What is immune system of human and how it’s functioning?

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Introduction

              Immune system is one of the system of human body which is responsible for the protection of human body from foreign particle e.g microbes either harmful or harmless and dust particle. It does not allow them to inter into the body through their defending boundaries  because human body is an isolated system which is performing their activities by setting within their boundaries  when any foreign body associated with them at that time they will not be able to keep on their activities due to these reason there is a specific system that  is human defense  system that can tackle these type of process and maintain the function of immune system. Human defiance  system is a combination of cells and physical barrier. First physical  barrier try to catch that entering foreign body if it fail to catch them then second system activate that is the combination of blood cell that will completely diminished it.

Composition of defense system

Actually defense system is made-up of physical barrier, chemical barrier, biological barrier and immune cells.

1-      Physical barrier

It the barrier which does not allow foreign particle to inter into the body through them they physically trap them.

Example:

              Skin

              Which is present through over the body  which has three layers by the combination of the layers they trap foreign particle and kill them.

How skin is a defense line and how it trap foreign particle?

Skin is made up of tightly packed skin cell and also contain keratin protein they provide dead nature to the skin surface when any foreign land on it they die due to lack of nutrient.

  Mucous membrane

Mucous membrane is present throughout the GIT ( Gastro Intestinal Tract)  which contain goblet cells they produce mucous which help in the traping of foreign particle.

   Hairs

Hairs present on the surface of skin and inside the external area of nose which also trap foreign particles.

2-      Chemical barrier

There are several chemical barrier which produce chemical to protect our body from foreign particles. E.g

Sweat gland:

              They present on the skin in different location where they produce sweat which is made up of  lysozyme which break down the cell wall of bacteria.

Sabaceous Gland:

                             These gland also present in the skin where they produce sebum which is made up of fatty acid which inhibit the growth of bacteria and  also decrease the acidity of skin which become more acidic for any normal foreign particle where they does not survive their lives.

Hydrochloric acid:

                             Hydrocholoric acid present in the Stomach which is secreted by the parietal cell. It kill bacteria and other microbes they are harmful or harmless for us.

Sliva

              Sliva contain enzyme called lysozyme which help in the killing of bacteria

Saruman

              A protective waxy fluid present inside the ear which is responsible for the trapping of microbes and does not allow them to approach the ear.

3-      Biological barrier

Human body contain several microbes or Bacteria they present inside the body or on the surface of body  in their location where they are harmless for the body and also synthesize several body requirement  they are called Normal flora of the body.

How Normal flora provide immune defense?

              Normal flora either on the surface or in the body where  they compete with foreign particle in different way the first method in which they will not provide any space for them as a result they unable to infect the body.

The second method  where they will not provide nutrient for them and all the available nutrient they will intake for themselves ( normal flora ) and there will not any thing left behind for the survival of foreign particle as a result they die.

In the third method normal flora produce harmful chemical after competing with the foreign body that toxin kill the bacteria and also activate the immune system to compete with foreign bodies.


4-      Cellular barrier

All cells of immune system originated from hematopoietic stem cell.

A.   Hematopoietic stem cells

 It  makes two type of cells

a.      Lymphoid common progenitor

It further synthesize three type of cells

a.1. T- cells

                      These cell form in the bone marrow in Lymphoid common progenitor and move toward thymus for the purpose of maturation where it become mature.

There are four type T-cells.

a.      Helper T-cells

It help other immune system to become alert for that purpose it release cytokines that alert immune system and initiate the production of antibody by activation of B cells.

b.      Cytoxic t-cells

Directly kill virus infected cell and other cancerous cell of the body.

c.       Regulatory T-cells

This type cell help the immune system by controlling its excessive reaction against foreign particle and also protect from autoimmune disorder.

d.      Memory T-cells

It remember previous memory if the same antigen attack in the body it work imidiately and kill them.

a.2. B-cells/

       This type of cells are most important in the specifically killing foreign particle by producing antibodies against them. It has three types

a.      Plasma B-cells

It produce antibodies after conformation of foreign bodies

b.      Memory B-cells

It store the information of pathogen even if they attack on the same host again it kill them immediately due to the presence of memory

c.       Suppressor B-cells

These type cells are responsible for the protection immune system after infection it suppress immune system and protect from autoimmune disorder

What is phagocytosis?

              It is the process of ingulfing microbes. It convert pathogen  into fragments  through six steps

1.      Chemotaxis

In this step phagocytes move toward  pathogen

2.      Adherence

In this step Phagocyte  physically attach with the foreign particle

3.      Engulfing

In this phase phagocytes engulf pathogen

4.      Fusion

In this step pathogen combine with lysosome of that cell( important for breaking downing of pathogen)

5.      Digestion

In this step phagocytes digest that pathogen with the help of their digestive enzyme they are present int their lysosome

for more about the digestion of humanhttps://healthduhs.blogspot.com/2026/05/how-food-is-convert-into-and-blood.html

6.      Exocytosis

In this step phagocytes expel out that harmless fragments  foreign particle form their surrounding into external area.

      

a.3.                             Natural Killer cells (NK Cells)        

            This type of  lymphoid cell help in the  non-directly killing of pathogen in which it makes holes on the wall of that pathogen due to this it liquid from surrounding rushes inside as a result it swell and brust.

b.      Myeloid common progenitor

It further synthesized six type of cell

b.1.  Neutrophils –

       most abundant type of WBCs which come first at the site of infection where it start its phagocytosis.

Macrophages are present at the site of infection after getting information about foreign particle they release interleukin-8 where it attract neutrophil to the site of infection and also some foreign bodies also release chemical which attract neutrophil to the site of infection.

Inflammatory substances also responsible for the attraction of neutrophils.

Neutrophils are professional phagocytosis.

 

b.2.  Eosinophils –

       This type of cells are important in the elimination of paracites and also protect from paracytic infection.

It is important in allergic reaction and Asthama. They release toxins  to kill paracytes.

c.3.Basophils –

This type of cells are important in allergic reaction where it release histamine and heparin that cause vasodilation.

d.3.Monocytes 

       Largest white blood cells which perform phagocytosis. It circulates in the blood  and differentiate in to macrophages and dendritic cell they migrate into the side of tissues.

e.4. Macrophages 

       It is the converted form of  monocytes that is living in tissue where it perform phagocytosis and also coordinated between immune response.

Macrophages have different name according to their location

e.g Kupper cell.

       Type of macrophages they live in the lives

f.5.Dendritic Cells

       These type of cells are important for displaying antigen for T-lymphocytes. It is a linkage between innate and adaptive immunity.

g.6.Mast Cells –

       These type of cells are located in the tissue where it release histamine and other inflammatory substance during allergic reaction inflammation and anaphylaxis. for more about human immune disease https://healthduhs.blogspot.com/2026/06/what-is-difference-between-aids-and-hiv.html

 Reference


 WHO -World Health Organisation
NIH- National Institute Of Health)

 CDC- Centre for Disease Control and prevention




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