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PSYC62H3 (280)

Chapter Three

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University of Toronto Scarborough
Suzanne Erb

Chapter Three: Basic Principles of Pharmacology The psychological effects of a drug at any particular time depend on many factors, including the individuals set and setting, the particular way the drug changes activities in the CNS, the route of administration, the amount administered, the frequency, etc. Drug originally referred to any substance used in chemistry or medicine; gradually restricted to any agent used in medicine or any ingredient in medicine; today used as a synonym for a narcotic agent or an illicit substance In general, a drug is a chemical that affects one or more biological processes. However, not all chemicals that affect biological processes are considered drugs. Substances that are commonly used for nutritional purposes, such as salt, water, proteins, fats, carbohydrates, vitamins, and minerals arent generally considered drugs, because theyre necessary for carrying out the normal biological functions of the body. However, certain vitamins and minerals that might be found in our diet, if isolated and used in certain quantities, might also be thought of as drugs 1994 Dietary Supplement Health and Education Act dietary supplement products may enter the market untested, and the FDA cant restrict the use of such supplements unless substantial harm has been proved o St johns wort very popular supplement herbal antidepressant documented evidence for effectiveness; considerable evidence for its interacting with a variety of medicines in adverse ways These properties indicate that pharmacologically, one or more ingredients in St. Johns wort would be considered a drug, but until theres legislation to change its status, the FDA cant regulate it as a drug Nicotine in the mid 1990s, governmental hearings were held to determine whether scientific evidence supported assumptions that nicotine is a drug. o If the FDA could prove that tobacco companies intended for cigarettes to provide nicotine to satisfy an addiction, the FDA would have the right to regulate cigarettes under the Federal Food, Drug, and Cosmetic Act, which considers a product to be a drug if the vendor intends it to be one o However, the US Supreme Court eventually ruled against allowing the FDA to regulate tobacco products. This decision was made on the basis of political and legal considerations and not on the basis of pharmacological principles Similar issue alcohol prefer not to view it as a drug, but its not used for nutritional value, so it should be considered a drug in that it affects the normal biological activities of the body Chemicals originating or produced within an organism that are used to carry out the normal biological functions in the body arent usually thought of as drugs referred to as endogenous substances Weve isolated a variety of substances found to be important in the functions of the body, have extracted or synthesized them, and have administered them in purified form to reverse neurological deficits LDopa From a pharmacological view, it seems most appropriate to define a drug as a non-food, nonmechanical substance (usually a chemical substance) that exerts an effect upon a living system Basic Chemical Principles Related to Psychopharmacology The water molecule H2O takes on a kind of V-shape, and theres an uneven distribution of charge: though electrically neutral overall, the oxygen end has a partial negative charge, while the two hydrogen ends have partial positive charges. Because of this, we say that the water molecule is polar Water molecules are attracted to each other very powerfully. The partial positive charge of the oxygen end of one molecule is attracted to the partial negative charge of the hydrogen end of another by a type of bond known as a hydrogen bond. This bonding results in the fluid characteristics of water; water tends to form beads or drops, in which the complex strings of water molecules are bound together with mutual attraction. Water is an excellent solvent for other substances that are polar or ionic Table salt when immersed in water, the NaCl crystals dissociate into Na+ and Cl- ions that easily dissolve in the water medium Organic chemists view on the chemistry of life a large component of living systems is in the aqueous phase (ie. Water based). Hydrophilic molecules dissolve easily in the aqueous phase. However, theyre also lipophobic. In chemistry, organic refers to the chemistry of carbon-based substances In living systems, the major constituents of the organic phase are hydrocarbons o Fats or lipids high degree of hydrocarbon content Eg. Cholesterol Aqueous and organic phases dont mix well Adding salt to chicken soup most of the Na+ and Cl- ions would dissolve in the aqueous phase (water) and few would dissolve in the fat Gasoline very high hydrocarbon content; doesnt mix well with water Phospholipids are a type of diglyceride; they have a polar head and two fatty acid hydrocarbon tails The polar head, which has ionic charges and polar components, is attracted to water, while the hydrocarbon tails are repelled by water, and attracted to each other as well as other hydrocarbon chains Nerve cell membranes are composed of a phospholipid bilayer o The polar heads point inward and outward toward the largely aqueous environments inside and outside the cell, while the fatty acid tails from each layer point toward the center of the membrane o This lipid bilayer provides a barrier to the movement of any polar and charged substances Any drug that is highly lipid-soluble would easily be stored in adipose tissue The cell membrane made up mostly of a lipid bilayer presents a barrier to the diffusion of any substance too water-soluble (lipophobic), and not transported by proteins o The stomach and intestines are lined with cells, and if a pill is introduced into the body, this would be the first barrier to entry into systemic circulation o BBB made up of tight junctions between the endothelial cells that compose the outer lining of the blood vessels; can provide a significant resistance to the entry of drugs and other substances into the brain, and subtle alterations in the chemical structure of drugs can yield substantial differences in passage across the BBB Ethanol relatively soluble in both water and lipid; one end of the molecule is a hydrocarbon, while the other end has oxygen and hydrogen, and interacts easily with water o Passes easily
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