Excretory system

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The excretory system is a passive biological system that removes excess, unnecessary or dangerous materials from an organism, so as to help maintain homeostasis within the organism and prevent damage to the body. It is responsible for the elimination of the waste products of metabolism as well as other liquid and gaseous wastes. As most healthy functioning organs produce metabolic and other wastes, the entire organism depends on the function of the system; however, only the organs specifically for the excretion process are considered a part of the excretory system.

As it involves several functions that are only superficially related, it is not usually used in more formal classifications of anatomy or function.


Excretory functions

Removes metabolic and liquid toxin wastes as well as excess water from the organism.

Within each kidney are an estimated one million microscopic nephrons. Filtering of the blood takes place within these areas. Each nephron contains a cluster of capillaries called a glomerulus. A cup-shaped sac called a bowmans capsule surrounds each glomerolus. The blood that flows through the glomerulus is under great pressure. This causes glomerulus, water, glucose and urea to enter the bowmans capsule. White blood cells, red blood cells and proteins remains in the blood. As the blood continues through the blood vessels, it winds around the renal tubule. During this time, reabsorption occurs. Glucose and chemicals , such as potassium ,sodium, hydrogen magnesium and calcium are reabsorbed into the blood. Almost all the water removed during filteration returns to the blood during the reabsorption phase. The kidneys control the amount of liquid in our bodies. Now only wastes are in the nephron. These wastes are called urine and include urea, water and inorganic salts. The cleansed blood goes into veins that carry the blood from the kidneys and back to the heart.

Component organs


Excretion by definition is passive and deals with metabolic wastes as filtered by the kidneys. Though the sweat may contain a trace amount of metabolic wastes, sweating is an active process of secretion not excretion, specifically for temperature control and pheromone release. Therefore, its role as a part of the excretory system is minimal at best. Specifically, the skin secretes a fluid waste called sweat.


The lungs and gills of organisms constantly secrete gaseous wastes from the bloodstream as a regular part of respiration.

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