How do your kidneys filter blood and make urine?

Blood enters each kidney through the renal artery and flows into about a million tiny filtering units called nephrons. Each nephron contains a glomerulus, a small knot of capillaries where blood pressure forces water, salts, glucose, urea, and other small molecules out of the blood into a cup-shaped structure called Bowman's capsule. This creates a fluid called the filtrate. As the filtrate travels through the nephron's tubules, the body reclaims what it needs. Glucose, most water, and essential salts are actively reabsorbed back into surrounding capillaries. Waste products like urea, excess salts, and toxins remain in the tubule or are actively secreted into it. The remaining concentrated fluid becomes urine, which drains into the renal pelvis and flows down the ureter to the bladder.