What are the structural and functional units of the kidney known as?

The correct answer is nephrons, as they are indeed the structural and functional units of the kidney. Each kidney contains approximately one million nephrons, which are responsible for filtering blood, reabsorbing necessary substances, and secreting waste products into the urine. The nephron consists of several key components, including the renal corpuscle (which houses the glomerulus and Bowman's capsule) and the renal tubule. This organization allows for the complex processes of filtration, reabsorption, and secretion that are essential for maintaining homeostasis in the body.

In contrast, glomeruli refer specifically to the network of capillaries within the nephron where the initial filtration of blood takes place, but they do not represent the entire functional unit. Renal pyramids are structures within the kidney that contain the collecting ducts and help transport urine to the renal pelvis, but they do not serve the functional role of filtration and reabsorption that nephrons do. The term filtration units is somewhat vague and does not specifically denote the organized structure and function that nephrons embody.