Pharmacology

Pharmacodynamics is the study of how drugs have effects on the body. The most common mechanism is by the interaction of the drug with tissue receptors located either in cell membranes or in the intracellular fluid.

Receptors are typically glycoproteins located in cell membranes that specifically recognize and bind to ligands. These are smaller molecules (including drugs) that are capable of 'ligating' themselves to the receptor protein.

Ion channels are pore-forming protein complexes that facilitate the flow of ions across the hydrophobic core of cell membranes.

Enzymes are proteins which act as catalysts to facilitate the conversion of substrates into products.

Drugs used in the clinic can have targets other than the major families of receptors, enzymes and ion channels. Pharmacologically important examples include but are not limited to transporters (both as drug targets and for their ability to modify drug action), structural components of the cell such as tubulin, and DNA (and RNA).

Endogenous peptides and proteins include well characterized families of neuropeptide transmitters, neuropeptide modulators, hormones, and fragments of functional proteins, which are essential in many biological processes. The peptides exert potent biological actions in virtually all systems in the body (see figure for examples).

There is wide variation in the structure and function of the different types of endogenous molecules which act as signal transmitters, from tiny gasses such as nitric oxide and carbon monoxide (sometimes referred to collectively as gasotransmitters), through neurotransmitters to peptide hormones and growth factors.

Desensitisation and tachyphylaxis

When the relation between drug dose (X-axis) and drug response (Y-axis) is plotted on a linear scale, the resulting curve is usually hyperbolic. Clinical responses that might be plotted in this way include change in heart rate, blood pressure, gastric pH or blood glucose. Non-clinical (biochemical) responses can also be plotted in this way including enzyme activity, accumulation of an intracellular second messenger, membrane potential, secretion of a hormone, or contraction of a muscle.

Before drugs can be clinically effective, they must be absorbed. Absorption is the process of a drug moving from its site of delivery into the bloodstream. The chemical composition of a drug, as well as the environment into which a drug is placed, work together to determine the rate and extent of drug absorption.

Drug distribution is the process of delivering a drug from the bloodstream to the tissues of the body – especially the tissue(s) where its actions are needed.

The primary objective of drug metabolism is to facilitate a drug’s excretion by increasing its water solubility (hydrophilicity).

Excretion is the removal of drugs and their metabolites from the body.

Autonomic pharmacology is the study of how drugs interact with the autonomic nervous system. The autonomic nervous system plays an important role in the control of the internal organs including the heart, lungs, gastrointestinal tract and vasculature.

The parasympathetic nervous system (PNS or cholinergic system)

The sympathetic nervous (adrenergic) system

Immunopharmacology, as its name suggests, is the branch of pharmacology that applies to the immune system. In general immunopharmacology describes the manipulation of the immune system and immune responses by pharmacological modulators, for the benefit of the host. This is an immense, and continually expanding field.