Physiological tolerance

From Wikipedia, the free encyclopedia

In physiology, tolerance occurs when an organism builds up a resistance to the effects of a substance after repeated exposure. This can occur with environmental substances such as salt or pesticides. It is also commonly encountered in pharmacology (see drug tolerance), when a subject's reaction to a drug (such as a painkiller or intoxicant) decreases so that larger doses are required to achieve the same effect.

There are two major mechanisms for tolerance:

• Dispositional tolerance: occurs because of a decreased quantity of the substance reaching the site it affects.
• Reduced responsiveness: the response to the substance is decreased by cellular mechanisms.^[1]

[edit] References

[edit] See also

• Desensitization
• Drug tolerance
• Tachyphylaxis
• Mithridatization