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How do ligands work?

William B. Salt II., MD
Gastroenterology
Chemical messenger molecules or ligands ("keys") float in your bloodstream and in the fluid that surrounds your cells. The cells contain receptor sites ("locks"). Receptor sites ignore all but the particular type of neuropeptide to which they are attracted. Let's consider just one type of chemical ligand called a neuropeptide. Imagine that a neuropeptide key enters the keyhole of a receptor site. As the key turns inside the lock, the message encoded in the neuropeptide is transmitted to the receptor site, which then opens the cell door to transmit information from the outside surface of the cell to its interior.

Messenger keys function in two different ways, as either agonists or antagonists. When functioning as an agonist, the neuropeptide key fits into the receptor site lock, turns appropriately and opens the door. Opening the door stimulates the specific action for which the given receptor site is responsible (pain relief, water conservation, sexual arousal, etc.). When functioning as an antagonist, the neuropeptide fits into the keyhole but won't open the lock. In this case, no message is transmitted and the designated action of the receptor site is blocked.
Irritable Bowel Syndrome & the MindBodySpirit Connection: 7 Steps for Living a Healthy Life with a Functional Bowel Disorder, Crohn's Disease, or Colitis (Mind-Body-Spirit Connection Series.)

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Irritable Bowel Syndrome & the MindBodySpirit Connection: 7 Steps for Living a Healthy Life with a Functional Bowel Disorder, Crohn's Disease, or Colitis (Mind-Body-Spirit Connection Series.)

Fast Facts on IBS: One in five people suffers from the frustrating symptoms of Irritable Bowel Syndrome (IBS). There is no simple answer--no pill, potion, or quick fix--that will cure IBS. But help...

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