How do the kidneys filter blood?

The kidneys are essential for cleaning your blood and keeping your body in balance. Every day, they filter about 180 liters (roughly 48 gallons) of blood. This constant process helps remove waste, control fluid levels, and regulate vital substances like salts and minerals.

Inside each kidney are about one million tiny filtering units called nephrons. Each nephron has two main parts: the glomerulus and the tubule. Blood enters the glomerulus, which acts like a sieve. It filters out small waste particles, excess water, and salts while keeping larger substances like proteins and blood cells inside the bloodstream.

The filtered fluid then travels through the tubule, where important substances like glucose, certain salts, and water are reabsorbed back into the body. The rest—mainly urea, creatinine, excess salts, and water—is turned into urine and passed to the bladder.

This system works around the clock. It adjusts how much water and salt to remove based on what your body needs at any given time. That is why you may notice changes in urine output depending on how much water you drink or how much you sweat.

In addition to removing waste, the kidneys help control blood pressure and support healthy red blood cell levels through hormone production. But at the heart of it all, their primary job is to act as a filtration system that keeps your blood clean and your body in proper balance.

People often ask how the kidneys manage to clean the blood so effectively. The answer lies in a complex but efficient system that filters waste, reabsorbs what the body needs, and works quietly every second to keep everything in balance.

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