What is the process of filtering blood and forming urine called?

The process of filtering blood and forming urine is primarily known as filtration. This refers specifically to the initial step in kidney function where blood passes through the glomeruli, which are tiny filtering units in the nephron. During this phase, water, electrolytes, and small molecules are separated from larger blood components, resulting in the formation of a filtrate that will eventually become urine. This process is essential for maintaining homeostasis and regulating the body’s fluid and electrolyte balance.

Following filtration, there are additional steps such as reabsorption and secretion that further modify the filtrate before it is eliminated as urine, but the foundational process that directly involves filtering the blood occurs at the initial filtration stage. Therefore, the term "filtration" accurately captures the key action of the kidneys in their role of forming urine from blood.