- Innate immunity is also known as native immunity.
- It is a resistance with which a person or lower animal is born and is non-specific.
- This type of immunity is present throughout our life.
- It may be of various types like species immunity, racial immunity or individual immunity.
- Various factors like age, hormones, nutrition, etc. influence the innate immunity in the host.
- Natural or innate immunity has three components. Among them physiochemical barriers are also one of them.
- They are the epithelial surface like skin and mucosae, and cilia while bactericidal secretions behave as chemical barriers.
- The animal body is a close system separated from the environment by skin and mucous membranes and they are impermeable to the particulate material of the size of the bacteria.
- The skin acts as a mechanical barrier to the invading microorganisms and also provides bactericidal secretions.
- The sebaceous secretions containing unsaturated fatty acids (oleic acid) and free saturated fatty acids have bactericidal and fungicidal
- The dry skin with high salt concentration in drying sweat inhibits or is lethal to many bacteria and fungi.
- The skin can be freed of transient flora easily but the resident flora cannot be removed even by washing or by the use of disinfectant.
- The superficial microorganisms of the resident flora may be diminished by vigorous surgical “scrubbing” but they get replenished rapidly from sebaceous and sweat glands.
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b) Nose, naso-pharynx and respiratory tract
- The moist surfaces of the mucous membrane lining of the nasal passage arrest various inhaled bacteria and other particulate material.
- Thus, the inspired air is largely freed of bacteria in the upper respiratory passage.
- Though some of the organisms skip this passage, they get trapped in the bronchial mucosa in the larynx and only a few may reach the bronchioles and alveoli.
- The sticky mucous secretions of respiratory mucosa and the hair like cilia sweep the secretions containing the foreign particulate.
- They are swept towards the oropharynx where it is swallowed or is coughed out.
- The cough reflex plays an important role of respiratory tract.
- The small particulate materials which manage to reach the alveoli are ingested by the phagocytic cells present there.
- The nasal and respiratory secretions contain muco-polysaccharides which can neutralize influenza and some other viruses.
- Inherited or acquired defect in the function of respiratory cilia or mucous or both make the lungs vulnerable to infection.
c) Mouth, stomach and intestinal tract
- Saliva possesses mild bactericidal action.
- The anaerobic colon bacteria produce fatty acids with antibacterial activity.
- Colonization resistance is offered by the predominant normal flora of the intestine.
- The intestinal anaerobic micro flora prevents the super infection by coliforms during antibiotic therapy.
- The low pH of gastric acid destroys most of the ingested bacteria.
- The conjunctiva is freed of bacteria and dust particles due to the activity of tears.
- Tears flush the eyes which contain lysozyme which is bactericidal in action.
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e) The genitourinary tract
- The flushing action of the slightly acidic urine maintains sterility of both male and female urethra.
- Semen is believed to contain antibacterial substances.
- The acid reaction of the vaginal secretion in female due to fermentation of glycogen by Lactobacillus acidophilus (normal flora) is markedly bactericidal towards most pathogenic microorganisms.
Physico-chemical barriers of innate immunity