Kidney filtration system. Artwork of blood vessels (veins, blue; arteries, red) surrounding a nephron (brown tubes) from the human kidney. Nephrons are where waste products and excess water are removed from the bloodstream in the kidney. Arterial blood enters a tight knot of capillaries (upper left) called a glomerulus, where fluids pass out of the blood into a hollow tubule (brown tubes). Blood vessels around a loop in the tubule (bottom) recover essential nutrients, salts and some water, and the filtered blood returns to the body in veins. The remaining fluid drains to the bladder as urine (yellow, lower right).