Several barriers protect organisms from infection, including mechanical, chemical, and biological barriers. The waxy cuticle of many leaves, the exoskeleton of insects, the shells and membranes of externally deposited eggs, and skin are examples of mechanical barriers that are the first line of defense against infection. However, as organisms cannot be completely sealed from their environments, other systems act to protect body openings such as the lungs, intestines, and the genitourinary tract. In the lungs, coughing and sneezing mechanically eject pathogens and other irritants from the respiratory tract. The flushing action of tears and urine also mechanically expels pathogens, while mucus secreted by the respiratory and gastrointestinal tract serves to trap and entangle microorganisms.
What is a mechanical barrier in insects that protects the insect? What is an example of a mechanical barrier on leaves? What responses protect the lungs by mechanically ejecting pathogens from the respiratory system? What is secreted by the respiratory tract to trap microorganisms? The flushing action of what expels pathogens from the eyes?