Following are Human Health and Diseases Notes for Class 12 Biology. These revision notes have been prepared by expert teachers of Class 12 Biology as per the latest NCERT, CBSE, KVS books released for the current academic year. Students should go through Chater 8 Human Health and Diseases concepts and notes as these will help you to revise all important topics and help you to score more marks. We have provided Class 12 Biology notes for all chapters in your book. You can access it all free and download Pdf.

Chapter 8 Human Health and Diseases Notes Class 12

CONCEPT MAP

I. COMMON DISEASES IN HUMANS:
● Pathogens
● Salmonella typhi -Typhoid
● Widal Test
● Streptococcus pneumoniae -Pneumonia
● Rhino virus -Common cold
● Plasmodium sps. -Malaria (P. vivax; P. malaria; P. falciparum)

● Ascaris lumbricoides -Ascariasis
● Wuchereria (W. bancrofti; W. malayi) -Elephantiasis/ Filariasis
● Microsporum; Trichophyton; Epidermatophyton -Ringworm.
● Personal hygiene/ Public hygiene.

II. IMMUNITY:
● What is Immunity? – Overall ability of the host to fight the disease-causing organisms, conferred by the immune system is called immunity.
● Innate Immunity:
Innate immunity is a non-specific type of defence, -present at the time of birth. Innate immunity consists of four types of barriers. These are —
(i) Physical barriers:
Skin on our body is the main barrier which prevents entry of the micro-organisms. 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 and tears -prevent microbial growth.
(i) Cellular barriers: Certain types of leukocytes (WBC) of our body –
Polymorpho-nuclear leukocytes (PMNL-neutrophils).
Monocytes.
Natural killer (type of lymphocytes in the blood).
Macrophages in tissues can phagocytose and destroy microbes.
(ii) Cytokine barriers: Interferons (proteins) secreted by Virus-infected cells to protect non-infected cells from further viral infection.
● Acquired Immunity:
Acquired immunity -on the other hand is pathogen specific -characterised by memory.

Body encounters a pathogen for the first time it produces a primary response –
● low intensity.
Subsequent encounter with the same pathogen elicits an anamnestic response (Secondary response)–
● Highly intensified.
This is ascribed to the memory, during the first encounter.
The primary and secondary immune responses are carried out by B-lymphocytes and T-lymphocytes present in our blood.
B-lymphocytes produce an ‘army’ of proteins called antibodies (Immunoglobins or -globulins) to fight pathogens in our blood.
The T-cells themselves do not secrete antibodies -but ‘help’ B cells to produce them.
Each antibody molecule has four peptide chains -two are small peptide chains called light chains and two are longer peptide chains called heavy chains.
Hence, an antibody is represented as H2L2.
Different types of antibodies are produced in our body. IgG, IgE, IgD, IgM and IgA are some of them.

As these antibodies are found in the blood, the response is also called as Humoral Immune response.
This is one of the two types of our acquired immune response – Antibody Mediated response.
The second type is called Cell-Mediated Immune response or cell-mediated immunity (CMI).
The T-lymphocytes mediate CMI – ‘Tissue/ Organ Rejection’: Why is it that the organs cannot be taken from just anybody? What is it that the doctors check? -Grafts from just any source – an animal, another primate, or any human beings cannot be made since the grafts would be rejected.
Tissue matching and blood group matching -essential before undertaking any graft/transplant -and even after this, the patient has to take immuno–suppresants all his/her life -else the patient’s life may deteriorate.
The body is able to differentiate ‘self’ and ‘nonself’ and the cell-mediated immune response is responsible for the graft rejection.

● Active and Passive Immunity:
⮚ Antigens (“Antibody generating”) -may be in the form of living or dead microbes or other proteins, – ‘Antibodies’ are produced in the host body in response to the antigen that has entered the host body produces

⮚ Active Immunity:
❖ When the host body produces Antibodies in response to Antigens entering the host body.
❖ Active immunity is slow.
❖ It takes time to give its full effective response.
❖ Injecting microbes deliberately during immunisation or infectious organisms entering the body -during natural infection induce ‘active immunity’.

⮚ Passive Immunity:
‘Ready-made antibodies’ (pre-formed antibodies or antibodies produced by other animals) -directly injected into our body to protect our body against foreign pathogenic agents it is called passive immunity.
Give reason as to why breast feeding is very important to an infant than weaning the infant on artificial substitute? Why is mother’s milk is considered very essential for the new born infant?
Examples of Passive Immunity:
● The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgA) to protect the infant from many diseases.
● The foetus also receives some antibodies from their mother, through the Placenta (IgG) during pregnancy.
● Vaccination and Immunisation:
It is based on the property of ‘memory’ of the immune system.
A vaccine is a preparation of antigenic proteins of pathogen or inactivated/weakened pathogen introduced into the body.
The antibodies produced in the body by the host (active immunity) against these antigens, would neutralise the pathogenic agents during actual infection.
The vaccines also generate memory – B and T-cells that recognise the pathogen quickly on subsequent exposure and overwhelm the invaders with a massive production of antibodies.
Passive Immunisation:
During an emergency -If a person is infected with some virulent microbes to which quick immune response is required as in tetanus, it is convenient to just directly inject the ‘pre-formed antibodies’, or ‘antitoxin’ (a preparation containing antibodies to the toxin).

Even in cases of snakebites, the pre-formed antibodies against the snake venom are injected to the patients.
Recombinant DNA technology -Single Cell Proteins:
● It has been made possible to prepare -in large quantities, the antigenic polypeptides of pathogens, by cloning those genes of the pathogen, in bacteria or yeast (‘suitable hosts’ for gene transfer during rDNA technique). Vaccines are produced in a large scale and hence easily available for immunisation, e.g., hepatitis B vaccine produced with the help of yeast.
● ALLERGIES:
▪ Allergy -an exaggerated response of the immune system to certain antigens present in the environment.
▪ Allergens -anything that causes allergic/ immune response – pollen, mites, food, dust, animal dander, etc.
▪ The antibodies produced to these are of IgE type.
▪ Allergy is due to the release of chemicals like histamine and serotonin from the mast cells.
▪ Determining the cause of allergy:
⮚ Use of drugs -anti-histamine, adrenalin and steroids quickly reduce the symptoms of allergy.

Auto Immunity:
Memory-based acquired immunity -based on the ability to differentiate foreign organisms (e.g., pathogens) from ‘self-cells’.
Rheumatoid arthritis is an auto-immune disease.

Immune System in the Body:
⮚ Components of our Immune system:
● Lymphoid organs -Bone marrow, Thymus, Spleen, Tonsil.
● Tissues -Lymph nodes, mucous membranes,
● Cells -Macrophages and
● Soluble molecules -Antibodies.
⮚ Lymphoid organs: Are the organs where origin and/or maturation and proliferation of lymphocytes occur.
⮚ Primary lymphoid organs –
❖ Bone marrow and Thymus.
▪ Here, immature lymphocytes differentiate into antigen-sensitive lymphocytes.

⮚ Secondary lymphoid organs –
❖ Spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix.
▪ The bone marrow -main lymphoid organ = all blood cells including lymphocytes are produced.
▪ The thymus is quite large at the time of birth but keeps reducing in size with age.
▪ At puberty, thymus reduces to a very small size.
▪ Both bone-marrow and thymus provide micro-environments for the development and maturation of T-lymphocytes.
▪ The spleen is a large bean shaped organ. It mainly contains lymphocytes and phagocytes.
▪ Spleen filters blood by trapping blood-borne microorganisms.
▪ Spleen also acts as a large reservoir of erythrocytes.
▪ The lymph nodes are small solid structures located at different points along the lymphatic system.
▪ Lymph nodes serve to trap micro-organisms or other antigens, that enter the lymph.
▪ Antigens trapped in the lymph nodes are responsible for the activation of lymphocytes present there and cause the immune response.

⮚ Mucosa Associated Lymphoid Tissue (MALT) -lymphoid tissue located within the lining of the major tracts (respiratory tract, digestive tract and urogenital tract).
● It constitutes about 50 % of the lymphoid tissue in human body.

III. AIDS:
⮚ AIDS =Acquired Immuno Deficiency Syndrome (not a congenital disease).
⮚ Causative organism: HIV =Human Immuno deficiency Virus (Retro virus -RNA virus)
⮚ ‘Syndrome’ =means a group of symptoms.

Transmission of HIV-infection:
(a) sexual contact with infected person
(b) by transfusion of contaminated blood and blood products
(c) by sharing infected needles as in the case of intravenous drug abusers and
(d) from infected mother to her child through placenta.

High risk individuals of getting this infection includes –
(i) individuals who have multiple sexual partners
(ii) drug addicts who take drugs intravenously
(iii) individuals who require repeated blood transfusions and
(iv) children born to an HIV infected mother.
❖ Very important -please note -HIV/AIDS is not spread by mere touch or physical contact.
❖ It spreads only through body fluids.
❖ It is, imperative (of vital importance), that HIV/AIDS infected persons are not isolated from family and society for their physical and psychological well-being.
❖ Time-lag between infection and appearance of AIDS symptoms -varying from a few months to many years (usually 5-10 years).
The virus enters host body and attacks the macrophages.
The viral RNA genome replicates to form ‘viral DNA’ with the help of the enzyme reverse transcriptase.
This viral DNA integrates into host cell’s DNA and directs the infected cells to produce virus particles.

The macrophages (act as ‘HIV factories’) continue to produce more virus.
Simultaneously, HIV enters helper T-lymphocytes (TH), replicates and produce more viruses.
The progeny viruses released in the blood attack other helper T-lymphocytes.
This leads to a progressive decrease in the number of helper T-lymphocytes.
Now, the person suffers from bouts of fever, diarrhoea and weight loss.
Decrease in the number of helper T lymphocytes, the person starts suffering from infections by bacteria especially Mycobacterium, viruses, fungi and even parasites like Toxoplasma.
The patient becomes very much immuno-deficient that he/she is unable to protect himself/herself against these infections.
Diagnostic test for AIDS is Enzyme Linked Immuno-Sorbent Assay (ELISA).
Treatment of AIDS with anti-retroviral drugs is only partially effective. They can only prolong life of the patient but death inevitable.

Prevention of AIDS:
⮚ AIDS has no cure. Prevention is the best option.
⮚ HIV infection, more often, spreads due to conscious behaviour patterns and does not happen inadvertently (accidentally) -like pneumonia or typhoid -but in certain it maybe inadvertent (accidental), infection from improperly screened blood products transfused in patients, new-borne (from HIV infected mothers) etc., due to poor monitoring.
⮚ The only excuse may be ignorance and it has been rightly said – “don’t die of ignorance”.
⮚ National AIDS Control Organisation (NACO) and other non-governmental organisation (NGOs) are doing a lot to educate people about AIDS.
⮚ A number of Programs (by WHO) to prevent the spreading of HIV infection.
● Making blood (from blood banks) safe from HIV.
● Ensuring the use of only disposable needles and syringes in public and private hospitals and clinics.
● Free distribution of condoms.
● Controlling drug abuse.
● Advocating safe sex and
● Promoting regular check-ups for HIV in susceptible populations.
⮚ AIDS/ HIV Infection should not be hidden – as, the infection will spread.
⮚ HIV/AIDS-infected people need help and sympathy -do not shun them from society.

IV. CANCER:
Cancer cells -there is breakdown of regulatory mechanisms – ‘contact inhibition’ -which ‘Normal cells’ show.
Cancerous cells just continue to divide giving rise tumors.
Tumors are of two types:
❖ Benign tumors –
● -Remain confined to their original location.
● Do not spread to other parts of the body.
● Cause little damage.
❖ Malignant tumors – Neoplastic or tumor cells –
● -Grow very rapidly.
● Invade and damage the surrounding normal tissues.
● Cells actively divide and grow and starve normal cells -by competing for vital nutrients.
● Cells slough from such tumors reach distant sites through blood -get lodged in the body, and start a new tumor called metastasis (most feared property of malignant tumors).

Causes of cancer:
Transformation of normal cells into cancerous neoplastic cells.
Carcinogens -agents that cause cancer.
Carcinogens -physical, chemical or biological agents.
Ionising radiations like X-rays and gamma rays and UV (non-ionizing radiations) cause DNA damage leading to neoplastic transformation.
The chemical carcinogens present in tobacco smoke have been identified as a major cause of lung cancer.
Cancer causing viruses called oncogenic viruses have genes called viral oncogenes.
Several genes called cellular oncogenes (c-onc) or proto-oncogenes have been identified in normal cells get activated under certain conditions, lead to oncogenic transformation of the cells.

Cancer detection and diagnosis:
● Early detection of cancers is essential.
● Cancer detection is based on biopsy and histopathological studies of the tissue and blood and bone marrow tests for increased cell counts in the case of leukemias.
● What is Biopsy? – (histopathological studies) -a piece of the suspected tissue cut into thin sections is stained and examined under microscope by a pathologist.
Useful techniques to detect cancers of the internal organs:
● Radiography (use of X-rays).
● CT (computed tomography) – uses X-rays to generate a three-dimensional image of the internal organs -and
● MRI (Magnetic Resonance Imaging) – uses strong magnetic fields and non-ionising radiations to accurately detect pathological and physiological changes in the living tissue.
● Antibodies against cancer-specific antigens are also used for detection of certain cancers.
● Techniques of molecular biology -can be applied to –
o Detect genes in individuals with inherited susceptibility to certain cancers, which predispose an individual to certain cancers helpful in prevention of cancers.
o Such individuals -advised to avoid exposure to particular carcinogens to which they are susceptible (e.g., tobacco smoke in case of lung cancer).

Treatment of cancer:
Approaches for treatment of cancer are surgery, radiation therapy and immunotherapy.
Radiotherapy –tumor cells are irradiated lethally, taking proper care of the normal tissues surrounding the tumor mass.
Chemotherapy –Chemotherapeutic drugs are used to kill cancerous cells.
o Majority of drugs have side effects -hair loss, anemia, etc.
o Most cancers are treated by combination of -surgery, radiotherapy and chemotherapy.
Tumor cells have been shown to avoid detection and destruction by immune system.
Therefore, the patients are given substances called biological response modifiers such as ‘α-interferon’ which activates their immune system and helps destroy the tumor.

V. DRUGS AND ALCOHOL ABUSE:
The drugs, which are commonly abused are -opioids, cannabinoids and coca alkaloids. Majority of these are obtained from flowering plants. Some are obtained from fungi.
Opioids:
Drugs, which bind to specific ‘opioid receptors’ present in our central nervous system and gastrointestinal tract.
Heroin –commonly called ‘smack’ is chemically ‘diacetylmorphine’ which is a white, odourless, bitter crystalline compound.
This is obtained by acetylation of morphine, which is extracted from the latex of poppy plant Papaver somniferum.

Generally taken by snorting and injection.
Heroin is a depressant and slows down body functions.
Cannabinoids: Groupe of chemicals which interact with cannabinoid receptors present principally in the brain. Natural cannabinoids are obtained from the inflorescences of the plant Cannabis
sativa.
The flower tops, leaves and the resin of cannabis plant are used in various combinations to produce marijuana, hashish, charas and ganja. Generally taken by inhalation and oral ingestion, these are known for their effects on cardiovascular system of the body.
Coca alkaloid or Cocaine:
⮚ Obtained from Erythroxylum coca.
⮚ It interferes with the transport of the neuro-transmitter dopamine. Cocaine commonly called coke or crack.
⮚ Usually snorted.
⮚ It has a potent stimulating action on central nervous system, producing a sense of euphoria and increased energy. Excessive dosage of cocaine causes hallucinations.
⮚ Other well-known plants with hallucinogenic properties are Atropa belladona and Datura.
⮚ Cannabinoids are also abused by some sportspersons.
⮚ Drugs often abused -barbiturates, amphetamines, benzodiazepines -normally used to help patients cope with mental illnesses like depression and insomnia.
⮚ Morphine -very effective sedative and painkiller, and is very useful in patients who have undergone surgery.
⮚ When hallucinogens are taken for a purpose other than medicinal use or in amounts/frequency that impairs one’s physical, physiological or psychological functions, it constitutes drug abuse.
⮚ Smoking also paves the way to hard drugs.
▪ Tobacco is smoked, chewed or used as a snuff.
▪ Tobacco contains a large number of chemical substances including nicotine, an alkaloid.
▪ Nicotine stimulates adrenal gland to release adrenaline and nor-adrenaline into blood circulation, both of which raise blood pressure and increase heart rate.
▪ Smoking is associated with increased incidence of cancers of lung, urinary bladder and throat, bronchitis, emphysema, coronary heart disease, gastric ulcer, etc.
▪ Tobacco chewing is associated with increased risk of cancer of the oral cavity.
▪ Smoking increases carbon monoxide (CO) content in blood and reduces the concentration of haem bound oxygen. This causes oxygen deficiency in the body.
▪ When one buys packets of cigarettes one cannot miss the statutory warning that is present on the packing which warns against smoking and says how it is injurious to health. Yet, smoking is very prevalent in society, both among young and old.

Adolescence and Drug/Alcohol Abuse:
⮚ The period between 12-18 years of age may be thought of as adolescence period. In other words, adolescence is a bridge linking childhood and adulthood.
⮚ Adolescence is accompanied by several biological and behavioural changes.
⮚ Common causes -Curiosity, need for adventure – excitement and experimentation -motivates youngsters towards drug and alcohol use.
⮚ A child’s natural curiosity motivates him/her to experiment.
⮚ Further complications – ‘effects’ that might be perceived as benefits, of alcohol or drug use.
⮚ First use of drugs or alcohol may be out of curiosity or experimentation – the child later starts using these to escape facing problems.
⮚ Stress, from pressures to excel in academics or examinations, persuade the youngsters to try alcohol and drugs.
⮚ The perception among youth that it is ‘cool’ or ‘progressive’ to smoke, use drugs or alcohol -another major cause for youth to start these habits.
⮚ Television, movies, newspapers, internet also help to promote this perception.
⮚ Unstable or unsupportive family structures and peer pressure -promote drug and alcohol abuse among adolescents.

Addiction and Dependence:
⮚ Addiction: A psychological attachment to certain effects –such as euphoria and a temporary feeling of well-being –associated with drugs and alcohol.
⮚ It drives people to take them even when not needed, or even when their use becomes self-destructive.
⮚ Repeated use of drugs, increases tolerance level of the receptors present in our body.
⮚ Hence, the receptors respond only to higher doses of drugs or alcohol leading to greater intake and addiction. the person gets addicted and becomes dependent on their use.
⮚ Dependence -tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome if regular dose of drugs/alcohol is abruptly discontinued.
⮚ Symptoms of dependence: Anxiety, shakiness, nausea and sweating, which may be relieved when use is resumed again.
⮚ Withdrawal symptoms: can be severe and even life threatening and the person may need medical supervision.
⮚ Dependence makes patient to ignore all social norms in order to get sufficient funds to satiate his/her needs. These result in many social adjustment problems.

Effects of Drug/Alcohol Abuse:
Reckless behaviour, vandalism and violence.
Excessive doses of drugs may lead to coma and death due to respiratory failure, heart failure or cerebral hemorrhage.
A combination of drugs or their intake along with alcohol generally results in overdosing and even deaths.
The most common warning signs of drug and alcohol abuse among youth include drop in academic performance, unexplained absence from school/college, lack of interest in personal hygiene, withdrawal, isolation, depression, fatigue, aggressive and rebellious behaviour, deteriorating relationships with family and friends, loss of interest in hobbies, change in sleeping and eating habits, fluctuations in weight, appetite, etc.
Far-reaching implications of drug/alcohol abuse -stealing and even murder.
It causes mental and financial distress to his/her entire family and friends.
High risk individuals – intravenous drugs addicts -likely to acquire serious infections like AIDS and Hepatitis B. The pathogens, are transferred from one person to another by sharing of infected needles and syringes. Both AIDS and Hepatitis B infections are chronic infections and ultimately fatal which can be transmitted through sexual contact or infected blood.
The use of alcohol during adolescence may also have long-term effects.
It could lead to excessive drinking in adulthood.
It damages nervous system and liver (cirrhosis).
During pregnancy -the use of drugs and alcohol adversely affects the foetus.
Drug abuse by athletes, by (mis)using narcotic analgesics, anabolic steroids, diuretics and certain hormones in sports to increase muscle strength and bulk and to promote aggressiveness and as a result increase athletic performance.
The side-effects of the abuse of anabolic steroids in females include masculinisation (features like males), increased aggressiveness, mood swings, depression, abnormal menstrual cycles, excessive hair growth on the face and body, enlargement of clitoris, deepening of voice.

In males it includes acne, increased aggressiveness, mood swings, depression, reduction of size of the testicles, decreased sperm production, potential for kidney and liver dysfunction, breast enlargement, premature baldness, enlargement of the prostate gland.
These effects may be permanent with prolonged use.
In the adolescent male or female, severe facial and body acne, and premature closure of the growth centers of the long bones may result in stunted growth.

8.5.4 Prevention and Control:
(i) Avoid undue peer pressure –
▪ Respect and nurture every child by his/her own choice and personality.
▪ A child should not be pushed unduly to perform beyond his/her threshold limits -be it studies, sports or other activities.
(ii) Education and counselling –
▪ Educating and counselling him/ her to face problems and stresses, and to accept disappointments and failures as a part of life.
▪ It would also be worthwhile to channelize the child’s energy into healthy pursuits like sports, reading, music, yoga and other extracurricular activities.
(iii) Seeking help from parents and peers –
▪ Help from parents and peers should be sought immediately so that they can guide appropriately.
▪ Help may even be sought from close and trusted friends –(a) for proper advice to sort out their problems, (b) helps the young to vent their feelings of anxiety and guilt.
(iv) Looking for danger signs –
▪ Alert parents and teachers -look for and identify ‘danger signs.
▪ ‘Friends’, should not hesitate reporting incidence of someone using drugs or alcohol -parents or teacher in the best interests of the drug/ alcohol addict.
▪ Appropriate measures to diagnose the malady and the underlying causes.
(v) Seeking professional and medical help –
▪ Seek help form of highly qualified psychologists, psychiatrists.
▪ De-addiction and rehabilitation programs.
▪ Affected individual -with sufficient efforts and will power, can get rid of the problem completely and lead a perfectly normal and healthy life.