Definition: Regulation of the osmotic pressure of an organism's body fluids to balance the concentration of water and solute or salt in the organism's body regardless of environmental conditions; it keeps the fluids from becoming too diluted or too concentrated.

-Osmosis is the diffusion of water through semi-permeable membrane. It is essential to balance the concentration of water and solute in the body. There are types of solutions that can occur in blood cell based on solute concentration: isotonic, hypotonic, and hypertonic. Hypertonic means there is higher solute(salt) concentration on the outside of the cell than on the inside of the cell and therefore the cell shrinks and becomes shriveled. In contrast, hypotonic means there is lower solute concentration, so the cell lyse or blows up. Finally, isotonic means normal or balanced, the solute concentration on the outside of the cell is similar to the inside of the cell. So, it is essential for the blood cells to balanced and to maintain the concentration in the body osmoregulation is being used.

-An organism that can regulate its body osmoalrity, concentration of solute to water, at a higher or lower concentration than the concentration of solutes around the environment is called osmoregulator. For example, a fish that lives in fresh water does not drink water to regulate osmolarity in its body because the fresh water contains lower concentration of solute than the fish contains. On the other hand, fish that lives in ocean, for example, drinks the seawater to maintain the homeostasis of its water content, since the sea water has higher concentration of solute.

                                    OCEAN                                                                                   FRESH WATER

-There are some exceptions for marine animals, meaning that some organisms do not require osmoregulation for their living and they are called, osmoconformers. Osmoconformers are marine organisms that maintain the internal osmolarity equal to their surrounding environment. An advantage of being an osmoconformer is that the organism does not have to regulate the osmolarity.

-In humans the kidney plays a huge part in the osmoregulation of the body’s internal environment. Regulation of water in the human body is carried out through the excretion of waste urine from the body. Hormones including: antidiuretic hormone, aldosterone and angiotensin II are used in the body to help to increase the permeability of thecollecting ducts that allows the water through in the kidney. This allows diffusing to occur easily, it also allows the kidney to be able to reabsorb water and prevent it from being excreted. Humans are also able to regulate by controlling the total amount of water that is passed out of the body through urine waste or sweat.