Which structures are considered the functional units of the kidneys?

The functional units of the kidneys are the nephrons. Each nephron is responsible for filtering blood, reabsorbing essential nutrients, and excreting waste products as urine. A nephron consists of a renal corpuscle, which includes the glomerulus and Bowman's capsule, and a renal tubule, where the reabsorption and secretion processes occur. This intricate structure allows the kidneys to maintain the body's fluid and electrolyte balance, regulate blood pressure, and remove waste products from the bloodstream.

While the glomeruli and Bowman's capsules are essential components of the nephron that contribute to the filtration process, they do not function independently as units of kidney function. The urethras play a role in excreting urine from the body but are not involved in the filtration or reabsorption processes that define kidney function.