Lesson 11: The Respiratory System (page 5 of 19)

Another name for the larynx is the voice box.

Trachea The trachea, or windpipe, divides into two principal bronchi (plural for bronchus) as it enters the lungs. The principal bronchi are further divided into smaller and smaller bronchi. When the bronchi become inflammed, a condition results which is referred to as bronchitis [bronchi + -itis, inflammation].Further divisions of the bronchi eventually lead to tiny tubes, called bronchioles, which lead to tiny air sacs known as alveoli. The alveoli are richly supplied with capillaries where the exchange of gases takes place between the red blood cells and the air. When the alveoli become inflammed due to an infection, a condition results which is referred to as pneumonia. Pneumonia can be viral or bacterial in nature and can also result from yeast or fungus infections.


The bronchial branches contain smooth muscle which is under the control of the autonomic (automatic) nervous system. Stimulation from the sympathetic division of the autonomic nervous system causes these smooth muscles to relax, dilating the bronchial branches allowing more air to pass through the lungs. This is what happens during the “fight or flight” response. When danger is perceived, the sympathetic nervous system is stimulated to prepare the body for immediate action. In the case of the lungs, this means allowing more air through so that more oxygen will be available for muscle contraction (to either fight or run away from the danger).When the parasympathetic division of the autonomic nervous system is stimulated, the smooth muscles of the bronchial branches contract, causing constriction of the bronchial branches allowing less air through the lungs. Normally the two divisions of the autonomic nervous system are in balance, but imbalances can occur. Overstimulation of the parasympathetic nervous system can cause such constriction of the airways that breathing becomes difficult, resulting in asthma (Greek for “gasping.”)

During the “fight or flight” response, stimulation from the sympathetic division of the autonomic nervous system causes the bronchial tubes to _________, allowing more air through the lungs.



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