The Excretory System

A lot of people think the excretory system has something to do with passing solid waste from the body (yes, I’m talking about poo.) Actually, it has nothing to do with that. The excretory system does have to do with eliminating waste, but it actually eliminates it by passing it out in urine. So, it’s a “pee” thing instead of a “poo” thing. That’s why the “excretory system” is sometimes referred to as the “urinary system.” The excretory system is responsible for filtering the blood and removing waste materials in the blood. Many of these waste products are the result of cellular metabolism. They consist primarily of a substance called urea, certain types of salts, and water. http://www.youtube.com/watch?v=qxb2_d9ilEw

The excretory system is responsible for the excretion of wastes that result from the normal operations of our cells. Remember that cells also must “eat” and pass waste. The waste from this cell metabolism then passes into our blood system. Different organs in the excretory system help eliminate these wastes from our body. These wastes are toxic to our cells and would cause the cells (and us) to die if we were not able to get them out of our bodies. The excretory system is made up of the kidneys (and the major blood vessels that go to them), the bladder, and small tubes known as ureters. Although not everyone includes them as part of the excretory system, the lungs, liver, and the skin also help the body to eliminate waste. The lungs, as we have learned, help us to eliminate carbon dioxide from our bodies. The liver filters toxins and other waste materials from the blood and converts the harmful nitrogenous wastes like ammonia into urea. Urea is then passed from the body through the kidney, bladder, and ureters. Urea and other liquid wastes are also released through small pores in our skin.)

The Kidneys The kidneys are bean shaped organs about 10 cm in length. They have several important functions. The kidneys aid homeostasis by helping the body to maintain the proper amount of water and minerals like salt. Too much water in our system throws off the balance of minerals and causes certain body systems to malfunction. Salts are important to the body, but only when the concentration is at the correct balance. (Remember how salt can affect the movement of water in and out of cells.) Regulations of salt are important for proper maintenance of blood pressure. The kidneys filter metabolic wastes like urea and uric acid from the blood.

If your kidneys are not functioning properly, a number of things could happen: Water would build up in your body causing swelling (mostly evident in your fingers, toes, and lower leg near the ankles and calves. ) Your blood pressure could become very high or very low You begin feeling very ill because the waste materials that should have been filtered out by the kidneys were not and they are poisoning your body. You have difficulty urinating. You can develop kidney stones.

Kidney Failure and Dialysis When a person’s kidneys fail to function, (s)he requires a medical procedure called “dialysis.” Dialysis is the process where a specialized machine filters the impurities from a person’s blood. Several times per week, a person is required to visit a dialysis center to have this procedure done. If the kidney failure is permanent, the person may be put on a donor list to receive a kidney transplant. http://www.youtube.com/watch?v=yfNKyPTc_6E

Once the waste material and water is filtered through the kidney, it passes downward through tubes known as ureters in the bladder where is stored until it is passed from the body by urinating.

The bladder is a muscular, elastic organ that stores liquid waste (mostly urea, water, and salts) until these wastes are passed from the body through the process of urination. In infants and sometimes in elderly people, the muscles controlling the bladder are weakened. This can lead to uncontrolled urination.

Urea, water, and salts are also released from sweat glands located below the outer layer of skin (epidermis.) This “sweat” or “perspiration” passes out of the body through small holes in the epidermis called pores. Sweating or perspiring also helps the body to cool off. Body odor is actually produced by bacteria that feed on the components of sweat. CLOSE reading article: affect of artificial sweeteners on kidney function

How Does the Process of Organ Donation Work? Read together Organ Donation: The Process http://organdonor.gov/about/organdonationprocess.html Watch Organ Donation: The Story of a Living Organ Donor and His Dad http://www.youtube.com/watch?v=ARSvSV4cuXc A Recipients Story- A Young Boy Loses His Life But Saves Another http://www.youtube.com/watch?v=KCpB4jTJ7vU Group discussion: If you learned that you were a match for someone not related to you, would you be willing to donate a kidney or part of your liver to that person? If you learned one of your parents or siblings was in need of a kidney or liver and you were a match, would you act as a donor? How would you feel about your organs being donated in the event of your passing? Are there any limitations you would place on whom could receive your organs (for example, would you make it clear you would not want your liver donated to someone whose liver had failed because he or she was an alcoholic?)