Metabolic Waste Products for Excretion

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The biological process involved in the removal of harmful metabolic wastes from the body is called excretion (Tomar, 2009, p. 40). The metabolisms within cells allow the body to function correctly, but this functioning resorts in waste products which are often useless and harmful. It is therefore important that the body removes these products to prevent harm. Tomar (2009, p. 40) suggests that the most common waste products are carbon dioxide, ammonia, uric acid, urea, creatinine, amino acids, various pigments and inorganic salts. In multicellular organisms, organs have evolved in order to deal with the waste products produced and enable them to be excreted from the body. In humans, these organs are the kidneys. The kidneys however, do not do all of the work on their own. They are part of an excretory system which also consists of two ureters, urinary bladder and a urethra (figure 1). Other parts may also play a role in the removal of metabolic waste such as the liver, skin and lungs, and the structures within these (e.g. sweat glands and alveoli).
The kidneys are bean shaped organs that consist of very thin walled capillaries and large numbers of filtration units called nephrons. They are located both sides of the backbone and are at the same level as the stomach. Each kidney has an inner concave side which is the location of a depression where the renal artery enters and the renal vein and ureters exit the kidneys. In a general term, the kidneys are a filter that removes certain substances from the circulatory system as well as large quantities of water. Some of these substances are reabsorbed into the blood whilst others are transferred to different areas of the body where they will be excreted.
Nitrogenous waste is part of th...

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