There are pair of kidneys that are purplish-brown and are located underneath the ribs toward the middle of the back. Their function is to:
Remove waste from the blood in the form of urineKeep substances stable in the bloodMake erythropoietin, a hormone which helps make red blood cellsMake Vitamin D activeRegulate blood pressure
The kidneys remove waste from the blood through tiny filtering units called nephrons. Each nephron is made up of a ball of small blood capillaries, called a glomerulus. There is also a small tube called a renal tubule, which drains the urine and joins other tubules carrying the urine out of the kidney to the ureter.
Urea, together with water and other wastes, forms the urine.