T HE K IDNEYS

A major function of the kidneys is to remove waste products & excess fluid from the body. These waste products and excess fluid are removed through the urine. The production of urine involves highly complex steps of excretion and reabsorption. This process is necessary to maintain homeostasis.

The kidneys are powerful chemical factories that perform the following functions: -remove waste products from the body -remove drugs from the body -balance the body's fluids -release hormones that regulate blood pressure -produce an active form of vitamin D that promotes strong, healthy bones -control the production of red blood cells

Each kidney is composed of three sections: the outer (renal) cortex, the (renal) medulla (middle part) and the hollow inner (renal) pelvis. The cortex is where the blood is filtered. The medulla contains the collecting ducts which carry filtrate (filtered substances) to the pelvis. The pelvis is a hollow cavity where urine accumulates and drains into the ureter.

The Parts of the Kidney

7 Kidney has two regions Cortex : outer Columns of cortex divide medulla into “pyramids” Medulla : inner Darker, cone-shaped medullary or renal pyramids Parallel bundles of urine-collecting tubules

H OW BLOOD IS F ILTERED The filtering units of the kidneys are the nephrons. There are approximately one million nephrons in each kidney. The nephrons are located within the cortex and medulla of each kidney. The tubes of the nephron are surrounded by cells and a network of blood vessels spreads throughout the tissue. Therefore, material that leaves the nephron enters the surrounding cells and returns to the bloodstream by a network of vessels.

P ARTS OF THE N EPHRON Each nephron consists of the following parts: 1) glomerulus 2) Bowman’s capsule 3) proximal tubule 4) loop of Henle 5) distal tubule 6) collecting duct

T HE G LOMERULUS The glomerulus is a mass of thin-walled capillaries. The Bowman’s capsule is a double- walled, cup-shaped structure. The proximal tubule leads from the Bowman’s capsule to the Loop of Henle. The loop of Henle is a long loop which extends into the medulla. The distal tubule connects the loop of Henle to the collecting duct.

H OW THE KIDNEY DOES ITS JOB ! (H OW THE BLOOD IS CLEANED ) The renal artery delivers the dirty blood to the kidney from the body. The blood then goes into the pyramid, then the medulla & finally the nephron. Then the blood goes into the afferent arteriole and then into the glomerulus where it is cleaned. After cleaning it leaves through the efferent arteriole, followed by the proximal tubule & the Henle’s Loop. Once the blood is in Henle’s loop, it separates into clean blood & wastes.

The clean blood goes to capillaries then venules, renal vein and back to the heart. The wastes go into the collecting tubule, renal pelvis (stored urine), ureter, bladder, and finally released from the body as urine through the urethra.

NOTE Since the kidneys control what leaves and what remains in the nephrons, they maintain the levels of water, ions and other materials nearly constant and within the limits to maintain homeostasis.