Detailed Notes 1 -Chapter 7 Human Health and Disease

Chapter 7 Human Health and Disease

Introduction

1. Historical Perspectives on Health:

   • Early Greek and Indian medical systems believed in a balance of ‘humors’ for health.
   • For instance, individuals with ‘black bile’ were associated with a hot temperament and susceptibility to fevers.
   • These ideas were based on reflective thought rather than empirical evidence.

2. Revolution in Medical Understanding:

   • William Harvey’s discovery of blood circulation challenged the humor theory.
   • Use of experimental methods and thermometers disproved the traditional beliefs.
   • It highlighted the importance of empirical evidence in understanding health.

3. Influence of Mind on Health:

   • Biology later emphasized the influence of the mind on health.
   • Neural and endocrine systems connect mental states to the immune system.
   • Mental well-being is recognized as a significant factor in maintaining health.

4. Factors Affecting Health:

   • Genetic disorders contribute to health issues from birth.
   • Infections pose a significant threat to health.
   • Lifestyle factors such as diet, exercise, rest, and habits impact overall health.

5. Definition of Health:

   • Health is more than just the absence of disease or physical fitness.
   • It encompasses complete physical, mental, and social well-being.
   • Good health leads to increased productivity, economic prosperity, and longevity.

6. Maintaining Good Health:

   • Balanced diet, personal hygiene, and regular exercise are essential.
   • Practices like yoga promote physical and mental health.
   • Awareness of diseases, vaccination, hygiene, waste disposal, and vector control are crucial for good health.

7. Identification of Disease:

   • Disease is characterized by the adverse effects on the functioning of one or more body organs or systems.
   • Signs and symptoms indicate the presence of disease.
   • Diseases are broadly classified into infectious and non-infectious categories.

8. Types of Diseases:

   • Infectious diseases spread easily from person to person and are common.
   • Some infectious diseases, like AIDS, can be fatal.
   • Non-infectious diseases, such as cancer, are also significant causes of morbidity and mortality.
   • Drug and alcohol abuse also have adverse effects on health.

7.1 COMMON DISEASES IN HUMANS

1. Bacterial Diseases:

   • Typhoid Fever: Caused by Salmonella typhi, transmitted through contaminated food and water. Symptoms include sustained high fever, weakness, stomach pain, constipation, and headache.
   • Pneumonia: Caused by bacteria like Streptococcus pneumoniae and Haemophilus influenzae. Symptoms include fever, chills, cough, headache, and difficulty breathing.

2. Viral Diseases:

   • Common Cold: Caused by rhinoviruses, transmitted through droplets from coughs or sneezes. Symptoms include nasal congestion, sore throat, cough, and fatigue.

3. Protozoan Diseases:

   • Malaria: Caused by Plasmodium species, transmitted by infected Anopheles mosquitoes. Symptoms include recurring fever, chills, and flu-like symptoms.

4. Helminthic Diseases:

   • Amoebiasis (Amoebic Dysentery): Caused by Entamoeba histolytica, transmitted through contaminated food and water. Symptoms include constipation, abdominal pain, and bloody stools.
   • Ascariasis: Caused by Ascaris lumbricoides, transmitted through contaminated food, water, or soil. Symptoms include internal bleeding, muscular pain, fever, and blockage of the intestinal passage.
   • Elephantiasis (Filariasis): Caused by Wuchereria bancrofti and Wuchereria malayi, transmitted by female mosquito vectors. Symptoms include chronic inflammation, particularly in the lymphatic vessels of the lower limbs.

5. Fungal Diseases:

   • Ringworm: Caused by fungi like Microsporum, Trichophyton, and Epidermophyton. Transmitted through contact with infected individuals or contaminated objects. Symptoms include dry, scaly lesions on the skin, nails, and scalp, accompanied by intense itching.

6. Prevention and Control Measures:

   • Personal hygiene: Cleanliness, consumption of clean water and food.
   • Public hygiene: Proper waste disposal, cleaning of water reservoirs, pools, and tanks.
   • Vector control: Elimination of breeding places, use of mosquito nets, insecticides, and introducing predators of mosquito larvae.
   • Vaccination and immunization programs: Control and eradication of diseases like smallpox, polio, diphtheria, pneumonia, and tetanus.
   • Antibiotics and other drugs: Effective treatment of infectious diseases.

7.2 IMMUNITY

1. Definition of Immunity:

   • Immunity refers to the body’s ability to defend itself against disease-causing organisms, known as pathogens.
   • Despite frequent exposure to pathogens, only a few instances lead to actual disease due to the body’s defense mechanisms.

2. Types of Immunity:

   • Innate Immunity: This is the natural, non-specific defense mechanism that the body possesses from birth. It provides immediate protection against a wide range of pathogens without prior exposure or recognition.
   • Acquired Immunity: Also known as adaptive immunity, it develops over time as a response to exposure to specific pathogens or foreign substances. This type of immunity is characterized by specificity and memory, meaning it can recognize and respond to particular pathogens upon subsequent encounters.7.2.1 Innate Immunity.

7.2.1 Innate Immunity

1. Physical Barriers:

   • The skin acts as the primary physical barrier, preventing the entry of microorganisms into the body.
   • Mucus coating the epithelial lining of the respiratory, gastrointestinal, and urogenital tracts also serves to trap and remove microbes.

2. Physiological Barriers:

   • Acid in the stomach, saliva in the mouth, and tears from the eyes create hostile environments for microbial growth, inhibiting their proliferation.

3. Cellular Barriers:

   • Certain types of white blood cells (leukocytes) in the body, such as polymorphonuclear leukocytes (PMNL-neutrophils), monocytes, natural killer cells (a type of lymphocyte), and macrophages, act as cellular barriers.
   • These cells are capable of phagocytosis, engulfing and destroying invading microbes to prevent infection.

4. Cytokine Barriers:

   • Virus-infected cells release proteins called interferons, which are part of the cytokine barrier.
   • Interferons help protect non-infected cells from further viral infection, acting as a form of communication between infected and uninfected cells to coordinate the immune response.

7.2.2 Acquired Immunity

1. Characteristics of Acquired Immunity:

   • Acquired immunity is specific to particular pathogens and is characterized by memory.
   • Upon first encounter with a pathogen, the body initiates a primary immune response of low intensity.
   • Subsequent encounters with the same pathogen trigger a highly intensified secondary or anamnestic response due to the body’s memory of the initial encounter.

2. Lymphocytes in Acquired Immunity:

   • Acquired immunity involves two types of lymphocytes present in the blood: B-lymphocytes and T-lymphocytes.

3. Role of B-Lymphocytes:

   • B-lymphocytes produce proteins called antibodies in response to pathogens.
   • Antibodies, also known as immunoglobulins (Ig), are proteins that circulate in the blood and help to fight off pathogens.
   • Different types of antibodies, such as IgA, IgM, IgE, and IgG, are produced in the body.

4. Humoral Immune Response:

   • The immune response involving the production of antibodies in the blood is known as the humoral immune response.
   • This is one of the two types of acquired immune responses, referred to as antibody-mediated immunity.

5. Cell-Mediated Immune Response:

   • The second type of acquired immune response is called cell-mediated immune response (CMI).
   • Cell-mediated immunity is mediated by T-lymphocytes, which do not produce antibodies themselves but assist B-cells in antibody production.

6. Organ Transplantation and Immune Response:

   • When organs such as the heart, liver, or kidney fail, transplantation may be the only remedy.
   • Tissue and blood group matching are essential before transplantation to minimize the risk of graft rejection.
   • The body’s ability to differentiate between ‘self’ and ‘non-self’ is mediated by the cell-mediated immune response, which can lead to graft rejection if the donor tissue is perceived as foreign.

7.2.3 Active and Passive Immunity

1. Active Immunity:

   • Active immunity occurs when a host is exposed to antigens, such as living or dead microbes or other proteins.
   • Upon exposure to antigens, the host’s body produces antibodies to fight off the foreign agents.
   • Active immunity is slow to develop and takes time to provide its full effective response.
   • Examples of active immunity include:
     • Immunization: Deliberate injection of microbes or antigens to induce immunity.
     • Natural infection: When infectious organisms enter the body and trigger the immune response.

2. Passive Immunity:

   • Passive immunity involves the direct administration of ready-made antibodies to protect the body against foreign agents.
   • Ready-made antibodies can be obtained from another individual or an animal that has already developed immunity.
   • Passive immunity provides immediate but temporary protection.
   • Examples of passive immunity include:
     • Mother’s milk: Colostrum, the yellowish fluid secreted by the mother during the initial days of lactation, contains abundant antibodies (IgA) to protect the newborn infant.
     • Transfer of antibodies from mother to fetus: During pregnancy, the fetus receives antibodies from the mother through the placenta, providing passive immunity to the newborn.

7.2.4 Vaccination and Immunisation

1. Principle of Vaccination:

   • Vaccination is based on the immune system’s ability to develop memory against pathogens.
   • A vaccine contains antigenic proteins of the pathogen or weakened/inactivated pathogens, which are introduced into the body.
   • The antibodies produced in response to the vaccine neutralize the pathogenic agents during actual infection.
   • Vaccines also stimulate the production of memory B and T cells, which recognize the pathogen quickly upon subsequent exposure and generate a rapid and robust immune response.

2. Passive Immunization:

   • In some cases, such as tetanus or snakebites, where a quick immune response is needed, preformed antibodies (antitoxins) are directly injected into the body.
   • These preformed antibodies neutralize the toxin or venom produced by the pathogen, providing immediate protection.
   • This type of immunization is known as passive immunization.

3. Advancements in Vaccine Production:

   • Recombinant DNA technology has revolutionized vaccine production by allowing the production of antigenic polypeptides of pathogens in bacteria or yeast.
   • Vaccines produced using this approach, such as the hepatitis B vaccine produced from yeast, enable large-scale production and greater availability for immunization.

7.2.5 Allergies

1. Definition and Causes of Allergies:

   • Allergy is the exaggerated response of the immune system to certain antigens (allergens) present in the environment.
   • Allergens can include substances like pollen, mites, animal dander, etc.
   • The immune system produces IgE antibodies in response to these allergens.

2. Symptoms of Allergic Reactions:

   • Common symptoms of allergic reactions include sneezing, watery eyes, a runny nose, and difficulty in breathing.

3. Mechanism of Allergic Reactions:

   • Allergic reactions occur due to the release of chemicals like histamine and serotonin from mast cells in response to allergen exposure.

4. Diagnosis and Treatment:

   • Diagnosis of allergies involves exposing or injecting the patient with small doses of possible allergens to study their reactions.
   • Drugs like anti-histamines, adrenaline, and steroids are commonly used to quickly reduce allergy symptoms.

5. Impact of Modern Lifestyle:

   • Modern-day lifestyle factors may contribute to increased sensitivity to allergens and lowered immunity.
   • Children in metro cities of India are experiencing a rise in allergies and asthma, potentially due to increased sensitivity to the environment.
   • This may be attributed to the protected environment provided early in life, which could lead to reduced exposure to potential allergens and subsequent hypersensitivity.

7.2.6 Auto Immunity

1. Basis of Autoimmunity:

   • Autoimmunity arises from a breakdown in the immune system’s ability to distinguish between self and non-self.
   • While the exact mechanisms behind this phenomenon are not fully understood, genetic factors and environmental triggers are believed to play significant roles.

2. Corollaries of Immune System Ability:

   • The immune system in higher vertebrates has evolved the ability to differentiate not only foreign organisms but also foreign molecules.
   • Most research in experimental immunology focuses on understanding how the immune system responds to foreign invaders.

3. Autoimmune Diseases:

   • Autoimmune diseases occur when the immune system mistakenly targets and attacks the body’s own cells and tissues.
   • Rheumatoid arthritis is one example of an autoimmune disease. Other examples include lupus, multiple sclerosis, type 1 diabetes, and Hashimoto’s thyroiditis.

4. Impact and Treatment:

   • Autoimmune diseases can result in chronic inflammation, tissue damage, and organ dysfunction.
   • Treatment often involves medications to suppress the immune response, manage symptoms, and reduce inflammation.
   • While there is currently no cure for autoimmune diseases, ongoing research aims to better understand their underlying mechanisms and develop more effective treatments.

7.2.7 Immune System in the Body

1. Components of the Immune System:

   • The human immune system comprises lymphoid organs, tissues, cells, and soluble molecules like antibodies.
   • It recognizes foreign antigens, mounts responses against them, and has the ability to remember them for future encounters.

2. Lymphoid Organs:

   • Lymphoid organs are where the origin, maturation, and proliferation of lymphocytes occur.
   • Primary lymphoid organs include the bone marrow and thymus, where immature lymphocytes differentiate into antigen-sensitive lymphocytes.
   • Secondary lymphoid organs, such as the spleen, lymph nodes, tonsils, Peyer’s patches in the small intestine, and the appendix, provide sites for interactions between lymphocytes and antigens, leading to the proliferation of effector cells.

3. Functions of Specific Lymphoid Organs:

   • Bone Marrow: Produces all blood cells, including lymphocytes. It serves as the main lymphoid organ.
   • Thymus: Located near the heart and beneath the breastbone, the thymus provides a microenvironment for the development and maturation of T-lymphocytes.
   • Spleen: Acts as a filter of the blood by trapping blood-borne microorganisms and contains a large reservoir of erythrocytes. It also houses lymphocytes and phagocytes.
   • Lymph Nodes: Small solid structures along the lymphatic system that trap microorganisms or other antigens present in the lymph and tissue fluid, activating lymphocytes and initiating immune responses.

4. Mucosa-Associated Lymphoid Tissue (MALT):

   • Lymphoid tissue located within the lining of major tracts like the respiratory, digestive, and urogenital tracts.
   • Constitutes approximately 50% of the lymphoid tissue in the human body.
   • MALT plays a crucial role in immune defense at mucosal surfaces, where pathogens often enter the body.