What are the functional units of the kidney called?

The functional units of the kidney are called nephrons. Nephrons are responsible for filtering blood, reabsorbing necessary substances, and excreting waste products in the form of urine. Each kidney contains approximately one million nephrons, which operate through a series of processes including filtration, secretion, and reabsorption to maintain the body’s fluid balance, electrolyte levels, and overall homeostasis.

Glomeruli, although important components of the nephron, refer specifically to the clusters of capillaries within the nephron where filtration begins. Ureters are tubes that carry urine from the kidneys to the bladder and do not play a role in the filtering process. Neural tissues relate to signaling within the body and are not involved in the kidney's primary functions. Therefore, the nephron is the correct answer as it encompasses the entire functional architecture necessary for kidney operations.