Health, disease and the development of medicines Revision Notes

Introduction to Non-Communicable Diseases (NCDs)

Non-communicable diseases (NCDs) are medical conditions or diseases that are not caused by infectious agents. They are chronic diseases that progress slowly and are of long duration. Examples include heart disease, cancer, diabetes, and chronic respiratory diseases. A key characteristic of many NCDs is that they often result from a complex interplay of various factors rather than a single cause.

Categories of Interacting Factors

The development of NCDs is typically influenced by four main categories of interacting factors: inherited factors (genetics), lifestyle choices (diet, exercise, smoking, alcohol), environmental factors (pollution, carcinogens), and social conditions (access to healthcare, education). These factors can combine in numerous ways, increasing or decreasing an individual's risk. For instance, an individual might have a genetic predisposition to a condition, but lifestyle choices could either trigger or mitigate its onset.

Cardiovascular Diseases (CVDs)

CVDs, including heart attacks and strokes, are primarily influenced by diet high in saturated fats, trans fats, and sodium; lack of physical activity; smoking; excessive alcohol consumption; and genetic factors. High blood pressure and high cholesterol are often a result of these interactions and contribute to CVD risk.

Cancers

Many cancers result from a combination of genetic mutations (inherited or acquired) and environmental triggers. Lifestyle factors such as smoking, alcohol, poor diet, obesity, and exposure to UV radiation or certain chemicals (environmental factors) significantly increase cancer risk.

Lung and Liver Diseases

Chronic lung diseases, like emphysema and chronic bronchitis, are strongly linked to smoking (lifestyle) and air pollution (environmental). Liver diseases, such as cirrhosis, can be caused by excessive alcohol consumption (lifestyle), viral infections (though this is less common for non-communicable context), or inherited conditions (genetics).

Diseases Influenced by Nutrition

Nutritional factors play a critical role in many NCDs. Obesity, a major risk factor for type 2 diabetes, CVDs, and some cancers, is largely driven by dietary choices and lack of physical activity. Type 2 diabetes itself arises from a combination of genetic predisposition, obesity, and sedentary lifestyle.

Leaf Cuticle as a Barrier

The leaf cuticle is a protective, waxy layer covering the epidermis of leaves and stems. Its primary functions include reducing water loss through transpiration and forming a physical barrier. This barrier deters pests from feeding directly on the leaf tissue and prevents the penetration of pathogens, such as bacteria and fungi, into the plant's internal cells.

Cell Wall as a Barrier

Every plant cell is surrounded by a rigid cell wall, located external to the cell membrane. Composed mainly of cellulose, the cell wall provides structural support and maintains cell turgor. Crucially, it acts as a strong physical barrier, making it difficult for pathogens to enter the cell and infect the plant. Some pathogens produce enzymes to break down cell walls, but the cell wall's robustness is an initial line of defense.

Layers of Protection

The combination of the waxy cuticle on the outer surface and the cell wall around individual cells provides a multi-layered defense system. The cuticle is the outermost defense, while the cell wall is the ultimate physical barrier that pathogens must breach to reach the cytoplasm. This double-barrier system significantly contributes to plant survival against environmental threats.

Chemical Defences Against Pests

Plants produce chemicals to deter or harm pests. Examples include nicotine, which is toxic to many insects, and tannins, which make plant tissues unpalatable. Some chemicals disrupt insect nervous systems or inhibit their growth and development. These compounds can act as direct toxins or antifeedants.

Chemical Defences Against Pathogens

Plants also produce chemicals with antimicrobial properties to combat pathogens like bacteria, fungi, and viruses. These chemicals can inhibit pathogen growth or kill them directly. Some plant compounds are involved in strengthening cell walls to prevent pathogen entry or spread after infection.

Human Applications of Plant Chemicals

Numerous plant-derived chemicals have medicinal value for humans. For instance, quinine from cinchona trees treats malaria. Salicylic acid from willow bark is a precursor to aspirin, used for pain. Other plant chemicals can have analgesic, anti-inflammatory, or antimicrobial effects, demonstrating their pharmaceutical potential.

Communicable Diseases

Communicable diseases are infectious diseases caused by pathogens (e.g., bacteria, viruses, fungi, protists). They can be transmitted directly or indirectly between individuals, from animals to humans, or from the environment. Transmission routes include airborne droplets, contaminated surfaces, ingestion of contaminated food/water, and vectors. Prevention often involves vaccination, hygiene practices, and isolation.

Non-Communicable Diseases

Non-communicable diseases (NCDs) are not infectious and cannot be spread from person to person. They are often long-lasting and result from a combination of genetic, lifestyle (e.g., diet, exercise, smoking), and environmental factors. Examples include heart disease, stroke, diabetes, cancer, and chronic respiratory diseases. Prevention typically focuses on lifestyle modifications and public health policies.