Immunology first line of defense

Immunology is all about our body's mechanism of protection from the harmful pathogens present outside our body in the environment. There are different levels of Defence for protection in our body. The first level of protection that the pathogens coming towards our body faces is called first line of Defence.

( Microbes = any micro-organism both harmful and harmless to human 

Pathogen = micro-organism that can cause disease)

From where pathogens can enter our body :

1. Skin : skin covers the internal organs of our body .It is the largest organ covering the most area of our body externally.
2. ear : hole of the ear is an entrance into the body.
3. Eye: eyes are not covered by the skin and exposed to the environment facing direct contact with pathogens
4. nose:  nostril is an entrance to the Airways which leads towards the internal organ lungs
5. Mouth:  mouth hole is the entrance to the body mainly to the gastrointestinal tract
6. Anus:  anus is the exit hole of the gastrointestinal tract and can also be an entrance for pathogen into the body.
7. Urethra : urethra is the exit hole of urine .pathogen can also enter through this hole.
8. Genitals:  female genital pore is vagina .male genital pore is common with the urethra. It can also lead towards the internal organs.

What are the first line of Defence taken by these entrances of our body :

A. Skin :

1. Keratin : The epidermis is consists of several layers of tightly packed epithelial cells that are dead and filled with waterproof protein called Keratin. Periodic shedding of epidermis removes microbes.

2. Antimicrobial agents : sweat contains dermcidin and defensin which Kills Bacteria .dermcidin is made of peptides that can break down bacteria both gram positive and Gram Negative bacteria. Defensin and lysozyme is secreted by sebaceous gland. Defensin is a host defence peptide displaying direct antimicrobial activity. lysozyme is an antimicrobial enzyme It Breaks the cell wall of Gram Positive Bacteria .

3. Low pH :  sweat contains lactic acid . Sebaceous glands secrete acids that form acid mantle. this is a thin acidic film on the surface of the skin and maintains the skin pH from 3-5. Most of the pathogens cannot tolerate low PH .

4. oily sebum : sebum provides an additional layer of Defence by sealing off the pore of the hair follicle preventing pathogen on the skin surface from invading sweat gland and surrounding tissues .

5. Skin flora or skin microbiota : The term skin flora refers to the microorganisms which reside on the skin, typically human skin. They are harmless on healthy skin. The benefits they can offer include preventing transient pathogenic organisms from colonizing the skin surface either by competing for nutrients or secreting Chemicals against them.

B. Ear :

1. Hair : Ear hair blocks entry of dust and pathogen inside the ear.

2. Ear wax : Ear wax is a sticky substance allowing pathogen to be trapped into place until they can be removed.

3. Cerumen :earwax is mostly made up of cerumen yellowish brown waxy substance produced by apocrine ceruminous gland in outer ear Canal. it is antibacterial agent and antifungal .

C. Eyes :

1. Eyelash : eyelashes block the entry of dust and pathogen inside eyes.

2. Tear film : tear film is a wet substance which keeps the eyes moist and it also contains lysozyme which is an antimicrobial protein which can kill bacteria.

D. Nose :

1. Hair : nose hair blocks the entry of dust and pathogen inside the nasal cavity.

2. Mucus : mucus traps the microbes and removes with other mechanism. Mucus is also present in the windpipe . mucus traps harmful substances virus, bacteria, Dust etc on the surface of the mucosa and the vibratory cilia move the mucus outwards to eliminate it.

E. Mouth :

1. Mucus : mucus traps harmful substances and move the mucus outwards to eliminate it. In the mouth mucus is produced by 3 salivary glands sublingual gland ,submandibular gland and parotid gland.

2. Lysozyme : In the mouth lysozyme is produced by two glands sublingual gland and submandibular gland. lysozyme is an antimicrobial protein which can kill pathogens. 

From the mouth when food reaches :

• Stomach : anyhow if pathogen gets an entry through the mouth when it reaches the stomach most of the pathogens gets destroyed by hydrochloric acid in the stomach.

• Large intestine : the naturally living microbes in the gut called the gut flora. Gut Flora community place a direct rule in defending against pathogens by fully colonizing the space making use of all available nutrients and bi secreting compounds that kill or inhibit pathogens that would compete for nutrients with it. Large intestine also has thick mucus layer for protection. Mucus significantly reduce attachment and biofilm formation.

F. Anus :

Mucus is present in the anus for blocking the pathogens to get entry through anus.

G. Urethra :

Urine flow prevents bacterial growth in urethra .

H. Genitals :

• Male : in case of male, genital pore and urethral pore is same. Semen contains antimicrobial antifungal agents.
• Female : in case of female, genital pore and urethral pore is different. For female genital pore is vagina. Acidic secretion in vagina inhibit growth of pathogen .