Human Health And Diseases

Class 12 | Biology — Zoology | Chapter 7

Class 12 Unit 7 Biology

UNIT 3 CHAPTER-7

Sneezing spreads diseases through the droplets of mucus

Chapter Outline

• 7.1 Common diseases in human beings
• 7.2 Maintenance of personal and public hygiene
• 7.3 Basic concepts of immunology
• 7.4 Immunodeficiency diseases
• 7.5 Autoimmune diseases
• 7.6 Adolescence – Drug and alcohol abuse
• 7.7 Mental health – Depression

Learning Objectives

• Learns about various bacterial, viral, fungal, protozoan and helminth diseases.
• Understands the life cycle of malarial parasite.
• Understands the basic concepts of immunology.
• Differentiates between innate immunity and acquired immunity, primary immune response and secondary immune response, active and passive immunity.
• Realizes the importance of immunization.
• Learns to comprehend the concept of hypersensitivity.
• Learns the ill effects of drugs and alcohol.
• Realizes the responsibility for their behaviour, health care and life styles.
• Understands the importance of mental health.

The World Health Organization (WHO) defines health as 'a state of complete physical, mental and social wellbeing and not merely absence of diseases.' We can also say "HEALTH IS WEALTH". When people are healthy, they are more efficient at work. Health increases longevity of people and reduces infant and adult mortality. Personal hygiene, regular exercise and balanced diet are very important to maintain good health.

7.1 Common Diseases in Human Beings

Disease can be defined as a disorder or malfunction of the mind or body. It involves morphological, physiological and psychological disturbances which may be due to environmental factors or pathogens or genetic anomalies or life style changes. Diseases can be broadly grouped into infectious and non-infectious types. Diseases which are transmitted from one person to another are called infectious diseases or communicable diseases. Such disease causing organisms are called pathogens and are transmitted through air, water, food, physical contact and vectors. The disease causing pathogen may be virus, bacteria, fungi, protozoan parasites, helminthic parasites, etc.

Infectious diseases are common and everyone suffers from such diseases at some time or the other. Most of the bacterial diseases are curable but all viral diseases are not. Some infectious diseases like AIDS may be fatal.

Non-infectious diseases are not transmitted from an infected person to a healthy person. In origin they may be genetic (cystic fibrosis), nutritional (vitamin deficiency diseases) and degenerative (arthritis, heart attack, stroke). Among non-infectious diseases, cancer is one of the major causes of death.

Bacterial Resistance

If an antibiotic is used too often to fight a specific bacterial infection, the bacteria may become resistant to the specific antibiotic. Hence the specific antibiotic can no longer be used to treat the bacterial infection. Some bacteria have developed resistance to many antibiotics. Therefore, infections caused by these bacteria are difficult to be cured. Risk of bacterial resistance can be reduced by observing the following steps:

1. Avoid using antibiotics to treat minor infections that can be taken care by our immune system.
2. Do not use an antibiotic to treat viral infections such as common cold or flu.
3. Always follow the prescription. Skipping doses or failing to complete the prescription may allow antibiotic resistance to develop.

7.1.1 Bacterial and Viral Diseases

Bacterial Diseases

Though the number of bacterial species is very high, only a few bacteria are associated with human diseases and are called pathogenic bacteria. Such pathogens may emit toxins and affect the body. Common pathogenic bacteria and the bacterial diseases are given in the table below. Bacteria spread through air, water or by inhaling the droplets or aerosols or even by sharing utensils, dresses with an infected person.

Typhoid fever can be confirmed by Widal test.

Table 7.1 – Bacterial Diseases in Human Beings

S.No	Diseases	Causative Agent	Site of Infection	Mode of Transmission	Symptoms
1	Shigellosis (Bacillary dysentery)	Shigella species	Intestine	Food and water contaminated by faeces or faecal oral route	Abdominal pain, dehydration, blood and mucus in the stools
2	Bubonic plague (Black death)	Yersinia pestis	Lymph nodes	Rat flea vector Xenopsylla cheopis	Fever, headache, and swollen lymph node
3	Diphtheria	Corynebacterium diphtheriae	Larynx, skin, nasal and genital passage	Droplet infection	Fever, sore throat, hoarseness and difficulty in breathing
4	Cholera	Vibrio cholerae	Intestine	Contaminated food and water or faecal oral route	Severe diarrhoea and dehydration
5	Tetanus (Lock jaw)	Clostridium tetani	Spasm of muscles	Through wound infection	Rigidity of jaw muscle, increased heart beat rate and spasm of the muscles of the jaw and face
6	Typhoid (Enteric fever)	Salmonella typhi	Intestine	Through contaminated food and water	Headache, abdominal discomfort, fever and diarrhoea
7	Pneumonia	Streptococcus pneumoniae	Lungs	Droplet infection	Fever, cough, painful breathing and brown sputum
8	Tuberculosis	Mycobacterium tuberculosis	Lungs	Droplet infection	Thick mucopurulent nasal discharge

Did You Know?

Common cold is caused by more than 150 different strains of Rhino viruses. Moreover their RNA genome keeps changing due to mutation. Hence it is very difficult to prepare a common vaccine for the disease.

Viral Diseases

Viruses are the smallest intracellular obligate parasites, which multiply within living cells. Outside the living cells they cannot carry out the characteristics of a living organism. Viruses invade living cells, forcing the cells to create new viruses. The new viruses break out of the cell, killing it and invade other cells in the body, causing diseases in human beings. Rhino viruses cause one of the most infectious human ailments called the "Common cold".

Viral diseases are generally grouped into four types on the basis of the symptoms produced in the body organs:

1. Pneumotropic diseases – respiratory tract infected (e.g., influenza)
2. Dermotropic diseases – skin and subcutaneous tissues affected (e.g., chicken pox and measles)
3. Viscerotropic diseases – blood and visceral organs affected (e.g., yellow fever and dengue fever)
4. Neurotropic diseases – central nervous system affected (e.g., rabies and polio)

Did You Know?

Nipah virus is a zoonotic virus (transmitted from animals to humans) and also transmitted through contaminated food. In infected people, it causes a range of illness from asymptomatic infection to acute respiratory illness and fatal encephalitis.

Table 7.2 – Viral Diseases in Human Beings

S.No	Diseases	Causative Agent	Site of Infection	Mode of Transmission	Symptoms
1	Common cold	Rhino viruses	Respiratory tract	Droplet infection	Nasal congestion and discharge, sore throat, cough and headache
2	Mumps	Mumps virus (RNA virus), Paramyxo virus	Salivary glands	Saliva and droplet infection	Enlargement of the parotid glands
3	Measles	Rubella virus (RNA virus), Paramyxo virus	Skin and respiratory tract	Droplet infection	Sore throat, running nose, cough and fever, reddish rashes on the skin, neck and ears
4	Viral hepatitis	Hepatitis-B virus	Liver	Parenteral route, blood transfusion	Liver damage, jaundice, nausea, yellowish eyes, fever and pain in the abdomen
5	Chicken pox	Varicella-Zoster virus (DNA Virus)	Respiratory tract, skin and nervous system	Droplet infection and direct contact	Mild fever with itchy skin, rash and blisters
6	Poliomyelitis	Polio virus (RNA virus)	Intestine, brain, spinal cord	Droplet infection through faecal oral route	Fever, muscular stiffness and weakness, paralysis and respiratory failure
7	Dengue fever (Break bone fever)	Dengue virus or Flavi virus (DENV 1-4 virus)	Skin and blood	Mosquito vector Aedes aegypti	Severe flu like illness with a sudden onset of fever and painful headache, muscle and joint pain
8	Chikungunya	Alpha virus (Toga virus)	Nervous system	Mosquito vector Aedes aegypti	Fever and joint pain, headache and joint swelling

7.1.2 Protozoan Diseases

About 15 genera of protozoans live as parasites within the human body and cause diseases.

Do You Know?

Swine flu was first recognised in the 1919 pandemic and still circulates as a seasonal flu virus. Swine flu is caused by the H1N1 virus strain. Symptoms include fever, cough, sore throat, chills, weakness and body aches. Children, pregnant women and the elderly are at risk from severe infection.

Amoebiasis also called amoebic dysentery or amoebic colitis is caused by Entamoeba histolytica, which lives in the human large intestine and feeds on mucus and bacteria. Infective stage of this parasite is the trophozoite, which penetrates the walls of the host intestine (colon) and secretes histolytic enzymes causing ulceration, bleeding, abdominal pain and stools with excess mucus. Symptoms of amoebiasis can range from diarrhoea to dysentery with blood and mucus in the stool. House flies (Musca domestica) acts as a carrier for transmitting the parasite from contaminated faeces and water.

African sleeping sickness is caused by Trypanosoma species. Trypanosoma is generally transmitted by the blood sucking Tsetse flies. Three species of Trypanosoma cause sleeping sickness in man:

1. Trypanosoma gambiense is transmitted by Glossina palpalis (Tsetse fly) and causes Gambian or Central African sleeping sickness.
2. Trypanosoma rhodesiense is transmitted by Glossina morsitans causing Rhodesian or East African sleeping sickness.
3. Trypanosoma cruzi is transmitted by a bug called Triatoma megista and causes Chagas disease or American trypanosomiasis.

Kala-azar or visceral leishmaniasis is caused by Leishmania donovani, which is transmitted by the vector Phlebotomus (sand fly). Infection may occur in the endothelial cells, bone marrow, liver, lymph glands and blood vessels of the spleen. Symptoms of Kala azar are weight loss, anaemia, fever, enlargement of spleen and liver.

Malaria is caused by different types of Plasmodium species such as Plasmodium vivax, Plasmodium ovale, Plasmodium malariae and Plasmodium falciparum. Plasmodium lives in the RBC of human; in its mature condition it is called as trophozoite. It is transmitted from one person to another by the bite of the infected female Anopheles mosquito.

Life Cycle of Plasmodium

Plasmodium vivax is a digenic parasite, involving two hosts – man as the secondary host and female Anopheles mosquito as the primary host. The life cycle of Plasmodium involves three phases namely schizogony, gamogony and sporogony.

The parasite first enters the human blood stream through the bite of an infected female Anopheles mosquito. As it feeds, the mosquito injects the saliva containing the sporozoites. The sporozoite within the blood stream immediately enters the hepatic cells of the liver. Further in the liver they undergo multiple asexual fission (schizogony) and produce merozoites.

After being released from liver cells, the merozoites penetrate the RBCs. Inside the RBC, the merozoite begins to develop as unicellular trophozoites. The trophozoite grows in size and a central vacuole develops pushing them to one side of cytoplasm and becomes the signet ring stage. The trophozoite nucleus then divides asexually to produce the schizont. The large schizont shows yellowish-brown pigmented granules called Schuffner's granules. The schizont divides and produces mononucleated merozoites. Eventually the erythrocyte lyses, releasing the merozoites and haemozoin toxin into the blood stream to infect other erythrocytes. Lysis of red blood cells results in cycles of fever and other symptoms.

This erythrocytic stage is cyclic and repeats itself approximately every 48 to 72 hours or longer depending on the species of Plasmodium involved. The sudden release of merozoites triggers an attack on the RBCs. Occasionally, merozoites differentiate into macrogametocytes and microgametocytes. When these are ingested by a mosquito, they develop into male and female gametes respectively.

In the mosquito's gut, the infected erythrocytes lyse and male and female gametes fertilize to form a diploid zygote called ookinete. The ookinete migrates to the mosquito's gut wall and develop into an oocyte. The oocyte undergoes meiosis by a process called sporogony to form sporozoites. These sporozoites migrate to the salivary glands of the mosquito. The cycle is now completed and when the mosquito bites another human host, the sporozoites are injected and the cycle begins anew.

The pathological changes caused by malaria affect not only the erythrocytes but also the spleen and other visceral organs. Incubation period of malaria is about 12 days. The early symptoms of malaria are headache, nausea and muscular pain. The classic symptoms first develop with the synchronized release of merozoites, haemozoin toxin and erythrocyte debris into the blood stream resulting in malarial paroxysms – shivering chills, high fever followed by sweating. Fever and chills are caused partly by malarial toxins that induce macrophages to release tumour necrosis factor (TNF-α) and interleukin.

Table 7.3 – Types of Malaria

S.No	Types of Malaria	Causative Agent	Duration of Erythrocytic Cycle
1	Tertian, benign tertian or vivax malaria	Plasmodium vivax	48 hours
2	Quartan malaria	Plasmodium malariae	72 hours
3	Mild tertian malaria	Plasmodium ovale	48 hours
4	Malignant tertian or quotidian malaria	Plasmodium falciparum	36 to 48 hours

Prevention of Malaria

It is possible to break the transmission cycle by killing the insect vector. Mosquitoes lay their eggs in water. Larvae hatch and develop in water but breathe air by moving to the surface. Oil can be sprayed over the water surface, to make it impossible for mosquito larvae and pupae to breathe. Ponds, drainage ditches and other permanent bodies of water can be stocked with fishes such as Gambusia which feed on mosquito larvae. Preparations containing Bacillus thuringiensis can be sprayed to kill the mosquito larvae since it is not toxic to other forms of life.

The best protection against malaria is to avoid being bitten by mosquito. People are advised to use mosquito nets, wire gauging of windows and doors to prevent mosquito bites. In the 1950's the World Health Organisation (WHO) introduced the Malaria eradication programme. This programme was not successful due to the resistance of Plasmodium to the drugs used to treat it and resistance of mosquitoes to DDT and other insecticides.

Do You Know?

Malaria vaccine is used to prevent malaria. The only approved vaccine as of 2015 is RTS,S (Mosquirix). It requires four injections and has relatively low efficacy (26 to 50 percentage). Due to this low efficacy, WHO does not recommend the use of RTS,S vaccine in babies between 6 and 12 weeks of age.

7.1.3 Fungal Diseases

Fungi was recognized as a causative agent of human diseases much earlier than bacteria. Dermatomycosis is a cutaneous infection caused by fungi belonging to the genera Trichophyton, Microsporum and Epidermophyton. Ringworm is one of the most common fungal diseases in humans. Appearance of dry, scaly lesions on the skin, nails and scalp are the main symptoms of the disease. Heat and moisture help these fungi to grow and makes them to thrive in skin folds such as those in the groin or between the toes. Ringworms of the feet is known as Athlete's foot caused by Tinea pedis. Ringworms are generally acquired from soil or by using clothes, towels and comb used by infected persons.

7.1.4 Helminthic Diseases

Helminthes are mostly endoparasitic in the gut and blood of human beings and cause diseases called helminthiasis. The two most prevalent helminthic diseases are Ascariasis and Filariasis.

Ascaris is a monogenic parasite and exhibits sexual dimorphism. Ascariasis is a disease caused by the intestinal endoparasite Ascaris lumbricoides commonly called the round worms. It is transmitted through ingestion of embryonated eggs through contaminated food and water. Children playing in contaminated soils are also prone to have a chance of transfer of eggs from hand to mouth. The symptoms of the disease are abdominal pain, vomiting, headache, anaemia, irritability and diarrhoea. A heavy infection can cause nutritional deficiency and severe abdominal pain and causes stunted growth in children. It may also cause enteritis, hepatitis and bronchitis.

Filariasis is caused by Wuchereria bancrofti, commonly called filarial worm. It is found in the lymph vessels and lymph nodes of man. Wuchereria bancrofti is sexually dimorphic, viviparous and digenic. The life cycle is completed in two hosts, man and the female Culex mosquito. The female filarial worm gives rise to juveniles called microfilariae larvae. In the lymph glands, the juveniles develop into adults. The accumulation of the worms block the lymphatic system resulting in inflammation of the lymph nodes. In some cases, the obstruction of lymph vessels causes elephantiasis or filariasis of the limbs, scrotum and mammary glands.

7.2 Maintenance of Personal and Public Hygiene

Hygiene is a set of practices performed to conserve good health. According to the World Health Organization (WHO), hygiene refers to "conditions and practices that help to maintain health and prevent the spread of diseases." Personal hygiene refers to maintaining one's body clean by bathing, washing hands, trimming fingernails, wearing clean clothes and also includes attention to keeping surfaces in the home and workplace, including toilets, bathroom facilities, clean and pathogen-free.

Our public places teem with infection, contamination and germs. It seems that every surface we touch and the air we breathe are with pollutants and microbes. It's not just the public places that are unclean, but we might be amazed at the number of people who do not wash their hands before taking food, after visiting the restroom, or who sneeze without covering their faces.

Many infectious diseases such as typhoid, amoebiasis and ascariasis are transmitted through contaminated food and water. Advancement in science and technology provide effective controlling measures for many infectious and non-infectious diseases. The use of vaccines and adopted immunization programmes have helped to eradicate small pox in India. Moreover a large number of infectious diseases like polio, diphtheria, pneumonia and tetanus have been controlled by the use of vaccines and by creating awareness among the people.

7.3 Basic Concepts of Immunology

Immunology is the study of immune system. This system protects an individual from various infective agents. It refers to all the mechanisms used by the body for protection from environmental agents that are foreign to the body. When the immune system does not function efficiently in an individual, it leads to infection causing disease.

The overall ability of body to fight against the disease causing pathogen is called immunity. It is also called disease resistance and the lack of immunity is known as susceptibility. Immunity is highly specific. Normally many of the responses of the immune system initiate the destruction and elimination of invading organisms and any toxic molecules produced by them. These immune reactions are destructive in nature and are made in response only to molecules that are foreign to the host and not to those of host itself. This ability to distinguish foreign molecules from self is another fundamental feature of the immune system.

However, occasionally, it fails to make its distinction and reacts destructively against the host's own molecules; such autoimmune diseases can be fatal to the organism. Almost all the macromolecules (e.g., proteins, polysaccharides, nucleic acids, etc.) as long as they are foreign to recipient organism can induce immune response. Any substance capable of eliciting immune response is called an ANTIGEN (ANTIbody GENerator). There are two broad classes of immunity responses namely, innate immunity and acquired immunity.

7.3.1 Innate Immunity

Innate immunity is the natural phenomenon of resistance to infection which an individual possesses right from the birth. The innate defense mechanisms are non-specific in the sense that they are effective against a wide range of potentially infectious agents. It is otherwise known as non-specific immunity or natural immunity.

Table 7.4 – Types of Innate Immunity

Type of Innate Immunity	Mechanism
1. Anatomical Barriers Skin Mucus membrane	Prevents the entry of microbes. Its acidic environment (pH 3 to 5) retards the growth of microbes. Mucus entraps foreign microorganisms and competes with microbes for attachment.
2. Physiological Barriers Temperature Low pH Chemical mediators	Normal body temperature inhibits the growth of pathogens. Fever also inhibits the growth of pathogens. Acidity of gastric secretions (HCl) kills most ingested microbes. Lysozyme acts as antibacterial agent and cleaves the bacterial cell wall. Interferons induce antiviral state in the uninfected cells. Complementary substances produced from leucocytes lyse the pathogenic microbes or facilitate phagocytosis.
3. Phagocytic Barriers	Specialized cells (Monocytes, neutrophils, tissue macrophages) phagocytose, and digest whole microorganisms.
4. Inflammatory Barriers	Tissue damage and infection induce leakage of vascular fluid, containing chemotactic signals like serotonin, histamine and prostaglandins. They influx the phagocytic cells into the affected area. This phenomenon is called diapedesis.

7.3.2 Acquired Immunity

The immunity that an individual acquires after birth is known as acquired immunity. It is the body's resistance to a specific pathogen. The unique features of acquired immunity are antigenic specificity, diversity, recognition of self and non-self and immunological memory.

Components of Acquired Immunity

Acquired immunity has two components – cell mediated immunity (CMI) and antibody mediated immunity or humoral immunity.

1. Cell mediated immunity: When pathogens are destroyed by cells without producing antibodies, then it is known as cell mediated immune response or cell mediated immunity. This is brought about by T cells, macrophages and natural killer cells.

2. Antibody mediated immunity or humoral immunity: When pathogens are destroyed by the production of antibodies, then it is known as antibody mediated or humoral immunity. This is brought about by B cells with the help of antigen presenting cells and T helper cells. Antibody production is the characteristic feature of vertebrates only.

Types of Acquired Immunity

Acquired immunity may be active immunity or passive immunity.

Table 7.5 – Differences Between Active and Passive Immunity

S.No	Active Immunity	Passive Immunity
1	Active immunity is produced actively by host's immune system.	Passive immunity is received passively and there is no active host participation.
2	It is produced due to contact with pathogen or by its antigen.	It is produced due to antibodies obtained from outside.
3	It is durable and effective in protection.	It is transient and less effective.
4	Immunological memory is present.	No memory.
5	Booster effect on subsequent dose is possible.	Subsequent dose is less effective.
6	Immunity is effective only after a short period.	Immunity develops immediately.

The immunological resistance developed by the organisms through the production of antibodies in their body is called active immunity. Active immunity is acquired through the use of a person's immune responses, which lead to the development of memory cells. Active immunity results from an infection or an immunization.

Passive immunity does not require the body to produce antibodies to antigens. The antibodies are introduced from outside into the organism. Thus, passive immunity is acquired without the activation of a person's immune response, and therefore there is no memory.

7.3.3 Immune Responses

The immune responses may be primary or secondary.

Do You Know?

The process of production of blood cells in the bone marrow is called haematopoiesis.

Primary Immune Response

The primary immune response occurs when a pathogen comes in contact with the immune system for the first time. During this, the immune system has to learn to recognize the antigen, produce antibody against it and eventually produce memory lymphocytes. The primary immune response is slow and short-lived.

Table 7.6 – Differences Between Primary and Secondary Immune Responses

S.No	Primary Immune Response	Secondary Immune Response
1	It occurs as a result of primary contact with an antigen.	It occurs as a result of second and subsequent contacts with the same antigen.
2	Antibody level reaches peak in 7 to 10 days.	Antibody level reaches peak in 3 to 5 days.
3	Prolonged period is required to establish immunity.	It establishes immunity in a short time.
4	There is rapid decline in antibody level.	Antibody level remains high for longer period.
5	It appears mainly in the lymph nodes and spleen.	It appears mainly in the bone marrow, followed by the spleen and lymph nodes.

Secondary Immune Response

The secondary immune response occurs when a person is exposed to the same antigen again. During this time, immunological memory has been established and the immune system can start producing antibodies immediately. Within hours after recognition of the antigen, a new army of plasma cells are generated. Within 2 to 3 days, the antibody concentration in the blood rises steeply to reach much higher level than primary response. This is also called as "booster response".

7.3.4 Lymphoid Organs

Immune system of an organism consists of several structurally and functionally different organs and tissues that are widely dispersed in the body. The organs involved in the origin, maturation and proliferation of lymphocytes are called lymphoid organs. Based on their functions, they are classified into primary or central lymphoid organs and secondary or peripheral lymphoid organs. The primary lymphoid organs provide appropriate environment for lymphocytic maturation. The secondary lymphoid organs trap antigens and make it available for mature lymphocytes, which can effectively fight against these antigens.

Primary Lymphoid Organs

Bursa of Fabricius of birds, bone marrow and thymus gland of mammals constitute the primary lymphoid organs involved in the production and early selection of lymphocytes. These lymphocytes become dedicated to a particular antigenic specificity. Only when the lymphocytes mature in the primary lymphoidal organs, they become immunocompetent cells. In mammals, B cell maturation occurs in the bone marrow and T cells maturation occurs in the thymus.

Thymus: The thymus is a flat and bilobed organ located behind the sternum, above the heart. Each lobe of the thymus contains numerous lobules, separated from each other by connective tissue called septa. Each lobule is differentiated into two compartments: the outer compartment or outer cortex, is densely packed with immature T cells called thymocytes, whereas the inner compartment or medulla is sparsely populated with mature thymocytes. One of its main secretions is the hormone thymosin. It stimulates the T cell to become mature and immunocompetent. By the early teens, the thymus begins to atrophy and is replaced by adipose tissue. Thus thymus is most active during the neonatal and pre-adolescent periods.

Bone marrow: Bone marrow is a lymphoid tissue found within the spongy portion of the bone. Bone marrow contains stem cells known as haematopoietic cells. These cells have the potential to multiply through cell division and either remain as stem cells or differentiate and mature into different kinds of blood cells.

Secondary or Peripheral Lymphoid Organs

In secondary or peripheral lymphoid organs, antigen is localized so that it can be effectively exposed to mature lymphocytes. The best examples are lymph nodes, appendix, Peyer's patches of gastrointestinal tract, tonsils, adenoids, spleen, MALT (Mucosal-Associated Lymphoid Tissue), GALT (Gut-Associated Lymphoid Tissue), BALT (Bronchial/Tracheal-Associated Lymphoid Tissue).

Did You Know?

Peyer's patches are oval-shaped areas of thickened tissue that are embedded in the mucus-secreting lining of the small intestine of humans and other vertebrate animals. Peyer's patches contain a variety of immune cells, including macrophages, dendritic cells, T cells, and B cells.

The tonsils (palatine tonsils) are a pair of soft tissue masses located at the back of the throat (pharynx). The tonsils are part of the lymphatic system, which help to fight infections. They stop invading germs including bacteria and viruses.

Spleen is a secondary lymphoid organ located in the upper part of the abdominal cavity close to the diaphragm. Spleen contains B and T cells. It brings humoral and cell mediated immunity.

Do You Know?

The adenoids are glands located in the roof of the mouth, behind the soft palate where the nose connects to the throat. The adenoids produce antibodies that help to fight infections. Typically, the adenoids shrink during adolescence and may disappear by adulthood.

Lymph Node

Lymph node is a small bean-shaped structure and is part of the body's immune system. It is the first one to encounter the antigen that enters the tissue spaces. Lymph nodes filter and trap substances that travel through the lymphatic fluid. They are packed tightly with white blood cells, namely lymphocytes and macrophages. There are hundreds of lymph nodes found throughout the body. They are connected to one another by lymph vessels.

Lymph is a clear, transparent, colourless, mobile and extracellular fluid connective tissue. As the lymph percolates through the lymph node, the particulate antigen brought in by the lymph will be trapped by the phagocytic cells, follicular and interdigitating dendritic cells. Lymph node has three zones: the cortex, paracortex and medulla.

The outermost layer of the lymph node is called cortex, which consists of B-lymphocytes, macrophages, and follicular dendritic cells. The paracortex zone is beneath the cortex, which is richly populated by T lymphocytes and interdigitating dendritic cells. The inner most zone is called the medulla which is sparsely populated by lymphocytes, but many of them are plasma cells, which actively secrete antibody molecules.

As the lymph enters, it slowly percolates through the cortex, paracortex and medulla, giving sufficient chance for the phagocytic cells and dendritic cells to trap the antigen brought by the lymph. The lymph leaving a node carries enriched antibodies secreted by the medullary plasma cells against the antigens that enter the lymph node. Sometimes visible swelling of lymph nodes occurs due to active immune response and increased concentration of lymphocytes. Thus swollen lymph nodes may signal an infection. There are several groups of lymph nodes. The most frequently enlarged lymph nodes are found in the neck, under the chin, in the armpits and in the groin.

Did You Know?

The mucosa-associated lymphoid tissue (MALT) is a diffuse system of small concentrations of lymphoid tissue in the alimentary, respiratory and urino-genital tracts. MALT is populated by lymphocytes such as T and B cells, as well as plasma cells and macrophages, each of which is well situated to encounter antigens passing through the mucosal epithelium. It also possesses IgA antibodies.

Gut-associated lymphoid tissue (GALT) is a component of the mucosa-associated lymphoid tissue (MALT) which works in the immune system to protect the body from invasion in the gut.

Bronchus Associated Lymphoid Tissues (BALT) also a component of MALT is made of lymphoid tissue (tonsils, lymph nodes, lymph follicles) found in the respiratory mucosae from the nasal cavities to the lungs.

Cells of the Immune System

The immune system is composed of many interdependent cells that protect the body from microbial infections and the growth of tumour cells. All these cells are derived from pluripotent haematopoetic stem cells. Each stem cell has the capacity to produce RBC, WBC and platelets. The only cells capable of specifically recognising and producing an immune response are the lymphocytes.

Table 7.7 – Cellular Composition of Adult Human Blood

Cell Type	Number of Cells per Microlitre	Approximate Percentage
Red blood cells	4,200,000 to 6,500,000	–
White blood cells – Agranulocytes
Lymphocytes	1500 to 4000	20 to 30
Monocytes	200 to 950	2 to 7
White blood cells – Granulocytes
Neutrophils	2000 to 7000	50 to 70
Basophils	50 to 100	Less than 1
Eosinophils	40 to 500	2 to 5
Platelets	150,000 to 500,000	–

Lymphocytes

About 20 to 30 percentage of the white blood cells are lymphocytes. They have a large nucleus filling most of the cell, surrounded by a little cytoplasm. The two main types of lymphocytes are B and T lymphocytes. Both these are produced in the bone marrow.

B lymphocytes (B cells) stay in the bone marrow until they are mature. Then they circulate around the body. Some remain in the blood, while others accumulate in the lymph nodes and spleen. T lymphocytes leave the bone marrow and mature in the thymus gland. Once mature, T cells also accumulate in the same areas of the body as B cells.

Lymphocytes have receptor proteins on their surface. When receptors on a B cell bind with an antigen, the B cell becomes activated and divides rapidly to produce plasma cells. The plasma cells produce antibodies. Some B cells do not produce antibodies but become memory cells. These cells are responsible for secondary immune response.

T lymphocytes do not produce antibodies. They recognize antigen presenting cells and destroy them. The two important types of T cells are Helper T cells and Killer T cells. Helper T cells release a chemical called cytokine which activates B cells. Killer cells move around the body and destroy cells which are damaged or infected.

Apart from these cells, neutrophils and monocytes destroy foreign cells by phagocytosis. Monocytes when they mature into large cells, they are called macrophages which perform phagocytosis on any foreign organism.

Did You Know?

Dendritic cells are called so because they are covered with long, thin membrane extensions that resemble dendrites of nerve cells. These cells present the antigen to T-helper cells. Four types of dendritic cells are known. They are Langerhans, interstitial cells, myeloid and lymphoid cells.

7.3.5 Antigens

The term antigen (Ag) is used in two senses: the first to describe a molecule which generates an immune response and the second, a molecule which reacts with antibodies. In general antigens are large, complex molecular substances that can induce a detectable immune response. Thus an antigen is a substance that is specific to an antibody or a T-cell receptor and is often used as a synonym for immunogen.

Do You Know?

The histocompatibility antigens are cell surface antigens that induce an immune response leading to rejection of allografts.

An immunogen is a substance capable of initiating an immune response.

Haptens are substances that are non-immunogenic but can react with the products of a specific immune response.

Substances that can enhance the immune response to an antigen are called adjuvants.

Epitope is an antigenic determinant and is the active part of an antigen.

A paratope is the antigen-binding site and is a part of an antibody which recognizes and binds to an antigen.

Do You Know?

Antigenicity is the property of a substance (antigen) that allows it to react with the products of the specific immune response.

Types of Antigens

On the basis of origin, antigens are classified into exogenous antigens and endogenous antigens. The antigens which enter the host from the outside in the form of microorganisms, pollens, drugs, or pollutants are called exogenous antigens. The antigens which are formed within the individual are endogenous antigens. The best examples are blood group antigens.

7.3.6 Antibodies

Antibodies are immunoglobulin (Ig) protein molecules synthesized on exposure to antigen that can combine specifically with the antigen. Whenever pathogens enter our body, the B-lymphocytes produce an army of proteins called antibodies to fight with them. Thus, they are secreted in response to an antigen (Ag) by the effect of B cells called plasma cells.

The antibodies are classified into five major categories, based on their physiological and biochemical properties:

• Immunoglobulin G (gamma)
• Immunoglobulin M (mu)
• Immunoglobulin A (alpha)
• Immunoglobulin D (delta)
• Immunoglobulin E (epsilon)

In the 1950s, experiments by Porter and Edelman revealed the basic structure of the immunoglobulin. An antibody molecule is Y shaped structure that comprises of four polypeptide chains, two identical light chains (L) of molecular weight 25,000 Daltons (approximately 214 amino acids) and two identical heavy chains (H) of molecular weight 50,000 Daltons (approximately 450 amino acids). The polypeptide chains are linked together by di-sulphide (S-S) bonds. One light chain is attached to each heavy chain and two heavy chains are attached to each other to form a Y shaped structure. Hence, an antibody is represented by H₂L₂.

The heavy chains have a flexible hinge region at their approximate middles. Each chain (L and H) has two terminals: C-terminal (Carboxyl) and amino or N-terminal. Each chain (L and H) has two regions. They have variable (V) region at one end and a much larger constant (C) region at the other end. Antibodies responding to different antigens have very different (V) regions but their (C) regions are the same in all antibodies.

In each arm of the monomer antibody, the (V) regions of the heavy and light chains combines to form an antigen-binding site shaped to 'fit' a specific antigenic determinant. Consequently each antibody monomer has two such antigen-binding regions. The (C) regions that forms the stem of the antibody monomer determine the antibody class and serve common functions in all antibodies.

The functions of immunoglobulin are agglutination, precipitation, opsonisation, neutralization, etc.

7.3.7 Antigen-Antibody Interaction

The reaction between an antigen and antibody is the basis for humoral immunity or antibody mediated immunity. The reaction between antigen and antibody occurs in three stages:

1. Formation of antigen-antibody complex
2. Visible events like precipitation, agglutination, etc.
3. Destruction of antigen or its neutralization

Binding Force of Antigen-Antibody Reaction

The binding force between antigen and antibody is due to three factors: closeness between antigen and antibody, noncovalent bonds or intermolecular forces, and affinity of antibody. When antigen and antibody are closely fitted, the strength of binding is great. When they are apart, binding strength is low. The bonds that hold the antigen to the antibody combining site are all non-covalent in nature. These include hydrogen bonds, electrostatic bonds, Van der Waals forces and hydrophobic bonds.

The chief applications of antigen-antibody reactions are: to determine blood groups for transfusion, to study serological ascertainment of exposure to infectious agents, to develop immunoassays for the quantification of various substances, to detect the presence or absence of protein in serum and to determine the characteristics of certain immunodeficiency diseases.

Different Types of Antigen-Antibody Reactions

The reaction between soluble antigen and antibody leads to visible precipitate formation, which is called precipitin reaction. Antibodies that bring about precipitate formation on reacting with antigens are called as precipitins.

Whenever a particulate antigen interacts with its antibody, it would result in clumping or agglutination of the particulate antigen, which is called agglutination reaction. The antibody involved in bringing about agglutination reaction is called agglutinin.

Opsonisation or enhanced attachment is the process by which a pathogen is marked for ingestion and destruction by a phagocyte. Opsonisation involves the binding of an opsonin (i.e., antibody), to a receptor on the pathogen's cell membrane. After opsonin binds to the membrane, phagocytes are attracted to the pathogen. This results in a much more efficient phagocytosis.

The neutralization reactions are the reactions of antigen-antibody that involve the elimination of harmful effects of bacterial exotoxins or a virus by specific antibodies. These neutralizing antibodies are known as antitoxins. This specific antibody is produced by a host cell in response to a bacterial exotoxin or corresponding toxoid (inactivated toxin).

7.3.8 Vaccines

A vaccine is a biological preparation that provides active acquired immunity to a particular disease and resembles a disease-causing microorganism and is often made from weakened or attenuated or killed forms of the microbes, their toxins, or one of its surface proteins. Vaccines "teach" our body how to defend itself when viruses or bacteria invade it. Vaccines deliver only very little amounts of inactivated or weakened viruses or bacteria, or parts of them. This allows the immune system to recognize the organism without actually experiencing the disease. Some vaccines need to be given more than once (i.e., a 'booster' vaccination) to make sure the immune system can overcome a real infection in the future. Vaccine initiates the immunization process.

The vaccines are classified as first, second and third generation vaccines. First generation vaccine is further subdivided into live attenuated vaccine, killed vaccine and toxoids.

• Live attenuated vaccines use the weakened (attenuated), aged, less virulent form of the virus. Example: Measles, mumps and rubella (MMR) vaccine and the Varicella (chickenpox) vaccine.
• Killed (inactivated) vaccines are killed or inactivated by heat and other methods. Example: Salk's polio vaccine.
• Toxoid vaccines contain a toxin or chemical secreted by the bacteria or virus. They make us immune to the harmful effects of the infection, instead of to the infection itself. Example: DPT vaccine (Diphtheria, Pertussis and Tetanus).
• Second generation vaccine contains the pure surface antigen of the pathogen. Example: Hepatitis-B vaccine.
• Third generation vaccine contains the purest and the highest potency vaccines which are synthetic in generation. The latest revolution in vaccine is DNA vaccine or recombinant vaccine.

Do You Know?

Vaccino therapy is the method of use of vaccine for treatment of disease.

Doctor Edward Jenner prepared first vaccine for small pox in 1796.

Polio vaccine was developed by Doctor Jonas Salk (vaccine consists of inactivated microorganism) and Doctor Albert Sabin (live attenuated oral polio vaccine).

Louis Pasteur (1885) discovered vaccine against rabies, anthrax and cholera.

BCG vaccine was developed by Calmette and Guerin against tuberculosis in France in the year 1908.

7.3.9 Vaccination and Immunization

Vaccination is the process of administrating a vaccine into the body or the act of introducing a vaccine into the body to produce immunity to a specific disease.

Immunization is the process of the body building up immunity to a particular disease. Immunization describes the actual changes in the body after receiving a vaccine. Vaccines work by fighting the pathogen and then recording it in their memory system to ensure that the next time this pathogen enters the body, it is eliminated far more quickly. Once the body is able to fight against the disease, it is believed to have built the immunity for it, also known as the body being immunized against the disease.

7.3.10 Hypersensitivity

Some individuals are very sensitive to some particles present in the environment. The exaggerated response of the immune system to certain antigens present in the environment is called allergy (allo-altered, erg-reaction). The substances to which such an immune response is produced are called allergens. An allergen is an antigen that causes an allergic reaction.

Allergic reactions begin within few seconds after the contact with the allergen and last about half an hour. The common examples of allergens are mites in dust, pollens and some proteins in insect venom. Hay fever and asthma are some common examples of allergy. Symptoms of allergic reactions include sneezing, watery eyes, running nose and difficulty in breathing.

Allergy is a form of over active immune response mediated by IgE and mast cells. It can also be due to the release of chemicals like histamine and serotonin from the mast cells. Anaphylaxis is the classical immediate hypersensitivity reaction. It is a sudden, systematic, severe and immediate hypersensitivity reaction occurring as a result of rapid generalized mast-cell degranulation.

7.4 Immunodeficiency Diseases

Immunodeficiency results from the failure of one or more components of the immune system. Primary immune deficiencies are caused by genetic developmental defects. Secondary immune deficiencies arise due to various reasons like radiation, use of cytolytic and immunosuppressive drugs and infections.

AIDS is an acronym for Acquired Immuno Deficiency Syndrome. It is the deficiency of immune system, acquired during the life time of an individual indicating that it is not a congenital disease. AIDS is caused by Human Immuno Deficiency Virus (HIV). It selectively infects helper T cells. The infected helper T cells will not stimulate antibody production by B-cells resulting in loss of natural defence against viral infection. On the basis of genetic characteristics and differences in the viral antigens, HIV is classified into the types 1 and 2 (HIV 1, HIV 2).

Structure of HIV

The human immunodeficiency virus belongs to the genus Lentivirus. When observed under the electron microscope, HIV is seen as a spherical virus, 100-120 nm in diameter, containing a dense core surrounded by a lipoprotein envelope. The envelope has glycoprotein (gp) spikes termed gp41 and gp120. At the core, there are two large single stranded RNA. Attached to the RNA are molecules of reverse transcriptase. It also contains enzymes like protease and ribonuclease. The core is covered by a capsid made of proteins. This is followed by another layer of matrix proteins.

HIV Transmission

The HIV is often located within the cells especially in macrophages. HIV can survive for 1.5 days inside a cell but only about 6 hours outside a cell. Routes of HIV transmission include unsafe sexual contact, blood-contaminated needles, organ transplants, blood transfusion and vertical transmission from HIV infected mother to child. HIV is not transmitted by insects or by casual contact.

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 the DNA of host cells and directs the infected cells to produce viral particles. The macrophages continue to produce virus and in this way acts like a HIV factory. Simultaneously, HIV enters into helper T-lymphocytes, 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. Due to decrease in the number of helper T lymphocytes, the person starts suffering from infections and becomes immune deficient and unable to protect against any infection.

A simple blood test is available that can determine whether the person has been infected with HIV. The ELISA test (Enzyme Linked Immuno Sorbent Assay) detects the presence of HIV antibodies. It is a preliminary test. Western blot test is more reliable and a confirmatory test. It detects the viral core proteins. If both tests detect the presence of the antibodies, the person is considered to be HIV positive.

AIDS has no cure. Prevention of AIDS is the best option. Advocating safe sex and promoting regular check-up, safe blood for transfusion, use of disposable needles, use of condoms during sexual contact, prevention of drug abuse, AIDS awareness programme by NACO (National AIDS Control Organisation), NGOs (Non-Governmental Organisations) and WHO are to prevent the spreading of AIDS.

7.5 Autoimmune Diseases

Autoimmunity is due to an abnormal immune response in which the immune system fails to properly distinguish between self and non-self and attacks its own body. Our body produces antibodies (auto antibodies) and cytotoxic T cells that destroy our own tissues. If a disease-state results, it is referred to as auto-immune disease. Thus, autoimmunity is a misdirected immune response.

Autoimmunity is evidenced by the presence of auto antibodies and T cells that are reactive with host antigens. When the cells act as antigens in the same body, they are called autoantigens.

Autoimmune diseases in human can be divided into two broad categories:

• Organ-specific diseases: The autoimmune process is directed mostly against one organ. The autoantibodies may block the functions performed by the organs. Examples include Hashimoto's thyroiditis, Graves' disease (thyroid gland) and Addison's disease (adrenal glands).
• Non-organ specific (systemic) disorders: Autoimmune activity is widely spread throughout the body. Rheumatoid arthritis and multiple sclerosis are examples for systemic disorders.

7.5.1 Tumour Immunology

A tumour or neoplasm is a group of cells whose growth has gone unchecked. When a tumour continues to grow and invades healthy tissue, it is called cancer. They spread to other parts of the body from the tumour and give rise to secondary tumour. This is known as metastasis. Tumour may be benign or malignant depending on its characteristics. Benign or non-cancerous tissues are capable of indefinite growth and do not invade other body parts. In the malignant tumour, the cells grow indefinitely, detach and migrate into healthy surrounding tissues.

Table 7.8 – Normal Cell vs Cancer Cell

Normal Cell	Cancer Cell
Small uniformly shaped nuclei, relatively large cytoplasmic volume	Large variably shaped nuclei, relatively small cytoplasmic volume
Conformity in cell size and shapes; cells arranged into discrete tissues	Variation in cell size and shapes; disorganised arrangement of cells
May possess differentiated cell structures; normal presentation of cell surface marker	Loss of normal specialised features; elevated expression of certain cell markers
Lower level of dividing cells; cell tissue clearly demarcated	Large number of dividing cells; poorly defined tumour boundaries

In normal cells, cell growth and differentiation is highly controlled and regulated. But in cancer cells, there is breakdown of this regulatory mechanism. Normal cells show a property called contact inhibition, which inhibits uncontrolled growth. Cancer cells do not have this property. As a result, cancerous cells divide continuously giving rise to mass of tissues called tumours.

When a cell undergoes malignant transformation, it acquires new surface antigen and may also lose some normal antigens. These antigens are present on the membranes of malignant cells and they induce an immune response. Both humoral and cellular responses can be observed in malignancy.

The concept of immunological surveillance postulates that the primary function of the immune system is to "seek and destroy" malignant cells that arise by somatic mutation. The efficiency of the surveillance mechanism reduces either as a result of ageing or due to congenital or acquired immune deficiencies, leads to increased incidence of cancer.

Scope of Immunology

The younger graduates in this field can find number of employment opportunities in Government as well as private hospitals. The scope of the immunology is immunotherapy, microbial immunology, clinical immunology, cellular immunology, allergy and immunology, translational immunology, transplantation immunology, neuro-inflammatory disorders, tumour immunology, vaccine immunology, inflammatory disorders, ocular immunology and inflammation.

Immunotherapy of Cancer

Immunotherapy also called biological therapy uses substances made by the body or in a laboratory (monoclonal antibodies) to improve or to resist the immune system function. Different approaches have been attempted in the immunotherapy of cancer. Immunotherapy appears to be important in getting rid of the residual malignant cells after the gross tumour has been removed. The best results in the treatment of cancer is to follow an integrated approach to therapy, combining surgery, radiotherapy, chemotherapy and immunotherapy.

7.6 Adolescence – Drug and Alcohol Abuse

Adolescence begins with a period of rapid physical and sexual development called puberty to maturity at 12 to 19 years of age. Adolescence is also a highly dynamic period of psychological and social changes in individuals. Adolescents are vulnerable to group (peer) pressure and many youngsters are pushed into experimenting with drugs and alcohol. Proper education and guidance would enable youth to say no to drugs and alcohol and to follow a healthy life style.

Alcohol is a psychoactive drug, which acts on the brain, affecting a person's mind and behaviour. It is a depressant, which slows down the activity of the nervous system.

The intake of certain drugs for a purpose other than their normal clinical use in an amount and frequency that impair one's physical, physiological and psychological functions is called drug abuse. The drugs which are commonly abused include opioids, cannabinoids, coca-alkaloids, barbiturates, amphetamines and LSD.

Opioids are drugs which bind to specific opioid receptors present in the central nervous system and intestinal tract. Heroin (smack) is chemically diacetyl morphine, which is white, odourless and bitter crystalline compound. It is obtained by acetylation of morphine, which is extracted from flowers of the poppy plant. Morphine is one of the strongest pain killer and is used during surgery. It is the most widely abused narcotic drug which acts as a depressant and slows down body functions.

Cannabinoids are a group of chemicals obtained from Cannabis sativa, the Indian hemp plant. Natural cannabinoids are the main source of marijuana, ganja, hashish and charas. It interferes in the transport of the neurotransmitter, dopamine and has a potent stimulating action on the CNS, producing increased energy and a sense of euphoria.

Table 7.9 – Classification of Drugs

Group	Drugs	Effects
Stimulants	Amphetamines, cocaine, nicotine and tobacco	Accelerates the activity of the brain
Depressants	Alcohol, Barbiturates, Tranquilizers	Slows down the activity of the brain
Narcotic/Analgesics	Opium, Morphine	Act as depressants on the Central Nervous System
Hallucinogens	Lysergic acid diethylamide (LSD), Phencyclidine	Distorts the way one sees, hears and feels
Stimulants, Depressants, Hallucinogens	Bhang (Marijuana), Ganja, Charas	Stimulating action on the CNS and affects the cardiovascular system

Cocaine is a white powder that is obtained from the leaves of the coca plant, Erythroxylum coca. It is commonly called coke or crack. Cocaine causes serious physical and psychological problems including hallucinations and paranoia. The other plants with hallucinogenic properties are Atropa belladonna and Datura.

Drugs like methamphetamine, amphetamines, barbiturates, tranquilizers, Lysergic acid diethylamide (LSD) are normally used as medicine to treat patients with mental illness like depression and insomnia and are often abused.

Tobacco is smoked, chewed and used as snuff. It increases the carbon monoxide content of blood and reduces the concentration of haem bound oxygen, thus causing oxygen deficiency in the body. Tobacco contains nicotine, carbon monoxide and tars, which cause problems in the heart, lung and nervous system. Adrenal glands are stimulated by nicotine to release adrenaline and nor adrenaline which increases blood pressure and heart beat.

7.6.1 Addiction and Dependence

Addiction is a physical or psychological need to do or take or use certain substance such as alcohol, to the point where it could be harmful to the individual. This addictive behaviour can be personally destructive to a person. Overtime addicts start to lose not only their jobs, homes and money, but also friendship, family relationships and contact with the normal world.

Addiction to drugs and alcohol can lead to a psychological attachment to certain effects such as euphoria and temporary feeling of wellbeing. Repeated use of drugs and alcohol may affect the tolerance level of the receptors present in the body. These receptors then respond only to highest doses of drugs and alcohol leading to greater intake and addiction.

Excessive use of drug and alcohol leads to physical and psychological dependence. When psychological dependence develops, the drug user gets mentally 'hooked on' to the drug. The drug user constantly thinks only about the drug and has continuous uncontrollable craving for it. This state called "euphoria" is characterized by mental and emotional preoccupation with the drug.

Physical dependence is a state in which the user's body requires a continuous presence of the drug. If the intake of the drug or alcohol is abruptly stopped, he or she would develop withdrawal symptoms. The withdrawal symptoms may range from mild tremors to convulsions, severe agitation and fits, depressed mood, anxiety, nervousness, restlessness, irritability, insomnia, dryness of throat, etc., depending on the type of drug abuse.

7.6.2 Effects of Drugs and Alcohol

Short-term effect appears only for a few minutes after the intake of drugs and alcohol. The abuser feels a false sense of well being and a pleasant drowsiness. Some short term effects are euphoria, pain, dullness of senses, alteration in behaviour, blood pressure, narcosis (deep sleep), nausea and vomiting.

Drugs and alcohol have long-term effects that lead to serious damages, because of the constant and excessive use. The physical and mental disturbance makes the life of the user unbearable and torturous. For example, heavy drinking permanently damages the liver and brain.

Did You Know?

Alcoholism is the inability to control drinking due to physical and emotional dependence on alcohol. Treatment involves counselling by a healthcare professional. Detoxification programme in a hospital or medical facility is an option for those who need additional assistance. Medications are available to reduce the desire to drink and smoke.

The use of alcohol during adolescence may have long-term effects. Alcohol interferes with the ability of the liver to break down fat. Over time fat accumulation and high levels of alcohol destroy the liver cells and a scar tissue grows in the place of dead cells. This scarring of the liver is called "Liver cirrhosis". Alcohol irritates the stomach lining due to the production of excess acid leading to ulcers. Excessive alcohol use weakens the heart muscle, causing scar tissue to build up in the cardiac muscle fibres. As a result, heavy drinkers have an increased risk of high blood pressure, stroke, coronary artery disease and heart attack. Korsakoff syndrome, a chronic memory disorder, is most commonly caused by alcohol misuse.

7.6.3 Prevention and Control

It is practically possible to prevent someone from using drugs and alcohol. Here are some ways that help to prevent drug and alcohol abuse:

1. Effectively Dealing with Peer Pressure

The biggest reason for teens to start on drugs is due to their friends or peer groups imposing pressure on them. Hence, it is important to have a better group of friends to avoid such harmful drugs and alcohol.

2. Seeking Help from Parents and Peers

Help from parents and peer group should be sought immediately so that they can be guided appropriately. Help may even be sought from close and trusted friends. Getting proper advice to sort out their problems would help the young to vent their feelings of anxiety and guilt.

3. Education and Counselling

Education and counselling create positive attitude to deal with many problems and to accept disappointments in life.

4. Looking for Danger Signs

Teachers and parents need to look for signs that indicate tendency to go in for addiction.

5. Seeking Professional and Medical Assistance

Assistance is available in the form of highly qualified psychologists, psychiatrists and de-addiction and rehabilitation programmes to help individuals to overcome their problems.

Alcoholic Anonymous

Alcoholic anonymous was started in 1935 by a businessman and a doctor who had been a "hopeless drunk" for many years. After the men helped each other to stop drinking and to stay sober, they then founded the alcoholic anonymous to help other alcoholics. Since that time alcoholic anonymous has spread throughout the world.

7.7 Mental Health – Depression

Mental health is a state of well being of the mind, with self esteem. Self esteem means liking yourself and being able to stand up for what you believe is right. Positive mental health is an important part of wellness. A mentally healthy person reflects a good personality. Activities of mentally healthy people are always appreciated and rewarded by the society as these persons are creative as well as cooperative with others. Mental health improves the quality of life.

Depression is a common mental disorder that causes people to experience depressed mood, loss of interest or pleasure, feelings of guilt or low self-worth, disturbed sleep, poor appetite, low energy and poor concentration.

Signs and Symptoms of Mental Depression

• Loss of self-confidence and self esteem
• Anxiety
• Not being able to enjoy things that are usually pleasurable or interesting

Lifestyle changes like exercise, meditation, yoga and healthy food habits can help to be relieved from depression. Exercise stimulates the body to produce serotonin and endorphins, which are neurotransmitters that suppress depression. Practicing exercise in daily life creates a positive attitude.

Participating in an Exercise Programme Can:

• Increase self-esteem
• Boost self-confidence
• Create a sense of empowerment
• Enhance social connections and relationships

Brain is one of the most metabolically active part of the body and needs a steady stream of nutrients to function. A poor diet may not provide the nutrients for a healthy body and may provoke symptoms of anxiety and depression.

Summary

Health is a state of complete physical and psychological wellbeing. Many other extended factors like microbes may cause illness to human body. Protozoans like Entamoeba, Plasmodium and Leishmania cause diseases such as amoebic dysentery, malaria and kala-azar respectively. Personal cleanliness and hygiene, proper disposal of waste, safe drinking water and immunization are very useful in preventing diseases.

Drug and alcohol abuse of young and adolescent is another cause of concern. Addiction to drugs and alcohol is happening due to peer pressure, examination-related and competition-related stresses. The addicted person should receive proper counselling, education and professional medical help to liberate themselves from all forms of addiction.

Immunology deals with a study of the immune system. The immune system recognises and eliminates the invaders, and the ability of the body to overcome the pathogen is called immunity. Immunity is classified into innate immunity and acquired immunity. Acquired immunity is further classified into cell mediated immunity and antibody mediated immunity as its components. Acquired immunity may be active or passive immunity. Immune response is the body's response to pathogens and it may be primary or secondary.

The organs involved in the origin, maturation and proliferation of lymphocytes are called lymphoid organs. Thymus, bone marrow are primary lymphoid organs. The secondary lymphoid organs are lymph node, MALT, GALT and BALT.

The malfunctioning of immune system leads to hypersensitivity, immunodeficiency or autoimmune diseases. A tumour or neoplasm is a group of cells whose growth has gone unchecked. The best results in the treatment of cancer is achieved by an integrated approach to therapy – surgery, radiotherapy, chemotherapy and immunotherapy.

Interesting Facts

1. Freezing does not kill bacteria; it only arrests their growth.
2. Antibiotics not only kill harmful bacteria, but also kill beneficial bacteria of our body.
3. UTI – Urinary Tract Infection is one of the most common bacterial infections affecting 150 million people each year worldwide.
4. World malaria day is on 25th April.
5. Iceland and the Faroe islands are the only countries in the world where there are "No mosquitoes" (Mosquito free countries).
6. VCRC – Vector Control Research Center is situated in Puducherry. WHO is collaborating with the Centre for Research and Training in Lymphatic Filariasis and Integrated Methods of Vector Control.
7. Sterile insect technique (SIT): The screw-worm fly was the first pest successfully eliminated from an area through the sterile insect technique, by the use of an integrated area-wide approach.
8. Zika virus could become a surgical weapon against brain cancer.

Evaluation

Exercise MCQ Questions

1. A 30 year old woman has bloody diarrhoea for the past 14 hours. Which one of the following organisms is likely to cause this illness?

a) Streptococcus pyogens b) Clostridium difficile c) Shigella dysenteriae d) Salmonella enteritidis

2. Exoerythrocytic schizogony of Plasmodium takes place in ____.

a) RBC b) Leucocytes c) Stomach d) Liver

3. The sporozoites of Plasmodium vivax are formed from ____.

a) Gametocytes b) Sporoblasts c) Oocysts d) Spores

4. Amphetamines are stimulants of the CNS, whereas barbiturates are ____.

a) CNS stimulant b) both a and b c) hallucinogenic d) CNS depressants

5. Choose the correctly matched pair.

a) Amphetamines – Stimulant b) LSD – Narcotic c) Heroin – Psychotropic d) Benzodiazepine – Pain killer

6. The Athlete's foot disease in human is caused by ____.

a) Bacteria b) Fungi c) Virus d) Protozoan

7. Cirrhosis of liver is caused by chronic intake of ____.

a) Opium b) Alcohol c) Tobacco d) Cocaine

8. The sporozoite of the malarial parasite is present in ____.

a) saliva of infected female Anopheles mosquito. b) RBC of human suffering from malaria. c) Spleen of infected humans. d) Gut of female Anopheles mosquito.

9. Match the pathogens with respective diseases caused by them and select the correct match using the code given below:

a. Leishmania donovani	1. Amoebiasis
b. Wuchereria bancrofti	2. Kala azar
c. Trypanosoma gambiense	3. Sleeping sickness
d. Entamoeba histolytica	4. Filariasis

1. a-2, b-4, c-3, d-1 2. a-2, b-4, c-1, d-3 3. a-3, b-1, c-2, d-4 4. a-1, b-4, c-3, d-2

10. Paratope is an ____.

a) Antibody binding site on variable regions b) Antibody binding site on heavy regions c) Antigen binding site on variable regions d) Antigen binding site on heavy regions

11. Allergy involves ____.

a) Immunoglobulin E b) Immunoglobulin G c) Immunoglobulin A d) Immunoglobulin M

12. Spread of cancerous cells to distant sites is termed as ____.

a) Metastasis b) Oncogenes c) Proto-oncogenes d) Malignant neoplasm

13. AIDS virus has ____.

a) Single stranded RNA b) Double stranded RNA c) Single stranded DNA d) Double stranded DNA

14. B cells that produce and release large amounts of antibody are called ____.

a) Memory cells b) Basophils c) Plasma cells d) Killer cells Exercise 15. Short Answer

15. Given below are some human organs. Identify one primary and one secondary lymphoid organ. Explain its role.

Liver, thymus, stomach, thyroid, tonsils

Exercise 16. Short Answer

16. Name and explain the type of barriers which involve macrophages.

Exercise 17. Short Answer

17. What are interferons? Mention their role.

Exercise 18. Short Answer

18. List out chemical alarm signals produced during inflammation.

Exercise 19. Long Answer

19. Explain the process of replication of retrovirus after it gains entry into the human body.

Exercise 20. Long Answer

20. Explain the structure of immunoglobulin with suitable diagram.

Exercise 21. Short Answer

21. What are the cells involved in innate immune system?

Exercise 22. Short Answer

22. What is vaccine? What are its types?

Exercise 23. Short Answer

23. A person is infected by HIV. How will you diagnose for AIDS?

Exercise 24. Long Answer

24. Autoimmunity is a misdirected immune response. Justify.

Exercise 25. Short Answer

25. List the causative agent, mode of transmission and symptoms for Diphtheria and Typhoid.

Exercise 26. Short Answer

26. A patient was hospitalized with fever and chills. Merozoites were observed in her blood. What is your diagnosis?

Exercise 27. Short Answer

27. (a) Write the scientific name of the filarial worm that causes filariasis.

(b) Write the symptoms of filariasis.

(c) How is this disease transmitted?

Exercise 28. Short Answer

28. List the common withdrawal symptoms of drugs and alcohol abuse.

Exercise 29. Short Answer

29. Why do you think it is not possible to produce vaccine against 'common cold'?

ICT Corner – Human Health and Diseases

Let us examine to know the chronic disease – systemic lupus erythematosus (SLE)

Procedure:

1. Step 1: Type the URL or scan the QR code to open the activity page. Click "To enter the lab" to start the test.
2. Step 2: Follow the interactive steps guided by the virtual lab starting from centrifugation and to ELISA.
3. Step 3: On the right, find the different headers such as "Diagnosis, Background, Notebook, Glossary and Help" and click to know the virtual procedure happening aside on the left.
4. Step 4: Find "Launch Gene Body" on the right bottom of the window, and click it to analyse and understand about the cloning.
5. Step 5: Complete this ELISA to know if a patient acquired the disease or not.

IMMUNOLOGY URL: http://media.hhmi.org/biointeractive/vlabs/immunology/index.html

Book-back Exercises — Questions & Answers

Answers generated strictly from the Samacheer Kalvi textbook content. Attempt each question first, then click "Show Answer" to check.

I. Choose the Correct Answer

1. A 30 year old woman has bleedy diarrhoea for the past 14 hours, which one of the following organisms is likely to cause this illness?

a) Streptococcus pyogens b) Clostridium difficile c) Shigella dysenteriae d) Salmonella enteritidis

Answer: c) Shigella dysenteriae

Explanation: Shigellosis (Bacillary dysentery) is caused by Shigella species and is characterized by abdominal pain, dehydration, blood and mucus in the stools, transmitted through food and water contaminated by faeces.

2. Exoerythrocytic schizogony of Plasmodium takes place in ___

a) RBC b) Leucocytes c) Stomach d) Liver

Answer: d) Liver

Explanation: The sporozoite within the blood stream immediately enters the hepatic cells of the liver, where they undergo multiple asexual fission (schizogony) and produce merozoites — this is the exoerythrocytic stage.

3. The sporozoites of Plasmodium vivax are formed from ___

a) Gametocytes b) Sporoblasts c) Oocysts d) Spores

Answer: c) Oocysts

Explanation: The oocyte undergoes meiosis by a process called sporogony to form sporozoites. The oocyte (oocyst) develops in the mosquito's gut wall and sporozoites migrate to the salivary glands of the mosquito.

4. Amphetamines are stimulants of the CNS, whereas barbiturates are ___

a) CNS stimulant b) both a and b c) hallucinogenic d) CNS depressants

Answer: d) CNS depressants

Explanation: According to the classification of drugs in the chapter, Amphetamines are stimulants that accelerate the activity of the brain, whereas Barbiturates are depressants that slow down the activity of the brain.

5. Choose the correctly matched pair.

a) Amphetamines - Stimulant b) LSD - Narcotic c) Heroin - Psychotropic d) Benzodiazepine - Pain killer

Answer: a) Amphetamines - Stimulant

Explanation: As per the drug classification table in the chapter, Amphetamines are listed under Stimulants that accelerate the activity of the brain.

6. The Athlete's foot disease in human is caused by ___

a) Bacteria b) Fungi c) Virus d) Protozoan

Answer: b) Fungi

Explanation: Ringworm of the feet is known as Athlete's foot, caused by Tinea pedis, which is a fungal disease (Dermatomycosis) caused by fungi belonging to the genera Trichophyton, Microsporum and Epidermophyton.

7. Cirrhosis of liver is caused by chronic intake of ___

a) Opium b) Alcohol c) Tobacco d) Cocaine

Answer: b) Alcohol

Explanation: Fat accumulation and high levels of alcohol destroy the liver cells and scar tissue grows in the place of dead cells. This scarring of the liver is called "Liver cirrhosis."

8. The sporozoite of the malarial parasite is present in ___

a) saliva of infected female Anopheles mosquito. b) RBC of human suffering from malaria. c) Spleen of infected humans. d) Gut of female Anopheles mosquito.

Answer: a) saliva of infected female Anopheles mosquito.

Explanation: As the mosquito feeds, it injects saliva containing the sporozoites into the human bloodstream. The sporozoites migrate to the salivary glands of the mosquito after sporogony.

9. Match the pathogens with respective diseases caused by them and select the correct match using the code given below:
a. Leishmania donovani    1. Amoebiasis
b. Wuchereria bancrofti    2. Kala azar
c. Trypanosoma gambiense    3. Sleeping sickness
d. Entamoeba histolytica    4. Filariasis

1. a-2, b-4, c-3, d-1 2. a-2, b-4, c-1, d-3 3. a-3, b-1, c-2, d-4 4. a-1, b-4, c-3, d-2

Answer: 1. a-2, b-4, c-3, d-1

Explanation: Leishmania donovani causes Kala-azar (2); Wuchereria bancrofti causes Filariasis (4); Trypanosoma gambiense causes Sleeping sickness (3); Entamoeba histolytica causes Amoebiasis (1).

10. Paratope is an

a) Antibody binding site on variable regions b) Antibody binding site on heavy regions c) Antigen binding site on variable regions d) Antigen binding site on heavy regions

Answer: c) Antigen binding site on variable regions

Explanation: A paratope is the antigen-binding site and is a part of an antibody which recognizes and binds to an antigen, located on the variable regions of the antibody.

11. Allergy involves

a) Immunoglobulin E b) Immunoglobulin G c) Immunoglobulin A d) Immunoglobulin M

Answer: a) Immunoglobulin E

Explanation: Allergy is a form of over active immune response mediated by IgE and mast cells. It can also be due to the release of chemicals like histamine and serotonin from the mast cells.

12. Spread of cancerous cells to distant sites is termed as

a) Metastasis b) Oncogenes c) Proto-oncogenes d) Malignant neoplasm

Answer: a) Metastasis

Explanation: Cancerous cells spread to other parts of the body from the tumour and give rise to secondary tumour. This is known as metastasis.

13. AIDS virus has

a) Single stranded RNA b) Double stranded RNA c) Single stranded DNA d) Double stranded DNA

Answer: a) Single stranded RNA

Explanation: At the core of HIV, there are two large single stranded RNA. Attached to the RNA are molecules of reverse transcriptase.

14. B cells that produce and release large amounts of antibody are called

a) Memory cells b) Basophils c) Plasma cells d) Killer cells

Answer: c) Plasma cells

Explanation: When receptors on a B cell bind with an antigen, the B cell becomes activated and divides rapidly to produce plasma cells. The plasma cells produce antibodies.

II. Short Answer Questions

15. Given below are some human organs. Identify one primary and one secondary lymphoid organ. Explain its role. Liver, thymus, stomach, thyroid, tonsils

Answer: Primary lymphoid organ – Thymus: The thymus is a flat, bilobed organ located behind the sternum. T lymphocytes mature in the thymus. It secretes the hormone thymosin which stimulates T cells to become mature and immunocompetent. It is most active during the neonatal and pre-adolescent periods.

Secondary lymphoid organ – Tonsils: The tonsils (palatine tonsils) are a pair of soft tissue masses located at the back of the throat (pharynx). They are part of the lymphatic system and help to fight infections by stopping invading germs including bacteria and viruses.

16. Name and explain the type of barriers which involve macrophages.

Answer: Macrophages are involved in Phagocytic barriers of innate immunity. Specialized cells such as monocytes, neutrophils and tissue macrophages phagocytose and digest whole microorganisms. Monocytes, when they mature into large cells, are called macrophages, which perform phagocytosis on any foreign organism entering the body.

17. What are interferons? Mention their role.

Answer: Interferons are chemical mediators that act as physiological barriers in innate immunity. They induce an antiviral state in the uninfected cells. They are produced as part of the body's non-specific defense mechanism, protecting uninfected cells from viral infection by alerting them and enhancing their resistance.

18. List out chemical alarm signals produced during inflammation.

Answer: During inflammatory response, tissue damage and infection induce leakage of vascular fluid containing chemotactic signals (chemical alarm signals). These are: Serotonin, Histamine and Prostaglandins. They influx the phagocytic cells into the affected area by a phenomenon called diapedesis.

19. Explain the process of replication of retrovirus after it gains entry into the human body.

Answer: After HIV (a retrovirus) enters the body, it enters into macrophages where the RNA genome of the virus replicates to form viral DNA with the help of the enzyme reverse transcriptase. This viral DNA gets incorporated into the DNA of host cells and directs infected cells to produce viral particles. The macrophages continue to produce virus (acting like an HIV factory). HIV also enters helper T-lymphocytes, replicates and produces progeny viruses that are released into the blood to attack other helper T-lymphocytes, leading to progressive decrease in their number.

20. Explain the structure of immunoglobulin with suitable diagram.

Answer: An antibody (immunoglobulin) is a Y-shaped structure comprising four polypeptide chains: two identical light chains (L) of molecular weight 25,000 Daltons (approximately 214 amino acids) and two identical heavy chains (H) of molecular weight 50,000 Daltons (approximately 450 amino acids). The chains are linked by di-sulphide (S-S) bonds. Each chain has a variable (V) region at one end and a larger constant (C) region at the other end. The V regions of heavy and light chains form the antigen-binding site. Each antibody monomer has two antigen-binding regions. An antibody is represented as H₂L₂. The heavy chains have a flexible hinge region. The C regions form the stem and determine the antibody class.

21. What are the cells involved in innate immune system?

Answer: The cells involved in the innate immune system are Monocytes, Neutrophils and Tissue macrophages (phagocytic barriers). These specialized cells phagocytose and digest whole microorganisms. During inflammation, phagocytic cells are recruited to the affected area. Natural killer cells also participate in innate immune defense.

22. What is vaccine? What are its types?

Answer: A vaccine is a biological preparation that provides active acquired immunity to a particular disease. It is often made from weakened (attenuated) or killed forms of microbes, their toxins, or surface proteins. Vaccines are classified into three generations:
First generation: (i) Live attenuated vaccines – e.g., MMR vaccine, Varicella vaccine. (ii) Killed vaccines – e.g., Salk's polio vaccine. (iii) Toxoids – e.g., DPT vaccine.
Second generation: Contains pure surface antigen – e.g., Hepatitis-B vaccine.
Third generation: Synthetic/recombinant vaccines including DNA vaccines; highest potency.

23. A person is infected by HIV. How will you diagnose for AIDS?

Answer: AIDS is diagnosed by two tests: (i) ELISA test (Enzyme Linked Immuno Sorbent Assay) – a preliminary test that detects the presence of HIV antibodies in the blood. (ii) Western blot test – a more reliable and confirmatory test that detects the viral core proteins. If both tests detect the presence of antibodies, the person is considered to be HIV positive.

24. Autoimmunity is a misdirected immune response. Justify.

Answer: Autoimmunity is due to an abnormal immune response in which the immune system fails to properly distinguish between self and non-self, and attacks its own body. The body produces antibodies (auto antibodies) and cytotoxic T cells that destroy our own tissues. When cells act as antigens in the same body, they are called autoantigens. Examples include Hashimoto's thyroiditis, Graves' disease, Addison's disease (organ-specific) and Rheumatoid arthritis, multiple sclerosis (systemic). Thus, instead of protecting the body, the immune system mistakenly attacks it — making it a misdirected immune response.

25. List the causative agent, mode of transmission and symptoms for Diphtheria and Typhoid.

Answer:

Diphtheria:
Causative agent: Corynebacterium diphtheriae
Mode of transmission: Droplet infection
Symptoms: Fever, sore throat, hoarseness and difficulty in breathing

Typhoid:
Causative agent: Salmonella typhi
Mode of transmission: Through contaminated food and water
Symptoms: Headache, abdominal discomfort, fever and diarrhoea. (Typhoid fever can be confirmed by Widal test.)

26. A patient was hospitalized with fever and chills. Merozoites were observed in her blood. What is your diagnosis?

Answer: The patient is suffering from Malaria. The presence of merozoites in the blood is characteristic of malaria caused by Plasmodium species. The sudden release of merozoites, haemozoin toxin and erythrocyte debris into the bloodstream results in malarial paroxysms — shivering chills and high fever, which matches the patient's symptoms. Malaria is transmitted by the bite of the infected female Anopheles mosquito.

27. (a) Write the scientific name of the filarial worm that causes filariasis. (b) Write the symptoms of filariasis. (c) How is this disease transmitted?

Answer:
(a) The scientific name of the filarial worm is Wuchereria bancrofti (commonly called filarial worm).
(b) Symptoms: The accumulation of worms blocks the lymphatic system resulting in inflammation of the lymph nodes. In some cases, obstruction of lymph vessels causes elephantiasis or filariasis of the limbs, scrotum and mammary glands.
(c) Transmission: The disease is transmitted by the female Culex mosquito. The female filarial worm gives rise to juveniles called microfilariae larvae. The life cycle is completed in two hosts — man and the female Culex mosquito.

28. List the common withdrawal symptoms of drugs and alcohol abuse.

Answer: When the intake of drugs or alcohol is abruptly stopped, the person develops withdrawal symptoms. These include: mild tremors, convulsions, severe agitation and fits, depressed mood, anxiety, nervousness, restlessness, irritability, insomnia, dryness of throat — depending on the type of drug abused. In a sense, the body becomes confused and protests against the absence of the drug.

29. Why do you think it is not possible to produce vaccine against 'common cold'?

Answer: It is not possible to produce a common vaccine against common cold because it is caused by more than 150 different strains of Rhinoviruses. Moreover, their RNA genome keeps changing due to mutation. Due to the large number of strains and continuous mutations in the genome, it is very difficult to prepare a single common vaccine that can be effective against all strains of Rhinoviruses causing common cold.

📝 Summary

1. Health is defined by the World Health Organization (WHO) as 'a state of complete physical, mental and social wellbeing and not merely absence of diseases,' and is maintained through personal hygiene, regular exercise, and a balanced diet.
2. Diseases are broadly classified into infectious (communicable) diseases — caused by pathogens like viruses, bacteria, fungi, protozoan and helminthic parasites transmitted through air, water, food, physical contact, and vectors — and non-infectious diseases such as genetic, nutritional, and degenerative conditions.
3. Bacterial diseases are generally curable, but bacteria can develop antibiotic resistance when antibiotics are overused or misused; viral diseases, such as AIDS, may not all be curable and can sometimes be fatal.
4. The chapter covers key concepts of immunology, including innate and acquired immunity, primary and secondary immune responses, active and passive immunity, hypersensitivity, immunodeficiency diseases, and autoimmune diseases.
5. The lesson also addresses important social health issues including the ill effects of drug and alcohol abuse during adolescence, and the significance of mental health and depression, encouraging students to take responsibility for their behaviour, healthcare, and lifestyle choices.