Tight cell junctions of the blood vessel endothelia of the central nervous system, which prevent microbes from entering the bloodstream leading to the brain and cerebrospinal fluid. Infection of the CNS can lead to fatal inflammation.

Blood-Brain Barrier

Epithelial cells that line the blood and lymphatic vessels, urogenital tract, and other tissues which defends against invading microbes.

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Types of physical barriers in innate immune physical defenses include:
- The skin barrier
- Mucous membranes
- Endothelial cells

Innate Immune Physical Defenses: Types of Physical Barriers

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The skin barrier is made up of three closely packed cell layers: the epidermis, dermis, and hypodermis (upper to bottom layer). The epidermis  consists of keratin, which provides mechanical strength to the skin surface, preventing enzymatic degradation. The acidic environment of the surface also prevents bacterial degradation and inhibits microbial growth. Skin shedding also sheds microbes on the skin surface. Damage to the skin barrier allows for pathogens to enter into deeper tissue.

(Photo credits in References)

Innate Immune Physical Barrier: The Skin Barrier

Membranes lining the nose, mouth, lungs, and urinary and digestive tracts consisting of epithelial cells - bound together by tight junctions - that secrete mucus. The mechanical movement of mucus moves microbes away from potential sites of infection.

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