Human Health and Diseases Biology Notes - Common Diseases, Immunity, AIDS, Cancer, Drugs and Adolescence

Common Infectious Diseases in Man

• Health is a state of complete physical, mental & social well-being. It is affected by genetic disorders, infections, and changes in lifestyle (food, water, rest, exercise, habits, etc.).
• Mind influences the immune system (through neural and endocrine systems) and thereby health.
• When the functioning of organs or systems of the body is adversely affected, it is called a disease.
• Diseases may be infectious (transmits from one person to another) or non-infectious (do not transmit, e.g., cancer).
• Disease-causing organisms are called Pathogens. Parasites are pathogens as they harm the host.

Good Humour Hypothesis

• Proposed by Hippocrates and the Indian Ayurveda system: Health is a state of body and mind where there is a balance of certain humours.
• Persons with ‘black bile’ belong to a hot personality and would have fevers.
• William Harvey disproved this hypothesis. He discovered blood circulation and demonstrated normal body temperature in persons with black bile using a thermometer.

1. Bacterial Diseases

Typhoid

• Pathogen is Salmonella typhi.
• Mode of transmission: It enters the small intestine through food and water and migrates to other organs via blood.
• Symptoms: Sustained high fever (39°-40° C), headache, weakness, stomach pain, constipation, and loss of appetite. Intestinal perforation and death may occur.
• Widal test is used for confirmation of the disease.
• Mary Mallon (Typhoid Mary) was a professional cook and a typhoid carrier who spread typhoid for several years through the food she prepared.

Pneumonia

• Pathogen is Streptococcus pneumoniae and Haemophilus influenzae.
• It infects lung alveoli. The alveoli get filled with fluid leading to respiratory problems.
• Mode of transmission: Inhaling the droplets/aerosols released by an infected person. Sharing glasses and utensils with an infected person.
• Symptoms: Respiratory problems, fever, chills, cough, headache. In severe cases, lips and fingernails turn grey to bluish color.
• Other bacterial diseases: Dysentery, plague, diphtheria, etc.

2. Viral Diseases

Common Cold

• Pathogen is Rhinoviruses.
• It infects the nose and respiratory passage but not the lungs.
• Mode of transmission: Inhaling droplets resulting from cough or sneezes. Through contaminated objects (pens, books, cups, doorknobs, computer accessories), etc.
• Symptoms: Nasal congestion and discharge, fever, headache, sore throat, cough, hoarseness, tiredness, etc.
• Common cold lasts for 3-7 days.

3. Protozoan Diseases

Malaria

• Pathogen is Plasmodium sp. (P. vivax, P. malariae, and P. falciparum).
• Most serious (malignant) malaria is caused by P. falciparum.
• Mode of transmission: By female Anopheles mosquito.
• Symptoms: Haemozoin (toxin released by Plasmodium) causes chill and high fever recurring every 3-4 days.

Amoebiasis (Amoebic Dysentery)

• Pathogen is Entamoeba histolytica.
• Mode of transmission: Houseflies (mechanical carriers) transmit parasites from faeces to food and water.
• Symptoms: Constipation, abdominal pain and cramps, stools with excess mucus and blood clots.

4. Helminth Diseases

Ascariasis

• Pathogen is Ascaris (intestinal parasite).
• Mode of transmission: Soil, water, vegetables, fruits, etc., contaminated with faeces containing eggs of parasites.
• Symptoms: Internal bleeding, muscular pain, fever, anemia, and blockage of intestinal passage.

Filariasis (Elephantiasis)

• Pathogen is Filarial worms or Wuchereria (W. bancrofti and W. malayi).
• Mode of transmission: Bite of female Culex mosquito.
• Symptoms: Filarial worms live in lymphatic vessels (usually of lower limbs). It causes chronic inflammation of the organs in which they live for many years. Limbs and genital organs may be deformed.

5. Fungal Diseases

Ring Worms

• Pathogens are Microsporum, Trichophyton, and Epidermophyton. They are seen in groin, between toes, etc.
• Mode of transmission: From soil or by using towels, clothes, combs, etc. Heat and moisture help fungi to grow.
• Symptoms: Dry, scaly lesions on skin, nails, scalp, etc. Intense itching.

Prevention and Control of Diseases

Personal Hygiene

• Keep the body clean. Use clean drinking water, food, etc.

Public Hygiene

• Proper disposal of wastes and excreta.
• Periodic cleaning and disinfection of water reservoirs, pools, cesspools, and tanks.
• Avoid contact with infected persons or their belongings (to control air-borne diseases).
• Standard practices of hygiene in public catering.
• Control and eliminate the vectors (e.g., mosquitoes).
  • Avoid stagnation of water.
  • Regular cleaning of household coolers.
  • Use of mosquito nets.
  • Introduce larvivorous fishes like Gambusia in ponds.
  • Spraying insecticides in ditches, drainage, and swamps.
  • Provide doors and windows with wire mesh.
• These precautions can avoid vector-borne diseases like Malaria, Filariasis, Dengue, and Chikungunya.

Vaccines and Antibiotics

• Vaccines and immunisation helped to control diseases like smallpox, polio, diphtheria, pneumonia, and tetanus.
• Drugs like antibiotics also helped to treat infectious diseases.

Human Immune System

• It is the system that gives immunity to the body by recognizing, responding, and remembering foreign antigens.
• It plays a role in allergic reactions, auto-immune diseases, and organ transplantation.
• It includes lymphoid organs, tissues, cells, and antibodies.

Lymphoid Organs

These are the organs where origin, maturation, and proliferation of lymphocytes occur. They are of two types: Primary and Secondary.

Primary Lymphoid Organs

The organs where lymphocytes mature and differentiate into antigen-sensitive lymphocytes. They are of two types:

1. Bone Marrow: The site of formation of all blood cells, including B and T-lymphocytes.
2. Thymus: A bilobed organ near the heart and beneath the breastbone. It is large at birth but reduces in size by puberty. Immature T-lymphocytes from bone marrow migrate to the thymus and mature.

Secondary Lymphoid Organs

The organs to which mature lymphocytes migrate from primary lymphoid organs, interact with antigens, and proliferate to become effector cells.

• Examples: Spleen, lymph nodes, tonsils, Peyer’s patches, mucosa-associated lymphoid tissue (MALT), and appendix.
• Spleen: A bean-shaped organ containing lymphocytes and phagocytes. It removes worn-out RBCs and microorganisms from blood and serves as a reservoir of erythrocytes in the fetus.
• Lymph Nodes: Found in the lymphatic system, they trap microorganisms or antigens, activating lymphocytes for an immune response.
• MALT: Located within the lining of respiratory, digestive, and urogenital tracts. It constitutes 50% of lymphoid tissue.

Immunity

The ability of the immune system to fight pathogens. It is of two types: Innate and Acquired.

Innate (Inborn) Immunity

• It is non-specific immunity present at birth.
• It includes four types of barriers:
  • Physical Barriers: Prevent entry of microbes. E.g., skin, mucus coating of respiratory, gastrointestinal, and urogenital tracts. Mucus traps microbes.
  • Physiological Barriers: Prevent microbial growth. E.g., gastric HCl, saliva, tears.
  • Cellular Barriers: Phagocytes like WBC (polymorphonuclear leukocytes, monocytes, natural killer lymphocytes), macrophages.
  • Cytokine Barriers: Virus-infected cells secrete interferon, protecting non-infected cells from further viral infection.

Acquired (Adaptive) Immunity

• It is pathogen-specific immunity developed during a lifetime.
• It is characterized by memory: the first encounter with a pathogen produces a primary response (low intensity), while a second encounter causes a secondary (anamnestic) response (high intensity).
• Primary and secondary immune responses are carried out by B-lymphocytes (B-cells) and T-lymphocytes (T-cells).
  • B-Lymphocytes: Produce antibodies, proteins that fight pathogens.
  • T-Lymphocytes: Help B-cells produce antibodies.

Structure of an Antibody Molecule: An antibody has four polypeptide chains: two light chains and two heavy chains (H2L2). Types of antibodies: IgG, IgA, IgM, IgE, IgD.

Types of Acquired Immune Response

1. Humoral Immune Response / Antibody-Mediated Immunity (AMI): Mediated by antibodies found in blood plasma, hence called humoral immunity.
2. Cell-Mediated Response / Cell-Mediated Immunity (CMI): Mediated by T-lymphocytes (T-cells). It distinguishes ‘self’ from ‘non-self’ and causes graft rejection.

Tissue and blood group matching are essential before grafts or transplants. Patients require lifelong immunosuppressants.

Types of Acquired Immunity

Acquired immunity is of two types: Active and Passive.

1. Active Immunity:

• Antibodies are produced in the host body upon exposure to antigens (e.g., living/dead microbes or proteins). It is a slow process and occurs in two ways:

a. Natural Active Immunity: Developed during natural infection by microbes.

b. Artificial Active Immunity: Developed by injecting microbes deliberately during immunization.

2. Passive Immunity:

• Readymade antibodies are directly given to the body. It is of two types:

a. Natural Passive Immunity:

• Antibodies (IgG) from mother → placenta → fetus.
• Antibodies (IgA) in colostrum → infants.

b. Artificial Passive Immunity:

• Anti-tetanus serum (ATS).

Immunization

Based on the ‘memory’ of the immune system. It is of two types:

Active Immunization (Vaccination)

• A vaccine (antigenic proteins or inactivated pathogen) is introduced, resulting in antibody production.
• Antibodies neutralize antigens during actual infection.
• Vaccines generate memory B and T cells, which recognize pathogens quickly.
• Examples: Polio vaccine, Hepatitis B vaccine, DPT vaccine.
• Vaccines are produced using DNA recombinant technology (e.g., Hepatitis B vaccine from yeast).

Passive Immunization

• Direct injection of pre-formed antibodies or antitoxin for quick response.
• Examples: Immunization against tetanus, snake venom.

Allergies

• It is the exaggerated response of the immune system to certain antigens present in the environment.
• Allergens: Substances causing allergy. E.g., mites in dust, pollens, animal dander, fur, etc.
• Antibodies produced against the allergens are IgE type.
• IgE binds on mast cells to release chemicals like histamine and serotonin from them. It results in allergic reactions.
• Symptoms: Sneezing, watery eyes, running nose, difficulty in breathing, wheezing, skin rashes, etc.
• Determination of cause of allergy: The patient is exposed to or injected with very small doses of possible allergens, and the reactions studied.
• Treatment: Drugs like anti-histamine, adrenaline, and steroids quickly reduce the symptoms of allergy.
• Asthma is a respiratory disease due to allergy.
• Modern-day lifestyle and protected environment provided early in life result in low immunity and more sensitivity to allergens. So, many children in metro cities suffer from allergies and asthma.

Autoimmunity

• In higher vertebrates, memory-based acquired immunity evolved based on the ability to differentiate foreign organisms from self-cells.
• Sometimes, due to genetic and other unknown reasons, the body attacks self-cells resulting in damage to the body. It is called auto-immune disease. E.g., Rheumatoid arthritis.

AIDS (Acquired Immuno Deficiency Syndrome)

• It is the deficiency of the immune system.
• Syndrome means a group of symptoms.
• It is caused by HIV (Human Immunodeficiency Virus), a retrovirus having RNA genome.
• AIDS was first reported in America (1981).
• In the last 25 years, it killed over 25 million persons.

Transmission

• Sexual contact with an infected person.
• Transfusion of contaminated blood and blood products.
• Sharing of infected needles.
• From infected mother to her child through placenta.

HIV does not spread by touch or physical contact. It spreads only through body fluids.

There is a time-lag (from a few months to 5–10 years) between the infection and appearance of symptoms.

High-Risk Groups for HIV

• Individuals with multiple sexual partners.
• Drug addicts who take drugs intravenously.
• Individuals who require repeated blood transfusions.
• Children born to an HIV-infected mother.

Replication of Retrovirus

Replication of Retrovirus

Life Cycle of HIV

HIV enters body → To macrophages (acts as HIV factory) → RNA genome replicates in presence of Reverse transcriptase to form viral DNA → Viral DNA incorporates into host DNA → Infected cells produce virus particles → HIV enters into helper T-cells (T_H lymphocytes) → Replicates & produce progeny viruses → Attack other T_H cells → T_H cells decrease → Weaken immunity.

• During this period, the person suffers from fever, diarrhea, and weight loss.
• Due to deficiency of T_H cells, they may be infected with Mycobacterium, viruses, fungi, & parasites like Toxoplasma.

Diagnosis

• ELISA test (Enzyme-linked Immuno-sorbent Assay).

Treatment

• Anti-retroviral drugs are partially effective. They can only prolong the life of the patient.

Prevention of AIDS

• Educate people about AIDS through organizations like National AIDS Control Organisation (NACO), non-governmental organizations (NGOs), WHO, etc.
• Make blood (from blood banks) safe from HIV.
• Use disposable needles and syringes.
• Advocate safe sex and free distribution of condoms.
• Control drug abuse.
• Regular check-ups for HIV in susceptible populations.

• Cancer is an abnormal and uncontrolled multiplication of cells resulting in the formation of tumour (masses of cells).
• Normal cells show a contact inhibition (contact with the other cells inhibits their uncontrolled growth). Cancer cells do not have this property.

Types of Tumours

• Benign tumours: Confined to the place of its origin. They do not spread to other parts. Cause little damage.
• Malignant tumours: Mass of proliferating cells (neoplastic or tumour cells) that grow rapidly, invade and damage the surrounding normal tissues. Due to active division and growth, they starve normal cells by competing for nutrients.
• Cells sloughed from tumours reach other sites via blood where they form a new tumour. This is called metastasis.

Causes of Cancer (Carcinogens)

• Physical agents:
  • Ionizing radiations like X-rays and gamma rays and non-ionizing radiations like UV.
• Chemical agents:
  • Tobacco smoke (major cause of lung cancer), vinyl chloride, caffeine, nicotine, mustard gas etc.
• Biological agents:
  • Oncogenic viruses, c-onc (cellular oncogenes or proto oncogenes) etc. When c-onc in normal cells is activated, the cells become oncogenic.

Cancer Detection and Diagnosis

• Biopsy: A thin piece of the suspected tissue is stained and examined under microscope (histopathological studies).
• In case of leukemia: Biopsy & histopathological studies. Blood & bone marrow tests for increased cell counts.
• Imaging techniques:
  • Radiography: Use of X-rays.
  • CT (Computerized tomography) scan: Uses X-rays to generate a 3D image of the internals of an object.
  • MRI (Magnetic Resonance Imaging): Uses magnetic fields and non-ionizing radiations to detect pathological changes in the living tissue.
• Use of Antibodies against cancer-specific antigens.
• Molecular biology technique: To detect cancer-related genes. Such individuals should avoid carcinogens (e.g., tobacco smoke).

Treatment of Cancer

• Radiotherapy: Tumour cells are irradiated lethally, without damaging surrounding normal tissues.
• Chemotherapy: Use of chemotherapeutic drugs. Many drugs have side effects like hair loss, anaemia etc.
• Immunotherapy: The patients are given biological response modifiers (e.g., α-interferon) which activates their immune system and helps in destroying the tumour.
• Surgery.

Most cancers are treated by combination of surgery, radiotherapy, and chemotherapy.

Drugs

Opioids

• They bind to specific opioid receptors in CNS and gastrointestinal tract. E.g., morphine, heroin, brown sugar.

• Morphine is extracted from latex of Papaver somniferum (poppy plant). It is a sedative & painkiller. Used in surgery.
• Heroin (smack or diacetylmorphine) is a white, odourless, bitter crystalline compound. It is obtained by acetylation of morphine. It is taken by snorting and injection. Heroin is a depressant and slows down body functions.

Cannabinoids

• They interact with cannabinoid receptors in the brain.
• Generally taken by inhalation and oral ingestion.
• Natural cannabinoids are obtained from inflorescences of Cannabis sativa (Hemp plant). Its flower tops, leaves & resin are used to make marijuana, hashish, charas & ganja.
• They affect cardiovascular system.
• Cannabinoids are abused by some sportspersons.

Coca Alkaloid or Cocaine (Coke or Crack)

• It is obtained from coca plant Erythroxylum coca.
• It interferes with transport of neurotransmitter dopamine.
• Cocaine is usually snorted.
• It stimulates CNS producing euphoria & increased energy.
• Excessive dosage of cocaine causes hallucinations.
• Atropa belladonna & Datura are also hallucinogenic plants.

Drugs like barbiturates, amphetamines, benzodiazepines, etc., are used as medicines to treat mental illnesses like depression & insomnia. But their abuse causes impairment of physical, physiological, or psychological functions.

Smoking

• Tobacco has been used by human beings for over 400 years.
• It is smoked, chewed, or used as a snuff.
• It contains many chemical substances like nicotine (an alkaloid). It stimulates adrenal gland to release adrenaline and nor-adrenaline, causing high BP and heart rate.
• Smoking causes cancers of lung, urinary bladder, and throat, bronchitis, emphysema, coronary heart disease, gastric ulcer, etc. Tobacco chewing causes oral cancer.
• Smoking increases CO content in blood and reduces oxyhaemoglobin. This causes O₂ deficiency in the body.

Adolescence & Drug/Alcohol Abuse

• Adolescence is ‘a period’ and ‘a process’ during which a child becomes mature in terms of his/her attitudes and beliefs for effective participation in society.
• Adolescence is a bridge linking childhood and adulthood (period of 12–18 years of age). It is a very vulnerable phase of mental and psychological development.

Causes of Drug/Alcohol Use in Adolescence

• Curiosity and Experimentation.
• Need for adventure and excitement.
• To escape facing problems.
• Stress from pressure to excel in academics or examination.
• Television, movies, newspapers, internet, etc.
• Unstable or unsupportive family structures & peer pressure.

Addiction and Dependence

• Addiction: It is a psychological attachment (euphoria and a temporary feeling of wellbeing) with drugs and alcohol. With repeated use of drugs, the tolerance level of the receptors increases. Thus, the receptors respond only to higher doses leading to greater intake and addiction.
• Dependence: It is the tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome if regular dose of drugs/alcohol is abruptly discontinued. This results in anxiety, shakiness, nausea, and sweating.
• Dependence leads to social adjustment problems.

Effects of Drug/Alcohol Abuse

• Reckless behaviour, vandalism, and violence.
• Coma and death due to respiratory failure, heart failure, or cerebral haemorrhage.
• Drugs mixed with alcohol may cause death.
• Damage of nervous system and liver cirrhosis.
• Mental and social distress to family and friends.
• Social problems like stealing and spread of infectious diseases (e.g., AIDS, hepatitis B).
• Use of drugs and alcohol by pregnant women affects the foetus (Foetal alcohol syndrome or FAS).
• Loss of sexual drive and necrospermia.
• Misuse of drugs by athletes (e.g., narcotic analgesics, anabolic steroids, diuretics, & certain hormones to increase muscle strength and bulk and to promote aggressiveness).

Warning Signs of Drug/Alcohol Abuse in Adolescence Period

• Drop in academic performance and absence from school.
• Lack of interest in personal hygiene.
• Withdrawal and isolation.
• Depression, fatigue, aggressive, and rebellious behaviour.
• Change in sleeping and eating habits.
• Fluctuations in weight, appetite, etc.
• Loss of interest in hobbies.
• Deteriorating relationships with family and friends.

Side Effects of Anabolic Steroid Abuse

In Males

• Acne.
• Mood swings & depression.
• Increased aggressiveness.
• Reduced testicles.
• Decreased sperm.
• Breast enlargement.
• Kidney & liver dysfunction.
• Premature baldness.
• Enlargement of prostate gland.

In Females

• Masculinisation.
• Mood swings & depression.
• Increased aggressiveness.
• Excessive hair growth.
• Abnormal menstrual cycle.
• Deepening of voice.
• Enlargement of clitoris.

In adolescent male & female: Severe facial and body acne, premature closure of the growth centres of the long bones resulting in stunted growth.

Prevention and Control

1. Avoid undue peer pressure.
2. Education and counselling.
3. Seeking help from parents and peers.
4. Looking for danger signs.
5. Seeking professional and medical help.
   • Psychologists and psychiatrists.
   • De-addiction and rehabilitation programs.