Anatomy of a Kidney

This cross section of a kidney, almost three times life-size, shows its blood supply and one of the filter tubules, a nephron, highly magnified. The nephron is a highly specialized coiled tubule measuring up to one inch in length. There are more than one million nephrons in each kidney. They function as the kidney's filter units. The kidneys filter unwanted materials from the blood and regulate the levels of water and chemicals in the body. As blood flows through a glomerular tuft, a tight knot of blood capillaries from which water and chemicals filter into the nephrons, fluid is forced into the Bowman's capsule. The Bowman's capsule, the expanded beginning of the tubule, acts as the nephron's collecting cup for fluid filtering from the blood. The filtrate then flows along the coiled tubule. Further waste material is secreted directly into the nephron tubule. At the same time, reaabsorption of essential chemicals into the capillaries takes place. The loop of Henle, the central region of the nephron, acts as the primary reabsorption area. Urine, the yellowish liquid remaining, passes from the nephron-collecting ducts into the renal pelvis, which lies at the core of the kidney and acts as a funnel to conduct the liquid into the ureter. Through the ureters, the urine is conducted away from the kidney and emptied into the bladder The cortex, or the outer region of the kidney, houses the glomreulus of each nephron. The medulla, or the inner region of the kidney, contains the loops of Henle and the collecting ducts.