It happens when receptors have been chronically exposed to an excessive amount of neurotransmitters, whether endogenous or in the form of drugs. ![]() Up regulation results in super-sensitized cells especially after repeated exposure to an antagonist drug or prolonged absence of the agonist.ĭown regulation involves decrease in the quantity of cellular component, such as RNA or protein, in response to an external stimulus. ![]() In this situation, the cells increase their production of cytochrome P 450 enzyme, which in turn increases their degradation of these molecules. An example of up regulation is the response of liver cells exposed to molecules like dioxin. Up regulation involves increase in the number of receptors due to external stimulation. Receptors are created, or expressed by the DNA of the cell, and they can be increased or up regulated when the signal is weak, or decreased/down regulated, when it is strong. The more receptors a cell has that are tuned to the message, the more the cell will respond to it. A cell’s ability to respond to a chemical message depends on the presence of receptors tuned to that message. When such signals bind to a receptor, they effectively direct the cell to do an activity, such as dividing, dying or allowing substances to be created, or to enter or exit the cell. This is a locally acting feedback mechanism.Īll living cells have the ability to receive the process signals which originate outside their membranes, which they do by means of receptors, usually found on a cell’s surface embedded in the cell membrane. Cells can increase (up regulate) or decrease (down regulate) the number of receptors to a given hormone or neurotransmitter to alter their sensitivity to different molecules.
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