Which of the following is the functional unit of the kidney?

The functional unit of the kidney is the nephron. Each kidney contains approximately one million nephrons, which are responsible for the essential tasks of filtering blood, reabsorbing nutrients, and excreting waste as urine.

The nephron comprises several key components, including the renal corpuscle (which consists of Bowman's capsule and the glomerulus) and the renal tubule, which includes the proximal convoluted tubule, loop of Henle, and distal convoluted tubule. Each part of the nephron plays a specific role in the filtration process: the glomerulus filters blood, while the tubules adjust the concentration of urine through reabsorption and secretion.

Understanding the nephron's structure and function is crucial for comprehending how the kidneys maintain homeostasis, regulate body fluids, and process metabolic waste. In contrast, while the medulla and cortex refer to regions of the kidney, they do not represent the basic functional unit. The convoluted tubules are parts of the nephron but do not encompass the entirety of its function. Therefore, the nephron stands out as the essential functional unit that performs the critical actions necessary for kidney operations.