Osmoregulation

• Water is the universal solvent and is essential to life
• Solvent


  A substance in which a solute dissolves
• Metabolic reactions occur in a solution composed of mainly water - when water content is too high or low, metabolic reactions slow down because the reactant travel too slowly to their reaction sites
• Osmoregulation 


  The active regulation of an organism's water content

  • maintains the fluid balance (water gain and loss) and the concentration of electrolytes and other solutes that keep the fluids from becoming too diluted or too concentrated
  • if the supply of water doesn't replace what's lost, the relative concentrations of solutes and solvents in tissue fluids become difficult to regulate - physiological functions are then affected
• Methods of Water Gain and Loss in Animals

  • gain - drinking, food consumption
  • loss - sweating, panting, urination
• Detecting Changes in Water Level

  • changes in water level in the blood (stimulus) can be detected by osmoreceptors in the hypothalamus
  • hypothalamus detects changes, acts as a modulator, receives information, and coordinates a response
  • hypothalamus alters the kidney membrane permeability to alter the concentration of urine, allowing wastes in the form of solutes to be excreted while conserving water
  • water can move in and out of cells and organisms via osmosis
• Osmosis 


  The passive diffusion of water across a membrane in response to a concentration gradient caused by an imbalance of molecules
• Tonicity

  • hypotonic: when the surroundings have a lower solute concentration than the cell - cytolysis, swells/turgid
  • hypertonic: when the surroundings have a higher solute concentration than the cell - plasmolysis, shrivels/plasmolysed
  • isotonic: when the surroundings are of equal concentration to the cell, no movement of water
• Osmoconformer 


  An organism in which internal solute concentrations are the same as their environment

  • doesn't maintain homeostasis of water/salt
  • eg. crabs, starfish
• Osmoregulator 


  An organism that has adaptations to regulate their internal water and solute concentrations, despite changes in the environment

  • eg. bony fish, marine mammals