Human Health and Disease Class 12 biology Chapter 8

Human Health and Disease Class 12 Biology Chapter 8

Human Health and Disease Class 12 Introduction

In Year 12 Human Health and Disease, students explore the complex factors that affect the health and balance of the human body. This comprehensive course examines the dynamics of health care and the mechanisms of various diseases. Topics include anatomy and physiology of organ systems,

The role of microbes and the body’s defense mechanisms. Students understand the impact of lifestyle choices, environmental factors, and genetic perspectives on health outcomes. This class provides a foundation for understanding the complexity of disease processes and promotes a holistic approach to maintaining optimal human health.

Human Health and Disease Class 12 About the author

Born in August 1925 in Kumbakonam in Tamil Nadu, Monkambu Sambasivan Swaminathan did his graduation and post-graduation in Botany from Madras University. He worked in different capacities in a large number of institutions in India and abroad and developed his expertise in genetics and plant breeding. The School of Cytogenetics and Radiation Research was established at the Indian

Agricultural Research Institute (IARI) enabled Swaminathan and his team to develop short-duration high-yielding varieties of rice, including scented Basmati. He is also known for the development of the concept of crop cafeteria, crop scheduling, and genetically improving yield and quality.

Swaminathan initiated collaboration with Norman Borlaug, which culminated in the ‘Green Revolution’ through the introduction of Mexican varieties of wheat in India. This was highly recognized and appreciated. He is also the initiator of ‘Lab-to-Land’, food security, and several other environmental programs. He has been honored with Padma Bhushan and several other prestigious awards, medals, and fellowships by institutions of excellence.

Human Health and Disease Class 12 Definition

Class 12 Human Health and Disease focuses on the study of the physiological and pathological aspects of the human body. It encompasses the understanding of the structure and function of healthy organs and systems, as well as the deviations leading to various diseases. The course explores the interactions between genetic, environmental, and lifestyle factors that influence health outcomes.

It equips students with knowledge about the mechanisms of disease, the body’s defense mechanisms, and preventive measures, laying the foundation for a comprehensive understanding of human health and its complexities.

Human Health and Disease Class 12 Important Notes

Introduction to Health:
- Definition of health and its dimensions.
- Factors influencing health, including genetics, environment, and lifestyle.
Disease and its Causes:
- Differentiating between health and disease.
- Understanding causes of diseases – pathogens, genetic factors, lifestyle choices.
Infectious Diseases:
- Types of pathogens (bacteria, viruses, fungi, parasites).
- Modes of transmission and prevention of common infectious diseases.
Non-Communicable Diseases:
- Understanding lifestyle-related diseases (cardiovascular, respiratory, and metabolic diseases).
- Factors contributing to non-communicable diseases.
Immunity:
- The immune system and its components.
- How the body defends itself against pathogens.
Vaccination:
- Importance of vaccination.
- Types of vaccines and their significance.
Cancer:
- Causes and mechanisms of cancer.
- Methods of cancer prevention and treatment.
Healthcare and Medical Practices:
- Overview of healthcare systems.
- Role of medical professionals and ethical considerations.
Personal and Community Health:
- Importance of personal hygiene.
- Community health initiatives and their impact.
Epidemiology:
- Basics of epidemiology and disease patterns.
- Studying disease distribution and control measures.

Human Health and Disease Class 12 Explanation

Health, for a long time, was considered as a state of body and mind where there was a balance of certain ‘humor’. This is what early Greeks like Hippocrates as well as the Indian Ayurveda system of medicine asserted. It was thought that persons with ‘black bile’ belonged to a hot personality and would have fevers. This idea was arrived at by pure reflective thought.

The discovery of blood circulation by William Harvey using experimental methods and the demonstration of normal body temperature in persons with black bile using a thermometer disproved the ‘good humor’ hypothesis of health. In later years, biology stated that the mind influences, through the neural system and endocrine system,

our immune system and that our immune system maintains our health. Hence, mind and mental state can affect our health. Of course, health is affected by –

(i) genetic disorders – deficiencies with which a child is born and deficiencies/defects which the child inherits from parents from birth;

(ii) infections and

(iii) lifestyle including food and water we take, rest and exercise we give to our bodies, habits that we have or lack, etc.

The term health is very frequently used by everybody. How do we define it? Health does not simply mean ‘absence of disease’ or ‘physical fitness’. It could be defined as a state of complete physical, mental and social well-being. When people are healthy, they are more efficient at work.

This increases productivity and brings economic prosperity. Health also increases the longevity of people and reduces infant and maternal mortality. A balanced diet, personal hygiene and regular exercise are very important to maintain good health. Yoga has been practiced since time immemorial to achieve physical and mental health.

Awareness about diseases and their effect on different bodily functions, vaccination (immunization) against infectious diseases, proper disposal of wastes, control of vectors and maintenance of hygienic food and water resources are necessary for achieving good health. When the functioning of one or more organs or systems of the body is adversely affected, characterized by various signs and symptoms, we say that we are not healthy, i.e., we have a disease.

Diseases can be broadly grouped into infectious and non-infectious. Diseases that are easily transmitted from one person to another, are called infectious diseases. Infectious diseases are very common and every one of us suffers from these at some time or other. Some of the infectious diseases like AIDS are fatal. Among non-infectious diseases, cancer is the major cause of death. Drug and alcohol abuse also affects our health adversely.

8.1 COMMON DISEASES IN HUMANS

A wide range of organisms belonging to bacteria, viruses, fungi, protozoans, helminths, etc., could cause diseases in man. Such disease-causing organisms are called pathogens. Most parasites are, therefore, pathogens as they cause harm to the host by living in (or on) them.

The pathogens can enter our body by various means, multiply and interfere with normal vital activities, resulting in morphological and functional damage. Pathogens have to adapt to life within the environment of the host.

For example, the pathogens that enter the gut must know a way of surviving in the stomach at low pH and resisting the various digestive enzymes. A few representative members from different groups of pathogenic organisms are discussed here along with the diseases caused by them. Preventive and control measures against these diseases, in general, are also briefly described.

Salmonella typhi is a pathogenic bacterium that causes typhoid fever in human beings. These pathogens generally enter the small intestine through food and water contaminated with them and migrate to other organs through blood. Sustained high fever (39° to 40°C),

weakness, stomach pain, constipation, headache, and loss of appetite are some of the common symptoms of this disease. Intestinal perforation and death may occur in severe cases. Typhoid fever could be confirmed by..

Widal test. A classic case in medicine, that of Mary Mallon nicknamed Typhoid Mary, is worth mentioning here. She was a cook by profession and was a typhoid carrier who continued to spread typhoid for several years through the food she prepared.

Bacteria like Streptococcus pneumoniae and Haemophilus influenzae are responsible for the disease pneumonia in humans which infects the alveoli (air-filled sacs) of the lungs. As a result of the infection, the alveoli get filled with fluid leading to severe problems in

respiration. The symptoms of pneumonia include fever, chills, cough and headache. In severe cases, the lips and fingernails may turn gray to bluish in color.

A healthy person acquires the infection by inhaling the droplets/aerosols released by an infected person or even by sharing glasses and utensils with an infected person. Dysentery, plague, diphtheria, etc., are some of the other bacterial diseases in man. Many viruses also cause diseases in human beings.

Rhinoviruses represent one such group of viruses that cause one of the most infectious human ailments – the common cold. They infect the nose and respiratory passage but not the lungs

. The common cold is characterized by nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness, etc., which usually last for 3-7 days. Droplets resulting from cough or sneezes of an infected person are either inhaled directly or transmitted through

contaminated objects such as pens, books, cups, doorknobs, computer keyboard or mice, etc., and cause infection in a healthy person. Some of the human diseases are caused by protozoans too. You might have heard about malaria,

a disease man has been fighting since many years. Plasmodium, a tiny protozoan is responsible for this disease. Different species of Plasmodium (P. vivax, P. malaria and P. falciparum) are responsible for different types of malaria. Of these, malignant malaria caused by Plasmodium falciparum is the most serious one and can even be fatal.

et us take a glance at the life cycle of Plasmodium (Figure 8.1). Plasmodium enters the human body as sporozoites (infectious form) through the bite of an infected female Anopheles mosquito. The parasites initially multiply within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture. The rupture of RBCs is associated with the release of a toxic substance, hemozoin,

which is responsible for the chill and high fever recurring every three to four days. When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito’s body and undergo further development.

The parasites multiply within them to form sporozoites that are stored in their salivary glands. When these mosquitoes bite a human, the sporozoites are introduced into his/her body, thereby initiating the events mentioned above.

It is interesting to note that the malarial parasite requires two hosts – human and mosquitoes – to complete its life cycle (Figure 8.1); the female Anopheles mosquito is the vector (transmitting agent) too.

Entamoeba histolytica is a protozoan parasite residing in the large intestine of humans, leading to amoebiasis, commonly known as amoebic dysentery. Clinical manifestations of this disease encompass symptoms such as constipation, abdominal pain, and cramps, with stools exhibiting excess mucus and blood clots.

Houseflies function as mechanical carriers, playing a pivotal role in transmitting the parasite from the feces of an infected person to food.

and food products, thereby contaminating them. Drinking water and food contaminated by the fecal matter are the main sources of infection. Ascaris, the common roundworm, and Wuchereria, the filarial worm, are some of the helminths known to be pathogenic to humans.

Ascaris, an intestinal parasite, causes ascariasis. Symptoms of this disease include internal bleeding, muscular pain, fever, anemia, and blockage of the intestinal passage.

The eggs of the parasite are excreted along with the feces of infected persons, contaminating soil, water, plants, etc. A healthy person acquires this infection through contaminated water, vegetables, fruits, etc.

Wuchereria (W. bancrofti and W. malayi), the filarial worms, cause a slowly developing chronic inflammation of the organs in which they live for many years, usually the lymphatic vessels of the lower limbs,

and the disease is called elephantiasis or filariasis (Figure 8.2). The genital organs are also often affected, resulting in gross deformities. The pathogens are transmitted to a healthy person through the bite by the female mosquito vectors.

Many fungi belonging to the genera Microsporum, Trichophyton, and Epidermophyton are responsible for ringworms, which is one of the most common infectious diseases in humans. The appearance of dry, scaly lesions on various parts of the body such as skin, nails, and scalp (Figure 8.3) are the main symptoms of the disease.

These lesions are accompanied by intense itching. Heat and moisture help these fungi to grow, which makes them thrive in skin folds such as those in the groin or between the toes. Ringworms are generally acquired from soil or by using towels, clothes, or even the comb of infected individuals.

Maintenance of personal and public hygiene is very important for the prevention and control of many infectious diseases. Measures for personal hygiene include keeping the body clean; and consuming of clean drinking water, food, vegetables, fruits, etc.

Public hygiene includes proper disposal of waste and excreta; periodic cleaning and disinfection of water reservoirs, pools, cesspools, and tanks; and observing standard practices of hygiene in public catering.

These measures are particularly essential where infectious agents are transmitted through food and water, such as typhoid, amoebiasis, and ascariasis. In cases of airborne diseases such as pneumonia and the common cold, in addition to the above measures, close…

contact with the infected persons or their belongings should be avoided. For diseases such as malaria and filariasis that are transmitted through insect vectors, the most important measure is to control or eliminate the vectors and their breeding places.

This can be achieved by avoiding stagnation of water in and around residential areas, regular cleaning of household coolers, use of mosquito nets, introducing fishes like Gambusia in

ponds that feed on mosquito larvae, spraying of insecticides in ditches, drainage areas, and swamps, etc. In addition, doors and windows should be provided with wire mesh to prevent the entry of mosquitoes.

Such precautions have become all the more important especially in the light of recent widespread incidences of the vector-borne (Aedes mosquitoes) diseases like dengue and chikungunya in many parts of India.

The advancements made in biological science have armed us to effectively deal with many infectious diseases. The use of vaccines and immunization programs has enabled us to completely eradicate a deadly disease like smallpox

A large number of other infectious diseases like polio, diphtheria, pneumonia, and tetanus have been controlled to a large extent by the use of vaccines.

Biotechnology (about which you will read more in Chapter 12) is at the verge of making available newer and safer vaccines. The discovery of antibiotics and various other drugs has also enabled us to effectively treat infectious diseases.

8.2 IMMUNITY

Every day we are exposed to a large number of infectious agents. However, only a few of these exposures result in disease. Why? This is because the body can defend itself from most of these foreign agents. This overall ability of the host to fight the disease-causing organisms, conferred by the immune system, is called immunity.

Immunity is of two types:

(i) Innate immunity and

(ii) Acquired immunity.

8.2.1 Innate Immunity

Innate immunity is a non-specific type of defense that is present at the time of birth. This is accomplished by providing different types of barriers to the entry of foreign agents into our body. Innate immunity consists of four types of barriers. These are —

(i) Physical barriers: The skin on our body is the main barrier that prevents entry of the micro-organisms. Mucus coating of the epithelium lining the respiratory, gastrointestinal, and urogenital tracts also helps in trapping microbes entering our body.

(ii) Physiological barriers: Acid in the stomach, saliva in the mouth, tears from eyes–all prevent microbial growth.

(iii) Cellular barriers: Certain types of leukocytes (WBC) of our body like polymorpho-nuclear leukocytes (PMNL-neutrophils) and.

monocytes and natural killer (a type of lymphocytes) in the blood as well as macrophages in tissues can phagocytose and destroy microbes.

(iv) Cytokine barriers: Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.

8.2.2 Acquired Immunity

Acquired immunity, on the other hand, is pathogen-specific. It is characterized by memory. This means that our body, when it encounters a pathogen for the first time, produces a response called the primary response, which is of low intensity.

Subsequent encounters with the same pathogen elicit a highly intensified secondary or anamnestic response. This is ascribed to the fact that our body appears to have memory of the first encounter.

The primary and secondary immune responses are carried out with the help of two special types of lymphocytes present in our blood, i.e., B-lymphocytes and T-lymphocytes. The B-lymphocytes produce an army of proteins in response to pathogens into our blood to fight with them. These proteins are called antibodies.

The T-cells themselves do not secrete antibodies but help B cells produce them. Each antibody molecule has four peptide chains, two small called light chains and two longer called heavy chains. Hence, an antibody is represented as H2 L2. Different types of antibodies are produced in our body. IgA, IgM, IgE, IgG are some of them.

A cartoon of an antibody is given in Figure 8.4. Because these antibodies are found in the blood, the response is also called as humoral immune response. This is one of the two types of our acquired immune response – antibody-mediated. The second type is called cell-mediated immune response or cell-mediated immunity (CMI).

The T-lymphocytes mediate CMI. Very often, when some human organs like the heart, eye, liver, kidney fail to function satisfactorily, transplantation is the only remedy to enable the patient to live a normal life. Then a search begins – to find a suitable donor. Why is it that the organs cannot be taken from just anybody? What is it that…

8.2.5 Allergies

When you have gone to a new place and suddenly you started sneezing, wheezing for no explained reason, and when you went away, your symptoms disappeared. Did this happen to you? Some of us are sensitive to some particles in the environment. The above-mentioned reaction could be because of allergy to pollen, mites, etc., which are different in different places.

The exaggerated response of the immune system to certain antigens present in the environment is called allergy. The substances to which such an immune response is produced are called allergens. The antibodies produced to these are of IgE type. Common examples of allergens are mites in dust, pollens, animal dander, etc.

Symptoms of allergic reactions include sneezing, watery eyes, running nose and difficulty in breathing. Allergy is due to the release of chemicals like histamine and serotonin from the mast cells. For determining the cause of allergy, the patient is exposed to or injected with very small doses of possible allergens, and the reactions studied.

The use of drugs like anti-histamine, adrenalin and steroids quickly reduces the symptoms of allergy. Somehow, modern-day lifestyle has resulted in lowering of immunity and more sensitivity to allergens – more and more children in metro cities of India suffer from allergies and asthma due to sensitivity to the environment. This could be because of the protected environment provided early in life.

8.2.6 Autoimmunity

Memory-based acquired immunity evolved in higher vertebrates based on the ability to differentiate foreign organisms (e.g., pathogens) from self-cells. While we still do not understand the basis of this, two corollaries of this ability have to be understood.

One, higher vertebrates can distinguish foreign molecules as well as foreign organisms. Most of the experimental immunology deals with this aspect.

Two, sometimes, due to genetic and other unknown reasons, the body attacks self-cells. This results in damage to the body and is called auto-immune disease. Rheumatoid arthritis, which affects many people in our society, is an autoimmune disease.

8.2.7 Immune System in the Body

The human immune system consists of lymphoid organs, tissues, cells, and soluble molecules like antibodies. As you have read, the immune system is unique in the sense that it recognizes foreign antigens, responds to these, and remembers them.

The immune system also plays an important role in allergic reactions, autoimmune diseases, and organ transplantation. Lymphoid organs: These are the organs where the origin and/or maturation and proliferation of lymphocytes occur.

The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate

into antigen-sensitive lymphocytes. After maturation, the lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer’s patches of the small intestine, and appendix.

Human Health and Disease Class 12

The secondary lymphoid organs provide the sites for the interaction of lymphocytes with the antigen, which then proliferate to become effector cells. The location of various lymphoid organs in the human body is shown in Figure 8.5.

The bone marrow is the main lymphoid organ where all blood cells, including lymphocytes, are produced. The thymus is a lobed organ located near the heart and beneath the breastbone.

The thymus is quite large at the time of birth but keeps reducing in size with age, and by the time puberty is attained, it reduces to a very small size. Both bone marrow and thymus provide micro-environments for the development and maturation of T-lymphocytes.

The spleen is a large bean-shaped organ. It mainly contains lymphocytes and phagocytes. It acts as a filter of the blood by trapping blood-borne microorganisms. The spleen also has a large reservoir of erythrocytes.

The bone marrow is the main lymphoid organ where all blood cells, including lymphocytes, are produced. The thymus is a lobed organ located near the heart and beneath the breastbone.

The lymph nodes are small solid structures located at different points along the lymphatic system. Lymph nodes serve to trap the microorganisms or other antigens that happen to get into the lymph and tissue fluid.

Antigens trapped in the lymph nodes are responsible for the activation of lymphocytes present there and cause the immune response.

There is lymphoid tissue also located within the lining of the major tracts (respiratory, digestive, and urogenital tracts) called mucosa-associated lymphoid tissue (MALT). It constitutes about 50 per cent of the lymphoid tissue in the human body.

8.3 AIDS The word AIDS stands for Acquired Immuno Deficiency Syndrome. This means deficiency of the immune system, acquired during the lifetime of an individual, indicating that

it is not a congenital disease. ‘Syndrome’ means a group of symptoms. AIDS was first reported in 1981 and in the last twenty-five years or so, it has spread all over the world killing more than 25 million persons.

AIDS is caused by the Human Immuno deficiency Virus (HIV), a member of a group of viruses called retrovirus, which have an envelope enclosing the RNA genome (Figure 8.6).

Transmission of HIV infection generally occurs by (a) sexual contact with an infected person, (b) by transfusion of contaminated blood and blood products, (c) by sharing infected needles

as in the case of intravenous drug abusers, and (d) from an infected mother to her child through the placenta. So, people who are at high risk of getting this infection include – individuals who have multiple.

sexual partners, drug addicts who take drugs intravenously, individuals who require repeated blood transfusions, and children born to an HIV infected mother.

Do you know–when do people need repeated blood transfusions? Find out and make a list of such conditions. It is important to note that HIV/AIDS is not spread by mere touch or physical contact; it spreads only through body fluids.

It is, hence, imperative, for the physical and psychological well-being, that the HIV/AIDS infected persons are not isolated from family and society. There is always a time-lag between the infection and the appearance of AIDS symptoms. This period may vary from a few months to many years (usually 5-10 years).

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 host cell’s DNA and directs the infected cells to produce virus particles (Figure 8.6). The macrophages continue to produce virus and in this way act like an HIV factory. Simultaneously, HIV enters into helper T-lymphocytes (TH), 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,

diarrhea, and weight loss. Due to a decrease in the number of helper T lymphocytes, the person starts suffering from infections that could have been otherwise overcome, such as those due to bacteria especially Mycobacterium, viruses, fungi, and even parasites like Toxoplasma.

The patient becomes so immunodeficient that he/she is unable to protect himself/herself against these infections. A widely used diagnostic test for AIDS is enzyme-linked immunosorbent assay (ELISA).

Treatment of AIDS with antiretroviral drugs is only partially effective. They can only prolong the life of the patient but cannot prevent death, which is inevitable.

Prevention of AIDS: As AIDS has no cure, prevention is the best option. Moreover, HIV infection, more often, spreads due to conscious behavior patterns and is not something that happens inadvertently, like pneumonia or typhoid.

Of course, infection in blood transfusion patients, newborns (from mother) etc., may take place due to poor monitoring. The only excuse may be ignorance, and it has been rightly said – “don’t die of ignorance”. In our country, the National AIDS Control Organisation (NACO) and

other non-governmental organizations (NGOs) are doing a lot to educate people about AIDS. WHO has started a number of programs to prevent the spreading of HIV infection. Making blood (from blood banks) safe from HIV, ensuring the use of only disposable needles and

syringes in public and private hospitals and clinics, free distribution of condoms, controlling drug abuse, advocating safe sex, and promoting regular check-ups for HIV in susceptible populations are some such steps taken up.

Infection with HIV or having AIDS is something that should not be hidden – since then, the infection may spread to many more people. HIV/AIDS-infected people need help and sympathy instead of being shunned by society.

Unless society recognizes it as a problem to be dealt with in a collective manner – the chances of wider spread of the disease increase manifold. It is a malady that can only be tackled by the society and medical fraternity acting together to prevent the spread of the disease.

Human Health and Disease Class 12 Question and Answer

Question:1 what is an auto immune disease? give an example.

Answer: It is a condition in which body’s immune system atack self sells of rheumatoid arthritis

Question:2 state the function of most cell in allergy response.

Answer: The chemical like histamine and serotonin are seleased from mast cell these chemical cause an exaggerated response to immune system called allergy response.

Question:3 why is colostrum a born to a newborn baby ?

Answer: colostrum (mather’s first milk) is rich in IGA antibodies it provides passive immunity to life new born and protect it from various infections

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

Answer: Drinking contaminated water is one of the main reason of water born diseases such as typhoid, cholera etc. To prevent from these diseases we should dispose of sewage, excreta etc. properly. We should check our water reservoirs regularly and drink water after boiling it.

Question:5 Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.

Answer: Once someone starts using alcohol or drugs, it is very difficult to kick the habit. According to him, alcohol is the only way to achieve normality. There are both physical and physiological reasons for resistance to cessation of activity. Long-term alcohol consumption can make a person so dependent that their nervous system only works normally in the presence of alcohol or drugs, and it seems difficult to lead a normal life without drinking alcohol.

Human Health and Disease Class 12 MCQ Question and Answer

Question:1 What is the primary function of the immune system in the human body?

Digestion
Protection against diseases
Transportation
Hormone secretion

Answer: c) Protection against diseases

Question:2 Which of the following is an example of a communicable disease?

Diabetes
Tuberculosis
Hypertension
Arthritis

Answer: b) Tuberculosis

Question:3 What is the causative agent of malaria?

bacteria
virus
fungus
Protozoa

Answer: d) Protozoa

Question:4 Which immunoglobulin is involved in immediate hypersensitivity reactions?

Answer: c) IgE

Question:5 Which organ is primarily responsible for detoxification and metabolism of drugs in the body?

Kidneys
Lungs
Liver
Stomach

Answer: a) Liver

Question:6 Antibiotics are effective against

Viruses
bacteria
fungi
both b and c

Answer: b) Bacteria

Question:7 Which of the following is a vector for the transmission of dengue fever?

Mosquito
Tick
Plea
Louse

Answer: a) Mosquito

Conclusion

In conclusion, the study of Human Health and Disease at the Class 12 level provides a comprehensive understanding of the intricate balance within the human body and the factors influencing well-being

NCERT Solution for Class 12 Biology Chapter 8