Health, disease and the development of medicines Revision Notes

Introduction to Inactive Pathogen Immunisation

Immunisation involves introducing a non-virulent form of a pathogen to the body. Inactive pathogens are microorganisms (like bacteria or viruses) that have been killed or treated so they cannot cause disease but still retain their antigenic properties. This method allows the immune system to recognise the pathogen's unique surface markers, called antigens, without suffering from the illness itself.

The Immune Response to Immunisation

When an inactive pathogen is introduced, the body's white blood cells, specifically lymphocytes, recognise its antigens. This triggers a primary immune response, where the lymphocytes produce specific antibodies to target these antigens and create memory cells. These memory cells are crucial; they remain in the bloodstream and lymphatic system. Should the body encounter the actual live pathogen later, these memory cells enable a much quicker and more vigorous secondary immune response. This rapid production of a high concentration of specific antibodies neutralises the pathogen before it can cause widespread infection, providing long-term immunity.

Benefits of Immunisation with Inactive Pathogens

Immunisation using inactive pathogens is a safe and effective way to achieve immunity. It avoids the risks associated with live attenuated vaccines, particularly for immunocompromised individuals. The protective memory response generated by such vaccines is often robust and can last for many years, significantly reducing the incidence and severity of infectious diseases within a population, contributing to herd immunity.

Weakened Immune System

Many diseases directly or indirectly compromise the immune system. For instance, HIV specifically targets and destroys T-helper lymphocytes, which are crucial for coordinating immune responses. This weakens the body's ability to identify and destroy pathogens, making individuals susceptible to opportunistic infections that would typically not cause illness in a healthy person. Other conditions, such as some cancers or treatments like chemotherapy, can also suppress bone marrow activity, reducing the production of white blood cells essential for immunity.

Damage to Physical Barriers and Body Systems

Diseases can damage the body's protective physical barriers, such as the skin and mucous membranes, which serve as the first line of defence against pathogens. For example, severe burns or certain skin conditions create open wounds that are entry points for bacteria and other microbes. Similarly, conditions like chronic obstructive pulmonary disease (COPD) can damage the respiratory tract lining, impairing its ability to clear pathogens. Damage to organs like the liver or kidneys can also compromise their vital roles in detoxification or waste removal, further stressing the body and reducing its resilience to new infections.

Resource Depletion and Chronic Stress

Battling a chronic or severe illness requires significant energy and resources from the body. This can lead to a depletion of nutritional reserves and a state of chronic physiological stress. When the body's resources are primarily directed towards managing one disease, it has fewer resources available to mount an effective immune response against new infections. This can prolong recovery from simple illnesses or make individuals more prone to developing complications from otherwise mild infections. For example, someone with uncontrolled diabetes may have a harder time fighting off bacterial infections due to impaired immune cell function and reduced tissue perfusion.

Diet, Exercise, Obesity, and Malnutrition

Diet and exercise are fundamental lifestyle factors influencing body weight and health. An imbalance where energy intake exceeds expenditure leads to obesity, a risk factor for many NCDs. Obesity is often assessed using Body Mass Index (BMI), calculated as mass (kg) / (height (m))^2. A BMI of 25.0 to 29.9 kg/m² is considered overweight, and 30.0 kg/m² or higher is obese. Malnutrition, either undernutrition or overnutrition, occurs when the body doesn't get the correct balance of nutrients, leading to health problems. Waist-to-hip ratio is another indicator of health risks associated with body fat distribution, with higher ratios indicating increased risk.

Alcohol and Liver Diseases

Alcohol consumption can significantly damage the liver, leading to a spectrum of liver diseases. The liver metabolises alcohol, and prolonged excessive intake can lead to stages of damage. Initially, fatty liver disease (steatosis) can develop, where fat accumulates in liver cells. Continued heavy drinking can progress to alcoholic hepatitis, which is inflammation of the liver, and eventually to cirrhosis, a severe condition where healthy liver tissue is replaced by scar tissue, impairing liver function irreversibly. These conditions can have devastating health consequences and even be fatal.

Smoking and Cardiovascular Diseases

Smoking is a major risk factor for cardiovascular diseases (CVDs), which affect the heart and blood vessels. Chemicals in tobacco smoke damage blood vessel walls, promoting the build-up of fatty plaques (atherosclerosis). This narrows arteries and makes them less elastic, leading to high blood pressure, heart attacks, and strokes. Smoking also increases blood clot formation and reduces oxygen-carrying capacity. The effects are systemic, impacting the entire circulatory system and significantly increasing mortality and morbidity from CVDs globally, nationally, and locally.

Multifactorial Nature of NCDs

Non-communicable diseases (NCDs) arise from the interaction of multiple factors rather than a single cause. These factors are typically categorised as genetic (inherited predispositions), lifestyle (diet, exercise, smoking, alcohol), and environmental (pollution, exposure to toxins).

Cardiovascular Diseases (CVDs)

CVDs, including heart attacks and strokes, are strongly linked to: high blood pressure, high cholesterol, obesity (influenced by diet), lack of exercise, smoking, and genetic history. These factors contribute to the hardening and narrowing of arteries.

Cancers

Many cancers have a multifactorial origin. Key factors include: inherited genetic mutations, exposure to carcinogens (e.g., tobacco smoke, asbestos, UV radiation), viral infections (e.g., HPV), poor diet, excessive alcohol, and lack of physical activity. These can lead to uncontrolled cell growth.

Lung Diseases

Conditions like chronic obstructive pulmonary disease (COPD) – including emphysema and chronic bronchitis – are primarily caused by long-term exposure to tobacco smoke. Other contributing factors include air pollution and occupational exposure to dusts and chemicals.

Liver Diseases

Liver diseases such as cirrhosis often result from: chronic excessive alcohol consumption, viral hepatitis (e.g., Hepatitis B and C), and non-alcoholic fatty liver disease (NAFLD), which is linked to obesity and type 2 diabetes (often driven by poor nutrition).

Nutritional Influence

Nutrition plays a critical role in NCD development. Diets high in saturated fats, sugar, and salt increase the risk of obesity, type 2 diabetes, high blood pressure, and certain cancers. Adequate nutrition, including fibre, vitamins, and minerals, is protective.