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Psychology 2020A/B Study Guide - Midterm Guide: Alcohol Dehydrogenase, Alcohol Tolerance, Acetaldehyde Dehydrogenase

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Riley Hinson
Study Guide

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Psychology 2020
A drug is a chemical compound that may produce psychological, behavioural and
physiological effects.
Psychoactive effects refer to alteration in cognitive, behavioural and motor processes eg
euphoria, distortions of time perception, hallucinations or increased libido.
Drugs are distributed throughout the body via the circulatory system
PROCESS: Administration, absorption, distribution, metabolism ad elimination are known
collectively as pharmacokinetics.
Processes involved in the interaction of the drug with receptors at the site of action are
known as pharmacodynamics.
Cytochrome P-450 is a term used for a very large group of enzymes, found primarily in the
endoplasmic reticulum of liver cells, that are involved in the metabolism of most drugs.
Injection: Absorption is more rapid following intraperitoneal(stomach) administration than
following intramuscular (muscle), which is more rapid than following subcutaneous (just
below skin/ into fatty layer).
Mainling in s the term used for intravenous injections in the drug subculture.
Skin popping is the term often used to refer to subcutaneous injections of illicit drugs
Drug Distribution:
Drugs that are guven by injection or via pulmonary route enter the circulation diffusinf
through pores in capillary walls.
Drugs taken orally must be lipid soluble to be absorbed from the digestive system since
there are no pores in the lining of the stomach or intestines.
Factors which affect entry of a drug into circulation:
1) Ionization most drugs are either weak acids or weak bases. Drugs that are weak acids
readily ionize in alkaline environments and become less ionized in acidic environments.
Reverse is true for week bases. Ionized molecules are not readily absorbed, therefore
percentage of nonionized molecules determines the rate of absorption. Ionized particles
penetrate cell membranes poorly compared to unionized particles.
2) Lipid solubility lipid soluble compounds penetrate cell membranes more readily than non
lipid soluble compounds more compounds than non-lipid soluble compounds. Compounds
that are lipid soluble are also usually unionized.
The brain is protected by the blood brain barrier. It restricts the permeability characteristics
of brain capillaries, by reducing the diffusion of water soluable or ionized molecules, but
does not impede lipid soluable or un-ionized molecules. The concept arose from the work of
Paul Ehrlich in 1882.
3) Receptor Binding Drigs exert their effects by binding with receptors at relevant target
tissue. A bind forms between charged groups in the receptor molecule and oppositely
charged groups on the drug.
An agonist is a drug that mimics the effect of a neurotransmitter. This may occur because
the agonist bonds to receptors, blocks reuptake or inhibits metabolic breakdown.

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Antagonists are compounds which reduce the effects of a receptor agonist by biding to
active receptors but producing no pharmacological action.
Drug Response Curve:
Drug dosages are usually expressed as milligrams (mg), or if given on weight basis, mg/kg.
The dose-response curve (DRC) I the most commonly used graphical presentation mode of
drug effects.
The ED50 is the dose of a drug that is effective in producing a response in 50% of the
experimental subjects. (allows you to compare potency)
LD50 refers to the dose which kills 50% of the subjects.
Therapeutic index for a given drug effect is given by the ratio LD50/ ED50. The higher the
ratio, the greater the difference btw the LD50 and ED50 and the less likelt chance that a
lethal or other non- lethal effect will occure.
Margin of safety is a more conservative measure of a drugs safety and is the ratio of the
Phenomena associated with chronic drug administration, can be depicted by the DRC.
Tolerance is represented by a shift to the right in the DRC. Sensitisation is depicted by a shift
to the left in the DRC.
Termination of Drug Action:
Drugs are eliminated by skin, lungs and kidneys.
The liver is important organ in this process because it is the major site of enzymatic
breakdown of drugs.
Cytochromme P450 enzyme family is the primary agent involved in drug metabolism.
Individuals differ in the level of CYP enzyme activity, which in turn affects how rapidly drugs
are metabolized.
Many drugs (eg: alcohol) induce the activity of CYP enzymes, and this results in a more rapid
metabolism of not only the original drug, but other drugs.

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Most often, enzymatic breakdown results in inactive molecules that are subsequently
excreted via urine.
Enzymatic breakdown most often results in metabolites thate are less soluble, are lagrer,
carry a greater charge, and are inactive or less active than the original compound. This is
important because these molecules are less rapidly reabsorbed from the kidney to the
Weak acids are excreted more readily when tubular urine is alkaline because the weak acids
become ore ionized and are “trapped” in tubular urine. Conversely weak acids are excreted
more if urine is acidic.
The relation between reabsorption and pH is frequently used in treatment of drug toxicity.
Elimination half-life time needed for half of a drug dose to be eliminated from the body
helps understand drug effects and is important when considering which drug to use for
certain medical conditions.
It takes about 6 half-lives for most of a drug to be eliminated and for a person to be
considered drug free.
Pot had a long half life hence naturally weens the body as it take a long time to leave.
“Steady State Concentration”- relatively steady blood concentration is required to maintain
effects of the drug.
Neuron and Neurotransmission
Drugs exert their actions by affecting neurotransmission.
The Neuron is the functional unit of the nervous system.
An action potential arriving at an axon terminal can cause the release from the
presynaptic element of substance known as neurotransmitters.
Neurotransmitter release: neurotransmitter substances are stored in synaptic vesicles in
the axon terminal the presynaptic element. The arriving action potential causes these
vesicles to attach to the presynaptic membrane and open exuding the stored
neurotransmitter. The exuded neurotransmitter crosses the synaptic cleft where it binds
to receptor elements (transmembrane proteins) on the postsynaptic membrane.
Neurotransmitters are basic components of CNS functioning. Most drugs exert their
action by affecting the synthesis, release or reuptake of neurotransmitters.
General model of the synthesis and breakdown of neurotransmitter substance:
1) Precursor substances (amino acids from diet), are the basic building blocks of
2) Synthesizing agents are needed to build neurotransmitters from the precursor
3) Once synthesized the neurotransmitter must be transported to the presynaptic
terminal and stored
4) The stored, or newly synthesized neurotransmitter is released.
5) Released neurotransmitters bind to postsynaptic receptors
6) The neurotransmitter becomes unbound, at which point it can bind again to the
receptor to produce additional action, attach to transporter proteins and be taken
back up (reuptake) into the presynaptic element to be used again, or attach to
proteins that breakdown the neurotransmitter. UP TO PAGE 9
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