1 minute read
Airway Defense Mechanisms
hemoglobin in the alveoli and gets passed through to the outside of the body during exhalation.
The Haldane effect determines the affinity of hemoglobin for oxygen and carbon dioxide. Hemoglobin that is completely saturated with oxygen will not easily bind to carbon dioxide. When oxygen is not bound to the hemoglobin molecule, hemoglobin will rapidly bind to carbon dioxide.
Advertisement
AIRWAY DEFENSE MECHANISMS
There are aspects of the airways that defend against pathogens and debris. The bifurcation of the airway and the anatomy of the nasopharynx will not allow foreign particles greater than 2 to 3 micrometers in diameter to pass through to the lower airways. Coughing generates turbulence that also defends the lower airways. Cilia in the respiratory tract beat upward to get rid of debris in the airways. Mucus gel in the airways will prevent pathogenic bacteria from entering the lungs.
Secretory IgA made by the immune system will bind and neutralize viruses and toxins and will prevent the passage of bacteria across the airway epithelium. A nonspecific barrier to pathogens is the presence of lactoferrin, lysozyme, and peroxide in the airways. Lactoferrin is bactericidal and peroxides act as oxygen free radicals to kill or stop bacteria. Lysozyme will kill bacteria and is made from macrophages or neutrophils in the lungs.
Epithelial cells act as a mucosal barrier. They are adherent to one another through several junctions, preventing the passage of pathogens. Pathogens that get through can be killed by phagocytic dendritic cells just beneath the epithelial basement membrane. They can take up antigens and migrate to the lymph nodes of the lungs, where they activate T cells, which are specific to a particular antigen. Eosinophils, basophils, and mast cells contribute to the activation of the respiratory tract in allergic diseases.
Within the alveoli, the type I cells and type II cells play a minor role in the immune system milieu of the alveoli. Surfactant will contribute to the human host lung defenses and enhance the killing of microbes. Alveolar macrophages are phagocytic cells that provide the major first line of defense against things that enter the alveoli. It is the job
