The Excretory System By Kara Weisman

*Organs of the excretory system include kidneys, liver, bladder, lungs, urethra and the skin.*

What is the excretory system? The excretory system provides a way for various wastes to be removed from the body. The Excretory system balances the chemical composition of body fluids by removing wastes and retaining the proper amounts of water, salts, and nutrients.

The Kidneys Kidneys are the main organs of the excretory system. They are dark purple in color and are shaped like kidney beans, hence the name. Kidneys act as the body’s filter. There is one kidney on each side of the spinal column, just above the waist. Our kidney’s filter one liter of blood per minute, pumped into them from the largest artery , called the aorta. The actual filtering process takes place within the kidney’s millions of microscopic nephrons. Nephrons are made up of tubes and closed in an even more complex network of capillaries. Kidneys excrete salts, water, and nitrogen wastes

The Liver The liver is considered both part of the digestive system and the excretory system. The liver can regenerate, or grow back, cells that have been destroyed by some short-term injury or disease The liver is the body's largest organ. It is located in the right part of the abdomen over the stomach and is protected by the lower ribs. The liver of an average sized adult weighs a little less than four and a half pounds. One of the liver’s primary jobs is to store energy in the form of glycogen, which is made from a type of sugar called glucose. The liver also functions as the body’s chemical factory. Several important proteins found in the blood are produced in the liver. Proteins & other nitrogenous compounds are broken down in the liver by deamination.  As a result of these reactions, a nitrogenous waste called urea is formed.

The Bladder The urinary bladder is the organ in the excretory system that stores urine after its formation by the kidneys finish the filtering process. Urine enters the bladder from the kidneys through two ureters and is discharged through the urethra. The bladder releases all of the urine. Average capacity of the adult bladder is about half a liter.

The Lungs The lungs excrete spices of the excretory system. As respiration occurs carbon dioxide is produced as a waste product.  As carbon dioxide builds up in body cells, it eventually diffuses out of the cells and into the bloodstream, which then circulates to the lungs. Water vapor also leaves the body from exhaling.

The Urethra Produces and excretes urine from the body. Urine is a transparent yellow fluid containing unwanted wastes, mostly excess water, salts, and nitrogen wastes. the body needs, at a minimum, to excrete about 0.5 liter (1 pint) of urine daily to get rid of its waste products . If blood sugar, or glucose is found in urine, that is a sign of diabetes. The one million microscopic nephrons that the kidney filters, performs this critical blood-filtering function and produces urine in the process.

The Skin An adult human has between one and four million sweat glands. Most eccrine glands are found on almost all of the surface of the body and the outside of the palms and soles. Cells at the base of the gland make sweat, a mixture of water, salt, and small amounts of metabolic waste products. As the sweat moves along , much of the salt is reabsorbed, preventing loss of this substance. When sweat reaches the outer surface of the skin, it evaporates, helping to cool the body in hot environments or during physical excersise.

How do theses structures work together to accomplish the functions of the system? As carbon dioxide builds up in body cells in the lungs, it eventually diffuses out of the cells and into the bloodstream, which then circulates to the kidneys which filters the blood and other excess wastes, which flows through the ureter and down into the urinary bladder which fills up and then you excrete the urine from your system through the urethra.

Helpful Websites to find more information: www.innerbody.com www.encarta.com www.google.com/images/excretorysystem

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