Nephron. Illustration of a nephron from the human kidney, surrounded by blood vessels. Nephrons are where waste products and excess water are removed from the bloodstream in the kidney. Arterial blood (red vessels) enters a tight knot of capillaries (upper centre) called a glomerulus, where fluids pass out of the blood into a hollow tubule (yell- ow). Blood vessels around a loop in the tubule (bottom) recover essential nutrients, salts & some water, and the filtered blood returns to the body in veins (blue). The remaining fluid drains to the bladder as urine. About 140 litres of fluid passes into the kidney tubules each day in a normal adult. Of this, 99% is reabsored.