In what organ does the majority of tubular reabsorption occur?

The majority of tubular reabsorption occurs in the kidneys, specifically within the renal tubules. After the initial filtration of blood that occurs in the glomerulus, the filtrate enters the renal tubules, where essential substances such as water, glucose, amino acids, and various ions are reabsorbed back into the bloodstream.

The nephron, the functional unit of the kidney, consists of several sections including the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. The proximal convoluted tubule is particularly crucial for reabsorption, handling about 65% to 70% of the filtrate, where selective reabsorption processes occur actively and passively.

Other organs listed, such as the liver, lungs, and heart, do not play significant roles in the tubular reabsorption process related to renal function. The liver is primarily involved in metabolism and detoxification, the lungs are responsible for gas exchange, and the heart functions in pumping blood. Each organ has specific roles that do not include managing the reabsorption of substances filtered from blood in the kidneys. Thus, the kidneys are unequivocally the organ where most tubular reabsorption takes place.