World Kidney Day
Kidney Facts
Kidneys health >> How do kidneys work? >> Zoom-in on urine production

Zoom-in on urine production

The nephrons in the kidneys work simultaneously to clean wastes from the blood, and then eliminate those wastes via urine. Let’s see how nephrons work: Each nephron is composed of 2 main parts, both with a specific role in urine formation: the glomerulus, which looks like a small balloon, and the tubule

Three main steps are involved: 

Part of the blood arriving in the kidneys is filtered in the glomerulus. The glomerulus is sphere-shaped and surrounded with small blood vessels which act as a filter. Only big molecules such as proteins and blood cells cannot pass, everything else passes into the nephrons -- about 180L per day!
Some substances that have passed the filter are still needed and are taken back from the tubule and transported into blood: glucose, required minerals, etc… and water -- 99% is reabsorbed! Reabsorption moves substances out of the tubules and into the blood.
Some substances are also secreted from the blood into the kidney tubules, where they are eventually eliminated in the urine. Secretion moves substances from the blood and into the tubules where they mix with the water and other wastes and are converted into urine.

These continuous exchanges enable the kidneys to produce about 1.5L of 
urine from about 180L of blood filtered per day. It then goes into the 'collecting ducts’ (in yellow) which bring urine into the ureters to finally reach the bladder, where it is stored waiting for elimination.

Did you know?  
Every day, kidneys do an extraordinary job by filtering the blood about 50 times !
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