Human Health and Disease

The chapter opens by fixing what the word health means, because students tend to write 'absence of disease' and lose the mark. NCERT defines health as a state of complete physical, mental and social well-being. Being free of disease is only a part of it; a person who is physically sound but under constant mental stress is not healthy in this sense.

There is a small piece of history that examiners occasionally pick out. The Greek physician Hippocrates and the Indian Ayurveda system held that health was a balance of four humours and that disease came from a disturbance of them. Two developments in the modern era ended that view: William Harvey's discovery of blood circulation using the experimental method, and the demonstration with a thermometer that a person supposedly carrying 'black bile' had a normal body temperature. Later, biology showed that health is affected by three groups of causes: genetic disorders (defects a child is born with), infections, and lifestyle (food, water, rest, exercise, habits).

Why does health matter beyond the individual? Good health raises productivity and brings economic prosperity, lengthens the life span and reduces infant and maternal mortality. NCERT lists the things that maintain health: a balanced diet, personal hygiene, regular exercise (yoga is named as one that has been practised since ancient times), awareness about diseases and their effects, vaccination against infectious diseases, proper disposal of wastes, control of vectors and hygienic food and water resources.

A disease is any condition in which the functioning of one or more organs or systems of the body is adversely affected, with characteristic signs and symptoms. Diseases are grouped into infectious ones, which spread from one person to another (they are still the major cause of death), and non-infectious ones, which do not spread; NCERT's example is cancer, the major cause of death among non-infectious diseases. Drug and alcohol abuse is treated separately because it damages health without any pathogen.

Organisms that cause disease are pathogens. NCERT covers them by group: bacteria, viruses, protozoans, helminths and fungi. Most pathogens enter with food and water, multiply, and interfere with the normal function of an organ. For each disease you need four things ready: the pathogen (with correct spelling and italics for the genus and species), the organ or tissue attacked, the symptoms, and the mode of transmission. One-mark questions come from any of the four.

Typhoid. Caused by the bacterium Salmonella typhi. It enters the small intestine through contaminated food and water and then migrates through blood to other organs. Symptoms are sustained high fever (39° to 40°C), weakness, stomach pain, constipation, headache and loss of appetite. In severe cases intestinal perforation can lead to death. It is confirmed by the Widal test. NCERT tells the story of Mary Mallon, 'Typhoid Mary', a cook who was a carrier and spread typhoid for years through the food she prepared; carriers matter because they show no symptoms.

Pneumonia. Caused by Streptococcus pneumoniae and Haemophilus influenzae, which infect the alveoli of the lungs. The alveoli fill with fluid, so gas exchange is severely reduced. Symptoms: fever, chills, cough and headache; in severe cases the lips and fingernails turn grey to bluish because of poor oxygenation. It spreads by inhaling droplets or aerosols released by an infected person, or by sharing glasses and utensils.

Common cold. Caused by rhinoviruses, which infect the nose and respiratory passage but not the lungs; this 'not the lungs' phrase is a favourite fill-in-the-blank. Symptoms: nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness, lasting 3 to 7 days. It spreads through droplets from coughs and sneezes and through contaminated objects such as pens, books, cups, doorknobs and computer keyboards.

Keep the bacterial and viral diseases separate in your head: a question like 'name a bacterial disease of the respiratory tract' wants pneumonia, while 'a viral disease of the respiratory tract' wants common cold.

Malaria is the single most examined disease in the chapter, because it carries a life cycle with two hosts and a diagram (NCERT Figure 7.1). It is caused by the protozoan Plasmodium. Three species are named: P. vivax, P. malariae and P. falciparum; P. falciparum causes the most serious, malignant malaria, which can be fatal. The vector is the female Anopheles mosquito; only the female bites because she needs a blood meal.

In the human host. When an infected female Anopheles bites, Plasmodium enters the blood as sporozoites, the infective stage. Sporozoites reach the liver and multiply in the liver cells. The parasites then burst out and attack the red blood cells (RBCs), where they multiply further and rupture the RBCs. The rupture releases a toxic substance, haemozoin, and it is haemozoin that produces the characteristic chill and high fever recurring every three to four days. Some parasites in the RBCs develop into the sexual stages, male and female gametocytes. A question on 'why does a malaria patient get fever in cycles' is answered with the RBC rupture and haemozoin.

In the mosquito. When a female Anopheles bites an infected person, she takes up gametocytes with the blood. Fertilisation and development take place in the mosquito's gut, forming sporozoites which are stored in the salivary glands. When this mosquito bites another human, the sporozoites are injected and the cycle begins again.

So the parasite needs two hosts: the human, in which the asexual stages occur, and the female Anopheles, in which the sexual stages (fertilisation and sporozoite formation) occur. Because the mosquito is where sexual reproduction takes place, it is called the definitive host and the human the intermediate host, though NCERT itself only says 'two hosts'.

For the 5-mark version, write the human phase and the mosquito phase as separate paragraphs, draw the cycle with the mosquito at the top and the human at the bottom, and label sporozoites, liver cells, RBCs, haemozoin release, gametocytes, fertilisation in the gut and sporozoites in the salivary glands.

Amoebiasis (amoebic dysentery). Caused by the protozoan Entamoeba histolytica, a parasite of the large intestine. Symptoms: constipation, abdominal pain and cramps, and stools with excess mucous and blood clots. Houseflies act as mechanical carriers, transferring the parasite from the faeces of an infected person to food and food products; drinking water and food contaminated by faecal matter are the main sources. 'Mechanical carrier' is the precise phrase to use; the fly does not host the parasite the way Anopheles hosts Plasmodium.

Ascariasis. Caused by the common roundworm Ascaris, an intestinal parasite (a helminth). Symptoms: internal bleeding, muscular pain, fever, anaemia and blockage of the intestinal passage. Eggs of the parasite are excreted with faeces and contaminate soil, water and plants; a healthy person gets infected through contaminated vegetables, fruits and water. So it is a soil- and water-borne infection acquired by ingestion, not by a vector.

Filariasis (elephantiasis). Caused by the filarial worms Wuchereria bancrofti and W. malayi. They live in the lymphatic vessels (usually of the lower limbs) and cause slowly developing chronic inflammation of the organs in which they live for many years. The gross deformity of the limbs and of the genital organs is what gives the name elephantiasis. The pathogen is transmitted by the bite of female mosquito vectors (the Culex mosquito, though NCERT just says female mosquito).

Ringworm. A fungal infection caused by the genera Microsporum, Trichophyton and Epidermophyton. Symptoms: dry, scaly lesions on the skin, nails and scalp with intense itching. Heat and moisture help the fungi grow, which is why the infection is common in skin folds such as the groin and between the toes. It is acquired from soil or by using towels, clothes or combs of infected people.

Examiners like a table with four columns: disease, pathogen, organ affected, mode of transmission. Practise writing all eight diseases of section 7.1 in that format; it is the fastest way to secure a 3-mark 'complete the table' question.

Since many of these diseases are preventable, the chapter ends section 7.1 with a set of public health measures. This paragraph is the source of the frequently asked 'suggest public health measures against infectious diseases' and 'how would you control vector-borne diseases' questions, and the exercise question 7.1 is the same thing.

Personal hygiene means keeping the body clean, and consuming clean drinking water, food, vegetables and fruits. Public hygiene means proper disposal of waste and excreta, periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks, and observing standard practices of hygiene in public catering. These measures are aimed at the diseases that spread through food and water, such as typhoid, amoebiasis and ascariasis.

For air-borne diseases such as pneumonia and common cold, the advice is to avoid close contact with the infected person or their belongings, in addition to the measures above.

For vector-borne diseases such as malaria and filariasis, the most important step is to control or eliminate the vectors and their breeding places. NCERT's list: avoid stagnation of water in and around residential areas; regularly clean household coolers; use mosquito nets; introduce fish like Gambusia in ponds, which feed on mosquito larvae; spray insecticides in ditches, drainage areas and swamps; and fit doors and windows with wire mesh to keep mosquitoes out. The chapter notes that these steps have become especially important given the recent widespread incidence of dengue and chikungunya in many parts of India, both spread by the Aedes mosquito.

Finally, the discovery of vaccines and immunisation programmes has allowed the eradication of smallpox and the control of polio, diphtheria, pneumonia and tetanus; and biotechnology is producing safer vaccines. Antibiotics and other drugs have made it possible to treat infectious diseases effectively. This is the answer to exercise 7.2, 'how has the study of biology helped us control infectious diseases'.

Immunity is the overall ability of the host to fight the disease-causing organisms, conferred by the immune system. Every day we are exposed to a large number of infectious agents, yet only a few of these exposures result in disease, because of this ability. Immunity is of two types: innate and acquired.

Innate immunity is non-specific and is present at birth. It provides different types of barriers to the entry of foreign agents into the body. NCERT lists four barriers, and a 3-mark question asks for all four with examples.

Physical barriers. The skin is the main barrier and prevents the entry of micro-organisms. The mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts helps in trapping microbes.

Physiological barriers. Acid in the stomach, saliva in the mouth and tears from the eyes prevent microbial growth. These work by chemical conditions rather than by physically blocking entry.

Cellular barriers. Certain types of leukocytes (white blood cells), namely the polymorpho-nuclear leukocytes (PMNL-neutrophils) and monocytes, and the natural killer (NK) lymphocytes in the blood, as well as macrophages in tissues, can phagocytose and destroy microbes. The question 'name the cellular barrier' is answered with these cells; 'monocytes' and 'natural killer cells' are the two most asked names.

Cytokine barriers. Virus-infected cells secrete proteins called interferons, which protect non-infected cells from further viral infection. Note that interferons are secreted by infected cells and act on neighbouring healthy cells; a common error is to say they destroy the virus directly.

Write each barrier with its two or three examples. A common lost mark is to list the skin under physiological barriers or the stomach acid under physical barriers.

Acquired immunity is pathogen specific and is characterised by memory. When the body meets a pathogen for the first time it produces a response called the primary response, which is of low intensity. A subsequent encounter with the same pathogen produces a highly intensified secondary or anamnestic response. The reason is the memory of the first encounter, carried in memory cells. This primary-versus-secondary contrast is asked as a 2-mark question and also as a graph in case-based questions: the secondary curve rises faster, higher and lasts longer.

Acquired immunity is carried out by two special types of lymphocytes, B-lymphocytes and T-lymphocytes. The B-lymphocytes produce an army of proteins called antibodies in response to pathogens in the blood. The T-cells do not secrete antibodies themselves but help B cells produce them.

Structure of an antibody (NCERT Figure 7.2). Each antibody molecule has four peptide chains: two small light chains and two longer heavy chains, so an antibody is written H₂L₂. The chains form a Y shape; the tips of the arms carry the antigen-binding sites. The chains are held by disulphide bonds. Different types of antibodies are produced in the body: IgA, IgM, IgE, IgG (the other class, IgD, is not named in NCERT).

Humoral immune response. Because antibodies are found in the blood, the response mediated by antibodies is called the humoral immune response, or antibody-mediated response; 'humor' is an old word for body fluid.

Cell-mediated immunity (CMI). The T-lymphocytes mediate cell-mediated immunity. Its importance shows up in organ transplantation. When a patient receives a graft of kidney, heart, eye or liver from a donor, the body is able to distinguish 'self' from 'nonself', and the cell-mediated immune response is responsible for graft rejection. That is why tissue (blood group) matching is done before grafting and why patients are given immuno-suppressants for life afterwards. 'Which type of immune response causes graft rejection?' is a standard 1-mark question and the answer is cell-mediated immunity.

So the two acquired responses are: B cells and antibodies (humoral) against pathogens in body fluids, and T cells (cell-mediated) against infected or foreign cells. Both keep memory cells.

This short section gives the chapter's most repeated 2-mark differentiation. Learn it as two clean definitions with an example of each.

Active immunity. When a host is exposed to antigens, which may be living or dead microbes or other proteins, the host's own body produces antibodies. This is active immunity. It is slow and takes time to give its full effective response, but it is long-lasting because memory cells are formed. It can be induced in two ways: by natural infection, or deliberately by injecting microbes during immunisation. Both count as active immunity because in both the body makes its own antibodies.

Passive immunity. When ready-made antibodies are given directly to protect the body against foreign agents, it is passive immunity. It is immediate in effect but short-lived, because no memory cells are formed and the borrowed antibodies are eventually broken down. NCERT gives two natural examples: the yellowish fluid colostrum secreted by the mother during the initial days of lactation has abundant antibodies (IgA) to protect the infant; and the foetus receives some antibodies from its mother through the placenta during pregnancy. Deliberate passive immunity, such as anti-tetanus serum, is covered in the next section.

The colostrum point is the basis of the popular question 'why are breast-fed babies more immune to diseases than bottle-fed babies?'. The answer is that mother's milk, especially colostrum, contains IgA antibodies that bottle-fed babies do not receive, so the breast-fed baby has passive immunity in its first weeks. Name the antibody class, IgA; that is where the second mark sits.

A quick way to fix the difference: 'active' means the body is active in making antibodies; 'passive' means the body passively receives antibodies made elsewhere.

The principle of immunisation or vaccination is based on the property of memory of the immune system. In vaccination, a preparation of antigenic proteins of the pathogen, or inactivated/weakened pathogen (a vaccine), is introduced into the body. The antibodies produced in the body against these antigens neutralise the pathogenic agents during actual infection. The vaccines also generate memory B and T cells, which recognise the pathogen quickly on subsequent exposure and overwhelm the invaders with a massive production of antibodies. Vaccination is therefore an example of artificially induced active immunity.

NCERT then describes passive immunisation. If a person is infected with some deadly microbes to which a quick immune response is required, as in tetanus, we need to inject preformed antibodies, or antitoxin (a preparation containing antibodies to the toxin) directly. Even in cases of snake bites, the injection given to patients contains preformed antibodies against the snake venom. This type of immunisation is called passive immunisation. The examiner's question is usually 'why is anti-tetanus serum given to a person with a deep wound instead of a vaccine?', and the answer is that the vaccine would take days to produce antibodies while the toxin acts fast, so ready-made antibodies are given for immediate protection.

The last paragraph is about modern vaccine production. Recombinant DNA technology allows the production of antigenic polypeptides of a pathogen in bacteria or yeast; vaccines produced this way allow large-scale production and hence greater availability for immunisation. NCERT's example is the hepatitis B vaccine produced from yeast. This links to Chapter 10 (Biotechnology and its Applications), and 'name the organism used to produce hepatitis B vaccine' is a standard 1-mark item: yeast.

NCERT exercise 7.5 asks you to discuss what 'a suitable gene' means in the context of DNA vaccines. The expected sense: a suitable gene is the piece of pathogen DNA that codes for an antigenic protein of the pathogen; when introduced into the host it is expressed to produce that antigen, which triggers antibody production and memory without any live pathogen.

Most of us know someone who starts sneezing when the dust flies. That is an allergy. NCERT defines allergy as the exaggerated response of the immune system to certain antigens present in the environment. The substances to which such an immune response is produced are called allergens. Examples of allergens: mites in dust, pollens, animal dander.

The mechanism is what earns marks. The antibodies produced against allergens are of the IgE type. Allergy is due to the release of chemicals like histamine and serotonin from the mast cells. So the chain is: allergen enters → IgE antibodies are made → on subsequent exposure the allergen binds IgE on mast cells → mast cells release histamine and serotonin → inflammatory symptoms. The symptoms NCERT lists: sneezing, watery eyes, running nose and difficulty in breathing.

To determine the cause of an allergy, the patient is exposed to or injected with very small doses of possible allergens and the reactions studied. Treatment uses drugs like anti-histamine, adrenalin and steroids, which quickly reduce the symptoms. The question 'what is the role of mast cells in allergy?' wants 'release of histamine and serotonin'; the question 'name the antibody involved in allergy' wants IgE; and 'name two drugs that reduce allergic symptoms' wants any two of the three listed.

The section ends with a social observation that examiners turn into a reasoning question: modern-day lifestyle has resulted in lowering of immunity and more sensitivity to allergens. More and more children in metro cities of India suffer from allergies and asthma due to sensitivity to the environment, and this may be because of the protected environment provided early in life. If asked why children in cities are more allergic, this is the expected answer.

This is the shortest section in the chapter, but it turns up as a 1- or 2-mark question because the definition is precise. Memory-based acquired immunity evolved in higher vertebrates on the basis of the ability to differentiate foreign organisms (for example pathogens) from self-cells. Although we still do not fully understand the basis of this, two corollaries of this ability have to be understood.

The first is that higher vertebrates can distinguish foreign molecules and foreign organisms from their own; this is the basis of graft rejection, which section 7.2.2 explained. The second is the failure case: sometimes, due to genetic and other unknown reasons, the body attacks self-cells. This results in damage to the body and is called an auto-immune disease. NCERT's single named example is rheumatoid arthritis, which affects many people in our society. If a question asks for another example you may add ones from general knowledge such as type 1 diabetes or myasthenia gravis, but rheumatoid arthritis is the safe NCERT answer.

Write the definition in two sentences: the immune system normally distinguishes self from non-self; in an auto-immune disease this discrimination fails and the immune system attacks the body's own cells. Then give the example. Students sometimes confuse auto-immunity with allergy: allergy is an exaggerated response to a harmless external antigen, auto-immunity is a response against the body's own cells. Another confusion is with immunodeficiency (AIDS), where the immune system is too weak; in auto-immunity it is misdirected, not weak. Keeping these three apart is enough to answer any variant of the question.

The human immune system consists of lymphoid organs, tissues, cells and soluble molecules like antibodies. The system recognises foreign antigens, responds to them and remembers them. It also plays a role in allergic reactions, auto-immune diseases and organ transplantation. Lymphoid organs are the organs where the origin and/or maturation and proliferation of lymphocytes occur. They are of two kinds.

Primary lymphoid organs are the bone marrow and the thymus, where immature lymphocytes differentiate into antigen-sensitive lymphocytes. The bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced. The thymus is a lobed organ located near the heart and beneath the breastbone; it is quite large at the time of birth but keeps reducing in size with age and is very small by the time of puberty. Both bone marrow and thymus provide micro-environments for the development and maturation of T-lymphocytes (thymus) and B-lymphocytes (bone marrow). 'Why does the thymus shrink with age' and 'what would happen if the thymus were removed at birth' are the reasoning questions from here: without a thymus, T cells cannot mature, so cell-mediated immunity and the helper function for B cells are lost.

Secondary lymphoid organs are where the mature lymphocytes migrate after maturation and where they interact with the antigen and proliferate to become effector cells. They are the spleen, lymph nodes, tonsils, Peyer's patches of the small intestine and appendix.

Spleen. A large bean-shaped organ. It mainly contains lymphocytes and phagocytes. It acts as a filter of the blood by trapping blood-borne micro-organisms, and it has a large reservoir of erythrocytes. Those two roles are the 2-mark question on the spleen.

Lymph nodes. Small solid structures located at different points along the lymphatic system. They trap micro-organisms or other antigens that enter the lymph and tissue fluid. Antigens trapped in the lymph nodes activate the lymphocytes present there and cause the immune response.

MALT. Within the lining of the major tracts (respiratory, digestive and urogenital) there is lymphoid tissue called mucosa-associated lymphoid tissue (MALT). It constitutes about 50 per cent of the lymphoid tissue in the human body. Exercise 7.7 asks for the full forms of MALT, CMI, AIDS, NACO and HIV; have all five ready.

AIDS stands for Acquired Immuno Deficiency Syndrome, a deficiency of the immune system acquired during the lifetime of an individual, indicating that it is not a congenital disease. 'Syndrome' means a group of symptoms. It was first reported in 1981 and in the following twenty-five years spread all over the world, killing more than 25 million persons (the NCERT figure).

AIDS is caused by the Human Immunodeficiency Virus (HIV), a member of a group of viruses called retroviruses, which have an envelope enclosing the RNA genome. Transmission generally occurs by (a) sexual contact with an infected person, (b) transfusion of contaminated blood and blood products, (c) sharing infected needles, as in the case of intravenous drug abusers, and (d) from an infected mother to her child through the placenta. So the people at high risk are those with multiple sexual partners, drug addicts who take drugs intravenously, individuals who require repeated blood transfusions, and children born to an HIV-infected mother. NCERT stresses that HIV does not spread by mere touch or physical contact; it spreads only through body fluids. There is always a time-lag between the infection and the appearance of AIDS symptoms, which can vary from a few months to 5 to 10 years.

Replication of HIV (NCERT Figure 7.3). After getting into the body, the virus enters macrophages. Its RNA genome replicates to form viral DNA with the help of the enzyme reverse transcriptase. This viral DNA gets incorporated into the host cell's DNA and directs the infected cells to produce virus particles. The macrophages continue to produce virus and in this way act like an HIV factory. Simultaneously HIV enters helper T-lymphocytes (T_H), replicates and produces progeny viruses. The progeny viruses released in the blood attack other helper T-lymphocytes. This is repeated, leading to a progressive decrease in the number of helper T-lymphocytes in the body of the infected person. During this period the person suffers from bouts of fever, diarrhoea and weight loss. Because of the loss of helper T cells the person becomes unable to produce any immune response, and is infected by bacteria, especially Mycobacterium, viruses, fungi and parasites like Toxoplasma. Note the order: macrophages first (the factory), then helper T cells (the count that falls).

Diagnosis is by ELISA (enzyme-linked immuno-sorbent assay). Treatment with anti-retroviral drugs is only partially effective; it can prolong life but cannot prevent death, which is inevitable.

Prevention. Since AIDS has no cure, prevention is the best option. In India, NACO (National AIDS Control Organisation) and NGOs educate people. WHO has started programmes: making blood from blood banks safe from HIV, ensuring use of disposable needles and syringes in public and private hospitals, free distribution of condoms, controlling drug abuse, advocating safe sex and promoting regular check-ups for HIV in susceptible populations. Infection is regarded as a social problem, and infected people need help and sympathy rather than being shunned. 1 December is World AIDS Day.

Cancer is one of the most dreaded diseases and a major cause of death worldwide. The chapter explains what goes wrong in a cancer cell, what causes it, how it is detected and how it is treated; any of these can be a 3- or 5-mark question.

What a cancer cell is. Normal cells show a property called contact inhibition: contact with other cells inhibits their uncontrolled growth. Cancer cells appear to have lost this property, so they continue to divide, giving rise to masses of cells called tumours. Tumours are of two types. Benign tumours normally remain confined to their original location, do not spread to other parts of the body and cause little damage. Malignant tumours are a mass of proliferating cells called neoplastic or tumour cells; they grow very rapidly, invade and damage the surrounding normal tissues, and compete with normal cells for vital nutrients. Cells sloughed from such tumours reach distant sites through blood, and wherever they get lodged they start a new tumour. This property is called metastasis, and it is the most feared property of malignant tumours. Exercise 7.12 (cancer cell versus normal cell) and 7.13 (metastasis) come straight from these lines.

Causes. The transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents called carcinogens. Ionising radiations like X-rays and gamma rays and non-ionising radiations like UV cause DNA damage leading to neoplastic transformation. The chemical carcinogens in tobacco smoke are the 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 which, when activated under certain conditions, lead to the oncogenic transformation of the cells.

Detection and diagnosis. Early detection 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 leukaemias. In biopsy a piece of the suspected tissue cut into thin sections is stained and examined under the microscope by a pathologist. Techniques like radiography (use of X-rays), CT (computed tomography) and MRI (magnetic resonance imaging) are very useful to detect cancers of the internal organs. CT uses X-rays to generate a three-dimensional image of the internals of an object; MRI uses strong magnetic fields and non-ionising radiations to detect pathological and physiological changes in living tissue. Antibodies against cancer-specific antigens are also used for detection of certain cancers, and techniques of molecular biology can detect genes in individuals with inherited susceptibility to certain cancers.

Treatment. The common approaches are surgery, radiation therapy and immunotherapy. In radiotherapy tumour cells are irradiated lethally while taking care of the surrounding normal tissues. Several chemotherapeutic drugs are used, and most have side effects such as hair loss and anaemia. Most cancers are treated by a combination of surgery, radiotherapy and chemotherapy. Because tumour cells avoid detection and destruction by the immune system, patients are given substances called biological response modifiers such as α-interferon, which activate their immune system and help destroy the tumour; this is immunotherapy.

NCERT reports that surveys and statistics show a rise in the use of drugs and alcohol, especially among the youth, and treats the topic as a health issue. The drugs commonly abused are opioids, cannabinoids and coca alkaloids, all obtained from flowering plants, plus some from fungi.

Opioids are drugs that bind to specific opioid receptors present in the central nervous system and gastrointestinal tract. Heroin, commonly called smack, is chemically diacetylmorphine, a white, odourless, bitter crystalline compound obtained by acetylation of morphine, which is extracted from the latex of the poppy plant Papaver somniferum. Heroin is a depressant and slows down body functions. Morphine itself is a very effective sedative and painkiller and is useful in patients who have undergone surgery.

Cannabinoids are a group of chemicals that interact with cannabinoid receptors present principally in the brain. Natural cannabinoids are obtained from the inflorescences of Cannabis sativa. The flower tops, leaves and resin are used in various combinations to produce marijuana, hashish, charas and ganja. Cannabinoids affect the cardiovascular system, and these days they are also being abused by some sportspersons.

Coca alkaloid or cocaine is obtained from the coca plant Erythroxylum coca, native to South America. It interferes with the transport of the neurotransmitter dopamine. Cocaine, commonly called coke or crack, is usually snorted. It has a potent stimulating action on the central nervous system, producing a sense of euphoria and increased energy; excessive dosage causes hallucinations. Other plants with hallucinogenic properties are Atropa belladona and Datura. Drugs used as medicines to help patients cope with mental illnesses like depression and insomnia, such as barbiturates, amphetamines, benzodiazepines and LSD, are also often abused. Smoking, alcohol and drugs are all forms of abuse.

7.5.1 Adolescence. Adolescence is the period between 12 and 18 years, a bridge between childhood and adulthood, marked by biological and behavioural changes. It is a vulnerable phase. NCERT names the causes of first use: curiosity, need for adventure and excitement, and experimentation; the pressure of peers; the wish to excel in school or examinations; unstable or unsupportive family structures; and television, movies, newspapers and the internet that promote the perception that smoking or drinking is 'cool'.

7.5.2 Addiction and dependence. Addiction is a psychological attachment to certain effects such as euphoria and a temporary feeling of well-being, which drives people to take the drug even when it is not needed. With repeated use, the tolerance level of the receptors in the body increases, so the receptors respond only to higher doses, and this is what leads to greater intake and addiction. Dependence is the tendency of the body to show a characteristic and unpleasant withdrawal syndrome if regular intake is abruptly discontinued; the symptoms include anxiety, shakiness, nausea and sweating, and in severe cases they may be life-threatening. Dependence leads the patient to ignore social norms in order to get sufficient funds to satisfy the need.

Effects. The immediate adverse effects of drugs and alcohol are reckless behaviour, vandalism and violence. Excessive doses lead to coma and death due to respiratory failure, heart failure or cerebral haemorrhage. A combination of drugs, or their intake with alcohol, generally results in overdosing and even death. The warning signs among youth include drop in academic performance, unexplained absence from school or 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 and appetite. There can be far-reaching implications too. If an abuser cannot get money, he or she may turn to stealing. Drug and alcohol abuse also affects the family and society, and intravenous drug abusers who share needles are at risk of serious infections like AIDS and hepatitis B. The viruses in both cases are transferred through infected needles and syringes; AIDS is fatal, and hepatitis B damages the liver. Chronic use of drugs and alcohol damages the nervous system and liver (cirrhosis). Use during pregnancy adversely affects the foetus.

Drugs in sports. Some sportspersons misuse cannabinoids, narcotic analgesics, anabolic steroids, diuretics and certain hormones to increase muscle strength and bulk and to promote aggressiveness. Anabolic steroids have side effects that are asked as a 3-mark question. In females: masculinisation (features like males), increased aggressiveness, mood swings, depression, abnormal menstrual cycles, excessive hair growth on face and body, enlargement of clitoris, deepening of voice. In males: acne, increased aggressiveness, mood swings, depression, reduction of the size of the testicles, decreased sperm production, potential for kidney and liver dysfunction, breast enlargement, premature baldness, enlargement of the prostate gland. In the young, in both boys and girls, severe facial and body acne and premature closure of the growth centres of the long bones, resulting in stunted growth.

Prevention and control. Prevention is better than cure, and the age most at risk is adolescence. NCERT's measures: (i) avoid undue peer pressure, respecting each child's own choice and personality rather than pushing to perform beyond their threshold in studies, sports or other activities; (ii) education and counselling to face problems and stresses and to accept disappointments and failures as a part of life, channelising the child's energy into sports, reading, music and yoga; (iii) seeking help from parents and peers so that guidance is received immediately; (iv) looking for danger signs, so that alert parents and teachers can take the proper steps; and (v) seeking professional and medical help from psychologists and psychiatrists and from de-addiction and rehabilitation programmes, with which the affected individual can overcome the problem completely and lead a normal life.

Tobacco, alcohol and nicotine belong here too. Nicotine stimulates the adrenal gland to release adrenaline and nor-adrenaline, which raise blood pressure and heart rate. Smoking is associated with cancers of the lung, urinary bladder, throat and oral cavity, bronchitis, emphysema, coronary heart disease and gastric ulcer; it increases carbon monoxide in the blood and reduces the oxygen concentration, causing oxygen deficiency in the body.