IMMUNITY

 Immunity is the ability of an organisms to resist a particular infection or toxin by the action of specific antibodies .

  The immunity is two types 

 I- Innate immunity or non-specific defance mechanism

II- Acquired immunity or specific defence mechanism 

1- Innate immunity 

This type of immunity is present in an organisms by birth.

The innate immunity includes certain barriers and defence  mechanism that keep foreign particles out of the body .

 There are 4 types of barriers  

a- physical barriers

b- physiological barriers 

c- cellular barriers

d- cytokine barriers

a - physical barriers 

These includes the skin , nasal , hairs , mucous , membrane of nose ,respiratory tract and digestive tract.

These form the first line of defence .

They prevent the entry of pathogens into the body primarily .

b- physiological barriers 

These includes 

Lysozymes - These are present in tears and is bacteriolytic and digests the bacterial walls .

Acid in stomach - The HCL is secreted in side the stomach which kills most of the ingested microorganisms .

Saliva - The antibacterial properties of saliva prevent many harmful pathogens from eating the body .

 Cellular barriers - certain types of leukocytes of our body like polymorpho-nuclear leukocytes monocytes and natural killer in the blood as well as macrophages in tissues can phagocytocite and destroy microbes .

d- cytokine barriers 

virus infected cells secreted proteins called interferons which protect non-infected cells from further viral infection .

II- Acquired immunity 

The immunity which develops during lifetime by exposure to suitable foreign agents like microorganisms is called acquired immunity .

It is pathogen specific and is characterized by memory .

When the body first encounter a pathogen it produce a response which takes long time to developed and of low intensity called as primary immune response .

And if the body encounters the same pathogen second time it produce highly intensified and quick response called as secondary immune response .

The primary and secondary immune responses are carried out with the help of two special type of lymphocytes present in our blood .

They are a-  B-lyphocytes - These are produce from the bone marrow and get matured in the bone marrow .

They produce an army proteins in response to pathogens into our blood to fight with them called antibodies .

T-lymphocytes - These are produce from the bone marrow but they migrate to the thymus for maturation .

The T-cells themselves do not produce antibody but helps beta cells to produce them.