After portal vein entry, which organ is the first major processing site for carbohydrates, amino acids, and water-soluble vitamins?

• A. Heart
• B. Pancreas
• C. Liver
• D. Lungs

Answer: (C)

Because nutrients absorbed from the gut enter the hepatic portal vein and are delivered to the liver before circulating systemically, the liver is the first major processing site for carbohydrates, amino acids, and water-soluble vitamins. In the liver, carbohydrates are converted to glucose, stored as glycogen, or released as needed. Amino acids are taken up for protein synthesis, conversion to other compounds, or deamination for energy and urea production. Water-soluble vitamins are stored or further metabolized there as required. The other organs listed don’t serve as the initial processing hub for these nutrients: the heart moves blood but doesn’t metabolism nutrients; the pancreas mainly provides digestive enzymes and hormones; the lungs handle gas exchange.