Excretory system

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The excretory system is a biological system that removes excess, unnecessary or dangerous materials from an organism. It is responsible for the elimination of oxygen waste products of metabolism as well as other nitrogeneous materials. Since the normal operation of most biological systems creates waste, the excretory system is not necessarily distinct from other systems. Instead, it often represents the various excretory processes of several different systems.

Excretory functions

Every organism, from the smallest protist to the largest mammal, must rid itself of the potentially harmful by-products of its own vital activities. This process in living things is called elimination, which may be considered to encompass all of the various mechanisms and processes by which life forms dispose of or throw off waste products, toxic substances, and dead portions of the organism.

Egestion is the act of excreting unusable or undigested material from a cell (as opposed to metabolized waste), as in the case of single-celled organisms, or from the digestive tract of multi-cellular organisms.

As defined above, elimination broadly defines the mechanisms of waste disposal by living systems at all levels of complexity. The term may be used interchangeably with excretion, though not all elimination necessarily takes place in the excretory system.

Component organs

Skin

The skin is another part of the excretory system: it eliminates sweat that helps cool the body and regulate the concentration of salt. The salt helps evaporate the water, cooling off the skin.

Liver

The liver is an organ of the digestive system. It also helps in excreting wastes from the body in a variety of processes. Laboratory analysis reveals a high concentration of a small organelle called a peroxisome, responsible for breakdown of several toxic substances. It also takes in nitrogenous wastes and converts them to urea to reduce their toxicity.

The liver absorbs drugs and other poisonous substances in the blood and changes their chemical structure to make them less toxic and easier to digest. This waste product is called bile and is excreted to the digestive tract, facilitating digestion of fats while also disposing of waste.

Kidneys

The key organs in the excretory system of vertebrates. (See protonephridia system for Platyhelminthes, metanephridia for Annelida, or the Malpighian tubes for insects and terrestrial arthropods.) The kidneys are placed on either side of the spinal column near the lower back. They are primarily responsible for filtering blood by removing nitrogenous wastes, though they also regulate blood pressure in a process called osmoregulation and also assist with the production of red blood cells.

Secretion

The separation, elaboration, and elimination of certain products arising from cellular functions in multi-cellular organisms is called secretion. Though these substances may be a waste product of the cell producing them, they are frequently useful to other cells of the organism. Examples of secretions are the digestive enzymes produced by intestinal and pancreatic tissue cells of vertebrate animals, the hormones synthesized by specialized glandular cells of plants and animals, and sweat secreted by glandular cells in the skins of some humans. Secretion implies that the chemical compounds being secreted were synthesized by specialized cells and that they are of functional value to the cell. The disposal of common waste products should not, therefore, be considered to be of a secretory nature.

See also

• Major systems of the human body

References

^[1] CLC Biology

1. ^ http://biology.clc.uc.edu/Courses/bio105/kidney.htm