20.1: Physical Defenses Overview
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- Ying Liu
- City College of San Francisco
Learning Objectives
- Describe the various physical barriers and mechanical defenses that protect the human body against infection and disease
- Describe the role of microbiota as a first-line defense against infection and disease
Nonspecific innate immunity can be characterized as a multifaceted system of defenses that targets invading pathogens in a nonspecific manner. In this chapter, we have divided the numerous defenses that make up this system into three categories: physical defenses , chemical defenses , and cellular defenses . However, it is important to keep in mind that these defenses do not function independently, and the categories often overlap. Table \(\PageIndex{1}\) provides an overview of the nonspecific defenses discussed in this chapter.
| Overview of Nonspecific Innate Immune Defenses | |
|---|---|
| Physical defenses | Physical barriers |
| Mechanical defenses | |
| Microbiome | |
| Chemical defenses | Chemicals and enzymes in body fluids |
| Antimicrobial peptides | |
| Plasma protein mediators | |
| Cytokines | |
| Inflammation-eliciting mediators | |
| Cellular defenses | Granulocytes |
| Agranulocytes |
Physical defenses provide the body’s most basic form of nonspecific defense. They include physical barriers to microbes, such as the skin and mucous membranes, as well as mechanical defenses that physically remove microbes and debris from areas of the body where they might cause harm or infection. In addition, the microbiome provides a measure of physical protection against disease, as microbes of the normal microbiota compete with pathogens for nutrients and cellular binding sites necessary to cause infection.
Interactive Element
Drag the different components of the innate immune defenses into their corresponding category.
Key Concepts and Summary
- Nonspecific innate immunity provides a first line of defense against infection by nonspecifically blocking entry of microbes and targeting them for destruction or removal from the body.
- The physical defenses of innate immunity include physical barriers, mechanical actions that remove microbes and debris, and the microbiome, which competes with and inhibits the growth of pathogens.
- The skin, mucous membranes, and endothelia throughout the body serve as physical barriers that prevent microbes from reaching potential sites of infection. Tight cell junctions in these tissues prevent microbes from passing through.
- Microbes trapped in dead skin cells or mucus are removed from the body by mechanical actions such as shedding of skin cells, mucociliary sweeping, coughing, peristalsis , and flushing of bodily fluids (e.g., urination, tears)
- The resident microbiota provide a physical defense by occupying available cellular binding sites and competing with pathogens for available nutrients.