Rigor científico de la Investigación-Acción

In order to understand how these two disciplines effect the field of forensic science there must be an understanding of the terms

associated with each.

Pharmacology is the study of drugs, of the body's reaction to drugs, the sources of drugs, their nature, and their properties.

A drug is an exogenous (introduced to the body from the outside) chemical that is capable of modifying physiological function within an organism.

A chemical can be any compound. A compound is two or more elements are bonded together in a fixed mass ratio that can be split into simpler substances. Almost anything can be considered a drug if it is used to change the physiological behavior of an organism.

Toxicology is the study of poisons. Specifically, it is the study of the adverse effects of chemicals on living organisms.

A poison is referred to in general terms as a chemical that can cause adverse effects, but that is as simplistic definition because almost all drugs can become poisons when taken in the wrong dose.

A dose is the optimal amount of drug needed to illicit the desired effect on an organism where adverse effects are less than desired effects. It is typically based on purity of the chemical and age, body weight, and tolerance of the individual to the drug being used.

Forensic toxicology is a combination of analytical chemistry and basic toxicology and is primarily concerned with the medicolegal aspects of harmful effects of chemicals on humans and animals. Forensic

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toxicology uses many different aspects of the pharmacology, chemistry, biochemistry, and physiology fields.

Toxicology is concerned with 4 basic physiological mechanisms, or phases, in the body:

• Absorption

• Distribution

• Metabolism

• Excretion

Absorption – absorption differs according to how the drug or poison was administered. Given orally, or through the mouth, a drug will often lose some or much of its potency because of first pass metabolism.

First pass metabolism simply means that prior to going into the blood stream to be carried to the target organ; it first passes through the liver. The liver is like one big filter and will often significantly

“deactivate” drugs with certain properties. If a drug or poison is administered through an IV directly into the blood stream the absorption is almost immediate, as are the effects.

Distribution – in this phase the toxicant (drug or poison) exits the blood and enters the space between the cells or goes directly into the cells. This is the phase in which the toxicant will reach the site of action called the target organ. Many things will affect the rate of distribution such as membrane transport, but these molecular mechanisms are beyond the scope of this course.

Metabolism – is the process of changing the drug as it passes through the body. This is done by means of enzymes. Enzymes are protein molecules that catalyze biochemical reactions. In simple terms, they are small chemicals your body makes in order to make chemical

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reactions speed up. These enzyme reactions will either result in a more or less toxic drug. Most of the time it is a less toxic version of the initial drug or poison, but there are exceptions to every rule.

Excretion – is the removal of the drug or poison from the blood and into pathways that will eliminate it from the body. The major pathway for excretion is through filtration in the kidney and then elimination through the urine, but some chemicals will be excreted through feces, sweat, breast milk, and exhalation. The manner of excretion is

dependent on the physical and chemical properties of the drug as it is metabolized.

In addition, in forensic toxicology there is also an emphasis on analytical chemistry, which is the laboratory methods used to determine the identity and exact amount of unknown substances

suspected in a criminal investigation. There will be another unit later in the course dedicated to analytical methods.

These unknown substances can come from the crime scene, a living suspect or victim, or a deceased suspect or victim.

The dose of poisoning or “overdose” is also critical information as are any drug interactions that may have contributed to the death of the victim. That is why separation and concentration of the drugs or drugs using analytical methods is so important.

Like all the other aspects of forensic science, all biological specimens must be maintained within the chain of custody in order to be valid in a courtroom.

The following chart illustrates how absorption, distribution, metabolism, and elimination occurs in the body:

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The chart above states this:

At any stage in the absorption, distribution, metabolism, and

elimination phases, the drug has at least two possible pathways. The pathway of toxicity and the pathway of detoxicity. These pathways are not an either/or choice. That means that some of the time the metabolism of the drug might make it less toxic and some of the time

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it might enhance its toxicity. It can, effectively, jump the arrow down the middle and participate in all any metabolic pathway according to its physical properties.

The column on the left is the pathway of toxicity. Along the way the molecule changes as it is metabolized, but when it reaches the target organ at the end of the pathway, it is still a toxic molecule.

The pathway on the right is the pathway of detoxification. The molecule changes as it is metabolized, but by the time it reaches the target molecule it is not toxic.

The molecular mechanisms that allow each of the pathways to function are too complicated to go into in this course, but if you are interested in this type of science you should consider taking biochemistry.

Pharmacology deals with the pathway on the right. The purpose of medicinal drugs is to provide physiological changes in the body by

having the drug reach the target organ without causing toxicity to the patient.

Regardless of how diligent drug research and production is, all drugs have risk and side effects.

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Exercises for Unit Fourteen Vocabulary

Define the Following:

Pharmacology

Drug

Chemical

Compound

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Toxicology

Poison

Dose

Forensic toxicology

Absorption

.

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Distribution

Metabolism

Excretion

Toxicity

Detoxification

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Label the chart:

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Explain the difference between the right and left sides of the chart.

Go to:

http://www.biocreations.com/animations/Nov1demo.swf

This website has two animations for you to look at. The one on the left is how a drug behaves when it is injected directly into the blood

stream, or an IV. The animation on the right shows how a drug behaves when it is taken by mouth, or orally.

Why are these two pathways to absorption, distribution, metabolism, and excretion so different?

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