Chapter 8

Human Health and Disease

Chapter 9

Strategies for Enhancement in

Food Production

Chapter 10

Microbes in Human Welfare

Biology is the youngest of the formalised disciplines of natural

science. Progress in physics and chemistry proceeded much

faster than in Biology. Applications of physics and chemistry in

our daily life also have a higher visibility than those of biology.

However, twentieth century and certainly twenty-first century

has demonstrated the utility of biological knowledge in

furthering human welfare, be it in health sector or agriculture.

The discovery of antibiotics, and synthetic plant-derived drugs,

anaesthetics have changed medical practice on one hand

and human health on the other hand. Life expectancy of

human beings have dramatically changed over the years.

Agricultural practices, food processing and diagnostics have

brought socio-cultural changes in human communities. These

are briefly described in the following three chapters of this unit.

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Born in August 1925 in Kumbakonam in Tamil Nadu, Monkambu Sambasivan

Swaminathan did his graduation and post-graduation in Botany from

Madras University. He worked in different capacities in large number of

institutions in India and abroad and developed his expertise in genetics

and plant breeding.

The School of Cytogenetics and Radiation Research established at the

Indian Agricultural Research Institute (IARI) enabled Swaminathan and his

team to develop short-duration high-yielding varieties of rice including scented

Basmati. He is also known for the development of the concept of crop

cafeteria, crop scheduling and genetically improving the yield and quality.

Swaminathan initiated collaboration with Norman Borlaug, which

culminated in the ‘Green Revolution’ through introduction of Mexican

varieties of wheat in India. This was highly recognised and appreciated. He

is also the initiator of ‘Lab-to-Land’, food security and several other

environmental programmes. He has been honoured with Padma Bhushan

and several other prestigious awards, medals and fellowships by institutions

of excellence.

M.S. SWAMINATHAN

(1925)

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Health, for a long time, was considered as a state of body

and mind where there was a balance of certain ‘humors’.

This is what early Greeks like Hippocrates as well as

Indian Ayurveda system of medicine asserted. It was

thought that persons with ‘blackbile’ belonged to hot

personality and would have fevers. This idea was arrived

at by pure reflective thought. The discovery of blood

circulation by William Harvey using experimental method

and the demonstration of normal body temperature in

persons with blackbile using thermometer disproved the

‘good humor’ hypothesis of health. In later years, biology

stated that mind influences, through neural system and

endocrine system, our immune system and that our

immune system maintains our health. Hence, mind and

mental state can affect our health. Of course, health is

affected by –

(i) genetic disorders – deficiencies with which a child is

born and deficiencies/defects which the child inherits

from parents from birth;

(ii) infections and

(iii) life style including food and water we take, rest and

exercise we give to our bodies, habits that we have or

lack etc.

CHAPTER 8

HUMAN HEALTH AND DISEASE

8.1 Common Diseases in

Humans

8.2 Immunity

8.3 AIDS

8.4 Cancer

8.5 Drugs and Alcohol Abuse

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The term health is very frequently used by everybody. How do we

define it? Health does not simply mean ‘absence of disease’ or ‘physical

fitness’. It could be defined as a state of complete physical, mental and

social well-being. When people are healthy, they are more efficient at

work. This increases productivity and brings economic prosperity. Health

also increases longevity of people and reduces infant and maternal

mortality.

Balanced diet, personal hygiene and regular exercise are very important

to maintain good health. Yoga has been practised since time immemorial

to achieve physical and mental health. Awareness about diseases and

their effect on different bodily functions, vaccination (immunisation)

against infectious diseases, proper disposal of wastes, control of vectors

and maintenance of hygiene in food and water resources are necessary

for achieving good health.

When the functioning of one or more organs or systems of the body is

adversely affected, characterised by appearance of various signs and

symptoms, we say that we are not healthy, i.e., we have a disease. Diseases

can be broadly grouped into infectious and non-infectious. Diseases

which are easily transmitted from one person to another, are called

infectious diseases. Infectious diseases are very common and every

one of us suffers from these at sometime or other. Some of the infectious

diseases like AIDS are fatal. Among non-infectious diseases, cancer is the

major cause of death. Drug and alcohol abuse also affect our health adversely.

8.1 COMMON DISEASES IN HUMANS

A wide range of organisms belonging to bacteria, viruses, fungi,

protozoans, helminths, etc., could cause diseases in man. Such disease-

causing organisms are called pathogens. Most parasites are therefore

pathogens as they cause harm to the host by living in (or on) them. The

pathogens can enter our body by various means, multiply and interfere

with normal vital activities, resulting in morphological and functional

damage. Pathogens have to adapt to life within the environment of the

host. For example, the pathogens that enter the gut must know a way of

surviving in the stomach at low pH and resisting the various digestive

enzymes. A few representative members from different groups of

pathogenic organisms are discussed here alongwith the diseases caused

by them. Preventive and control measures against these diseases in general,

are also briefly described.

Salmonella typhi is a pathogenic bacterium which causes typhoid

fever in human beings. These pathogens generally enter the small intestine

through food and water contaminated with them and migrate to other

organs through blood. Sustained high fever (39° to 40°C), weakness,

stomach pain, constipation, headache and loss of appetite are some of

the common symptoms of this disease. Intestinal perforation and death

may occur in severe cases. Typhoid fever could be confirmed by

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Widal test : A classic case in medicine, that of Mary Mallon nicknamed

Typhoid Mary, is worth mentioning here. She was a cook by profession

and was a typhoid carrier who continued to spread typhoid for several

years through the food she prepared.

Bacteria like Streptococcus pneumoniae and Haemophilus influenzae

are responsible for the disease pneumonia in humans which infects the

alveoli (air filled sacs) of the lungs. As a result of the infection, the alveoli

get filled with fluid leading to severe problems in respiration. The symptoms

of pneumonia include fever, chills, cough and headache. In severe cases,

the lips and finger nails may turn gray to bluish in colour. A healthy

person acquires the infection by inhaling the droplets/aerosols released

by an infected person or even by sharing glasses and utensils with an

infected person. Dysentery, plague, diphtheria, etc., are some of the other

bacterial diseases in man.

Many viruses also cause diseases in human beings. Rhino viruses

represent one such group of viruses which cause one of the most infectious

human ailments – the common cold. They infect the nose and respiratory

passage but not the lungs. The common cold is characterised by nasal

congestion and discharge, sore throat, hoarseness, cough, headache,

tiredness, etc., which usually last for 3-7 days. Droplets resulting from

cough or sneezes of an infected person are either inhaled directly or

transmitted through contaminated objects such as pens, books, cups,

doorknobs, computer keyboard or mouse, etc., and cause infection in a

healthy person.

Some of the human diseases are caused by protozoans too. You might

have heard about malaria, a disease man has been fighting since many

years. Plasmodium, a tiny protozoan is responsible for this disease. Different

species of Plasmodium (P. vivax, P. malaria and P. falciparum) are

responsible for different types of malaria. Of these, malignant malaria caused

by Plasmodium falciparum is the most serious one and can even be fatal.

Let us take a glance at the life cycle of Plasmodium (Figure 8.1).

Plasmodium enters the human body as sporozoites (infectious form)

through the bite of infected female Anopheles mosquito. The parasites

initially multiply within the liver cells and then attack the red blood cells

(RBCs) resulting in their rupture. The rupture of RBCs is associated with

release of a toxic substance, haemozoin, which is responsible for the chill

and high fever recurring every three to four days. When a female Anopheles

mosquito bites an infected person, these parasites enter the mosquito’s

body and undergo further development. The parasites multiply within

them to form sporozoites that are stored in their salivary glands. When

these mosquitoes bite a human, the sporozoites are introduced into his/

her body, thereby initiating the events mentioned above. It is interesting

to note that the malarial parasite requires two hosts – human and

mosquitoes – to complete its life cycle (Figure 8.1); the female Anopheles

mosquito is the vector (transmitting agent) too.

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Entamoeba histolytica is a protozoan parasite in the large intestine of

human which causes amoebiasis (amoebic dysentery). Symptoms of

this disease include constipation, abdominal pain and cramps, stools

with excess mucous and blood clots. Houseflies act as mechanical carriers

and serve to transmit the parasite from faeces of infected person to food

Figure 8.1 Stages in the life cycle of Plasmodium

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and food products, thereby contaminating them.

Drinking water and food contaminated by the faecal

matter are the main source of infection.

Ascaris, the common round worm and Wuchereria,

the filarial worm, are some of the helminths which are

known to be pathogenic to man. Ascaris, an intestinal

parasite causes ascariasis. Symptoms of these disease

include internal bleeding, muscular pain, fever, anemia

and blockage of the intestinal passage. The eggs of the

parasite are excreted along with the faeces of infected

persons which contaminate soil, water, plants, etc. A

healthy person acquires this infection through

contaminated water, vegetables, fruits, etc.

Wuchereria (W. bancrofti and W. malayi), the filarial

worms cause a slowly developing chronic inflammation

of the organs in which they live for many years, usually

the lymphatic vessels of the lower limbs and the disease

is called elephantiasis or filariasis (Figure 8.2). The

genital organs are also often affected, resulting in gross

deformities. The pathogens are transmitted to a healthy

person through the bite by the female mosquito vectors.

Many fungi belonging to the genera

Microsporum,

Trichophyton and Epidermophyton are

responsible for ringworms which is one of

the most common infectious diseases in man.

Appearance of dry, scaly lesions on various

parts of the body such as skin, nails and

scalp (Figure 8.3) are the main symptoms of

the disease. These lesions are accompanied

by intense itching. Heat and moisture help

these fungi to grow, which makes them thrive

in skin folds such as those in the groin or

between the toes. Ringworms are generally

acquired from soil or by using towels, clothes

or even the comb of infected individuals.

Figure 8.2 Diagram showing

inflammation in one

of the lower limbs due

to elephantiasis

Figure 8.3 Diagram showing ringworm

affected area of the skin

Maintenance of personal and public hygiene is very important for

prevention and control of many infectious diseases. Measures for personal

hygiene include keeping the body clean; consumption of clean drinking

water, food, vegetables, fruits, etc. Public hygiene includes 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 particularly essential where the

infectious agents are transmitted through food and water such as typhoid,

amoebiasis and ascariasis. In cases of air-borne diseases such as

pneumonia and common cold, in addition to the above measures, close

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contact with the infected persons or their belongings should be avoided.

For diseases such as malaria and filariasis that are transmitted through

insect vectors, the most important measure is to control or eliminate the

vectors and their breeding places. This can be achieved by avoiding

stagnation of water in and around residential areas, regular cleaning of

household coolers, use of mosquito nets, introducing fishes like Gambusia

in ponds that feed on mosquito larvae, spraying of insecticides in ditches,

drainage areas and swamps, etc. In addition, doors and windows should

be provided with wire mesh to prevent the entry of mosquitoes. Such

precautions have become more important especially in the light of recent

widespread incidences of the vector-borne (Aedes mosquitoes) diseases

like dengue and chikungunya in many parts of India.

The advancements made in biological science have armed us to

effectively deal with many infectious diseases. The use of vaccines and

immunisation programmes have enabled us to completely eradicate a

deadly disease like smallpox. A large number of other infectious diseases

like polio, diphtheria, pneumonia and tetanus have been controlled to a

large extent by the use of vaccines. Biotechnology (about which you will

read more in Chapter 12) is at the verge of making available newer and

safer vaccines. Discovery of antibiotics and various other drugs has also

enabled us to effectively treat infectious diseases.

8.2 IMMUNITY

Everyday we are exposed to large number of infectious agents. However,

only a few of these exposures result in disease. Why? This is due to the

fact that the body is able to defend itself from most of these foreign agents.

This overall ability of the host to fight the disease-causing organisms,

conferred by the immune system is called immunity.

Immunity is of two types: (i) Innate immunity and (ii) Acquired

immunity.

8.2.1 Innate Immunity

Innate immunity is non-specific type of defence, that is present at the

time of birth. This is accomplished by providing different types of barriers

to the entry of the foreign agents into our body. Innate immunity consist

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 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

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monocytes and 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

interferons which protect non-infected cells from further viral

infection.

8.2.2 Acquired Immunity

Acquired immunity, on the other hand is pathogen specific. It is

characterised by memory. This means when our body encounters a

pathogen for the first time it produces a response called primary

response which is of low intensity. Subsequent encounter with the same

pathogen elicits a highly intensified secondary or anamnestic response.

This is ascribed to the fact that our body appears to have memory of the

first encounter.

The primary and secondary

immune responses are

carried out with the help

of two special types of

lymphocytes present in our

blood, i.e., B-lymphocytes and

T-lymphocytes.

The B-lymphocytes produce an

army of proteins in response to

pathogens into our blood to fight

with them. These proteins are

called antibodies. The

T-cells themselves do not secrete

antibodies but help B cells to

produce them. Each antibody

molecule has four peptide chains,

two small called light chains and

two longer called heavy chains.

Hence, an antibody is represented

as H

. Different types of antibodies are produced in our body. IgA, IgM,

IgE, IgG are some of them. A cartoon of an antibody is given in Figure

8.4. Because 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. The second type is

called cell-mediated immune response or cell-mediated immunity

(CMI). The T-lymphocytes mediate CMI. Very often, when some human

organs like heart, eye, liver, kidney fail to function satisfactorily,

transplantation is the only remedy to enable the patient to live a normal

life. Then a search begins – to find a suitable donor. Why is it that the

organs cannot be taken from just anybody? What is it that the doctors

Figure 8.4 Structure of an antibody molecule

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check? Grafts from just any source – an animal, another primate, or any

human beings cannot be made since the grafts would be rejected sooner

or later. Tissue matching, blood group matching are essential before

undertaking any graft/transplant and even after this the patient has to

take immuno–suppresants all his/her life. The body is able to differentiate

‘self’ and ‘nonself’ and the cell-mediated immune response is responsible

for the graft rejection.

8.2.3 Active and Passive Immunity

When a host is exposed to antigens, which may be in the form of living

or dead microbes or other proteins, antibodies are produced in the host

body. This type of immunity is called active immunity. Active immunity

is slow and takes time to give its full effective response. Injecting the

microbes deliberately during immunisation or infectious organisms

gaining access into body during natural infection induce active

immunity. When ready-made antibodies are directly given to protect

the body against foreign agents, it is called passive immunity. Do you

know why mother’s milk is considered very essential for the new-

born infant? The yellowish fluid colostrum secreted by mother during

the initial days of lactation has abundant antibodies (IgA) to protect the

infant. The foetus also receives some antibodies from their mother,

through the placenta during pregnancy. These are some examples of

passive immunity.

8.2.4 Vaccination and Immunisation

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 pathogen or inactivated/weakened pathogen (vaccine) are

introduced into the body. The antibodies produced in the body 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. If a person is infected

with some deadly microbes to which quick immune response is required

as in tetanus, we need to directly inject the preformed antibodies, or

antitoxin (a preparation containing antibodies to the toxin). Even in cases

of snakebites, the injection which is given to the patients, contain preformed

antibodies against the snake venom. This type of immunisation is called

passive immunisation.

Recombinant DNA technology has allowed the production of antigenic

polypeptides of pathogen in bacteria or yeast. Vaccines produced using

this approach allow large scale production and hence greater availability

for immunisation, e.g., hepatitis B vaccine produced from yeast.

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8.2.5 Allergies

When you have gone to a new place and suddenly you started sneezing,

wheezing for no explained reason, and when you went away, your

symptoms dissappeared. Did this happen to you? Some of us are sensitive

to some particles in the environment. The above-mentioned reaction could

be because of allergy to pollen, mites, etc., which are different in different

places.

The exaggerated response of the immune system to certain antigens

present in the environment is called allergy. The substances to which

such an immune response is produced are called allergens. The antibodies

produced to these are of IgE type. Common examples of allergens are

mites in dust, pollens, animal dander, etc. Symptoms of allergic reactions

include sneezing, watery eyes, running nose and difficulty in breathing.

Allergy is due to the release of chemicals like histamine and serotonin

from the mast cells. For determining the cause of allergy, the patient is

exposed to or injected with very small doses of possible allergens, and the

reactions studied. The use of drugs like anti-histamine, adrenalin and

steroids quickly reduce the symptoms of allergy. Somehow, modern-day

life style 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. This could be

because of the protected environment provided early in life.

8.2.6 Auto Immunity

Memory-based acquired immunity evolved in higher vertebrates based

on the ability to differentiate foreign organisms (e.g., pathogens) from self-

cells. While we still do not understand the basis of this, two corollaries of

this ability have to be understood. One, higher vertebrates can distinguish

foreign molecules as well as foreign organisms. Most of the experimental

immunology deals with this aspect. Two, sometimes, due to genetic and

other unknown reasons, the body attacks self-cells. This results in damage

to the body and is called auto-immune disease. Rheumatoid arthritis

which affects many people in our society is an auto-immune disease.

8.2.7 Immune System in the Body

The human immune system consists of lymphoid organs, tissues, cells

and soluble molecules like antibodies. As you have read, immune system

is unique in the sense that it recognises foreign antigens, responds to

these and remembers them. The immune system also plays an important

role in allergic reactions, auto-immune diseases and organ

transplantation.

Lymphoid organs: These are the organs where origin and/or maturation

and pr

oliferation of lymphocytes occur. The primary lymphoid organs

are bone marrow and thymus where immature lymphocytes differentiate

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into antigen-sensitive lymphocytes. After maturation the

lymphocytes migrate to secondary lymphoid organs like spleen,

lymph nodes, tonsils, Peyer’s patches of small intestine and

appendix. The secondary lymphoid organs provide the sites for

interaction of lymphocytes with the antigen, which then proliferate

to become effector cells. The location of various lymphoid organs

in the human body is shown in Figure 8.5.

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. The thymus is quite large at the time of birth but

keeps reducing in size with age and by the time puberty is

attained it 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.

It acts as a filter of the blood by trapping blood-borne micro-

organisms. Spleen also has 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 the

micro-organisms or other antigens, which happen to get into the lymph

and tissue fluid. Antigens trapped in the lymph nodes are responsible for

the activation of lymphocytes present there and cause the immune

response.

There is lymphoid tissue also located within the lining of the major

tracts (respiratory, digestive and urogenital tracts) called mucosa-

associated lymphoid tissue (MALT). It constitutes about 50 per cent of

the lymphoid tissue in human body.

8.3 AIDS

The word AIDS stands for Acquired Immuno Deficiency Syndrome.

This means deficiency of immune system, acquired during the lifetime of

an individual indicating that it is not a congenital disease. ‘Syndrome’

means a group of symptoms. AIDS was first reported in 1981 and in the

last twenty-five years or so, it has spread all over the world killing more

than 25 million persons.

AIDS is caused by the Human Immuno deficiency Virus (HIV), a

member of a group of viruses called retrovirus, which have an envelope

enclosing the RNA genome (Figur

e 8.6). Transmission of HIV-infection

generally occurs by (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. So, people who are at high

risk of getting this infection includes - individuals who have multiple

Figure 8.5 Diagrammatic

representation

of Lymph nodes

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Figure 8.6 Replication of retrovirus

sexual partners, drug addicts who take drugs intravenously, individuals

who require repeated blood transfusions and children born to an HIV

infected mother. Do you know–when do people need repeated blood

transfusion? Find out and make a list of such conditions. It is important

to note that HIV/AIDS is not spread by mere touch or physical contact; it

spreads only through body fluids. It is, hence, imperative, for the physical

and psychological well-being, that the HIV/AIDS infected persons are

not isolated from family and society. There is always a time-lag between

the infection and appearance of AIDS symptoms. This period may vary

from a few months to many years (usually 5-10 years).

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After getting into the body of the person, the virus enters into macrophages

where RNA genome of the virus replicates to form viral DNA with the help of

the enzyme reverse transcriptase. This viral DNA gets incorporated into host

cell’s DNA and directs the infected cells to produce virus particles (Figure 8.6).

The macrophages continue to produce virus and in this way acts like a HIV

factory. Simultaneously, HIV enters into helper

T-lymphocytes (T

), replicates and produce 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. Due to decrease in

the number of helper T lymphocytes, the person starts suffering from infections

that could have been otherwise overcome such as those due to bacteria

especially Mycobacterium, viruses, fungi and even parasites like Toxoplasma.

The patient becomes so immuno-deficient that he/she is unable to protect

himself/herself against these infections. A widely used 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

the life of the patient but cannot prevent death, which is inevitable.

Prevention of AIDS : As AIDS has no cure, prevention is the best option.

Moreover, HIV infection, more often, spreads due to conscious behaviour

patterns and is not something that happens inadvertently, like pneumonia

or typhoid. Of course, infection in blood transfusion patients, new-borns

(from mother) etc., may take place due to poor monitoring. The only excuse

may be ignorance and it has been rightly said – “don’t die of ignorance”.

In our country the National AIDS Control Organisation (NACO) and other

non-governmental organisation (NGOs) are doing a lot to educate people

about AIDS. WHO has started a number of programmes 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, are some such steps taken up.

Infection with HIV or having AIDS is something that should not be

hidden – since then, the infection may spread to many more people.

HIV/AIDS-infected people need help and sympathy instead of being

shunned by society. Unless society recognises it as a problem to be dealt

with in a collective manner – the chances of wider spread of the disease

increase manifold. It is a malady that can only be tackled, by the society

and medical fraternity acting together, to prevent the spread of the disease.

8.4 CANCER

Cancer is one of the most dreaded diseases of human beings and is a major

cause of death all over the globe. More than a million Indians suffer from

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cancer and a large number of them die from it annually. The mechanisms

that underlie development of cancer or oncogenic transformation of cells,

its treatment and control have been some of the most intense areas of

research in biology and medicine.

In our body, cell growth and differentiation is highly controlled and

regulated. In cancer cells, there is breakdown of these regulatory

mechanisms. Normal cells show a property called contact inhibition by

virtue of which contact with other cells inhibits their uncontrolled growth.

Cancer cells appears to have lost this property. As a result of this, cancerous

cells just continue to divide giving rise to masses of cells called tumors.

Tumors are of two types: benign and malignant. Benign tumors normally

remain confined to their original location and do not spread to other parts

of the body and cause little damage. The malignant tumors, on the

other hand are a mass of proliferating cells called neoplastic or tumor

cells. These cells grow very rapidly, invading and damaging the

surrounding normal tissues. As these cells actively divide and grow they

also starve the normal cells by competing for vital nutrients. Cells sloughed

from such tumors reach distant sites through blood, and wherever they

get lodged in the body, they start a new tumor there. This property called

metastasis

is the most feared property of malignant tumors.

Causes of cancer : Transformation of normal cells into cancerous

neoplastic cells may be induced by physical, chemical or biological agents.

These agents are called carcinogens. Ionising radiations like X-rays and

gamma rays and non-ionizing radiations like UV 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. Furthermore, several genes called cellular oncogenes

(c-onc) or proto oncogenes have been identified in normal cells which,

when activated under certain conditions, could lead to oncogenic

transformation of the cells.

Cancer detection and diagnosis : Early detection of cancers is essential

as it allows the disease to be treated successfully in many cases. 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. In biopsy, a piece of the suspected tissue cut into thin sections

is stained and examined under microscope (histopathological studies) 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. Computed tomography 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 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

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Figure 8.7 Chemical structure of Morphine Figure 8.8 Opium poppy

applied to detect genes in individuals with inherited susceptibility to

certain cancers. Identification of such genes, which predispose an

individual to certain cancers, may be very helpful in prevention of

cancers. Such individuals may be advised to avoid exposure to

particular carcinogens to which they are susceptible (e.g., tobacco

smoke in case of lung cancer).

Treatment of cancer : The common approaches for treatment of cancer

are surgery, radiation therapy and immunotherapy. In radiotherapy,

tumor cells are irradiated lethally, taking proper care of the normal tissues

surrounding the tumor mass. Several chemotherapeutic drugs are used

to kill cancerous cells. Some of these are specific for particular tumors.

Majority of drugs have side effects like hair loss, anemia, etc. 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

αα

α-interferon which activates their

immune system and helps in destroying the tumor.

8.5 DRUGS AND ALCOHOL ABUSE

Surveys and statistics show that use of drugs and alcohol has been on

the rise especially among the youth. This is really a cause of concern as it

could result in many harmful effects. Proper education and guidance

would enable youth to safeguard themselves against these dangerous

behaviour patterns and follow healthy lifestyles.

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 are the drugs, which bind to specific opioid receptors present

in our central nervous system and gastrointestinal tract. Heroin

(Figure 8.7), commonly called smack is chemically diacetylmorphine which

is a white, odourless, bitter crystalline compound. This is obtained by

acetylation of morphine (Figure 8.7), which is extracted from the latex of

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poppy plant Papaver somniferum (Figure 8.8). Generally taken by snorting

and injection, heroin is a depressant and slows down body functions.

Cannabinoids are a group of chemicals (Figure 8.9), which interact

with cannabinoid receptors present principally in the brain. Natural

cannabinoids are obtained from the inflorescences of the plant Cannabis

sativa (Figure 8.10). 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.

Figure 8.9 Skeletal structure of

cannabinoid molecule

Figure 8.10 Leaves of Cannabis sativa

Coca alkaloid or cocaine is obtained from coca

plant Erythroxylum coca, native to South America. It

interferes with the transport of the neuro-transmitter

dopamine. Cocaine, commonly called coke or crack is

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 (Figure 8.11). These days cannabinoids are also

being abused by some sportspersons.

Drugs like barbiturates, amphetamines,

benzodiazepines, and other similar drugs, that are

normally used as medicines to help patients cope with

mental illnesses like depression and insomnia, are often

abused. Morphine is a very effective sedative and painkiller, and is very useful

in patients who have undergone surgery. Several plants, fruits and seeds

having hallucinogenic properties have been used for hundreds of years in

folk-medicine, religious ceremonies and rituals all over the globe. When these

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.

Figure 8.11 Flowering branch of Datura

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Smoking also paves the way to hard drugs. Tobacco has been used

by human beings for more than 400 years. It 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 haembound 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. Knowing the dangers of smoking

and chewing tobacco, and its addictive nature, the youth and old need to

avoid these habits. Any addict requires counselling and medical help to

get rid of the habit.

8.5.1 Adolescence and Drug/Alcohol Abuse

Adolescence means both ‘a period’ and ‘a process’ during which a child

becomes mature in terms of his/her attitudes and beliefs for effective

participation in society. 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. Adolescence, thus is a

very vulnerable phase of mental and psychological development of an

individual.

Curiosity, need for adventure and excitement, and experimentation,

constitute common causes, which motivate youngsters towards drug

and alcohol use. A child’s natural curiosity motivates him/her to

experiment. This is complicated further by effects that might be perceived

as benefits, of alcohol or drug use. Thus, the first use of drugs or alcohol

may be out of curiosity or experimentation, but later the child starts

using these to escape facing problems. Of late, stress, from pressures to

excel in academics or examinations, has played a significant role in

persuading the youngsters to try alcohol and drugs. The perception

among youth that it is ‘cool’ or progressive to smoke, use drugs or

alcohol, is also in a way a major cause for youth to start these habits.

Television, movies, newspapers, internet also help to promote this

perception. Other factors that have been seen to be associated with drug

and alcohol abuse among adolescents are unstable or unsupportive

family structures and peer pressure.

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8.5.2 Addiction and Dependence

Because of the perceived benefits, drugs are frequently used repeatedly.

The most important thing, which one fails to realise, is the inherent

addictive nature of alcohol and drugs. Addiction is a psychological

attachment to certain effects –such as euphoria and a temporary feeling

of well-being–associated with drugs and alcohol. These drive people to

take them even when these are not needed, or even when their use becomes

self-destructive. With repeated use of drugs, the tolerance level of the

receptors present in our body increases. Consequently the receptors

respond only to higher doses of drugs or alcohol leading to greater intake

and addiction. However, it should be clearly borne in mind that use of

these drugs even once, can be a fore-runner to addiction. Thus, the

addictive potential of drugs and alcohol, pull the user into a vicious circle

leading to their regular use (abuse) from which he/she may not be able

to get out. In the absence of any guidance or counselling, the person gets

addicted and becomes dependent on their use.

Dependence is the tendency of the body to manifest a characteristic

and unpleasant withdrawal syndrome if regular dose of drugs/alcohol

is abruptly discontinued. This is characterised by anxiety, shakiness,

nausea and sweating, which may be relieved when use is resumed again.

In some cases, withdrawal symptoms can be severe and even life

threatening and the person may need medical supervision.

Dependence leads the patient to ignore all social norms in order to

get sufficient funds to satiate his/her needs. These result in many social

adjustment problems.

8.5.3 Effects of Drug/Alcohol Abuse

The immediate adverse effects of drugs and alcohol abuse are manifested

in the form of 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.

There may even be some far-reaching implications of drug/alcohol

abuse. If an abuser is unable to get money to buy drugs/alcohol he/she

may turn to stealing. The adverse effects are just not restricted to the

person who is using drugs or alcohol. At times, a drug/alcohol addict

becomes the cause of mental and financial distress to his/her entire family

and friends.

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Those who take drugs intravenously (direct injection into the vein

using a needle and syringe), are much more likely to acquire serious

infections like AIDS and Hepatitis B. The viruses, which are responsible

for these diseases, 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. Both 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 heavy drinking in adulthood. The chronic use of drugs and

alcohol damages nervous system and liver (cirrhosis). The use of drugs

and alcohol during pregnancy is also known to adversely affect the foetus.

Another misuse of drugs is what certain sportspersons do to enhance

their performance. They (mis)use 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 use 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 centres of the

long bones may result in stunted growth.

8.5.4 Prevention and Control

The age-old adage of ‘prevention is better than cure’ holds true here also.

It is also true that habits such as smoking, taking drug or alcohol are

more likely to be taken up at a young age, more during adolescence.

Hence, it is best to identify the situations that may push an adolescent

towards use of drugs or alcohol, and to take remedial measures well in

time. In this regard, the parents and the teachers have a special

responsibility. Parenting that combines with high levels of nurturance

and consistent discipline, has been associated with lowered risk of

substance (alcohol/drugs/tobacco) abuse. Some of the measures

mentioned here would be particularly useful for prevention and control

of alcohol and drugs abuse among adolescents

(i) Avoid undue peer pressure - Every child has his/her own choice

and personality, which should be respected and nurtured. A child

should not be pushed unduly to perform beyond his/her threshold

limits; be it studies, sports or other activities.

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SUMMARY

Health is not just the absence of disease. It is a state of complete physical,

mental, social and psychological well-being. Diseases like typhoid,

cholera, pneumonia, fungal infections of skin, malaria and many others

are a major cause of distress to human beings. Vector-borne diseases

like malaria especially one caused by Plasmodium falciparum, if not

treated, may prove fatal. Besides personal cleanliness and hygiene,

public health measures like proper disposal of waste, decontamination

of drinking water, control of vectors like mosquitoes and immunisation

are very helpful in preventing these diseases. Our immune system plays

the major role in preventing these diseases when we are exposed to

disease-causing agents. The innate defences of our body like skin,

mucous membranes, antimicrobial substances present in our tears,

saliva and the phagocytic cells help to block the entry of pathogens

into our body. If the pathogens succeed in gaining entry to our body,

specific antibodies (humoral immune response) and cells (cell mediated

immune response) serve to kill these pathogens. Immune system has

memory. On subsequent exposure to same pathogen, the immune

response is rapid and more intense. This forms the basis of protection

(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 channelise

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. Besides getting proper advise to sort out their problems,

this would help young to vent their feelings of anxiety and guilt.

(iv) Looking for danger signs - Alert parents and teachers need to

look for and identify the danger signs discussed above. Even friends,

if they find someone using drugs or alcohol, should not hesitate to

bring this to the notice of parents or teacher in the best interests of

the person concerned. Appropriate measures would then be required

to diagnose the malady and the underlying causes. This would help

in initiating proper remedial steps or treatment.

(v) Seeking professional and medical help - A lot of help is available

in the form of highly qualified psychologists, psychiatrists, and de-

addiction and rehabilitation programmes to help individuals who

have unfortunately got in the quagmire of drug/alcohol abuse. With

such help, the affected individual with sufficient efforts and will power,

can get rid of the problem completely and lead a perfectly normal

and healthy life.

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afforded by vaccination and immunisation. Among other diseases, AIDS

and cancer kill a large number of individuals worldwide. AIDS caused

by the human immuno-deficiency virus (HIV) is fatal but can be

prevented if certain precautions are taken. Many cancers are curable if

detected early and appropriate therapeutic measures are taken. Of late,

drug and alcohol abuse among youth and adolescents is becoming

another cause of concern. Because of the addictive nature of alcohol

and drugs, and their perceived benefits like relief from stress, a person

may try taking these in the face of peer pressure, examinations-related

and competition-related stresses. In doing so, he/she may get addicted

to them. Education about their harmful effects, counselling and seeking

immediate professional and medical help would totally relieve the

individual from these evils.

EXERCISES

1. What are the various public health measures, which you would suggest

as safeguard against infectious diseases?

2. In which way has the study of biology helped us to control infectious

diseases?

3. How does the transmission of each of the following diseases take place?

(a) Amoebiasis (b) Malaria (c) Ascariasis (d) Pneumonia

4. What measure would you take to prevent water-borne diseases?

5. Discuss with your teacher what does ‘a suitable gene’ means, in the

context of DNA vaccines.

6. Name the primary and secondary lymphoid organs.

7. The following are some well-known abbreviations, which have been

used in this chapter. Expand each one to its full form:

(a) MALT (b) CMI (c) AIDS (d) NACO

(e) HIV

8. Differentiate the following and give examples of each:

(a) Innate and acquired immunity (b) Active and passive immunity

9. Draw a well-labelled diagram of an antibody molecule.

10. What are the various routes by which transmission of human immuno-

deficiency virus takes place?

11. What is the mechanism by which the AIDS virus causes deficiency of

immune system of the infected person?

12. How is a cancerous cell different from a normal cell?

13. Explain what is meant by metastasis.

14. List the harmful effects caused by alcohol/drug abuse.

15. Do you think that friends can influence one to take alcohol/drugs? If

yes, how may one protect himself/herself from such an influence?

16. Why is that once a person starts taking alcohol or drugs, it is difficult

to get rid of this habit? Discuss it with your teacher.

17. In your view what motivates youngsters to take to alcohol or drugs and

how can this be avoided?

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