Which organ is primarily responsible for the excretion of nitrogenous wastes?

The kidneys are the primary organs responsible for the excretion of nitrogenous wastes from the body. They play a crucial role in filtering blood to remove waste products, particularly urea, creatinine, and uric acid, which are byproducts of protein metabolism. The kidneys accomplish this through a complex process that includes filtration, reabsorption, and secretion.

As blood passes through the kidneys, the nephrons— the functional units of the kidneys— filter out these nitrogenous wastes, which then get concentrated in urine. This urine is ultimately excreted from the body, thereby maintaining the body's balance of electrolytes, water, and waste products.

Other organs listed, such as the liver, play different roles in metabolism and detoxification but are not the primary means of nitrogenous waste excretion. The lungs are involved in gas exchange rather than waste products from metabolism, and the heart is primarily a muscular organ responsible for pumping blood, not for waste elimination.