Module 7 Intro

Module 7—The Digestive and Respiratory Systems

Lesson Summary

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 your nose to the alveoli in your lungs, energy and matter exchange occur. An inhalation may contain foreign objects. These objects, such as dust, pollen, or germs, are filtered out by cilia and mucus that line the respiratory tract from the nose to the bronchioles. By the time 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, trachea, and finally to the nose or mouth in every exhalation. You were able to see these structures through various animations and a virtual dissection. The mechanics of breathing are controlled by air pressure and the need to get rid of carbon dioxide. As cellular respiration proceeds, carbon dioxide builds up.

Your body has chemoreceptors that are sensitive to changes in carbon dioxide levels. Nerve messages are relayed to the brain and then back to the muscle that controls breathing—the diaphragm. In a relaxed shape, the diaphragm is curved up toward the lungs.

As the diaphragm contracts, space or volume increases in the chest cavity. This decreases the pressure inside the chest cavity and makes the internal pressure lower than the air pressure in the external environment. In order to restore equilibrium, air moves from areas of high pressure to low pressure. As a result, you inhale.

As you inhale, the pressure within the chest cavity increases so that it becomes greater than the external air pressure. In order to restore equilibrium, air moves from areas of high pressure to low pressure. As a result, you exhale. Your diaphragm has also been signaled to relax by higher levels of carbon dioxide.

You also learned that there are several parts to your breath as determined by a spirograph. Breathing is a continuous process that is cyclic. You can control how you breathe, but you cannot control if you breathe.

Your respiratory system also plays another role in maintaining equilibrium through energy exchange. As heat is produced in cellular respiration, it is transported by the circulatory system. Heat dissipates into the lungs and is transferred to the external environment with each exhalation.

While this lesson looked primarily at the respiratory system as an individual body system, it should be noted that there are many other systems involved in ensuring that the respiratory system works to maintain homeostasis.

Lesson Glossary

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

Their wavelike movements waft particles of dust and debris outward; Latin for “eyelash.”