Health, disease and the development of medicines study guide

The human body possesses multiple non-specific defence mechanisms to prevent pathogens from entering and causing illness. These defences are categorised as physical barriers and chemical defences. Physical barriers like the skin provide a tough, impermeable outer layer. Internally, mucous membranes line various tracts, trapping pathogens, which are then expelled, often with the help of cilia. Chemical defences involve substances that destroy or inhibit pathogen growth. For example, enzymes such as lysozymes found in tears and saliva break down bacterial cell walls. Hydrochloric acid in the stomach maintains a very low pH environment, killing most ingested microbes. These combined defences form the first line of protection against infection.

The presence of one disease can notably increase an individual's vulnerability to acquiring other diseases. This heightened susceptibility often results from the initial illness weakening the body's primary defence system, the immune system. When the immune system is compromised, its ability to identify and combat new pathogens is reduced, making the body less effective at fighting off new infections. Additionally, certain diseases can cause physical damage to tissues and organs, creating entry points or favourable conditions for secondary invaders. For example, respiratory illnesses can damage the lining of the airways, making it easier for bacteria or viruses to establish new infections. Chronic diseases, such as diabetes or autoimmune disorders, can also exert a prolonged stress on the body, further impairing immune function and metabolic processes, which collectively lower overall resistance to new health threats.