cover letter for a phd application research paper about cars dissertation on poultry wastewater topics for argument research papers help on dissertation thesis binding service university of manchester homework diary

Preksha Dhyana: Human Body Part II (Health Care): [7] Diseases And (Body's) Defences

Published: 22.04.2010
Updated: 02.07.2015

Throughout life a human being is constantly at war. Enemies lurk both without and within. Potentially harmful microbes swarm in air, water, food, and on the surfaces of objects handled and used by human beings. They assemble at the major entrances into the body, ready to slip inside, if there is a breach in the defences. Some even exist inside the body, kept at bay by the body defenders, but ready to assail, multiply and spread, if exposure, malnutrition or mental stress temporarily lowers the resistance.

Homeostatic mechanisms involving the circulatory, the excretory, the neuro-endocrine and other systems normally function to maintain the dynamic equilibrium of body processes. They are a major line of protection against disease. But one weak link, for example, a heart rendered less efficient by degenerative changes, can lead to a chain reaction of physiological catastrophe. Even the body itself can sometime become its own enemy, attacking its own cells instead of the invaders.

Some major types of diseases alonwith the body's powerful defences are discussed here.


A complete catalogue of the diseases and afflictions that can beset humanity would make one blanch. There are literally thousands of them. Most of them would fit under one of a few basic categories: bacterial, viral, fungus and other parasitic diseases, cancer and degenerative diseases. The causes of some diseases that afflict us have not yet been determined.

Bacterial Diseases

Bacteria are microscopic single-celled organisms with a rather primitive structure. A single bacterium, under favourable condition, can give rise to 2,50,000 descendents - which can fit comfortably on the head of a pin—in a matter of hours. It is this potential to multiply to staggering numbers that makes bacteria so dangerous. They can be classified in three main types: (i) rod-shaped bacilli (ii) spherical cocci and (iii) corkscrew-shaped spirilla.

Not all bacteria are pathogenic (i.e. cause diseases). Some actually perform useful services to plants and ultimately to animals and human beings. Some bacteria living in the human intestinal tract, not only do not cause disease but contribute vitamins for the nutrition of their host.

Pathogens of typhoid, scarlet and rheumatic fevers, tuberculosis, cholera, pneumonia, syphilis and food-poisoning are some of the disease-causing bacteria. The causes and means of transmission of these and other diseases remained obscure until the 19th century. The germ theory of disease—that contagious diseases are caused by microscopic germs and are transmitted vdirectly or indirectly) form one infected organism to another—was the result of the work of Pasteur in 1865. Pathogen of T.B. was discovered by Robert Koch in 1882. Later, causative agents of many bacterial diseases were identified and the means by which they were transmitted were determined.

Germs of infectious diseases may be transferred by direct contact with a sick person or by less direct routes, e.g. food-handlers, who do not take appropriate sanitary measures after excretion, can spread disease from their hands to food and from there to the consumers of food. Flies that alight on excrement and then on food can spread bacteria; biting insects can deposit or inject disease-germs into their victims.

After the germ has gained access into the body by one means or another, an incubation period follows. During this time, bacteria multiply without any outward sign of infection. After a period that varies from a few hours to a matter of weeks or months, depending on the disease, the numbers of the pathogens are so great that the normal life-processes of the host are disturbed and symptoms of disease become manifest. Pitched battles are carried on within the body between the body-defences and the invaders.

The harm caused by pathogenic germ is usually produced by poisons manufactured by them. These are of two types: exotoxins and endotoxins. Exotoxins diffuse out from the bacterial cell into the tissues of the host organism. These are proteins and are powerful poisons. Those of tetanus, for example, are far more powerful than any snake venom. Endotoxins are produced within the bacterial cell and are released when the cell disintegrates. They are less poisonous than exotoxins. Bacteria of typhoid (fever) produce endotoxins. Generally bacteria produce either exotoxins or endotoxins, but not both.

Viral Diseases

Viruses are micro-organisms. Some pathogenic viruses are so tiny that they cannot be seen with the most powerful optical microscope and pass through a filter, fine enough to trap the smallest bacteria. They are so rudimentary that many scientists do not consider them to be truly alive. They lie at the very borderline of life. Viruses can reproduce only within a living host.

Many diseases including poliomyelitis, influenza, measles, yellow fever and the common cold are traced to viruses. Virus-caused disease can be prevented by vaccines, in which the genetically changed attenuated virus has lost most of its virulence but still retains enough similarity to the original form to produce immunity to the original disease.

Fungus Diseases

Familiar bread-mold and penicillin are fungi. Air, soil and water teem not only with microbes, but with microscopic spores of fungi and the effects of fungi on our lives are far greater than is realized. Fungus diseases of human beings range from common skin-infection such as ringworm to severe systemic mycosis. Fungi normally feeding on decomposing matter in the soil may wreak havoc on the human beings, if they are accidentally introduced by inhalation or through a wound. On the credit side are the yeasts and numerous antibiotic producing fungi.

Other Parasitic Diseases

Millions of people are infested with tapeworms feeding inside one's intestinal tract and other parasites. Parasites that afflict human beings are: amoebae, responsible for amoebic dysentery, plasmodia that produce malaria, protozoa such as trypanosomes of sleeping sickness, and various flat worms and round worms.

A well-adapted parasite does not kill its host or even sicken very severely. Trouble arises when it is transmitted to a new host. For example, trypanosome infestation, that causes sleeping sickness, is endemic among the native tropical African animals. But for them it is only a minor inconvenience. When, however, the trypanosomes carried by tsetse flies enter the human beings and their livestock, they run wild. Multiplying explosively in their blood streams, they destroy blood cells. Then they move on to the nervous system, destroying tissues of the brain and spinal cord, producing lethargy and often death. The malaria-parasite is transmitted to human beings (and other animals) by the bite of an infested mosquito which has drawn blood from an infested person. Malaria is the most prevalent disease in the world.

Filariasis (Elephantiasis)

One of the most bizarre diseases, transmitted by a mosquito-bite, is filariasis. Larvae of parasitic filarial worms are injected under the skin by a mosquito carrying infected blood. The larvae make their way into the lymphatic system where they mature into hair like worms about two inches long. They obstruct the lymphatics and prevent the return of fluid to the blood stream. The result is edema, i.e. accumulation of fluid in the tissue spaces. In extreme cases, an affected limb swells up to a gigantic size.

Advances against parasitic diseases have been achieved through two major approaches: first through drugs that kill the parasites (quinine for malaria) and second through environmental control of the intermediate host (extermination of mosquitoes).

Parasites, in living off their victims' tissues and body-products, sap the energies of the hosts, leaving them in a debilitated state. Then the victim can fall prey to bacterial or viral diseases that may in turn prove fatal.


Cancer strikes the young as well as the old, although it becomes far more prevalent in middle and old age. If you ask people what disease they fear most, the answer will invariably be—cancer. Cancer is an insidious disease in which the cells exhibit a wild uncontrolled growth. Whereas normal heathy cells "recognize" their neighbours and cease growing upon contact with them, cancer-cells show no such recognition and continue wild growth, piling over one another, literally choking out their normal neighbours. Cancer may attack virtually any tissue of the body: lung, brain, breast, skin, bone, blood, liver and so on. A critical factor in the deadliness of this disease is the phenomenon of migration (metastasis). Cancer cells dislodge from their original site, enter the blood stream or lymph channels and are dispersed to other regions of the body. They continue the growth patterns of the original cancerous tissue at the new sites.

Why do cells suddenly run wild and how can the process be controlled or reversed? Despite extensive research, the field still holds more questions than answers. The experimental evidence seems to indicate that in some manner DNA play a fundamental role in cancer. The nature of this role is obscure. There is considerable evidence also that a virus plays a strategic role in the onset of at least some human cancers, but whether viruses are causative factors in all cancers is not known. Further evidence seems to indicate that virus invasion (or DNA mutation) will not result in cancer, unless certain contributing factors called carcinogens are present at the same time. Certain chemical substances such as mycotoxins (poisons produced by fungi) have been shown to be carcinogens. Exactly how they act is still unclear.

Immune system is also involved in the prevention and development of cancer. It is believed that little cancers are continually getting started, being recognized as foreign, and then being killed by the body's defence mechanisms before they can cause trouble. In a cancer victim, however, the defence mechanism has somehow failed to recognize the cancer cells as foreign and has allowed them to multiply unhindered.

For years the standard treatments for cancer have been surgery, radiation and chemotherapy. If the cancer is caught before migration, a cure can be affected by cutting out the affected tissues and any surrounding ones suspected of harbouring cancer cells. Deep-seated cancers may be destroyed by exposure to radiations. Finely focused beams of X-rays, radio-active cobalt, gold and other radiation-sources are used. Recently laser beams which can be focused far more sharply than X-rays have been used. One of the problems with chemotherapy is that drugs kill not only cancer-cells but normal ones as well. The drugs may be so toxic that doses sufficient to eradicate cancer also kill the patient. In "combination chemotherapy" an antidote is given in sequence to rescue the patient from the drug's toxic effects.

Perhaps the most promising approaches against cancer are those that involve bolstering or stimulation of the body's own defence mechanisms. These include injections of immuno-stimulators to mobilize the body's defences.

Degenerative Diseases

Some key part and systems of the human body gradually deteriorate with age, wear out and break down. Some of the degenerative changes due to aging process, such as the progressive loss of nerve-cells, decalcification of bones, were discussed in a previous section. Degenerative diseases of the heart and blood-vessels are not only number one killer of this age but also contribute to senility, (through a less efficient supply of blood to the brain), deafness, kidney-failure, etc. Building up of fat-deposits in the artery walls raise the blood-pressure, overloading the heart and increasing the possibility of the thrombosis which can cause damage to heart, brain or other vital organs. Hardening of.the arteries can force a gradual slow-down of activities and a blunting of mental acuity.

What causes degenerative diseases? Are they a natural slowing down of the body's built-in 'clock' or are they pathological processes, which could be arrested or reversed? Current feeling among the medical community is that the degenerative heart-disease is mostly produced by the combined factors of a whole life-style. Over-consumption of carbohydrates and saturated fats, an over-sedentary life and the constant stressful conditions and responsibilities are believed to contribute to building up of fat-deposits and hypertension. Prevention is the most important feature of the treatment and management of heart-disease. A prudent and balanced diet, a regular programme of exercise including postures (geared to one's physical condition), a life- style that cuts down unnecessary tensions, regular relaxation and meditation are approaches that can positively reduce the risk of heart-attack.

The Body's Defences

The body's defences operate 24 hours-a-day throughout our lives. If these defences are breached, illness and even death may follow. Skin is the first of several lines of defence to fall back upon. Few micro-organisms can penetrate trough unbroken skin. The mucous membranes that line the oral and nasal cavities are covered with a sticky mucus that immobilizes microbes. Antimicrobial secretions add to the defence of these and other portals into the body. Sterilizing acid-bath deals with the microbes that reach the stomach.

Formidable as these defences are, they can be breached and frequently are. Microbes can, then, slip pass, and penetrate. When infection occurs, additional defences are called on. These may be either non-specific defence-mechanism such as interferon[1] or specific immune responses.


Removing the tonsils to prevent recurrent throat and ear infections was a medical fad sometime ago. Paradoxically, tonsils frequently fell victims to the surgeon's knife precisely because they were doing their job. The tonsils guard the doors of the respiratory tract which is an open invitation to a world filled with germs. Tonsils, located at the back of the throat, are actually one of three separate pairs of lymphatic structures that provide a protective barrier for the mouth, throat, larynx, trachea and lungs. They contribute lymphocytes and immune substances to the body's defences and must not be removed, unless due to recurrent severe infections, they swell and block the respiratory and digestive passages.


It is known for a long time that the body is capable of producing proteins called antibodies, which react with invading microbes, inactivating or killing them. A variety of antibodies are found in the circulating blood even in a healthy person. They are all proteins called immuno-globulins. Five groups have been found, differing in chemical properties and biological functions. Some provide most of the specific immunity against microbes. Some are involved in allergic reactions. The total picture of antibody-production and the action of the immunity-system as a whole is, however, very complex indeed.

B and T Cells and Antibodies

There are two major classes of lymphocytes. They are called B-Cells and T-Cells. Precursors of both are originally formed in the bone-marrow. Some of these then migrate to the thymus gland where they are transformed into T-lymphocytes (T for thymus). The other precursors take a different route. In birds, the transformation into B-Cells occurs in a gastrointestinal structure called bursa (B for bursa). Human beings do not have a bursa and although it is believed that a comparable site exists, it is not yet known where or what it is.

There are structural as well as functional differences between the two types of lymphocytes. T-Cells somehow help B-Cells to become active antibody producers. T-Cells can also suppress B-cell activity. This role is important in the recognition of "self cells and chemicals that keep the antibody system from destroying our own body tissues. T-Cells can also act directly as killers. Another important function of the T-Cells is to conduct an immune surveillance. If a body-cell becomes malignant, patrolling T-Cells which perceive it as antigen (i.e. foreign), are sensitized and attack it and other similar cells. It is believd that body-cells become malignant at the rate of one everyday, but are promptly killed off by T-Cells. Thus an efficient surveillance by T-Cells is an important defence against cancer and other diseases caused by antigens. While T-Cells travel through the body (most of the circulating lymphocytes are T-Cells) and exert effect locally, B-Cells remain in the lymph-nodes and the synthesized antibodies are sent out through the bloodstream to the site where they are needed.

Antibodies fight invading microbes in several ways, e.g. they prevent viruses from attacking to the host cell-membranes and thus prevent them from multiplying.


We can have a life-time protection against many diseases by developing active immunity, either stimulated by an actual attack or provoked by vaccines. Vaccines have dramatically changed our lives. The control of small-pox through vaccines has been so successful that this disease has finally disappeared entirely from the face of the earth. Many doctors never see a single case of diphtheria which was a major childhood-killer before vaccines. Emergency protection provided by an injection of antibodies that someone else has produced against the disease, is called passive immunity. In such cases, it is wise to obtain a vaccination to develop active immunity after the emergency is over, because the introduced antibodies are rapidly lost from the body.

The antibodies that are transferred to the fetus and then to the infant, through its mother's milk confer passive immunity to any disease for which the mother possesses antibodies, and provide valuable protection during the time when the infant's own immunity system is not yet functioning effectively.

Autoimmune Diseases

The body is constantly at war. Its defenders are dedicated to the task of killing all foreign invaders. But sometimes they fail to recognize, and attack and kill the very cells they have been entrusted to defend. The results are disastrous for the body. Such a failure to recognize its own cells can result from a number of causes which result in the production of antibodies or sensitized lymphocytes against the body's own cells. Autoimmune damage may also occur accidentally, if the release of chemicals by the system kills not only the invaders but also the normal cells—the "innocent bystanders". Some form of arthritis, anaemia, some muscular disorders and other diseases are believed to be the results of autoimmune reactions.

Hypersensitivity and Allergy

A hypersensitive immunity system reacts to environmental antigens - such as microscopic pollen grains, dust particles to an inappropriately extreme degree as though they were major threats to life. Such a complex of immune responses is called allergy and the antigens that cause it are called allergens. They may be carried in the air and inhaled; they may be constituents of food; or they may come in contact with the skin. In susceptible individuals, allergens stimulate the production of a special class of antibodies. The result is watery eyes, sneezing, bronchial spasm (asthma) or skin rashes.


Jump to occurrence in text

Published by:
Jain Vishva Bharati
Ladnun-3 41 306 (Rajasthan) Editor: Muni Mahendra Kumar © Jain Vishva Bharati Edition: May, 1993 Typeset by: 
Lucky Photocomputers
Sardarpura, Jodhpur
Printed at Konark Press. Delhi-92. Phone 2245424, 2248066.

Share this page on:
Page glossary
Some texts contain  footnotes  and  glossary  entries. To distinguish between them, the links have different colors.
  1. Body
  2. Brain
  3. DNA
  4. Fear
  5. Meditation
  6. Thymus Gland
Page statistics
This page has been viewed 1369 times.
© 1997-2021 HereNow4U, Version 4.5
Contact us
Social Networking

HN4U Deutsche Version
Today's Counter: