Health, disease and the development of medicines Revision Notes

Bacterial Infections

Cholera is a bacterial infection that primarily affects the small intestine, causing severe diarrhoea and dehydration. It is often spread through contaminated water. Tuberculosis (TB) is another bacterial infection, mainly impacting the lungs but capable of affecting other parts of the body. TB can cause persistent coughing, chest pain, and weight loss, and is spread through airborne droplets.

Fungal and Protist Infections

Chalara ash dieback is a fungal disease that devastates ash trees, causing leaf loss and characteristic lesions on the bark. This can lead to the death of the tree. Malaria is a disease caused by protists transmitted through mosquito bites. The protists infect red blood cells and liver cells, leading to cycles of fever, chills, and anaemia, which can be life-threatening.

Viral Infections

Human Immunodeficiency Virus (HIV) is a viral infection that specifically targets and destroys white blood cells, which are crucial components of the body's immune system. Over time, the destruction of these cells impairs the immune system, making the individual susceptible to opportunistic infections and certain cancers. This advanced stage of HIV infection is known as Acquired Immunodeficiency Syndrome (AIDS).

Communicable Diseases

These are infectious diseases caused by pathogens like bacteria, viruses, fungi, or protists. They can be transmitted from one host to another. Transmission pathways include direct contact, airborne droplets, contaminated food/water, or vectors. Examples: common cold, flu, measles, tuberculosis, athlete's foot.

Non-Communicable Diseases

These diseases are not infectious and cannot be spread between people. They are often chronic, developing over a long period. Factors include genetics, lifestyle choices (diet, exercise, smoking), and environmental exposures. Examples: heart disease, diabetes, cancer, asthma, stroke.

Key Differences

The primary difference lies in transmissibility. Communicable diseases are transmissible (infectious), while non-communicable diseases are not. The causes also differ: pathogens for communicable, and a mix of genetic, lifestyle, and environmental factors for non-communicable. Prevention strategies vary significantly for each type.

Physical Barriers of Defence

Physical barriers are the body's first line of defence, aiming to prevent pathogens from entering. Skin serves as a tough, impermeable outer layer. Mucus, a sticky fluid produced by mucous membranes (e.g., in the respiratory tract), traps airborne pathogens. Cilia are tiny hair-like structures that line the respiratory tract; they rhythmically sweep mucus containing trapped pathogens towards the throat to be swallowed or expelled, preventing them from reaching the lungs.

Chemical Defences Against Pathogens

Chemical defences work to destroy pathogens that overcome physical barriers. Lysozymes are enzymes present in tears, saliva, and other bodily secretions. They act by breaking down the peptidoglycan cell walls of bacteria, effectively killing them. Hydrochloric acid (HCl) is produced in the stomach, creating a highly acidic environment (pH 1.5-3.5). This extreme acidity is lethal to most microorganisms ingested with food and drink, thus preventing them from causing infections in the digestive system.

Selective Toxicity of Antibiotics

Antibiotics exhibit selective toxicity, meaning they are harmful to bacteria but not to human cells. This is because they target specific cellular processes or structures unique to bacteria. Examples include the bacterial cell wall, which is absent in human cells, and bacterial ribosomes, which have structural differences from human ribosomes.

Why Antibiotics Don't Treat Viral Infections

Antibiotics are ineffective against viruses because viruses lack the cellular machinery and structures that antibiotics target. Viruses replicate by hijacking the host's cellular processes, rather than performing their own, rendering antibiotic mechanisms irrelevant. Therefore, antibiotics should not be used to treat viral diseases like the common cold or flu.