<h2>Protective Mechanisms</h2>
<p>The air that organisms breathe contains <strong>particulate matter</strong> such as dust, dirt, viral particles, and bacteria that can damage the lungs or trigger allergic <a data-lesson="disruptions-in-the-immune-system" data-subject="biology" data-tutorial="immune-system" href="https://app.ulearngo.com/biology/immune-system/disruptions-in-the-immune-system">immune</a> responses. The <a data-lesson="respiratory-system" data-subject="biology" data-tutorial="human-biology" href="https://app.ulearngo.com/biology/human-biology/respiratory-system">respiratory system</a> contains several protective mechanisms to avoid problems or <a data-lesson="summarizing-the-plant-body" data-subject="biology" data-tutorial="plant-form-and-physiology" href="https://app.ulearngo.com/biology/plant-form-and-physiology/summarizing-the-plant-body">tissue</a> damage. In the nasal cavity, hairs and mucus trap small particles, viruses, bacteria, dust, and dirt to prevent their entry.</p>
<p>If particulates do make it beyond the nose, or enter through the mouth, the bronchi and bronchioles of the lungs also contain several protective devices. The lungs produce <strong>mucus</strong>—a sticky substance made of <strong>mucin</strong>, a complex glycoprotein, as well as salts and water—that traps particulates. The bronchi and bronchioles contain cilia, small hair-like projections that line the walls of the bronchi and bronchioles (see the figure below). These cilia beat in unison and move mucus and particles out of the bronchi and bronchioles back up to the throat where it is swallowed and eliminated via the esophagus.</p>
<p>In humans, for example, tar and other substances in cigarette smoke destroy or paralyze the cilia, making the removal of particles more difficult. In addition, smoking causes the lungs to produce more mucus, which the damaged cilia are not able to move. This causes a persistent cough, as the lungs try to rid themselves of particulate matter, and makes smokers more susceptible to respiratory ailments.</p>
<div class="wp-caption alignnone" style="width: 544px"><img alt="In this micrograph, cilia are long, thin, hairlike projections." height="544" src="https://data.ulearngo.com/assets/ce01674c-b4f9-42c1-b21d-b929cfffa62e" width="544"/><p class="wp-caption-text">The bronchi and bronchioles contain cilia that help move mucus and other particles out of the lungs. (credit: Louisa Howard, modification of work by Dartmouth Electron Microscope Facility)</p></div>

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Protective Mechanisms

Biology studies life and living organisms. Biology can be divided into different sections that cover the morphology, physiology, anatomy, behavior, and so on of living organisms.

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Discover the principles and mechanics of gas exchange, the various respiratory surfaces and protective mechanisms, and the transport of oxygen and carbon dioxide in human bodily fluids in this tutorial on the respiratory system.


Protective Mechanisms

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