Health, disease and the development of medicines Revision Notes

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.

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.

Chlamydia: A Bacterial STI

Chlamydia is a bacterial infection spread through unprotected sexual contact (vaginal, anal, oral). Many infected individuals show no symptoms, especially in the early stages, making it easy to unwittingly transmit the infection. Symptoms, if present, can include unusual discharge, pain during urination, or abdominal pain. Left untreated, Chlamydia can lead to serious health issues such as pelvic inflammatory disease (PID) in women, which can cause infertility, or epididymitis in men. It is treatable with antibiotics.

HIV: A Viral STI

HIV (Human Immunodeficiency Virus) is a viral infection that primarily spreads through specific bodily fluids during sexual activity, sharing needles, or from mother to child. HIV attacks CD4+ T cells, which are crucial components of the immune system. This weakens the body's ability to fight off other infections and diseases. While there is no cure for HIV, antiretroviral therapy (ART) can effectively manage the viral load, allowing individuals with HIV to live long, healthy lives and significantly reducing the risk of transmission. Without treatment, HIV can progress to AIDS (Acquired Immunodeficiency Syndrome).

Preventing STI Spread

Prevention of STIs like Chlamydia and HIV largely relies on stopping the transmission routes. Key strategies include: consistent and correct use of barrier methods such as condoms during all types of sexual activity; regular STI testing, especially between partners or after unprotected encounters; reducing the number of sexual partners; and avoiding the sharing of needles or injection equipment. Education on sexual health and access to testing and treatment services are vital in controlling the spread of these infections in wider populations.

Understanding Pathogens

Pathogens are harmful microorganisms that cause infectious disease in their hosts. They may infect animals, including humans, or plants by damaging cells or interfering with normal functions.

Four Main Groups of Pathogens

1. Viruses: Non-cellular; reproduce by entering and hijacking host cells.
2. Bacteria: Single-celled prokaryotes; can release toxins or invade tissues.
3. Fungi: May be single-celled or multicellular; invade tissues or secrete enzymes.
4. Protists: Single-celled eukaryotes; some are parasites damaging their host from the inside.