Receptors in Pharmacology

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will explain the fundamental nature of how drugs exert their effects on the body, if the same drug can have different effects on the body, and why side effects occur in the context of this all.

How Drugs Work

Have you ever wondered how drugs work in the body?

Drugs, in the context of this lesson, are chemical substances used in medicine that are intended to exert a particular biological effect on the body.

How is it that this thing, a molecule of a drug you can't even see with your eyes, is able to force your body's tissue and organs to follow commands they otherwise wouldn't? It almost seems miraculous, but at its fundamental level, it's actually pretty straightforward. Soon you'll learn the basic but important nature of how drugs exert their effects on a body.

Drugs and Receptors

As a person types, their fingers press a different key on the laptop's keyboard. The depression of a key forces a signal to relay a message to the computer. Once that signal is appropriately relayed and interpreted, an output, a specific letter, appears on the screen.

The tissue and organs in your body are riddled with receptors, biological molecules, typically proteins, where drugs bind in order to initiate a chain of reactions that end up causing a drug's effects.

This image shows a receptor spanning a grey cellular membrane. Not all receptors look like this but this is a good example of a common type.
receptor

The receptors are just like the keys on a keyboard, and the fingers are like drug molecules plunging into them. When a drug molecule binds to a receptor, the receptor is forced to relay a message into the cell it is attached to. The message is a signal to a tissue or organ cell to perform a certain action, one that results in an output of a specific nature.

For example, there is a molecule found naturally in the body, one that can also be administered synthetically as a drug, called epinephrine. When epinephrine binds its specific receptor on the blood vessels running through the skin, it causes the blood vessels to constrict. But epinephrine has different actions, depending on where it binds. For instance, if it binds to the receptors of the heart, it will cause the heart to beat faster.

So, it's the same drug, the same molecule, but its outputs are different depending on which part of the body it binds to and which receptors it activates. That's just like saying if an index finger were to press on the letter 'R' on the keyboard, an 'R' would appear on screen. But if the index finger were to move to a different location on the keyboard and press the spacebar, a completely different reaction or output occurs, one that results in a space instead of a letter.

Actually, this helps to partially explain side effects, or unintended or unwanted effects of a drug. Some side effects occur because many organs and tissue share the same receptors. We may want a drug to exert its beneficial, therapeutic effects, in one organ but because another organ has the same receptors, it will inevitably react to the drug as well.

And given what we just learned about the different reactions a drug can create in different organs, you can only imagine that some of the effects a drug causes in organs we're not intending to treat may be quite undesirable.

Different Sites of Action

Maybe you're wondering: can every drug molecule do the same thing epinephrine does? Well, of course not. Otherwise, every drug you take will cause your heart to beat faster, which we know doesn't occur.

So what gives? Why doesn't every different kind of drug molecule cause the same reaction in the body?

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