Class 12 Human Health and Disease Quick revision Notes

 

Class 12 Human Health and Disease Quick revision Notes


Health and Related Aspects, Common Human Diseases and Immunity

Health

  • Health is a state of complete physical, mental and social well-being.
  • Health is affected by genetic disorders, infections, sedentary lifestyle (Junk food, lack of exercise, habits, etc.).

Human Diseases and Immunity

  • Disease : A disease can be defined as and condition that may lead to discomfort, distress, health problems or death of the affected person.
  • Congenital diseases : These are diseases that are present since birth. For instance, a hole in the heart of an infant. They are caused by some genetic abnormalities or metabolic disorder or malfunctioning of an organ.
  • Acquired diseases : These are diseases that may occur after birth during one’s lifetime.

Based on their ability or inability to spread from one individual to another, acquired diseases are of two types :
(a) Infectious or Communicable diseases : The diseases which can be transmitted from a diseased person to a healthy person through infectious agents are known as infectious or communicable diseases. For example, tuberculosis, measles, malaria, etc.
(b) Non-infectious or Non-communicable diseases : The diseases which cannot be transmitted from an affected individual to a healthy person are known as non-infectious or non-communicable diseases. For example, high blood pressure, cancer, allergy, obesity, etc.


  • Among non-infectious diseases, cancer is the major cause of death.
  • Pathogens are disease-causing organisms.
  • Parasites are pathogens as they harm the host by living in or on them.
  • Pathogens have to adapt to live within the environment of the host.

Common Infectious Diseases in Man
1. BACTERIAL DISEASES
(a) Typhoid

  • Pathogen : Salmonella typhi.
  • Mode of transmission : It enters the small intestine through food and water and migrates to other organs through blood.
  • Symptoms : Sustained high fever (39°- 40°C), weakness, stomach pain, constipation, headache and loss of appetite. Intestinal perforation and death may occur.
  • Confirmation : The Widal test is used for confirmation of the disease.

(b) Pneumonia

  • Pathogen : Streptococcus or Diplococcus pneumoniae & Haemophilus influenzae.
  • Mode of transmission : Inhaling the droplets/aerosols released by an infected person. Sharing glasses and utensils with an infected person.
  • Symptoms : Infects lung’s alveoli. The alveoli get filled with fluid leading to respiratory problems. Fever, chills, cough, headache.
  • Severe cases : Lips and fingernails turn grey to a bluish colour.
  • Dysentery, plague, diphtheria are some other bacterial diseases in humans.

2. VIRAL DISEASES
(a) Common cold

  • Pathogen : Rhino viruses
  • Mode of transmission : Inhaling droplets resulting from cough or sneezes through contaminated objects.
  • Symptoms : Infects nose and respiratory passage. Nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness, etc. last for 3-7 days.

3. PROTOZOAN DISEASES
(a) Malaria

  • Pathogen : Plasmodium sp. (P. vivax, P. malariae, P. ovale. and P. falciparum).
  • Mode of transmission : Biting of female Anopheles mosquito.
  • Symptoms : Hemozoin causes chill and high fever recurring every 3-4 days.
  • Life cycle of Plasmodium : The life cycle of Plasmodium has three phases - Schizogony, gamogony and sporogony.
  • Female Anopheles mosquito is the primary host, while man is the secondary host.

Life cycle of plasmodium in Man :
(a) The infective stage of Plasmodium is the sporozoite, which is injected into the blood of the human by the bite of female Anopheles mosquito.
(b) From the human blood, sporozoites reach the liver cells where they multiply.
(c) The liver cells rupture to liberate the parasites into the blood where they attack the RBCs, multiply and cause their rupture.
(d) The rupture is associated with the release of a toxin called hemozoin, which is responsible for the recurring chill and high fever within 3 - 4 days.
(e) The development of gametocytes takes place in the RBCs, which are of two types : male gametocytes or microgametocytes, and female gametocytes or macrogametocytes.

Life cycle of Plasmodium in Female Anopheles Mosquito
(a) When a female Anopheles mosquito sucks the blood of an infected human host, it receives the RBCs including gametocytes.
(b) Further development occurs in the stomach wall of the mosquito, the gametes fuse to form a zygote.
(c) The zygote undergoes further development to form sporozoites.
(d) The sporozoites after liberation from the stomach wall move to different organs in the body cavity, but many of them penetrate the salivary glands.
(e) The mosquito now becomes infective, when the female Anopheles mosquito bites a healthy person, the sporozoites are injected in his / her blood along with saliva.

(b) Amoebiasis (Amoebic dysentery) or Enteritis.

  • Pathogen : Entamoeba histolytica, found in the large intestine of humans.
  • Mode of transmission : Houseflies (mechanical carriers) transmit parasites from the faeces of an infected person to food and water and thereby contaminating them.
  • Symptom : Constipation, abdominal pain and cramps, stools with excess mucous and blood clots.

4. HELMINTH DISEASES
(a) Ascariasis

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

(b) Filariasis (Elephantiasis)

  • Pathogen : Filarial worms or Wuchereria (W. bancrofti & W. malayi).
  • Mode of transmission : Bite of female Culex moModesquito.
  • 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
(a) Ring worms

  • Pathogens : Microsporum, Trichophyton & Epidermophyton. They are seen in groin between the toes.
  • Mode of transmission : From soil or by using towels, cloths, comb, etc., of an infected person. Heat and moisture help fungi to grow.
  • Symptoms : Appearance of dry, scaly lesions on various body parts such as skin, nails and scalp. Intense itching.

Other Infectious Diseases
(i) Bacterial Diseases


(ii) Viral Diseases


Prevention and Control of Diseases
1. Personal Hygiene : Keep the body clean. Use clean drinking water, food, etc.
2. Public Hygiene
(a) Proper disposal of wastes and excreta.
(b) Periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks.
(c) Avoid contact with infected persons or their belongings (to control air-borne diseases).
(d) Standard practices of hygiene in a public gathering.
(e) Control and eliminate the vectors (e.g., mosquitoes) and their breeding places by following methods :
(i) Avoid stagnation of water.
(ii) Regular cleaning of household coolers.
(iii) Use of mosquito nets.
(iv) Introduce larvivorous fishes like Gambusia in ponds.
(v) Spraying insecticides in ditches, drainage and swamps.
(vi) Doors and windows should be provided with wire mesh to prevent the entry of mosquitoes.
These precautions can avoid vector-borne diseases like malaria, filariasis, dengue and chikungunya.

Immune System

  • It is the system that gives immunity to the body by recognizing, responding and remembering foreign antigens.
  • It plays an important role in an allergic reaction, auto-immune disease and organ transplantation.
  • It includes lymphoid organs, tissues, cells and soluble molecules like antibodies.

Lymphoid Organs

  • These are the organs where origin, maturation and proliferation of lymphocytes occurs.
  • These are of two types namely; primary lymphoid organs and secondary lymphoid organs.
(a) Primary Lymphoid Organs
  • Here, immature lymphocytes differentiate into antigen-sensitive lymphocytes e.g., Bone marrow and thymus.
  • Bone marrow is the main lymphoid organ and is the site of formation of all the blood cells including lymphocytes.
  • Thymus is large during birth but gradually reduces in size and becomes very small in size at puberty.
  • Growth and maturation of T-lymphocytes takes place here.
(b) Secondary Lymphoid Organs
  • The organs to which matured lymphocytes migrate, interact with antigens and then proliferate to become effector cells e.g., Spleen, lymph nodes, tonsils, Peyer’s patches, MALT and appendix are called secondary lymphoid organs. They are :
(i) Spleen :
(i) It is a bean-shaped organ.
(ii) It contains lymphocytes and phagocytes.
(iii) It removes worn-out RBCs and micro-organisms from blood.
(iv) It is a reservoir of erythrocytes in the foetus.

(ii) Lymph Nodes
(i) These are found in the lymphatic system.
(ii) They trap micro-organisms or other antigens that enter the lymph and tissue fluid.
(iii) The trapped antigens activate lymphocytes and cause an immune response.
(iii) Mucosa Associated Lymphoid Tissue (MALT) :
(i) It is located within the lining of respiratory, digestive and urinogenital tracts.
(ii) It constitutes 50% of lymphoid tissue in the human body.

Immunity

  • It is the ability of the immune system of the body to fight against the disease-causing organisms.
  • It is of two types, namely Innate immunity and Acquired immunity.
(a) Innate Immunity
  • It is the non-specific defence present at the time of birth.
  • It provides barriers to the entry of foreign agents into our body.
  • It consists of four types of barriers :

(i) Physical Barriers

  • Skin on our body is the first and main barrier that prevents entry of the micro-organisms. It is the first line of defence.
  • Mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts also help in trapping microbes entering our body.

(ii) Physiological Barriers : Acid in the stomach, saliva in the mouth, tears from eyes–all prevent microbial growth.
(iii) Cellular Barriers : Certain types of leukocytes (WBC) of our body like polymorpho-nuclear leukocytes (PMNL- neutrophils) and monocytes are natural killer (type of lymphocytes) in the blood, as well as macrophages in tissues can phagocytose and destroy microbes.
(iv) Cytokine Barriers : Virus-infected cells secrete proteins called interferon which protect non-infected cells from further viral infection.

(b) Acquired Immunity

  • It is a pathogen-specific immunity.
  • It is not present since birth but develops during the lifetime of an individual.
  • It is characterized by memory i.e., during the first encounter of a pathogen; our body produces a primary response in low intensity. The second encounter with the same pathogen produces a secondary (anamnestic) response in high intensity.
  • The primary and secondary immune responses are carried out with B-lymphocytes and T-lymphocytes.
(a) B-lymphocytes (B-cells) : Produce antibodies.
(b) T-lymphocytes : Help B-cells to produce antibodies.

Structure of an Antibody Molecule

  • Each antibody has 4 polypeptide chains namely, 2 small light chains and 2 large heavy chains (H2L2).
  • In our body different types of antibodies such as : IgG, IgA, IgM, IgE & IgD are produced.
  • Acquired immune response is of two types namely humoral mediated response and cell-mediated response.
(a) Humoral or Antibody-Mediated Response/Antibody-Mediated Immunity (AMI)
  • Antibodies are found in blood plasma. So, it is called as humoral immune response.
  • It includes B-lymphocytes and T-lymphocytes. The latter help the former to produce antibodies.

(b) Cell-Mediated Response/Cell-Mediated Immunity (CMI)

  • It is T-lymphocytes (T-cells) mediated (CMI).
  • CMI causes Graft rejection.
  • The body can differentiate ‘self’ and ‘non-self’.
  • Tissue matching and blood group matching are essential before undertaking any graft / transplant. After this, the patient has to take immune-suppressants for all his life.

Acquired immunity is of two types i.e., active and passive Immunity.
(a) Active Immunity
The immunity in which antibodies are produced in a host body when the host is exposed to antigens (e.g., living or dead microbes or other proteins) is known as active immunity.
It is a slow process.
It is produced in two ways :
(a) Natural Active Immunity : During natural infection by microbes.
(b) Artificial Active Immunity : Injecting the microbes deliberately during immunization.

(b) Passive Immunity :

  • Here, readymade antibodies are directly given to protect the body.
  • It is of two types :
(a) Natural Passive Immunity : e.g., Antibodies (IgG) from mother → Placenta → Foetus → Antibodies (IgA) in colostrum → infants.
(b) Artificial Passive Immunity : e.g., Anti-tetanus serum (ATS).

Immunization

  • This is based on the ‘memory’ of the immune system.
  • It is of two types namely; Active immunization and Passive immunization.
(a) Active Immunization (Vaccination)
  • A preparation of vaccine (antigenic proteins of pathogen or inactivated pathogen) is introduced into the body.
  • The antibodies produced in the body against the antigens neutralize the pathogenic agents during actual infection.
  • The vaccines also generate memory B and T-cells that recognize the pathogen quickly e.g., Polio vaccine, Hepatitis B vaccine, DPT vaccine etc.
  • The vaccines produced by conventional methods e.g., small pox-vaccines are called first-generation vaccine. Those which are synthetic vaccine are the third generation vaccine.
  • Vaccines are produced using DNA recombinant technology (e.g., Hepatitis B vaccine produced from Yeast). Such vaccines are called as second-generation vaccines.

(b) Passive Immunization
It is the direct injection of preformed antibodies or antitoxin. It is for quick immune response e.g., Immunization against tetanus, snake venom, etc.

Allergies

  • It is the exaggerated or hypersensitive response of the immune system to certain antigens present in the environment.
  • Allergens are substances causing allergy e.g., mites in dust, pollens, animal dander, fur, etc.
  • Antibodies produced against the allergens are of IgE type.
  • Allergy is due to the release of chemicals like histamine and serotonin from the mast cells.
  • Symptoms : Sneezing, watery eyes, running nose, difficulty in breathing, etc.
  • Determination of cause of allergy : The patient is exposed to or injected with very small doses of possible allergens and the reactions were studied.
  • Treatment, Drugs like anti-histamine, adrenaline and steroids quickly reduce the symptoms of allergy.
  • Modern-day lifestyle results in lowering of immunity and more sensitivity to allergens.
  • Asthma is a respiratory disease due to allergy.

Auto Immunity

  • It is caused due to genetic and other unknown reasons. The body attacks self cells. This results in auto-immune disease.
  • It is memory-based acquired immunity evolved in higher vertebrates based on the ability to differentiate foreign organisms (such as pathogens) from self-cells : e.g., rheumatoid arthritis.

AIDS (Acquired Immunodeficiency Syndrome)

  • Syndrome is a group of symptoms.
  • AIDS is the deficiency of the immune system.
  • It is caused by HIV (Human Immunodeficiency Virus), a retrovirus having an RNA genome.
  • AIDS was first reported in America (1981).

Modes of Transmission :
(a) Sexual contact with an infected person.
(b) Transfusion of contaminated blood and blood products.
(c) Sharing of infected needles.
(d) From infected mother to her child through the placenta.

High risk of getting HIV includes
(a) Individuals with multiple sexual partners.
(b) Drug addicts who take drugs intravenously using infected syringes.
(c) Individuals who require a repeated blood transfusion.
(d) Children born to an HIV infected mother.

HIV does not spread by touch or physical contact

  • It spreads only through body fluids.
  • There is always a time-lag (from few months to 5-10 years) between the infection and appearance of symptoms.

Life Cycle of HIV Virus :

  • HIV enters into 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 (TH) → Replicate and produce progeny viruses → Attack another helper T-cells → T-cells decrease → Weaken immunity.
  • HIV infected person may be infected with Mycobacterium, viruses, fungi and parasites like Toxoplasma.

Diagnosis of AIDS : ELISA test (Enzyme-linked immune-sorbent Assay) PCR-Test, western blotting, etc.

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

Prevention of AIDS
• Educate peoples about AIDS.
• Making blood (from blood banks) safe from HIV.
• Use of disposable needles and syringes.
• Advocating safe sex and free distribution of condoms.
• Controlling drug abuse.
• Regular check-ups for HIV in a susceptible population.
.

Cancer
• Cancer is an abnormal and uncontrolled multiplication of cells resulting in the formation of tumor (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.
• Tumors are of two types : namely, Benign tumor and Malignant tumor.

(a) Benign Tumor
• It is confined to the place of its origin and does not spread to other parts of the body.
• It is harmless or causes less damage to the body.
(b) Malignant Tumor
• It spreads and invades nearby tissues.
• It is harmful.
Metastasis : The spread of cancer cells from one part of the body to another.

Types of Cancer
• Carcinoma : cancer of epithelial cells.
• Sarcoma : cancer of connective tissues.
• Melanomas : cancer of melanocytes.
• Leukemia : blood cancer.
• Lymphomas : cancer of spleen and lymph nodes.
Causes of Cancer (Carcinogens)
(a) Physical agents : e.g., Ionizing radiations like X-rays and gamma rays and non-ionizing radiations like UV.
(b) Chemical agents : Tobacco smoke (a major cause of lung cancer), vinyl chloride, caffeine, nicotine, mustard gas, etc.
(c) Biological agents : e.g., oncogenic viruses, cellular oncogenes (c-onc) or proto oncogenes, etc. When a C-onc in normal cells is activated, the cells becomes oncogenic.

Cancer Detection and Diagnosis
(a) Biopsy : A thin piece of the suspected tissue is stained and examined under a microscope (histopathological studies).
(b) In case of Leukemia : Biopsy and histopathological studies. Blood and bone marrow tests for increased cell counts.
(c) Radiography (use of X-rays) : CT (Computerized tomography) scan and MRI (Magnetic Resonance Imaging).
(d) Use of antibodies against cancer-specific antigens.
(e) Techniques of molecular biology to detect genes related to cancer. Such individuals may be advised to avoid exposure to particular carcinogens (e.g., tobacco smoke).

Treatment of Cancer
Most cancers are treated by a combination of surgery, radiotherapy and chemotherapy.
(a) Radiation therapy : Tumour cells are irradiated lethally without damaging surrounding normal tissues.
(b) Chemotherapy : Use of chemotherapeutic drugs. Many drugs have side effects like hair loss, anaemia, etc.
(c) Immunotherapy : The patients are given biological response modifiers (e.g., a-interferon) which activates their immune system and helps in destroying the tumour.


IMPORTANT DIAGRAMS :







Drugs and Adolescence

Drugs and their effects
Drugs
• These can alter the activity of the nervous system.
• They are also called as psychotropic drugs or mood-altering drugs or neurological drugs.
• These drugs change the mood, feelings, behaviour and power of perception.
• The sources of most of the drugs are mainly flowering plants and some fungi.


Types of Drugs
• The drugs, which are commonly abused are opioid, cannabinoids and coca alkaloids.
• These drugs are of the following main types :
1. Depressants
• Depress brain activity.
• They include