Credit: NIH.

A nephron is the microscopic unit of the kidney consisting of a glomerulus (a filtering funnel consisting of a cluster of tiny blood capillaries) cupped in a structure called a Bowman's capsule, with an attached long, narrow tubule. There are about one million nephrons in each kidney. Blood enters the kidney under pressure, and water and wastes are forced into the tubule by a process known as ultrafiltration. Some water, salts, and other essential molecules are reabsorbed into the bloodstream; the remaining filtrate, urine, is passed to the bladder for excretion from the body.