Terms about osmosis and homeostasis

Term	Definition
Homeostasis	keeping variables like the body's water, temperature, etc. stable
Receptor or sensor	Part of the body that measures the variable and notices a change in the internal situation
Set Point	The normal range for the variable.
Control (integrating) center	This is the part of the body that knows what level the variable should be at (the SET POINT). The sensor tells the integrating center what the variable's level is, and the integrating center compares that level to the set point and tells the effector what it should do to bring the variable back to set point.
Effector	Part of the body that reacts to correct the change in the variable
Negative feedback	When the response to a stimulus caused by a change in the body corrects that change and makes the stimulus go away
Positive feedback	When the response to a stimulus caused by a change in the body makes that change greater and makes the stimulus stronger
Osmosis	Movement of water across a semipermeable membrane
Solutes	Molecules dissolved in a solvent (water)
Osmolarity or osmotic pressure	The total concentration of all the solutes dissolved in a solution
Isosmolar	Two solutions that have the same osmolarity
Hyperosmolar	A solution that has more solutes
Hypoosmolar	A solution that has fewer solutes
Tonicity	Refers to whether a solution will cause water to diffuse into or out of living cells
Isotonic	A solution with the same tonicity as cells - it won't make them swell or shrink
Hypotonic	A solution with a low concentration of molecules that won't enter cells. There are more solutes in the cells than in this solution, so water will enter the cells and they will swell
Hypertonic	A solution with a high concentration of solute molecules that cannot enter the cells. There are more solutes in this solution than in the cells, so water will leave the cells and they will shrink