Osmoregulation

Osmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain the homeostasis of the organism's water content; that is, it keeps the organism's fluids from becoming too diluted 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 tends to move into it. Pressure must be exerted on the hypertonic side of a selectively permeable membrane to prevent diffusion of water by osmosis from the side containing pure water.

Osmotic concentration refers to the measure of solute concentration, defined as the number of osmoles of solute per litre of solution. These particles must be osmotically active for the process of osmosis to take place.

Keeping this regulation precise is critical in maintaining life in a cell. The water potential of the blood in the body has to be kept relatively constant because drastic changes in the water potential of the blood can result in serious problems.

5. Using the 5 components, describe how the body responds to an increase in osmotic concentration (identify clearly the detector, processing centre and effectors).

Stimulus: Water potential of blood increases (e.g. large intake of water)
-> An increase in osmotic pressure or decrease in water concentration in plasma
Receptor: Hypothalamus stimulated
-> Osmoreceptors in hypothalamus
Modulator: Hypothalamus
-> Sends message for release of ADH from posterior lobe of pituitary
-> Nerve impulses from drinking centre of hypothalamus
Corrective mechanism/effector:
Less ADH released by pituitary gland into the bloodstream
Less ADH transported to the kidneys
Cells in the walls of the collecting ducts become less permeable to water
Less water reabsorbed into the bloodstream
More water excreted
Urine is more diluted
More urine produced
Response: Water potential of blood decreases
-> Increased reabsorption