Which term describes the process of urine formation in the kidneys?

The process of urine formation in the kidneys is primarily described by the term "filtration." Filtration refers to the initial step in urine formation that occurs in the glomeruli of the nephrons, where blood plasma is filtered through a semipermeable membrane. This filtration process allows water, ions, and small molecules to pass while retaining larger molecules and cells in the bloodstream.

Following filtration, the filtrate produced contains waste products, which will further undergo processes such as reabsorption and secretion before the final urine is formed. While terms like excretion and urination are related to the overall process of removing waste from the body, they do not specifically refer to the formation of urine in the kidneys themselves, as they pertain more to the final elimination stages. Reabsorption describes the process where certain substances, like glucose and specific ions, are absorbed back into the bloodstream from the filtrate after filtration has occurred.

Thus, filtration accurately captures the essential first step in the formation of urine, distinguishing it from later processes involved in urine processing and elimination.