Pharmacodynamics: How Drugs Affect the Body

Lecture 1: Introduction to Pharmacology: Pharmacodynamics

• Pharmacology definition: The study of the interaction between a chemical substance and a living system (pharmakon = drug or poison, ologos = science).
• Drug definition: A chemical substance, natural or synthetic, affecting a biological system (human, animal, insect, or cell).
• Pharmacology subdivisions:
  • Pharmacodynamics: Describes the effect of a drug on the body and the mechanism of its action (receptor binding or interactions).
  • Pharmacokinetics: Describes the effect of the body on the drug, determining how quickly and to what extent it appears at the target site (absorption, distribution, metabolism, elimination).
  • Pharmacotherapeutics: The clinical use and indications for a drug.
  • Toxicology: The study of the toxic effects of drugs or toxins.
• Cell signaling: How cells communicate, either electrically (neural transmission) or chemically (ligands, e.g., hormones, neurotransmitters).
  • Ligand: A small molecule interacting with a specific receptor site.
  • Types of cell signaling (based on distance):
    • Autocrine: Signal from a cell to itself.
    • Paracrine: Signal from a cell to a neighboring cell
    • Endocrine: Signal from a cell to a distant cell.
• Three types of cell surface receptors:
  • Ligand-gated ion channels: Ligand binding opens or closes a channel, altering ion flow, leading to rapid response (e.g., milliseconds).
  • G protein-coupled receptors (GPCRs): Ligand binding activates a G protein, which in turn activates another enzyme, leading to a cascade of effects with a response time of seconds to minutes.
  • Enzyme-linked receptors: Ligand binding activates an intracellular enzyme, leading to a longer response lasting minutes or hours.
• Intracellular receptors (DNA-linked receptors): Lipid-soluble ligands cross the membrane and bind to intracellular receptors which regulate gene expression, resulting in a delayed response (hours or days).
• Drug Affinity: The ability of a drug to bind to a specific receptor (determined by the strength of bonds and their number).
• Drug Efficacy (Intrinsic Activity): The ability of a drug to produce a biological effect, related to the number of drug-receptor complexes formed, with a maximal response reached when all receptors are occupied.
• Non-receptor-mediated effects: Some drugs exert effects via interactions not involving receptors (e.g., antacids, osmotic diuretics).

Explore pharmacodynamics, a pharmacology subdivision describing the effects of drugs on the body and their mechanisms of action. It includes receptor binding and cell signaling. Learn how drugs interact with biological systems.