Which organ is concerned with the processing and excretion of urine?

The kidneys are the primary organs involved in the processing and excretion of urine. They perform crucial functions such as filtering blood to remove waste products and excess substances, which are then excreted as urine. Within the kidneys, the nephrons are the fundamental structural and functional units that facilitate this process through filtration, reabsorption, and secretion.

As blood passes through the kidneys, waste products such as urea and creatinine are filtered out, while essential substances like water, electrolytes, and nutrients are reabsorbed back into the bloodstream. The final product, urine, is then transported to the bladder for storage and eventual excretion from the body.

Other organs mentioned in the options have different functions; the liver is primarily involved in metabolism and detoxification, the pancreas produces digestive enzymes and hormones such as insulin, and the bladder serves as a storage organ for urine produced by the kidneys. Therefore, the kidneys are the correct choice when considering the organ responsible for processing and excreting urine.