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It depends on what type of organism. A virus acts differently than a bacteria and is harder to treat. Fungi can cause diseases like ringworm. The organism has to overwhelm the persons' lines of defense.

Our bodies are made in such a way as we try to fight off an attack from any thing.

We have several lines of defenses. If the first line is breached, the second has to be overwhelmed and then the third for the organism to infect and cause disease.

First line of defense:

Barriers at the Portal of Entry

Inborn nonspecific barriers

Impede any invasion whether living or dead

Very difficult to penetrate the skin

Flushing effects of sweat, tears, mucous and urine

Anatomical barriers:

1. Skin: Hair follicles, Skin glands

2. Mucous membranes Digestive tract, Urinary tract, Respiratory tract

3. Eye

The trachea contain cilia that entrap and propel particles out of the respiratory tract.

Nonspecific (will act against) all chemical barriers

1.Sebaceous secretions: antimicrobial

2. Eyelid glands - meibomian gland: antimicrobial

3. Tears and saliva - lysozyme (antimicrobial)

4. Acidic pH: Sweat, Stomach, Skin, Semen, Vagina

Genetic (born with) barriers

Different level of sensitivity, resistance and genetic differences to infectious agents: malaria, Tuberculosis, Leprosy, Fungal infections

If and when the first line is breached,

Second line of defense

A cellular and chemical system, Comes immediately in play if first line is breached

Phagocytes engulf all infectious agents they come across, Inflammation helps to localize infections

Third line of defense (takes time)

The development of resistance to infectious agents by the body

Surveillance of the body

Recognition of foreign material

Destruction of foreign material or agent

Involves nonspecific and

Specific immune defense systems

White blood cells (WBCs) or leukocytes are involved

WBC

WBC recognize "self" markers on the host cell

Do not attack or do not respond to host cell (self cells)

WBC recognize "nonself" markers on the invading microbe

Attack or Mark for destruction

WBC do not destroy self cells, while nonself cells are recognized and destroyed.

Systems

All systems are integrated

No single cell is far away from protection no matter how isolated

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12y ago

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