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Excretory System Function and Parts Excretion • Different organs in the body have roles for the removal of waste products. • The removal process is known as EXCRETION. • The excretory system is the system in the body that collects wastes produced by cells and removes the wastes from the body. Why is excretion necessary? • In order for cells to stay alive, they must continually intake water and other molecules. • The cells would continue to get bigger and bigger if they only took in molecules • They must also export molecules – These molecules may be important signaling molecules such as hormones, or they may be molecules of glucose on their way to other cells, or they may be waste products of cellular metabolism that cells need to dispose. The Excretory System • The structures of the excretory system are: – – – – Kidneys (2) Ureters (2) Urinary bladder Urethra The Excretory System • The waste eliminated is –Urea: a chemical that comes from the breakdown of proteins –Water The Job of the Kidneys • They are responsible for cleaning the blood by removing metabolic wastes and excess water and excreting them as urine. • Besides removing urea, it also removes excess salts or glucose, the remnants of drugs (reason for urine tests), and excess water. The Kidney Nephrons The kidneys are champion filters but the real workers are the nephrons. Each of your kidneys contains about a million nephrons: The tiny filtering factories that actually remove the waste from blood and produce the urine. Formation of Urine • If there is too much water in the blood, the kidneys/nephrons will remove it and put in urine. • If there is not enough water in the blood, the kidneys/nephrons will not remove it. • If there is too much urea or other liquids in the blood, the kidneys/nephrons will remove these too. • By regulating the internal environment and keeping if free of harmful levels of chemicals the kidneys normally maintain homeostasis. The Hard-working Kidneys • The two kidneys in the body receive between 1100 – 2000 liters (1160 – 2100 quarts or 500 gallons) of blood per day – about the volume of a car! • Because the body has only about 5.6 liters of blood, your blood runs through the kidneys to be cleaned about once every four minutes. Other Organs of Excretion • The lungs: remove carbon dioxide and excess water as water vapor when you exhale. • The skin: removes water and salt when you sweat. • The liver: removes wastes from the blood – The liver works both excretory and digestion making urea and bile.