Key Points - Common Diseases in Humans

What is Health?
- Health is the state of complete physical, mental, and social well being.
- Health increases productivity and ensures longevity.

Ways to Ensure Good Health
- Balanced diet
- Personal hygiene
- Exercise
- Awareness about prevention and control of diseases
- Proper waste disposal and control of vectors
- Vaccination

Why do Diseases Occur?
- Genetic reasons − Innate deficiencies and inheritable defects
- Infections
- Sedentary life style − Junk food, consumption of alcohols/drugs, lack of exercise

Pathogenic Diseases
- Pathogens are the parasites that enter the human body through various means, then multiply, and interfere with normal vital activities.

Bacterial Diseases
- Typhoid
= Pathogen − ?

Salmonella typhi
= Spreads through − Contaminated food and water
= Site of infection − Small intestine
= Symptoms − High fever, stomach pain, headache, loss of appetite, constipation, and intestinal perforations in severe cases
= - Confirmatory test − Widal test

Pneumonia
= Pathogens − ?
Streptococcus pneumoniae? and ?Haemophilus influenzae
= Spreads through − Droplets/aerosols released from infected person, sharing of glasses or utensils
= Site of infection − Alveoli (gets filled with fluid, difficulty in breathing)
= Symptoms − Fever, chills, cough, headache, lips and nails become grey in severe cases

Viral Diseases
- Common cold
= Pathogen − Rhino viruses
= Site of infection − Nose and respiratory passage
= Spreads through − Droplets released from coughing or sneezing, or contaminated objects
= Symptoms − Nasal congestion and discharge, sore throat, cough, headache, tiredness

Protozoan Diseases
- Malaria

= - Pathogen − ?
Plasmodium ? sps. (P.vivax, P. falciparum, P. malari)
Vector − Female ?
Anopheles? mosquito
Symptoms − High grade fever, chills
Amoebiasis
= Pathogen − ?
Entamoeba histolytica
= Vector − Housefly
= Site of infection − Large intestine
= Symptoms − Constipation, abdominal pain, cramps, stools with mucous, and blood clots

Fungal Diseases
- Ringworms
= Pathogens − Genera 
?
Microsporum?

Trichophyton?  and Epidermophyton
= Spreads through − Towels, clothes, comb (Fungus is acquired from soil)
= Symptoms − Appearance of dry, scaly lesions on various body parts with intense itching

Diseases Caused by Worms
- Ascariasis

Pathogen − Round worm, ? Ascaris
Spreads through − Water, vegetables, fruits contaminated by faeces of infected person
= Symptoms − Internal bleeding, muscular pain, fever, anaemia, blockage of intestinal passage
- Elephantiasis? (filariasis)
?
= Pathogen − ?
Wuchereria? (?
W.malayi? and ?
W.bancrofti?
)
= Spreads through − Bite of female mosquito vector
= Symptom − Chronic inflammation of the organs, usually the lymphatic vessels of lower limb

Life Cycle of  Plasmodium
Plasmodium? requires two hosts to complete its life cycle.
When female Anopheles? mosquito bites a healthy human being, it releases Plasmodium?
, which lives in its body as sporozoite (infectious form).
- The parasites multiply (asexual reproduction) in the liver cells and finally burst the liver cells. Sporozoites are released in blood.
- Parasites enter RBCs and further multiply (asexual reproduction) here and finally burst RBCs also.
- Bursting of RBCs is accompanied by release of a toxic substance called haemozoin (associated with fever and chills).
- In the RBCs, only sporozoites change into gametocytes (sexual stage).

Gametocytes multiply.
- When the diseased person is bitten by a female ?
Anopheles? mosquito, gametocytes are introduced into the mosquito.
- Gametocytes fertilise and develop inside the intestine of mosquito to form sporozoites.
- Sporozoites are stored in the salivary glands of mosquito and are released into the healthy person who is bitten by this mosquito.

Immunity
What is immunity?
- The ability of body to fight the disease­causing organisms is called immunity.

Types of immunity
- Immunity is of two types − innate immunity and acquired immunity.

- Innate immunity?
− It is present from the time of birth. It is non­specific. It consists of 4 kinds of barriers.
= Physical barriers − Skin and mucus coating of respiratory, gastrointestinal, and urogenital tract prevent entry of microbes into body.
= Physiological barriers − Acid in stomach, saliva in mouth, tears from eyes
= Cellular barriers − Blood has leukocytes such as polymorpho nuclear leukocytes, monocytes, etc. and tissue has macrophages which phagocytose the microbes.
= Cytokine barriers − Special proteins called interferons are secreted by virus­infected cells that prevent the further spread of viral infection.

- Acquired immunity ?
− It is acquired, which means that it is produced in response to an encounter with a pathogen based on memory. It is pathogen specific.
= When a pathogen for the first time infects a person, low intensity immune response is generated (primary response).
= When the same pathogen attacks again, intensified immune response in generated, thereby preventing the occurrence of disease (secondary response).
= Acquired immunity involves two types of cells − B­lymphocytes and T­ lymphocytes.
= B­lymphocytes − Secrete proteins called antibodies in response to pathogens ?
Antibodies? are specialized proteins with 4 peptide chains (2 light and 2 heavy), hence denoted as HL. IgA IgM,

2.IgE, etc. are examples of some of the antibodies. They generate humoral immune response? (found in blood).
= T­lymphocytes − They help B­cells to produce antibodies. They generate ? cell ­mediated immune response?
. This response helps the body to differentiate between ‘self’ and ‘non­self’ as occurs in case of graft rejection.

Difference between active immunity and passive immunity
- Active Immunity
= This is the naturally acquired immunity produced in the host body in response to an antigen.
= Immunization and body naturally getting immune to a microbe that had caused infection previously are examples of active immunity.
- Passive immunity
= When ready­made antibodies are provided to an individual to protect against foreign agents
= Colostrums present in mother’s milk contain IgA. Also, the foetus gets antibodies from mother through placenta.

How does vaccination help?
- Vaccines are nothing but inactivated pathogens.
- These inactivated pathogens when introduced in the body produce a primary immune response and antibodies are produced against the pathogen.
- Memory B and T­cells are produced.
- Now when the pathogen again attacks the person, memory B and
T­cells generate a massive immune response and the pathogen is killed.

Problems of immune system

- Allergies
= Exaggerated immune response to certain antigens present in environment
= Allergens − Substances in response to which allergy is produced
E.g., dust, pollen, etc.
= Antibodies involved − IgE type
= During allergic reactions, chemicals such as histamines and serotonins are released.
= Symptoms − Sneezing, watery eyes, difficulty in breathing, etc.
= Allergy test − Patient is injected with small doses of allergens to monitor his response.
= Antihistamines, adrenalins, and steroids may be given so that the symptoms of allergy subside.

- Autoimmunity
= In autoimmunity, body generates immune response against its own cells.
= Reasons − Genetic and other unknown reasons
= Example − Rheumatoid arthritis is an autoimmune disease.

Human immune system
- Lymphoid organs are of two types − primary lymphoid organs and secondary lymphoid organs.
- Primary lymphoid organs consist of bone marrow and thymus. Here, immature lymphocytes are differentiated to form antigen­sensitive lymphocytes.
= Bone marrow − Here, all blood cells including lymphocytes are produced.
= Thymus − It is responsible for maturation of T­lymphocytes. This lobed organ is situated near the heart and keeps on reducing in size as the age increases.
- Secondary lymphoid organs − Lymphocytes migrate here after attaining maturity. It includes spleen, lymph nodes tonsils, Peyer’s patches, and appendix.
= Spleen − Large bean­shaped organ containing lymphocytes and phagocytes, which acts as a filter for blood
= Lymph nodes − Located at different points throughout the immune system, they trap the antigens present in lymph or tissue fluid, and these antigens cause activation of lymphocytes and generation of immune response.
- MALT (Mucosal­associated lymphoid tissue) − Lines major tracts (respiratory, digestive, urogenital, etc)? constitutes 50% of lymphoid tissue in body

AIDS & Cancer

AIDS (Acquired Immuno Deficiency Syndrome)
- Caused by HIV (Human Immunodeficiency Virus) [HIV is a retrovirus (RNA virus)]
- Transmission of HIV occurs through:
= Sexual contact with infected person
= Sharing infected needles (as in case of intravenous drug abusers)

Transfusion of contaminated blood
= Infected mother to child through placenta
Time lag between infection and appearance of symptoms − Few months to many years (5­10 years)
- How does AIDS infection spread?
= Virus enters the body of a person and enters macrophages.
= Here, virus replicates (viral RNA reverse transcribes to viral DNA, which gets incorporated into hosts DNA and subsequently new viral particles are produced).
= Macrophages become a virtual HIV factory.
= Thereafter, HIV enters helper T­lymphocytes, replicates, and produces progenies.
= As the progenies are released, they attack other T­lymphocytes.
= Therefore, T­lymphocytes start decreasing in number and immune response of the person becomes weak.
= Even infections which could be overcome easily start aggravating.
- Diagnosis of AIDS − By ELISA (Enzyme Linked Immuno Sorbent Assay)
- Treatment −?
No permanent cure? antiretroviral therapies can prolong the life of patient
- Prevention of AIDS
= Ensuring use of disposable syringes
= Screeningblood from blood banks
= Advocating safe sex
= NACO (National AIDS Control Organization) and many NGOs are doing a lot to create awareness among people.

Cancer
- The process of development of cancer is called ? oncogenic transformation.
- Normal cells have the property of contact inhibition (stoppage of growth on coming in contact with other cells), but cancer cells lose this property.
- As a result, cancer cells divide continuously to give rise to mass of cells (tumours).
- Tumours are of 2 types − benign and malignant.
- Benign tumours − Remain confined to their original location and do not spread
- Malignant tumours− These exhibit ? metastasis? i.e., the cells sloughed from such tumours reach distant sites and wherever they reach, new tumour is formed.
- Malignant tumours actually represent cancer. The cells actively divide, grow, and starve the normal cells of vital nutrients.

- Causes of cancer
= Carcinogens − ?
Physical, chemical, and biological agents that cause cancer Example ­ ionizing radiations (X­rays and gamma rays), non­ionizing radiations (UV)
= Oncogenic (cancer­causing) viruses?
− They have viral oncogenes (cancer­causing genes).
= Sometimes normal genes in our body called proto­oncogenes get converted into cellular oncogenes that cause cancer.

- Diagnosing cancer
= Biopsy and histopathological studies
= Biopsy?
− Suspected tissue is cut into thin sections and examined microscopically
= Radiography?
, CT scan (computed tomography), and MRI (Magnetic resonance imaging) are techniques of diagnosing cancers.
= C T Scan?
− 3­D imaging of internals of an organ is generated by X­rays.
= MRI Scan?

− Pathological and physiological changes in a living tissue are detected by using magnetic fields and non­ionising radiations.
= Immunological and molecular biological diagnostic techniques can all be used to detect cancers.
= Identifying certain genes, which make an individual susceptible to cancers, can help to prevent cancers.
- Treatment of cancer
= Radiotherapy ?
− Tumour cells are irradiated to death. Also, proper care is taken for protecting surrounding normal tissues.
= Chemotherapy ?
− Drugs specific for particular tumours are used to kill cancer cells. They have side effects such as hair loss, anaemia, etc.
= Immunotherapy?
− Biological response modifiers such as α­ interferons are used. They activate the immune system of patient and helps in destroying the tumour.

Commonly Abused Drugs
Opioids (Heroin)
- Source: Acetylation of morphine extracted from the latex of poppy plants (Papaver somniferum)
- Consumed by: Snorting or injection
- Properties: White, bitter and odourless
- Mode of action: Binds to opioid receptors present in the CNS and GI tract
- Effect: It is a depressant? slows down body functions

Cannabinoids
- Source: Inflorescences of the plant ?

Cannabis sativa
- Consumed by: Inhalation or oral ingestion
- Mode of action: Binds to cannabinoid receptors present in the brain
- Effect: Affects the cardiovascular system

Cocaine
- Source: Coca plant ?

Erythroxylum coca?
, found in South America
- Consumed by: Snorting
- Mode of action: Interference with transfer of neurotransmitter, dopamine
- Effect: Stimulates the CNS, producing a sense of euphoria and increased energy? excessive dosages cause hallucination

Drugs Normally Used as Medicines
- Drugs like barbiturates, amphetamines, benzodiazepines, LSD (Lysergic acid diethyl amides) are used as medicines to help patients with mental illness and insomnia.
- Morphine: It is a pain killer which is used for patients who have undergone surgery, but it is also abused.

Nicotine
- Present in tobacco, which is smoked, chewed or snuffed
- Mode of action: Stimulates the adrenal gland to release adrenaline and nor­adrenaline
- Effect: Increases blood pressure and heart rate

Ill Effects of Smoking
- Increased risk of diseases like bronchitis, emphysema, coronary heart disease, gastric ulcer and cancer (throat, lung and urinary bladder)
- Increased carbon monoxide levels in blood, leading to oxygen deficiency

Alcohol / Drug Abuse
Causes of alcohol/ Drug Abuse
- Alcohol / drug abuse normally starts in adolescence (period between 1.­18 yrs − transition phase between childhood and adulthood).
- Many adolescents are motivated towards drugs/ alcohol due to curiosity and experimentation.
- Peer pressure, academic stress, unstable family structure further incline youth towards alcohol/ drug abuse.
- Perception of consuming alcohol / drug being cool and progressive and use of alcohol/drug in television, movies, etc. further promote this habit.

Alcohol/ Drug Addiction
- When a person uses alcohol/ drug repeatedly, he becomes addicted.
- Addiction refers to psychological attachment to certain effects such as euphoria and temporary feeling of well­being associated with use of alcohol or drugs.
- In addiction, tolerance level of receptors present in our body increases towards the drug.
- This drives the person to use them even when they are not required or when they tend to harm his health / family life.
- Subsequently, the user runs into a vicious circle of addiction and subsequent dependence.
- Dependence leads to manifestation of withdrawal syndrome on discontinuation of use.
- Withdrawal syndrome − Anxiety, nausea, sweating, shakiness, and sometimes may be lethal

Effects of Alcohol/ Drug Abuse
- Immediate effect − Vandalism, violence, and reckless behaviour
- Drop in academic performance, lack of interest in personal hygiene, rebellious behaviour, and change in eating and sleeping patterns, weight and appetite fluctuations
- Mental, psychological, and financial loss not only to the user, but also to his family
- Those who take drugs intravenously have a high risk of acquiring deadly diseases such as AIDS and hepatitis B.
- Damage to nervous system and liver (cirrhosis)
- Use of anabolic steroids by sportsperson have adverse effects:
= In females − Increase of masculinity, aggressiveness, depression, abnormal menstrual cycle, facial hair growth, enlargement of clitoris, and deepening of voice
= In males − Acne, aggressiveness, depression, reduction in size of testicles, decreased sperm production, enlargement of prostate gland, breast enlargement, premature baldness
- Ultimately, prolonged use of alcohol/drugs leads to coma and death.

Preventing Alcohol/ Drug Abuse
- It is better to prevent the inclination of an individual towards alcohol/ drugs right from adolescence. Some of the ways of prevention are:
= Avoid peer pressure − Understand the unique personality and capabilities of a child
= Education and counselling − A child must be taught to accept success and failure equally. Especially during adolescence, he must be inclined towards constructive activities such as music, yoga, sports, reading based on his interest.
= Help from parents and peers − This includes proper guidance, advice, and trust to overcome problems such as stress and guilt.
= Identifying danger signals − If any sign of symptom of alcohol / drug abuse is seen in the adolescent by family or friends, then it should not be ignored because prevention is better than cure.
- Seeking medical help − Psychologists and rehabilitation programs surely help an addict. Medical help should be sought to prevent further damage.