Important Notes For NEET Biology - Human Health and Disease

Find below the important notes for the chapter, Human Health and Disease as per NEET Biology syllabus. This is helpful for aspirants of NEET and other exams during last-minute revision. Important notes for NEET Biology- Human Health and Disease covers all the important topics and concepts useful for the exam. Check BYJU’S for the full set of important notes and study material for NEET Biology and solve the NEET Biology MCQs to check your understanding of the subject.

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Biology Human Health and Disease NEET exams

Human Health and Disease – Important Points, Summary, Revision, Highlights

Types of DiseasesCommon DiseasesLifecycle of PlasmodiumImmunityAIDSCancerDrugs and Alcohol Abuse

Health and Disease 

Health, as defined by the World Health Organisation, is a state of mental, social as well as physical being. Disease being the opposite, is a hindrance in the well being of our body that affects the functioning of organs and organ systems. Thus, the relationship between health and disease can be thought of as the state of entire well being and not just the absence of disease. Human health and diseases is an important topic that needs to be studied for a better understanding of our body.

Types of Diseases

The human body suffers from many diseases, it can be due to genetic defects, infections or an unhealthy lifestyle.

Diseases can be classified into two types:

  1. Congenital Diseases: Genetic defects present by birth. This may be due to gene mutation, chromosomal aberration or environmental effects. Chromosomal and gene defects are transmitted to the next generation. E.g. Haemophilia, colour blindness, Down syndrome, Turner’s syndrome, etc.
  2. Acquired Diseases: Diseases acquired during a lifetime.
    1. Infectious or communicable disease: transmitted from one person to another
    2. Non-communicable disease: doesn’t spread by infection
    3. Deficiency disease: caused due to deficiency of an important nutrient, enzyme or hormones, e.g. anaemia, kwashiorkor, beriberi, diabetes, etc.
    4. Allergies: hypersensitivity to foreign substances, e.g. pollen, dust, mites, etc.

Common Diseases in Humans

  • The disease-causing organism is known as a pathogen, e.g. bacteria, virus, protozoan, fungi, worms
  • There are many ways by which a pathogen can enter our body. Here is a table of most common diseases found in humans.

Name of the disease

Causing agent/ pathogen Vector/ mode of infection Symptoms


Typhoid Salmonella typhi (Bacteria) -by contaminated food and water -continued high fever, headache, stomachache, constipation and loss of appetite -can be diagnosed by Widal test

-intestinal perforation in severe cases

Pneumonia Streptococcus pneumoniae, Hemophilus influenzae (Bacteria) -by inhaling droplets or aerosols released by an infected person or using infected utensils -fever, chills, cough and headache -respiration problems due to fluid that gets filled in the alveoli
Common cold Rhinoviruses -by cough, sneezes and contaminated objects -nasal congestion and discharge, sore throat, cough, headache -nose and respiratory passage
Malaria Plasmodium falciparum, P. vivax (Protozoan) -female anopheles mosquito is a vector

-spread by mosquito bite

-high fever with chills -the parasite multiplies in liver cells, attacks RBCs and rupture
Amoebic dysentery Entamoeba histolytica (Protozoan) -houseflies are a carrier

-spread by contaminated food by the faecal matter

-constipation, abdominal pain, mucous and blood in the stool -infection in the large intestine
Ascariasis Ascaris (Helimenthes) -contaminated water, vegetables, fruits

-parasite eggs are excreted our in faeces of the infected person, which contaminates soil

-muscular pain, internal bleeding, anaemia, fever -blockage of intestinal passage
Filariasis/ Elephantiasis Wuchereria bancrofti, W. malayi (Helminthes) -bloodsucking black flies and female mosquitos act as a vector -inflammation of the lower limb and genital organs -lymphatic vessels, especially of the lower limbs, get blocked
Ringworms Microsporum, Trichophyton, Epidermophyton (Fungi) -spread from the soil, using a towel, clothes or comb of an infected person -dry scaly lesions, itchy skin in the groin or between the toes -effects skin, nail scalp

The lifecycle of Plasmodium (malarial parasite)

  • Plasmodium enters in the body by the bite of female Anopheles mosquitos
  • The infectious form is sporozoites, that comes from the saliva of female anopheles when they bite
  • It multiplies in the liver cells and then attacks RBCs resulting in RBCs rupture
  • Haemozoin, a toxic substance gets released
  • The gametocyte produced in the human blood gets transferred to the mosquito when it bites an infected person
  • Macro and micro gametocyte undergo fertilization, transformation and sporogenesis in the mosquito’s intestine and sporozoites are formed
  • Sporozoites migrate to salivary gland of mosquito and the cycle is repeated
  • Plasmodium sp needs human and female Anopheles mosquito to complete their lifecycle


Life cycle of the malarial parasite; Plasmodium


Types of Immunity

  • The ability of the body to protect and fight against any pathogen or foreign bodies is called immunity
  • The immune system defends our body against any infection
  • There are two types of immunity:
    1. Innate immunity: is present at the time of birth. There are 4 types of barriers present in the defence mechanism of our body.
      1. Physical barriers: skin and mucous coating of the epithelial lining of respiratory, gastrointestinal and urinary tract
      2. Physiological barriers: saliva, tears and stomach acid
      3. Cellular barriers: neutrophils, monocytes, natural killer lymphocytes
      4. Cytokine barriers: interferons secreted by virus-infected cells
    2. Acquired immunity is something that we acquire during the lifespan and is pathogen-specific.
      • The primary response of low intensity is initiated after the first encounter with a pathogen
      • Subsequent infection results in a highly intensified secondary response or amnestic response due to memory of the first response
      • B-lymphocytes produce antibodies in response to foreign antigen
      • Antibodies (H2L2) are Y shaped protein molecule with 4 peptide chains; 2 light and 2 heavy
      • There are five types of antibodies or immunoglobulins present in humans; IgG, IgM, IgD, IgA and IgE
      • IgG is the most abundant antibody found in the blood
      • IgG is transferred to a foetus through the placenta and protects the infant until their own immunity develops
      • IgA is present in the breast milk, colostrum, the yellowish fluid secreted initially during lactation has an abundant IgA
      • IgE is involved in the allergic reaction
      • The antibody-mediated response is known as humoral immune response
      • T-lymphocytes mediate, cell-mediated response or CMI
      • Cell-mediated response is responsible for distinguishing between self from non-self and graft rejection after transplantation

Active immunity: Antibodies are produced in the host body in response to antigen. Effective response takes some time. Vaccination, where an attenuated pathogen is injected is a type of active immunity.

Passive immunity: Giving readymade antibodies to get the quick response against a pathogen is termed as passive immunity. Injecting antitoxin for snakebite, which contains antibodies against the venom is passive immunisation.

Recombinant DNA technology has helped in producing large-scale vaccine production.

The hepatitis-B vaccine is produced from yeast.


  • Exaggerated immune response to certain environmental antigens, e.g. pollens, dust, mites, etc.
  • IgE antibody is produced during an allergic reaction
  • Mast cell releases histamine and serotonin during an allergic reaction
  • Antihistamines, adrenalin and steroids reduce the allergic symptoms

Auto Immunity

  • When body attack self-cells it results in auto-immune disorder
  • Rheumatoid arthritis is an auto-immune disorder

Immune System in The Body

The Immune System - Lymphoid Organs

  • The human immune system comprises lymphoid organs, cells and antibodies
  • Primary lymphoid organs: bone marrow and thymus. Here lymphocytes develop, mature and differentiate to antigen-specific lymphocytes
  • Secondary lymphoid organs: spleen, lymph nodes, tonsils, Peyer’s patches in small intestine and appendix. These are the site for reaction with antigen and they become effector cells after the proliferation
  • The spleen acts as a filter of the blood. It contains lymphocytes and phagocytes and a large number of erythrocytes are present
  • Lymph nodes trap the antigens present in the lymph or tissue fluid
  • Mucosa-associated lymphoid tissue (MALT): the mucosal lining of respiratory, urinary are digestive tract accounts for the 50% of total lymphoid tissues present in the body

AIDS (Acquired Immuno Deficiency Syndrome)

  • Caused by HIV (Human Immuno Deficiency Virus)
  • It is a retrovirus with RNA as its genome
  • The virus produces viral DNA in the host by the enzyme reverse transcriptase
  • The viral DNA gets incorporated into the host genome and multiple copies of the virus are produced
  • The virus attacks helper T-cells, where it replicates and multiplies, resulting in the marked decrease in the number of T lymphocytes
  • The infected person becomes immunodeficient after the virus attacks T- helper cells
  • AIDS patient become prone to various infections like mycobacterium, toxoplasma, fungal and other viral infections
  • ELISA (Enzyme-Linked Immuno-Sorbent Assay) is a widely used diagnostic test for AIDS
  • AIDS may be transmitted by sexual intercourse, contaminated blood transfusion, using an infected syringe or from mother to foetus through the placenta
  • NACO (National AIDS Control Organisation) works for the awareness and prevention of AIDS by educating people

HIV virus replication cycle
HIV Virus Replication Cycle


  • Cancer is caused due to uncontrolled cell division leading to the formation of tumours
  • There is a breakdown of regulatory mechanism in oncogenic transformation of normal cells
  • Cancerous cells lack contact inhibition property, which inhibits further growth of cell on contact with other cells
  • Benign tumours are non-invading and remain confined to their original location
  • Malignant tumours have invading ability and damage surrounding tissues
  • Metastasis: It is a property of malignant tumour when cells sloughed off from it reach distant sites and form a tumour in the various parts of the body
  • Cancer is caused due to DNA damage or genetic mutation resulting in the faulty regulation of the cell division
  • Cancer can also be caused due to the activation of proto-oncogenes present in normals cells under certain condition
  • Carcinogens: ionising radiation (e.g. X-rays, gamma rays), non-ionising radiation (UV rays), chemical agents (e.g. present in tobacco), viral oncogenes of oncogenic viruses
  • Cancer can be diagnosed by using a CT scan (computed tomography), MRI (magnetic resonance imaging), X-ray, PET scan (positron emission tomography) or by histopathological studies of tissue and blood
  • Cancer can also be diagnosed using molecular biology techniques to identify inherited susceptible genes for certain cancers
  • Antibodies against cancer antigens can also be used for diagnostic purpose
  • Cancer can be treated by surgery, transplantation, immunotherapy, radiation therapy
  • 𝛂-interferon act as biological response modifier, which activates the immune system to destroy tumour

Drugs and Alcohol Abuse

  • Opioids, cannabinoids and coca alkaloids are commonly abused drugs
  • There are opioid receptors present in our CNS and GI tract, where opioid drugs bind
  • Diacetylmorphine is commonly known as heroin or smack. It is extracted from the latex of poppy plant Papaver somniferum. It is obtained by acetylation of morphine
  • Cannabinoids bind with the cannabinoid receptors present in the brain. They affect the cardiovascular system
  • Cannabinoids, e.g. marijuana, hashish, charas, ganja, etc. are obtained from the flower tops, leaves, resins of the plant Cannabis sativa
  • Cocaine or coca alkaloid is obtained from the plant Erythroxylum coca.
  • Cocaine acts by interfering with the transport of dopamine, a neurotransmitter
  • Atropa belladonna and Datura also have hallucinogenic properties
  • Sportspersons also take cannabinoids to enhance their performance, muscle relaxation and reduce anxiety
  • Morphine is used as sedative and pain killer
  • Barbiturates, amphetamines, benzodiazepines, etc. are used as a medicine for depression, insomnia and other mental illness
  • Nicotine (alkaloid) present in tobacco stimulates the release of adrenalin and nor-adrenalin hormone by the adrenal gland. It increases heart rate and blood pressure
  • Smoking causes oxygen deficiency by increasing the concentration of carbon monoxide in the blood thereby decreasing the concentration of oxygen bound to haemoglobin
  • The excessive use of drugs and alcohol damages the nervous system and causes liver cirrhosis
  • The misuse of narcotic analgesic, anabolic steroids, diuretics to enhance performance and increase muscle strength is frequently done by sports person
  • Anabolic steroids induce masculinisation and aggressiveness in females

Explore the next chapter for important points with regards to the NEET exam only at BYJU’S. Check the NEET Study Material for all the important concepts and related topics.

Also see:

NEET Flashcards: Human Health And Disease

NEET Flashcards: Strategies For Enhancement In Food Production

NEET Flashcards: Microbes In Human Welfare

NEET Flashcards: Biotechnology Principles And Processes

NEET Flashcards: Biotechnology And Its Applications

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Frequently Asked Questions


What is meant by human health?

Human health is the state of complete mental, social and physical well being.


Why is human health important?

Human health is important because it is directly related to the economy of the world. Good health promotes the economy and its developing factors.


What are the causes that harm human health?

Common causes that harm human health include environmental pollution, natural disasters, climate change and lack of access to healthcare.


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