Immunity

IMMUNITY

Definition:

               Ability of the body to fight against any foreign agent that could be harmful to the body in order to protect body from any harm.

Immunity is majorly provided by different body barriers like skin, mucous membranes and the body fluids like blood and lymph. Different organs and tissues also play a major roll in provision of immunity like lymph nodes, spleen, thymus and bone marrow.

Now if we discuss immunity on the basses of provision by different organs it would be divided under to major terms:

• Innate immunity
• Acquired immunity

Innate immunity

This is the type of immunity that you have by birth, and it also keeps you alive just after your birth. Without this immunity you can't survive no matter how much heroic measures are taken.

And it is provided by,

1. Physical barriers:
   Skin and Mucous membranes lining different body openings.
   
   
   How?
   All the epithelia that are exposed to the external environment like skin and mucous membranes of oral cavity ,urethra and vagina have tight junctions in between there cells which do not let the micro organisms(residing as the normal flora on the skin and mucous membranes of the body) and any other harmful material to pass.
   
   
   
   
2. Body secretions:
   HCL of stomach, lysozyme present in tears and saliva.
   
   
   HCL of stomach:
   Intense low pH of stomach can not be favorable to any living organism so when any microorganism enters GIT ,its digested n no more harmful.
   
   
   Lysozome:
   A hydrolytic enzyme present in saliva n tears, that attacks cell wall of the bacteria leaving it non-pathogenic.
   
   
   
   
3. After passing through these barriers, if a bacteria is strong enough to enter the body tissues through broken skin part or mucosa, macrophages are there to engulf him and kill him.(Macrophages are actually monocytes which when enter the tissues from blood become mature, enlarge in size in ready to engulf bacteria and kill them.)
   
   
   
   
4. Then if bacteria survives tissue macrophages, it enters the tissue fluid and then lymphatics.Once they have entered lymphatics they must have to pass through lymph nodes (lymph filtering organs),where must b killed.
   
   
   
   
5. If survived it enters the blood where different WBCs like neutrophils and eosinophils are ready to attack rendering it non-pathogenic,blood also pass through spleen that is a blood filtering organ lined by macrophages.
   
   
   
   
6. Also the bacteria entering via GIT first enter liver through hepatic portal system  where liver macrophages are waiting to engulf and kill them.

Here ends the acquired immunity then if foreign agent again survives it further involves lymphocytes which form the acquired immunity.

Acquired Immunity:

Type of immunity that is gained or obtained through experience of any past infection.

Its major components are cells: Lymphocytes T and B, organs and tissues: Thymus, spleen, bone marrow.

Acquired immunity is further divided in two types:-

1. Cell mediated immunity.(supplied by T cells)
2. Humoral immunity. (by B cells)

Cell mediated immunity:

Supplied by T cell(called T cells because there maturation take place in thymus...so thymus cells or T cells). And the immunity is called so because in this cells are involved as a whole.

It functions by following mechanism:
Whenever any bacterium enters the body it is phagocytosed and the antigen is sent to the T cells which form some memory cells for the future use n some activated T cells against that particular antigen.

Activated T cells then thrown into the blood where they fight against that particular foreign material by producing toxins to that foreign invader and killing them.

T-cells are also involved in tissue rejection after an organ transplant.

Humoral  immunity:
Provided by B-cells( these cells are called so because first these where discored for a bird gland called bursa of fabricious was found to have a role in immunity)
This type of immunity is called so because no whole cell is involved but the activated cell produce antibodies that fight against the invader.

Antibody:

These specialized proteins called immunoglobins and are different types like IgG, IgA, IgM, IgE and IgD depending upon the function molecular weight and area and body secretions n fluid for action.

Have heavy and light chains and constant and variable zones.
Constant zones are for maintaining structure where as variable zones r for producing variety in types.

Mechanism of humoral immunity:

In case of any invader B-cells divide producing memory cells and activated B-cells.

Activated B-cells produce antibodies that act in two ways....one by producing antitoxins against the bacterial toxins and the second by attaching themselves to the antigens present on the bacterial wall making them more susceptible to phagocytosis.

Primary & Secondary response to any infection:

Memory cells that are formed in cell mediated and humoral immunity are the basis for secondary responce to any infection after an infection has already accured producing a primary responce.

Secondary response is nothing else but a more intense response of lymphocytes  against any infection which does not let the person to be diseased.

Vaccination:

Secondary response is also the basis for the process called vaccination in which heat killed, dead ,weak,non-virulent & non-pathogenic bacteria are injected to the body to elicit the primary response. So that whenever an actual infection occur body's response would be so intense that no disease would produce.

Then on the basis of this primary and secondary response of body here's another classification.

1. Active immunity.
2. Passive immunity.

Active immunity:

In which foreign agent enters the the body.The body respond against it and become self immune to the future infections it may b Artificial as in case of vaccination or Natural as in case measles like infection in which body is self vaccinated and immunized to a particular infection.

Its permanent.

Passive infection:

In this type of immunity an antisera(serum containing antibodies against a particular infection) are injected to the body rendering it immune to that particular infection for a short duration of time.

As the antiseras given in case of snake venom poisoning, rabies, infectious hepatitis, tetanus.

Its of temporary value.

So here we are done with immunity (one of the most beautiful systems Allah has put in our body)  that play a major role in our survival on this beautiful earth. May this article help you in understanding of immunity, clearing your concepts for both entrance examination and Fsc exam...GOD BLESS YOU!!!

Entry # 13

By Kiran Ghumman