Unit D

Module 9 ~ Lesson 1


In this lesson, you explored the following question:

  • How do the principal structures of the respiratory system act to exchange matter and transfer thermal energy between the body and the external environment?

The respiratory system is a sophisticated exchange system. From the nose to the alveoli, energy and matter exchanges occur. An inhalation may contain foreign objects, such as dust, pollen, or germs, that are filtered out by cilia and mucus that line the respiratory tract from the nose to the bronchioles. By the time the inhaled air reaches the alveoli, the only substance present and ready to diffuse into the bloodstream is oxygen.

Alveoli, or air sacs, also collect carbon dioxide that diffuses from the bloodstream. Carbon dioxide moves from millions of alveoli through the bronchioles, to the bronchi, then the trachea, and finally to the nose or mouth in every exhalation. The mechanics of breathing are controlled by air pressure and the need to get rid of carbon dioxide. As cellular respiration proceeds in your cells, carbon dioxide build-up occurs.

There are several parts to your breath as demonstrated by a spirograph. Breathing is a continuous process that is cyclic.


chemoreceptor: detects chemical stimuli in the environment and turns stimuli into electrical nerve impulses that signal parts of the body to respond accordingly

cilia: small, hairlike organs on the surface of some cells, particularly cells lining the upper respiratory tract; wavelike movements waft particles of dust and debris outward; Latin for "eyelash"