Adaptations to control the water balance in organisms living in hypertonic, hypotonic, or terrestrial environments. osmoregulator An animal whose body fluids have a different osmolarity than the environment, and that must either discharge excess water if it lives in a hypotonic environment or take in water if it inhabits a hypertonic environment. osmosis(oz- moh-sis) [Gk. osmos, impulse, thrust] The diffusion of water across a selectively permeable membrane.
This is the process of regulating the amount of water that exists within the confines of an animal's body. It is important in two cases in the life of an amphibian. First, in tadpole life, the animal must keep water from entering the body in extremely great quantities. In this condition, water generally tries to move into the body because the cells have a lower concentration of water than does the external environment. In terrestrial life, the animals must attempt to conserve water since the tendency shifts to water moving from the body to the external environment.
Active regulation of osmotic pressure to maintain homeostasis of the body's water content. Regular pulsations have been noted in the excretory duct by light microscopy in C. elegans and other species under certain conditions that suggest the excretory system is required for osmoregulation ( Nelson and Riddle, 1984; Bird and Bird, 1991). These pulsations are only seen in dauer larvae in C. elegans, but have been noted to vary in rate according to the tonicity of the environment surrounding the whole animal, suggesting that outflow from the canal cell regulates the water balance of the whole animal. Some researchers believe that the amphid sheath cell may also play a role in osmoregulation in some nematode species ( Wright, 1980; Ashton and Schad, 1996).
Osmoregulation is the active regulation of the osmotic pressure of bodily fluids to maintain the homeostasis of the body's water content; that is it keeps the body's fluids from becoming too dilute or too concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. The higher the osmotic pressure of a solution the more water wants to go into the solution.