Human Health and Diseases
Easy Overview
Your body is under constant attack — bacteria, viruses, fungi, parasites. So why aren't you sick all the time? Because you have an immune system that's essentially a secret army patrolling your body 24/7. This chapter covers how that army works, what happens when it fails, and the drugs we use when it needs backup.
Types of immunity — your personal bodyguards
Innate immunity is what you're born with — skin, mucus, stomach acid, inflammatory response. It's the generic bouncer at the door. Adaptive immunity is specific — it remembers the pathogen and creates targeted antibodies. That's why you only get chickenpox once. Vaccines work by teaching adaptive immunity without making you sick.
Antibody structure — the Y-shaped killer
Antibodies are Y-shaped proteins. The tips of the Y bind to antigens (pathogen markers). The stem of the Y signals other immune cells to come destroy the invader. There are five types (IgG, IgA, IgM, IgE, IgD), each with different jobs. IgG is the most common and hangs around in your blood for years — that's long-term memory.
Common diseases — what actually makes you sick
Typhoid (Salmonella) gives you prolonged fever and is spread through contaminated food. Pneumococcus causes pneumonia — lungs fill with fluid. Malaria (Plasmodium) is spread by mosquitoes and causes fever cycles. Ringworm is a fungal skin infection. Know the pathogen, the vector (if any), and the symptoms. That's what exams ask.
Cancer — when cells forget to stop dividing
Normal cells know when to stop dividing. Cancer cells don't — they just keep multiplying. They form tumors, invade nearby tissues, and spread (metastasis) through blood or lymph. Causes: tobacco, radiation, certain viruses (HPV), genetics. Treatment includes surgery, radiation, chemotherapy, and immunotherapy. Early detection saves lives.
Drugs and addiction — the brain on substances
Opioids (like heroin) bind to pain receptors and give euphoria — then addiction. Cannabinoids (marijuana) affect memory and coordination. Cocaine gives an intense high followed by a crash. Alcohol depresses the CNS. All of them mess with the brain's reward system (dopamine). Addiction isn't weakness — it's your brain rewired to crave the substance.
AIDS and HIV — the immune system's worst nightmare
HIV attacks helper T-cells (CD4 cells) — the generals of your immune army. Without them, your body can't fight off even minor infections. AIDS is the final stage when T-cell count drops below 200. Spread through unprotected sex, infected blood, and from mother to child. Not curable, but manageable with antiretroviral therapy (ART).
Key Points
- •Innate immunity: non-specific, present at birth (skin, mucous, phagocytes)
- •Adaptive immunity: specific, has memory (antibodies, lymphocytes)
- •Antibodies (immunoglobulins): IgG (most abundant), IgA (mucosa), IgM (first response), IgE (allergy), IgD (B-cell receptor)
- •Common diseases: Typhoid (Salmonella typhi), Pneumonia (Streptococcus pneumoniae), Malaria (Plasmodium), Ringworm (fungal)
- •Cancer: uncontrolled cell division; benign (localized) vs malignant (metastatic); carcinogens trigger mutations
- •Addictive drugs: opioids (heroin), cannabinoids (marijuana), cocaine, alcohol — all affect dopamine pathway
- •HIV attacks helper T-cells → AIDS; transmitted via blood, sex, mother-to-child; diagnosed by ELISA/Western blot
- •Vaccines induce active immunity by exposing the body to weakened/inactivated pathogens
Practice Questions
- Differentiate between innate and adaptive immunity with examples.
- Describe the structure of an antibody. Which class is most important for long-term immunity?
- Explain the life cycle of Plasmodium and why malaria causes fever cycles.
- How does HIV cause AIDS? Why do AIDS patients die from common infections?
- What are the effects of opioids and cocaine on the nervous system? Why are they addictive?