The removal of microbes and debris from the respiratory tract through the expulsion of mucus by respiratory cilia and subsequent mechanical actions of coughing, swallowing, or sneezing. Disruption of this escalator leads to an increased frequency of bacteria in the respiratory tract and constant infections.

Mucociliary Escalator

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.

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Innate Immune Physical Barrier: The Skin Barrier

The flushing of urine out the body keeps the urinary tract sterile by washing out microbes that may take up residence. For the eyes, if microbes get past the initial barriers of eyelashes and eyelids, they can get flushed out with tears via blinking.

Innate Immune Mechanical Defenses: Urine and Tear Flushing

A nonspecific innate immune mechanical defense of the digestive tract that protects against ingested microbes. The digestive system contracts to move mucus mixed with stomach material, including trapped microbes, through the intestines, rectum, and anus until final expulsion from the body in feces.

Peristalsis

Types of mechanical defenses in innate immune physical defenses include:
- Skin shedding
- Mucociliary escalator
- Peristalsis
- Flushing action of urine and tears

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Types of physical defenses in the innate immune response include:
- Physical barriers
- Mechanical defenses
- Microbiome

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Types of Innate Immune Physical Defenses

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Physical Defenses of Nonspecific Innate Immunity (Table 17.2). Reprinted from OpenStax Microbiology (p. 691), by N. Parker, M. Shneegurt, A.-h. Thi Tu, B. M. Forester, and P. Lister, 2016, Rice University. Copyright 2016 by Rice University.

Physical Defenses of Nonspecific Innate Immunity Table

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

Innate Immune Physical Defenses: Types of Mechanical Defenses

Resident microbiota can serve to protect the body against harmful pathogens, such as by competing with opportunistic pathogens (taking up binding sites and competing for resources) prevents pathogen attachment and proliferation. They can also contribute to chemical defenses. The disruption of microbiota can increase susceptibility to infection.

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