📌 Infectious diseases are easily transmitted from one person to another, whereas non-infectious diseases are not transmitted person to person; cancer is a non-infectious example.
★ Must-know
Typhoid is caused by Salmonella typhi and is acquired through contaminated food or water.
Pneumonia is caused by Streptococcus pneumoniae or Haemophilus influenzae and affects the lung alveoli, which fill with fluid.
Cholera is caused by Vibrio cholerae, spreads through contaminated food or water, and causes diarrhoea.
Tuberculosis is caused by Mycobacterium tuberculosis, can cause fever, cough and blood-stained sputum, and is preventable with BCG vaccination.
Further detail
Typhoid symptoms include sustained fever of 39° to 40°C, weakness, stomach pain, constipation, headache and loss of appetite.
Severe typhoid can cause intestinal perforation and death, and the Widal test is used for diagnosis.
Mary Mallon, known as Typhoid Mary, was a carrier cook associated with typhoid.
Pneumonia can spread through inhaled droplets or aerosols from an infected person and through contaminated shared objects.
Pneumonia symptoms include fever, chills, cough and headache; severe cases may cause the lips and fingernails to turn greyish blue.
Leprosy, also called Hansen's disease, is caused by Mycobacterium leprae and can cause light-coloured skin patches, loss of sensation, and deformities of the toes and fingers.
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The common cold is caused by rhinovirus and affects the nose and respiratory passages rather than the lungs.
Malaria-causing species include:
In humans, malaria sporozoites enter through an infected female Anopheles mosquito bite, multiply in liver cells, then infect and rupture red blood cells; released parasites infect new red blood cells.
Amoebiasis is caused by Entamoeba histolytica and spreads through food or water contaminated by its tetranucleate cyst; houseflies can act as mechanical carriers.
Ascariasis is caused by Ascaris, an intestinal roundworm, and infection follows ingestion of eggs from contaminated water, vegetables or fruits after faecal contamination of soil, water or plants.
Filariasis is caused by Wuchereria worms, including W. bancrofti and W. malayi, and affects lymphatic vessels, usually in the lower limbs, causing chronic inflammation and deformity; genital organs may also be affected.
Ringworm is caused by fungi of the genera Microsporum, Trichophyton and Epidermophyton and produces dry, scaly, intensely itchy lesions on the skin, nails or scalp.
Further detail
Common cold symptoms include nasal congestion and discharge, sore throat, hoarseness, cough, headache and tiredness, usually lasting 3–7 days.
The common cold spreads through cough or sneeze droplets and contaminated objects such as pens and books.
Rupture of malaria-infected red blood cells releases haemozoin, causing recurring chills and high fever every 3–4 days.
🔄 The mosquito stage proceeds as follows:
Amoebiasis affects the large intestine and can cause constipation, abdominal pain, cramps, and stools containing excess mucus and blood clots.
Ascariasis can cause internal bleeding, muscular pain, fever, anaemia and blockage of the intestinal passage.
Ringworm fungi thrive in heat and moisture, especially in skin folds, and spread from soil or contaminated towels, clothes or combs.
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📌 For food- and water-borne diseases such as typhoid, amoebiasis and ascariasis, emphasize good personal and public hygiene.
Further detail
📌 For airborne diseases such as pneumonia and the common cold, avoid close contact with infected people and their belongings.
Smallpox has been completely eradicated with the help of vaccines.
Vaccines have controlled polio, diphtheria, pneumonia and tetanus to a large extent, while antibiotics and other drugs enable effective treatment of infectious diseases.
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📌 The primary immune response occurs at first exposure to a pathogen and has low intensity, whereas the secondary response follows subsequent exposure to the same pathogen and is highly intensified because of memory.
B lymphocytes produce antibodies against pathogens and mediate humoral immunity.
T lymphocytes mediate cell-mediated immunity and help B lymphocytes produce antibodies without secreting antibodies themselves.
Further detail
📌 Humoral immunity is antibody-mediated because antibodies are found in blood, whereas cell-mediated immunity is mediated by T lymphocytes and is responsible for graft rejection.
The antibody classes listed are IgA, IgM, IgG and IgE; IgE is associated with allergic responses, and IgG is the most abundant and crosses the placenta.
Active immunity develops slowly after immunization with microbes or after natural infection.
Innate defense is present at birth; acquired defense remembers specific pathogens.
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Further detail
Recombinant DNA technology enables large-scale production of antigenic polypeptides in bacteria or yeast; the hepatitis B vaccine is given as an example of production using yeast.
Allergens include dust mites, pollens and animal dander, and allergic responses involve IgE antibodies.
Allergy symptoms can include sneezing, watery eyes, a runny nose and difficulty breathing; histamine and serotonin released from mast cells cause symptoms.
Antihistamines, adrenaline and steroids can quickly reduce allergic symptoms.
Examples of autoimmune diseases are:
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The immune system comprises lymphoid organs, tissues, cells and soluble molecules such as antibodies.
Bone marrow is the main lymphoid organ and produces all blood cells, including lymphocytes.
The thymus is a lobed organ near the heart and breastbone, is large at birth and shrinks with age, and provides the environment for T-lymphocyte development and maturation.
Further detail
The spleen contains lymphocytes and phagocytes and serves as a reservoir of erythrocytes.
Lymph nodes trap microorganisms and antigens, activating lymphocytes and initiating an immune response.
Secondary lymphoid organs and tissues include:
MALT is lymphoid tissue in the lining of the respiratory, digestive and urogenital tracts and constitutes about 50% of human lymphoid tissue.
★ Must-know
AIDS is caused by HIV, a retrovirus, and was first reported in 1981.
HIV can be transmitted through sexual contact, contaminated blood or blood products, shared infected needles, and from an infected mother to a child through the placenta.
HIV is not spread by mere touch or physical contact and is transmitted through body fluids.
HIV uses reverse transcriptase to convert its RNA into DNA, which integrates into host-cell DNA and directs production of virus particles.
HIV enters helper T lymphocytes, replicates and produces progeny viruses that infect further helper T lymphocytes, progressively reducing their number.
Further detail
The time between HIV infection and the appearance of AIDS symptoms can range from a few months to many years, usually 5–10 years.
Macrophages can survive while HIV replicates and releases viruses, acting as HIV factories.
AIDS can involve fever, diarrhoea, weight loss, opportunistic infections and, in some cases, central nervous system infection with confusion, headache or seizures.
Antiretroviral drugs are partially effective against HIV/AIDS.
HIV prevention includes education, safe blood supplies, disposable needles and syringes, condom distribution, control of drug abuse, safe sex and regular testing in susceptible populations; infected people need support rather than isolation.
HIV reduces helper T-cell numbers → immune deficiency and opportunistic infections.
★ Must-know
📌 Normal cells exhibit contact inhibition, whereas cancer cells lose contact inhibition.
📌 Benign tumors remain confined to their original location, whereas malignant tumors invade and damage surrounding normal tissues.
Cancer diagnosis can use histopathology of stained suspected tissue, increased blood or bone-marrow cell counts in leukaemia, radiography, CT, MRI, antibodies against cancer-specific antigens, and molecular biology to detect inherited susceptibility genes.
Cancer treatments include: surgery to remove tumors, radiation therapy to lethally irradiate tumor cells while protecting surrounding tissue, chemotherapy with drugs that kill cancer cells, immunotherapy using biological response modifiers such as alpha-interferons to activate the immune system
Further detail
Carcinogens are agents that transform normal cells into cancerous cells; physical carcinogens include ionizing X-rays and gamma rays and non-ionizing ultraviolet light, which can damage DNA.
Chemical carcinogens occur in tobacco smoke, which is identified as a major cause of lung cancer.
Oncogenic viruses carry viral oncogenes, while cellular oncogenes or proto-oncogenes are normal-cell genes that can cause oncogenic transformation when activated under certain conditions.
CT uses X-rays to produce three-dimensional images of internal organs, whereas MRI uses strong magnetic fields and non-ionizing radiation to detect pathological or physiological changes in living tissue.
Chemotherapy can cause hair loss and anaemia, and some chemotherapeutic drugs are tumor-specific.
Benign tumors stay localized; malignant tumors invade and can metastasize.
★ Must-know
The commonly abused drug groups listed are opioids, cannabinoids and coca alkaloids; most are obtained from flowering plants, while some come from fungi.
Heroin, or smack, is diacetylmorphine, a white, odourless, bitter crystalline compound obtained by acetylating morphine extracted from the latex of the poppy Papaver somniferum; it is snorted or injected and depresses body functions.
Further detail
Opioids bind to specific receptors in the central nervous system and gastrointestinal tract.
Cannabinoids interact with cannabinoid receptors, principally in the brain, and natural cannabinoids come from Cannabis sativa inflorescences.
Marijuana, hashish, charas and ganja are forms made from different combinations of cannabis flower tops, leaves and resin; cannabinoids may be inhaled or ingested orally and affect the cardiovascular system.
Cocaine, also called coke or crack, comes from the South American coca plant Erythroxylum coca and interferes with dopamine transport.
Cocaine is usually snorted and stimulates the central nervous system, producing euphoria and increased energy; excessive doses can cause hallucinations.
★ Must-know
Nicotine stimulates the adrenal gland and increases blood pressure and heart rate; smoking is associated with emphysema, cancers of the lungs, throat and urinary bladder, and increased carbon monoxide in blood.
Excessive drug doses can cause coma and death through respiratory failure, heart failure or cerebral haemorrhage.
Prevention and support measures include: avoiding undue peer pressure, education and counselling about stress and failure, seeking help from parents and peers, watching for warning signs, obtaining professional or medical help through psychological, psychiatric, de-addiction or rehabilitation services
Further detail
Alcohol abuse can cause liver cirrhosis.
Warning signs of substance abuse among young people include declining academic performance, unexplained school or college absence, poor personal hygiene, withdrawal, isolation, depression, fatigue, aggression, rebellious behaviour, deteriorating relationships, loss of interest in hobbies, changed sleep or eating habits, and weight or appetite fluctuations.
Intravenous drug use increases the likelihood of serious infections such as AIDS and hepatitis B, while chronic drug and alcohol use damages the nervous system and liver and substance use during pregnancy can harm the foetus.
Sportspeople may misuse narcotic analgesics, anabolic steroids, diuretics and hormones to increase muscle strength or bulk, promote aggressiveness or improve athletic performance.
Anabolic steroid effects listed for females include masculinisation, increased aggressiveness, mood swings, depression, abnormal menstrual cycles, excessive facial and body hair, clitoral enlargement and deepening of the voice.
Anabolic steroid effects listed for males include acne, increased aggressiveness, mood swings, depression, reduced testicle size, decreased sperm production, liver and kidney dysfunction, breast enlargement, premature baldness and prostate enlargement.
Take a 11-question practice quiz on Human Health and Disease, with every answer explained.
1. Which description captures health as a whole rather than as the mere absence of disease?
2. A disease in a case study is identified as cancer and is not transmitted from one person to another. How should it be classified?
Memorize the key concepts of Human Health and Disease with 10 flashcards.
What does health encompass?
Complete physical, mental, and social well-being.
Which measures help maintain good health?
A balanced diet, personal hygiene, regular exercise including yoga, disease awareness, vaccination, proper waste disposal, vector control, and clean food and water resources.
Which bacterium causes typhoid?
Salmonella typhi.
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