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Osmoregulation
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<p>Osmoregulation is the active regulation of the <a href="/facts/Osmotic_pressure/6oWKTsXV">osmotic pressure</a> of an <a href="/facts/Organism/j8JkL09u">organism</a>'s <a href="/facts/Body_fluid/RkAXIBVN">body fluids</a>, detected by <a href="/facts/Osmoreceptor/MJKzV6kn">osmoreceptors</a>, to maintain the <a href="/facts/Homeostasis/rloTGAHa">homeostasis</a> of the organism's <a href="/facts/Water/0lkXnJPK">water</a> content; that is, it maintains the <a href="/facts/Fluid_balance/sKmwSJ8a">fluid balance</a> and the <a href="/facts/Concentration/wqBmz5od">concentration</a> of <a href="/facts/Electrolyte/4YE8bIVa">electrolytes</a> (<a href="/facts/Salt_(chemistry)/lsSKwGpn">salts</a> in <a href="/facts/Solution_(chemistry)/MGchhMQV">solution</a> which in this case is represented by body fluid) to keep the body fluids from becoming too diluted or concentrated. Osmotic pressure is a measure of the tendency of water to move into one <a href="/facts/Solution_(chemistry)/MGchhMQV">solution</a> from another by <a href="/facts/Osmosis/vYPfyX76">osmosis</a>. The higher the osmotic pressure of a solution, the more water tends to move into it. Pressure must be exerted on the <a href="/facts/Tonicity/ev5qcKQh">hypertonic</a> side of a selectively permeable <a href="/facts/Biological_membrane/ljBsfK4r">membrane</a> to prevent <a href="/facts/Diffusion/KbAxroBa">diffusion</a> of water by osmosis from the side containing pure water. </p><p>Although there may be hourly and daily variations in osmotic balance, an animal is generally in an osmotic steady state over the long term. Organisms in aquatic and terrestrial environments must maintain the right concentration of <a href="/facts/Solutes/MGchhMQV">solutes</a> and amount of water in their body fluids; this involves <a href="/facts/Excretion/mspsTfnv">excretion</a> (getting rid of <a href="/facts/Metabolic_waste/qGH5b3od">metabolic nitrogen wastes</a> and other substances such as <a href="/facts/Hormone/WFnBnINJ">hormones</a> that would be toxic if allowed to accumulate in the <a href="/facts/Blood/03zEulkj">blood</a>) through organs such as the <a href="/facts/Skin/4havlLzG">skin</a> and the <a href="/facts/Kidneys/HBspPrv9">kidneys</a>. </p>