 Excretion  The process by which the body collects and removes wastes.  Includes the following organs: › Liver, Lungs, skin, and kidneys

 Converts impurities and poisons in the body to less harmful substances.  Forms Urea from a harmful waste product of protein breakdown. › Urea can be safely transported to the kidneys via blood.

 Lungs remove carbon dioxide and water when you exhale.  Sweat glands in the skin also serve an excretory function because water and urea are excreted in perspiration.

 Diagram on Pg. 255  Filter urea and other wastes from the blood  Major organs in the excretory system  Size of a fist  Wastes are eliminated in urine

 Main organ involved in water balance  Hormones sent from the brain signal the kidneys to release more or less water in urine depending on the amount of water in the body.  Your body will produce less urine on a hot day when you have sweat a lot.

 Each kidney contains about a million Nephrons, tiny filtering units that remove wastes and produce urine. › 1 st needed materials and wastes are filtered from the blood. › Needed materials are returned to the blood, and the wastes are eliminated from the body. › Pg. 256 Figure 8

 Blood enters the kidneys  Blood enters a glomerulus, cluster of tiny blood vessels in a nephron.  Urea, salts, glucose, and some water are filtered from the glomerulus into a thin- walled capsule.

 The capsule around the glomerulus is connected to a long, twisting tube.  The tube is surrounded by tiny blood vessels.  As filtered material flows through the tube, the glucose, most of the water, and other needed materials pass from the tube back into the blood.

 Urea and other wastes, such as excess vitamins and harmful substances, stay in the tube.  The fluid that remains in the tube is urine.  Eventually, the urine drains into a larger tube called a ureter, which carries it from a kidney to the bladder.