CHAPTER 8 :

HUMAN HEALTH AND

DISEASES

• Health:• Health is 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 long life and reduces infant and maternal mortality.

• The good health is maintained by balanced diet, personal hygiene and regular exercise.

• The health is affected by –1. Genetic disorders .2. Infections.3. Life style including Diet, rest and exercise. Drug

and alcohol abuse also affect our health adversely.• Diseases are grouped into infectious and non-

infectious.• Diseases which are easily transmitted from one

person to another are called infectious diseases.• Diseases which are not transmitted from one

person to another are called non infectious diseases..

• Cancer is the non-infectious that cause death.

• COMMON DISEASES IN HUMANS:• organisms belonging to bacteria, viruses, fungi,

protozoans, helminths, etc., could cause diseases in man. Such disease causing organisms are called pathogens.

• TYPHOID: • Pathogen: Salmonella typhi (bacterium)• Organs affected: small intestine, migrate to other organs

through blood.• Method of transmission: contamination of food and

water.

• Symptoms:• High fever (390 to 400 C)• Weakness, stomach pain, constipation, headache

and loss of appetite.• Intestinal perforation may leads to death.• Test: Typhoid fever could be confirmed by Widal

test.

• PNEUMONIA:• Pathogen: Streptococcus pneumoniae and

Haemophilus influenzae.• Organs affected: Alveoli of lungs, alveoli get filled

with fluid.

• Method of transmission: Inhaling the droplets/aerosols released by infected person.

• Symptoms:• Fever, chills, cough and headache.• In severe cases the lips and finger nails turn gray to

bluish colour.

• COMMON COLD:• Pathogen: Rhino viruses.• Organs affected: nose and respiratory passage• Method of transmission: • Direct inhalation of droplets from infected person.• Through contaminated objects like pen, books, cups,

computer key board.

• Symptoms:• Nasal congestion and discharge, sore throat,

hoarseness, cough. tiredness, etc.,• It usually last for 3-7 days.

• MALARIA: • Pathogen: Plasmodium. (P. vivax, P. malariae, P.

ovale, P. falciparum)• Malignant malaria caused by P. falciparum is fatal.• Organs affected: liver, RBC.• Method of transmission: By biting of female

anopheles mosquito (vector)

• Symptoms: high fever and chill, fever occurs on every alternate day, vomiting.

• life cycle of malaria parasite:• The malarial parasite requires

two hosts – human and Anopheles, to complete their life cycle.

• Life cycle of plasmodium starts with injecting sporozoites through the bite of infected female Anopheles mosquitoes.

• The parasite initially multiplied within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture.

• There is release of a toxic substance called hemozoin from the ruptured RBCs. It is responsible for the chill and high fever.

• From the infected human the parasite enters into the body of Anopheles mosquito during biting and sucking blood.

• Further development takes place in the body of Anopheles mosquitoes.

• The female mosquito takes up gametocytes with the blood meal.

• Formation of gametes and fertilization takes place in the intestine of mosquito.

• The zygote develops further and forms thousands of sporozoites.

• These sporozoites migrated into the salivary gland of mosquito.

• When the mosquito bite another human sporozoites are injected.

• AMOEBIASIS (Amoebic dysentery)• Pathogen: Entamoeba histolytica a

protozoan parasite.• Organs affected: large intestine of

man• Method of transmission: • House fly acts as mechanical carrier.• Contamination water and food with

faecal matter.• Symptoms:• Loose motion and abdominal pain.• Stools with excess mucous and

blood clots.

• ASCARIASIS: • Pathogen: Ascaris lumbricoids

(nematode)• Organs affected: intestine of

man• Method of transmission:

Contaminated water, vegetables, fruits.

• Symptoms: • Internal bleeding, muscular

pain, fever, anemia.• Blockage of the intestinal

passage.

• FILARIASIS OR ELEPHANTIASIS:• Pathogen: Wuchereria

(W.bancrofti and W. Malayi) (nematode parasite)

• Organs affected: lymphatic vessels of the lower limbs, genital organs.

• Methods of transmission: biting of infected female culex mosquito.

• Symptoms:• Chronic inflammation of the

organs. • Abnormal swelling of lower limb,

scrotum, penis.• Hence the disease named as

elephantiasis or Filariasis.

• RING WORMS:• Pathogen: Microsporum,

Trichophyton and Epidermophyton (fungi)

• Organs affected: Skin, nails, folds of skin, groin.

• Method of transmission: • Acquired from the soil. • Using towel, clothes or even comb

of infected individuals.• Symptoms: • Appearance of dry, scaly lesions in

skin nails and scalp.• Lesion accompanied with intense

itching.

• PREVENTION AND CONTROL OF INFECTIOUS DISEASES:• Maintenance of personal and public hygiene. • Personal hygiene includes Consumption of clean drinking

water, food vegetable fruits. Keeping the body clean.• Public hygiene includes Proper disposal of waste and excreta• Periodic cleaning water reservoirs, pools.• Avoiding close contact with the infected persons.• For vector borne diseases controlling vectors and the

breeding places.• Avoiding stagnation of water in and around residential

areas.• Use of mosquito nets.• Window and doors must be fitted with wire mesh.• All these precautions are use full for vector borne disease

like dengue and Chickungunya, malaria and filarial etc.

Immunity: Immunity is the ability of an organism to resist infection or to overcome infection.• There are two types of immunity: 1. Innate (non-specific) Immunity.2. Acquired (specific) Immunity.• Innate or Non-specific Immunity: It is the inborn or natural

immunity. It is of two types, 1. Surface barrier.2. Cellular and Biochemical barrier.

• Surface barrier: It is the first line body defense. It includes the external barriers that checks the entry of pathogens into body.

• It is identified as physical barrier and Physiological (chemical) barrier.

Physical barrier:

The important physical barrier are skin, hair and cilia of nasal cavity, mucous lining and muscular action. Skin:• The skin prevents entry

of pathogens.• The sweat produced by

sweat gland and oil produced by sebaceous gland are bactericidal and fungicidal properties.

• Mucus lining: The mucus lining found in respiratory tract, digestive tract, urinary tract and reproductive tract secretes mucus. The mucus traps the microbes and makes them immobilize.

Physiological barriers:Chemical secretion like lysozymes, skin secretion, saliva and ear wax forms physiological barriers.Lysozyme: • It is an antibacterial enzyme present in tears, nasal secretion,

saliva, and most of the body fluids. It lyses the bacterial cell.Skin secretion : • The sweat and sebum has antibacterial and antifungal

properties. It avoids the growth of bacteria and fungus on skin.

Saliva:• The saliva contains lysozyme that lyses the

bacteria. • Gut secretion:• The gastric juice contains dil HCl. It kills the

microbes enters through food.• Ear wax :• The ear wax secreted in external auditory canal is

bactericidal in nature. It repels the insects. It traps the dust.

Cellular and biochemical barrier:It is the second line body defense. It includes 1. Phagocytes2. Natural killer cells (NK cells)3. Interferons.4. Inflammatory response. • Phagocytes: The process of engulfing and destroying

the microbe by some cells is called phagocytosis. • The cells that involves in phagocytosis are called

phagocytes.• The neutrophils and monocytes (macrophages)

types of WBC are the important phagocytic cells.

Process of phagocytosis

• Natural killer cells (NK Cells):

• Natural killer cells are non-phagocytic large lymphocytes.

• It mainly recognizes the viral infected cells and tumor cells.

• It destroys them by secreting cytolysin. Hence these are called killer cells.

• Interferon: • Interferon are the antiviral glycoprotein

produced by viral infected animal cell. It protects the neighboring cells from viral infection.

• It mainly stimulates neighboring cells to synthesis a protein that interfere with viral replication. It also activates macrophages and NK cells to recognize infected cells.

Interferon:

• Inflammatory response: It is the localized response to injury, infection or irritation. The symptoms are getting redness, swelling, pain, increasing body temp etc.

• Acquired (specific) immunity:• It is the defense mechanism acquired by healthy

person against specific pathogens and infection. It forms the third line body defense.

• Lymphocytes are the important components activating specific body defense.

• The two types of lymphocytes are T- lymphocyte and B – lymphocyte.

• T – lymphocytes• The undifferentiated

lymphocytes originate from the stem cells of bone marrow,

• Some of them migrate to thymus gland and differentiated into T-lymphocyte. .

• B– lymphocytes: • The undifferentiated

lymphocytes originate from the stem cells of bone marrow.

• some migrate to Bursa equivalent and differentiated into B-lymphocyte.

• Bursa equivalent is a hypothesized lymphoid tissue in bone marrow.

• (Bursa equivalent is found in mammals, Bursa fabricius is found in birds.)

• Antigen: Any foreign substance that enters our body and stimulates immune response is called antigen.

Antigen has two properties:• Antigenicity: It is the ability of an antigen to generate

specific immune response to produce antibody.• Immunogenicity.• It is the ability of an antigen to react with specific

antibody.• Biochemically antigens are proteins, large

polysaccharides, lipids, fatty acids or nucleic acids. Sometimes entire pathogen acts as antigen.

Antibody or immunoglobin (Ig)• The protein molecule that produced by B-

lymphocytes against a specific antigen is called antibody.

• These are mainly classified in to 5 types. They are, IgM, IgA, IgD,IgE, IgG. ( MADE-G)

• IgM is a pentamer and is a mega globulin. It is the first reaches the injured site.

• IgA is the secretory antibody. • IgD it binds to B - Lymphocytes and acts as a surface

receptor.• IgE play imp role in allergy.• IgG crosses placenta and protects foetus.

Structure of Antibody.• Antibody is mainly known

as immunoglobulin. It is a Y shaped made up of four polypeptide chains.

• Among four chains two are longer chains called heavy chains.

• Two are smaller called light chain.

• The four polypeptide chains are held together by di-sulphide bond.

• Each chain contains constant and variable region.

• In constant region the amino acid sequence are constant and same in all antibodies.

• In variable region the amino acid sequence varies with different antibodies.

• The variable region is present at the tip of Y arm forms antigen binding site.

Role of B – lymphocytes:• The lymphocytes produced at bone marrow

differentiates in bursa equivalent in to B – lymphocyte.• When the antigen enters in to the body number of B –

lymphocytes stimulated to produce antibody.• Once the antigen specific antibody producing B –

lymphocyte activated, it multiplies rapidly to produce number of cloned cells.

• The cloned B – lymphocytes differentiates in to plasma cells. These cells produces specific antibody against antigen in large quantity.

• The cloned B – lymphocyte that undifferentiated remains as memory B cells. When the same antigen enters again in future, memory cells response rapidly to destroy them.

Cell mediated immunity ( CMI ): It is the immunity mediated by T – lymphocytes.Role of T – lymphocytes:• The lymphocytes produced at bone marrow

differentiates in thymus in to T – lymphocyte. It does not produce any antibody. It directly acts on antigen.

• When the antigen enters in to the body, the antigen specific T – lymphocyte stimulated and becomes active.

• The activated T – lymphocyte multiplies rapidly to produce number of cloned cells.

According to function of T – lymphocyte, these are identified in to ,• Killer T-cells: These T - cells recognizes specific

pathogen and destroys by lyses.• Helper T – cells: These T – cells helps in stimulating

antigen specific B – cells to produce antibody.• Suppressor T – cells: These T – cells suppress the

immune response of both B and T cells, when infection is controlled.

• Memory T – cells: These T – cells are programmed to recognize and response to the specific antigen that enters in future.