Human health and disease

Table of Contents

The Article covers Topics- Immune System, Lymphoid Organs, Types of Lymphoid Organs . Article also covers AIDS and Cancer in detail.


What is Immune System?


The system that protects the body against pathogen called immune system 

it consists of lymphoid organs tissues cells and soluble antibodies it recognises an antigen, respond to these and remember them.

it also play a key role in allergic reactions, autoimmune diseases as well as organ transplantation or graft transplantation .

What are the Lymphoid organs:

These are the organs where origin and maturation as well as multiplication or proliferation of lymphocytes occur.

Types of Lymphoid organs:

There are two categories of lymphoid organs: primary and secondary lymphoid organs.

1 . Primary Lymphoid Organs:

These are lymphoid organs where T and B lymphocytes form and mature such as Bone marrow and Thymus gland.

Bone marrow:

It is present in the long bones (such as femur-thigh bone, humerus- forehand bones etc.)of the body and contain red and white Bone marrow.

In bone marrow Hemopoietic stem are cells presents which are the basis of all blood cells.

Bone marrow is the main Lymphoid organ, where all the blood cells including Lymphocytes are formed. Maturation of B cells occur here.

The name of B cells is derived due to the Bursa of Fabricus which is found in birds. 

it is the lymphoid organ in the birds found in the digestive tract. It has been Noticed that, if Bursa of fabricus will remove completely ,the birds become Immuno deficient.

Thymus gland :

It is a bilobed organ located near the heart just below the breastbone or chest bone. 

it is quite light large at the time of birth but with the increasing of age its size decreases

it is the site of T cell maturation hens T cell is called Thymus gland derived cells.

2 . Secondary Lymphoid organs:

Those organs where the  differentiation and storage of B and T cells take place are called secondary Lymphoid organs 

specific immune response to antigen usually develop in these secondary organs some common secondary lymphoid organs.


It is a large bean shaped organ contain lymphocytes and phagocytes it is the largest secondary lymphoid organ.


three pairs or total six tonsils act as filter to protect body from bacteria and help in the formation of WBC.

it is found in buccal cavity e near the attachment of tongue.

Payer’s Patches:

It is located in small intestine along the ileum. it is also the Lymphoid organ which produces lymphocytes.

Lymph nodes:

These are small solid structure located at different points along the lymphatic system.

It acts to trap the  microorganisms for antigen which enter in lymph tissue fluid.

MALT(Mucosal associated lymphoid tissue):

It is located within the living of major tribes such as respiratory digestive and urogenital tracts it constitutes about 50% of total lymphoid tissue in the body.

The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen proliferate to become effector cells.


AIDS(Acquired Immuno Deficiency Syndrome)


It is a disorder of cell mediated immunity (CMI) of the body.

In this reduction of helper T cell population and progressively increase in HIV population. 

The overall result is that loss of natural defence that is immunodeficiency against pathogenic infection

It was first discovered in 1981 in USA. The HIV name was given by International Committee on Viral Nomenclature(ICVN) in 1986. In India it was first detected in Chennai in 1986.

AIDS virus may have some how passed from a monkey host into human population in Africa during 1960. hence South Africa is considered as World AIDS Capital.

Every year day 1st December celebrated as the World AIDS day.

Causative Agent: 

The AIDS virus is called HIV virus which is RNA containing retrovirus.

Structure of HIV:

it is a spherical in shape with 90 to 120 nm in diameter. its genome consists of single stranded RNA filament segmented into two identical parts and associated with reverse transcriptase enzyme.

The envelope consists of lipid layer derived from host cell membrane and the paper pin like projecting structure called glycoproteins(gp) spikes help in attachment with Host cell

Below the lipid layer, two protein coat present which protect the RNA genome of virus.

How HIV virus infects human being?


Mode of infection of or Life cycle of HIV virus:

On entry in the human body, it enters Macrophage where RNA genome of virus undergoes reverse transcription in the presence of enzyme reverse transcriptase to form viral DNA.

Then viral DNA gets incorporated into host cell genome and direct the infected Macrophage to produce new virus particle.

In this way macrophage become or act as a HIV factory

simultaneously HIV enters helper T cell .and undergoes replication to produce other viruses

The above causes progressive decrease of T-cell population resulting immunodeficiency and the person may suffer from fever diarrhoea, weight loss, and other pathogenic infection like Mycobacterium and Toxoplasma.


How AIDS Transmitted


HIV usually transmitted by body fluids buy the following

Transfusion of HIV infected blood or blood products

Use of contaminated needles with HIV 

Use of shaving Razors contaminated with HIV  Through Artificial Insemination

In organ transplantation 

From HIV infected mother to the child through placenta

Unsafe sexual relation for more than one sexual partner.

AIDS cannot be transmitted by:

From the crowded transport 

insect bites 

shaking hands with HIV patient 

sharing travel of HIV patient 

coughing and sneezing from HIV patient

 sharing utensils and phones etc. of HIV patient


The symptoms include headache rashes on the body lethargy weight loss and the bouts of fever

Incubation period:

the incubation period of AIDS ranges between humans few months to many (5-10) years.


It can be diagnosed by ELISA  (enzyme linked immunosorbent sorbent assay) test and Western Blotting.

Western blotting test is used for confirmation of ELISA positive case.

There is no permanent cure for AIDS till now.

Use of certain drugs can prolong the life of HIV patient.

AZT (Azitothymidine) or Adobe dine was the first drug used for the treatment of AIDS.

 other drug is Didanosine (Dideoxyioanosine-DDI)

Most of these drugs are actually target on the enzymes required for HIV virus replication

Prevention from AIDS HIV virus:

People should be educated about aids.

Every year 1st December called as the World AIDS day.

Before Blood Transfusion, Artificial Insemination(AI) and Organ Transplantation, proper test should be done

Proper disposal of needles and syringes 

Avoid tattoos, Ears and Nose penetrations from unqualified people  

Sexual relationship should be safe.

Agencies working on AIDS in India:

Many people are ignored about aids and it has been said that “don’t die of ignorance”

NACO (national AIDS control organisation) and NGOs (non government organisation) are doing good work to educate people about AIDS.

What is Cancer?


It is an abnormal and uncontrolled division of cells that invades and describe the surrounding tissues 

it can be defined as uncontrolled proliferation of cells without any differentiation.

Definition of Oncology?

Study of Cancer is called oncology and the specialist is called Oncologist.

Difference between cancer cell and normal cell:

Normal cells have limited lifespan

Their production is regulated in such a manner that a number of cell become constant 

Normal cell show a property called contact inhibition

Due to this property they contact with other cells and inhibit their uncontrolled growth but cancer cell  have lost the property  of contact inhibition.

Hence it undergo uncontrolled growth, resulting tumor or neoplasm forms.

Benign or non malignant tumor

In this the neoplastic cell remain clustered together in a single mass and cannot spread to other side.

Benign tumor cells closely resemble to normal cell and it is non cancerous.

Malignant or Cancerous Tumor

Do not remain localised at the same site and progressively spread to other parts of the body.

Cancer cell enter the blood and lymph circulation any spread throughout the body and cause tumor formation at the new areas of the body. This is called Metastasis the form tumor is called secondary tumor.

Cause of cancer

The agents that initiate or promote tumor formation called carcinogens. These agents categorised into following groups

Physical agents:

It includes the radiations such as UV rays, X rays, gamma rays and beta rays is etc.

Chemical agents:

it includes certain chemicals such as benzopyrene benzene nicotine caffeine artificial sweetener and pesticides etc.

Biological agents:

This include cancer causing genes which is found in some viruses and normal bodies cells.

Cancer causing viruses or Oncovirus:

Many viruses like hepatitis B virus (HBV) and SV-40 virus etc. contain the cancer causing genes also called oncogenes and such viruses are called on Oncovirus.

Cellular oncogenes(c-onc) or Protoncogenes:

It is found in normal bodies cells any change in cell internal environment convert these genes into oncogenes.

More than 100 different types c-onc genes are known.

How to Detect and Diagnosed Cancer?


The detection and diagnosis vary with the location and stages of cancer

Bone marrow biopsy:

In a piece of suspected tissue cut into thin section and stained and examined under the microscope by pathologist.

Detection of abnormal count or increase in Leukemia

Techniques such as Radiography, C.T(computed tomography) scan and MRI (Magnetic resonance Imaging) are very useful to detect cancer of internal organs.

Antibodies against cancer specific antigen are also used to detect the cancer cell.

How Cancer is Treated:


It involves the removal of entire cancerous tissue

Radiation therapy:

It involves the exposure of cancerous part to X rays which destroys rapidly growing cells.


Certain anticancer drugs used which check cell division by inhibiting DNA synthesis of tumor cells.

Majority of drugs have side effects like hair loss and loss of blood or Anaemia etc.


Alpha Interferons (types of cytokine) used which activates immune system and help in destroying the cancer.

Types of cancer:


Cancer of epithelial cells of. Lungs, skin, uterus etc.


Cancer of muscle


Cancer of bones


Cancer of adipose tissue

Leukemias or Blood Cancer:

Cancer of blood cells


Cancer of connective tissues and muscles tissues.

for other topics click below link


Human Health & Disease Class 12 NCERT Notes(Part:2)

Human Health & Disease Class 12 NCERT Concise Notes-1

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