WASTE

Food which cannot be digested travels through the alimentary canal and leaves our bodies as faeces. Other wastes, for example worn-out tissues and cells, leave the body via the skin as sweat, or the lungs as carbon dioxide, or leave the bloodstream via the kidneys to the excreted as urine.

Kidneys act as filters. The renal artery, which brings blood to the kidneys, is divided into a large network of capillaries. These filter out waste matter and impurities dissolved in water. Useful materials and, after cleansing, most of the water, are returned  into the blood. Waste liquid or urine travels down the ureters to the bladder, where it is stored  before being excreted through the urethra. Urine contains various wastes dissolved in water, including urea( a product of poisonous ammonia, neutralized by the liver). The kidneys also control the balance of water and other substances in the body. So the most of the body’s waste are removed through the lungs and kidneys. When kidneys fail, kidney machines are used to filter the blood and take out poisonous waste materials.

·        The lungs get rid of waste materials, including water and carbon dioxide. If you breathe on a cold mirror, you can see the droplets of water which you breathe out.

·        Sweating through the skin is another way of excreting waste. Liquid is passed from the blood vessels into the sweat glands, and then out through the pores in the skin. We get rid of about a litre of water each day through the skin. In hot weather, we lose more water this way. Sweating is one way the body keeps cool.

·        Each kidney contains a million microscopic tubes with filters, called nephrons. Liquid waste passes through these via collecting ducts into the ureters, which carry it to the bladder.