Health, disease and the development of medicines Study Guide

The human body possesses a multi-layered defence system to protect itself from pathogens, which are disease-causing microorganisms like bacteria, viruses, and fungi. This system includes both physical barriers and chemical defences. Physical barriers act as the first line of defence, preventing pathogens from entering the body. These include the skin, which forms a tough, waterproof outer layer, as well as mucus and cilia found in the respiratory and digestive tracts that trap and remove pathogens. Chemical defences work by destroying pathogens that manage to bypass the physical barriers. Examples include lysozymes, enzymes found in tears and saliva that break down bacterial cell walls, and hydrochloric acid in the stomach, which creates a highly acidic environment lethal to most ingested pathogens. Together, these mechanisms provide a comprehensive protective shield, crucial for maintaining health and preventing infection.

Antibiotics are a class of antimicrobial drugs specifically designed to combat bacterial infections. Their effectiveness stems from their ability to target and interfere with biological processes vital to bacteria, but which are either absent or sufficiently different in human cells. For instance, many antibiotics inhibit bacterial cell wall synthesis. Bacterial cells possess a rigid cell wall, which human cells lack. By preventing its formation or damaging its structure, the antibiotic weakens the bacterium, leading to its death. Other antibiotics might target bacterial protein synthesis by binding to bacterial ribosomes, which differ structurally from human ribosomes. This specificity is crucial; it allows antibiotics to eliminate the invading bacteria without causing significant harm to the host’s cells. This fundamental difference means antibiotics are ineffective against viral infections or other types of pathogens, as these organisms do not share the targeted bacterial processes.