Human Health and Disease

Health does not mean just no fever. Health means your body works well, your mind is calm, and you feel good with people around you. If any of these breaks, you are not fully healthy.

We fall sick because of two types of reasons. Infectious diseases are caused by germs that can go from one person to another, like bacteria, virus, fungus, worms. For example cold spreads by touching and sneezing. Non-infectious diseases do not spread, like cancer from uncontrolled cell growth, or allergy.

Think of your body like a city. Bacteria like typhoid bacteria Salmonella typhi enter through dirty food and water, like thieves entering through dirty gate. Virus like rhinovirus causing common cold enters through nose, makes nose runny. Fungus likes skin and hair, protozoa like amoeba live in intestine. Worms like Ascaris live in gut and steal your food. Each thief has different way to enter and different police test to catch it.

Malaria is very common. It is caused by Plasmodium, a small protozoa. Female Anopheles mosquito is the carrier. When mosquito bites, it injects sporozoites which go to liver, grow, then enter red blood cells, burst them every 48-72 hours, so you get chill and high fever with shaking. Plasmodium has four types: vivax, falciparum most dangerous, malariae, ovale.

Common cold is caused by rhinovirus. It affects nose and throat, not lungs. Symptoms runny nose, sore throat, tired 3-7 days. Spreads by droplets when someone sneezes.

Ascariasis is caused by roundworm Ascaris. Its eggs come in contaminated water vegetables, hatch in intestine, cause stomach pain, block intestine. Filariasis or elephantiasis is caused by Wuchereria worm carried by Culex mosquito, worm lives in lymph vessels, legs swell like elephant leg, so name elephantiasis.

Ringworm is not worm, it is fungus that grows on skin, makes round red itchy patches. Spreads by using towel clothes of infected person, especially in hot sweaty areas.

Imagine your house has security at many levels. First gate is skin and mucus in nose that traps germs, this is physical barrier. Stomach acid kills many germs chemical barrier. Blood has white cells that eat germs cellular barrier, and proteins like interferon that warn other cells.

This is innate immunity, present from birth, same for all germs, non-specific.

Then there is special security that remembers face. If a germ enters, body makes army. First time response slow and weak called primary response. Second time same germ enters, response fast and strong called secondary response, because body remembers. This memory is the basis of vaccines.

Acquired immunity is of two types. If your body makes antibodies itself after infection or vaccine, it is active immunity, takes time but long lasting. If you get ready antibodies from mother through milk or injection like antitoxin, it is passive immunity, fast but short lived.

Foetal life gets antibodies from mother placenta, baby gets IgA from breast milk colostrum, very important.

Body has two main armies. B cells make Y shaped proteins called antibodies that float in blood and catch germs, this is humoral immunity because blood was called humor. Each antibody has two arms that fit only one germ like lock and key. Structure is 2 heavy chains 2 light chains, types IgG most common IgA in milk IgM first IgE allergy IgD.

T cells do not make antibodies, they directly kill infected cells or help B cells, this is cell mediated immunity. When organ transplant happens, body sees new organ as foreign and T cells reject it, so doctors give immunosuppressants.

Vaccination is like giving a dummy thief to police for practice. Weakened or dead germ or its toxin is injected, body makes memory cells without getting disease. Later real germ comes, body attacks quickly. Example polio, tetanus, hepatitis B vaccines.

Allergy is when immunity becomes over active to harmless things like pollen, dust, peanuts. Body makes IgE antibodies which release histamine from mast cells, causing sneezing watery eyes runny nose. Drugs like antihistamine reduce it. Autoimmunity is when immunity attacks own body like rheumatoid arthritis where body attacks joints.

AIDS is caused by HIV virus that attacks helper T cells CD4, which are commander of army. Without commander, body cannot fight even small infections. HIV spreads by unsafe sex, infected blood transfusion, sharing needles, mother to child, not by hugging or mosquito. Virus has RNA, makes DNA inside human cell using reverse transcriptase, then hides. No vaccine yet, but ART antiretroviral therapy keeps virus low. Prevention condom avoid sharing needles test blood.

Cancer is when cells forget to stop growing and divide non-stop forming tumor. Normal cells have contact inhibition they stop when touching others, cancer loses it. Tumor can be benign stays at one place not dangerous, malignant spreads to other parts metastasis dangerous. Causes chemicals tobacco smoke called carcinogens, UV radiation, viruses like HPV causes cervical cancer. Oncogenes are mutated genes that cause cancer, tumor suppressor p53 normally stops cancer. Treatment surgery removal, radiotherapy high energy kills, chemotherapy drugs kill rapidly dividing cells hair loss side effect, immunotherapy boost immunity, early detection helps.

Drugs and alcohol ruin health. Opioids like heroin smack from poppy plant Papaver, depress brain relieve pain but addictive. Cannabinoids like marijuana ganja from Cannabis affect heart and mind. Coca alkaloid cocaine coca plant from Erythroxylum cracks gives excitement but damages brain heart. Smoking tobacco causes lung cancer mouth cancer. Alcohol affects liver brain. Addiction is psychological need, dependence needs more drug, withdrawal without drug shaking anxiety. Peer pressure curiosity films cause start. Say no, talk to family, do sports, seek help counselling.