Excretion

Definitions

Action by which waste of the organization is rejected with-outside.

In a strict sense

In animal physiology, the researchers noticed that the majority of the cells, of fabrics have need to live to be in a medium whose hydrous conditions and the ionic conditions are controlled. For example the cells of the Homme are in a medium whose osmolarity is of 300 mosmol/L. (Alligator 278 mosmol/L, Duck 300 mosmol/L, Rana esculenta 210 mosmol/L, Locust 104 mosmol/L, the Lobster 974 mosmol/L, Aurélia 1092 mosmol/L, Astéraia 1012 mosmol/L.) The excretion allows maintains it Osmolarité interior medium of the animal in values which guarantees its homeostasis.

Associated definitions

But the excretion also includes in the common direction the elimination of part of waste of the metabolism and in particular that of the proteinic metabolism with the elimination of the Urée.

One also uses the verb to excrete to qualify the whole of process by which the product of a gland is rejected out of this one (by channels). This excretion can be gas, liquid or even solid.

Osmotic regulation

Principles of the osmotic regulation

When the organization controls their ionic homeostasis they can act on two factors:

concentration of ions
the volume of their interior liquid

This checks the relation n=c*v Or N corresponds to the osmolarity C with the ionic concentration and v with volume.

According to the medium in which he saw, an animal will absorb water if this one is at disposal in order to dilute and evacuate the electrolytes in excess, or to actively reject ions in the external medium without losing water.

Strategies of the aquatic animals

All the living beings do not live under the same conditions of mediums. For example a fish of sea water will have a medium of life containing much more Sodium chloride that a fresh water fish. The sea water fish will thus have more difficulty in lose ions whereas the fresh water fish has more difficulty in keep its ions. Some to be alive are known as osmoconforme because they adopt the osmotic pressure of the medium, if this one remains about constant. (For example sea water 1047 mosmol L^-1)

Others are called osmoregulators, i.e. it has a osmolarity different from that of their mediums of life.

Strategies of the terrestrial animals

For the terrestrial animals the strategy of regulation of the osmolarity is articulated primarily with the factor water. Indeed the only effective means of controlling its osmolarity consist in adapting its hydrous catches according to the needs. There exist also complementary strategies.

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