A drug may be described simply as a chemical substance that affects the activity of living processes. As a therapeutic agent, the drug serves to prevent, treat, or reverse an undesirable physiological or pathophysiological process. In general, the action of a drug results from an interaction of the drug molecule with a macromolecular structure associated with a cell, the consequence of which is a change in cellular function and, relatedly, in physiological function. In such a process, a drug may act to inhibit or mimic the actions of an endogenously produced chemical or to modify the response of cellular components to the actions of endogenously produced chemicals. Specific sites at which drugs act to produce an observable response include receptors (macromolecular sites at which chemicals interact to influence cellular function) and enzymes. A chemical is considered to be an agonist when it interacts with a receptor to produce a response, be it an increase or a decrease in cellular activity, whereas a chemical is considered to be an antagonist when it interacts with a receptor to block the response induced by an agonist. Accordingly, the observed effect of an antagonist relies on its capacity to inhibit the actions of other substances on cellular function.

The physiological actions of a drug are determined by: (1) the receptors or enzymes on which the drug acts, (2) the cells on which the receptors are located, and (3) the access of drug to cells on which the appropriate receptors are located. A cell may possess more than one receptor sensitive to the actions of a drug, although, in general, a drug exhibits concentration dependence in its selectivity for receptors, and, therefore, selection of appropriate doses of a drug is important in obtaining the desired therapeutic and physiological action. Nevertheless, the selectivity or specificity of many drugs and chemicals is sufficient to provide a basis upon which receptors may be described. However, it is important to recognize that receptors are not unique to specific cells. Consequently, an agonist or antagonist can influence the biological activity of all tissues comprising cells that express the appropriate receptor, provided it has equivalent and free access to the receptors.

Dealing With Asthma Naturally

Dealing With Asthma Naturally

Do You Suffer From ASTHMA Chronic asthma is a paralyzing, suffocating and socially isolating condition that can cause anxiety that can trigger even more attacks. Before you know it you are caught in a vicious cycle Put an end to the dependence on inhalers, buying expensive prescription drugs and avoidance of allergenic situations and animals. Get control of your life again and Deal With Asthma Naturally

Get My Free Ebook

Post a comment