration from liver production directly to kidneys before excretion, per renal physiology of waste delivery.

Why the others are wrong:

• A. Hepatic portal vein: Transports amino acids to liver; urea low as production occurs downstream in liver.
• C. Hepatic vein: Delivers urea from liver but concentration equilibrates lower in systemic mixing before reaching renal artery.
• D. Renal vein: Carries filtered blood from kidneys; urea reduced after glomerular filtration and excretion.

Final answer: B