Introduction: Most animals need air in order to survive. They take in air through specialized structures called lungs or gills. Once inside, other specialized structures remove the oxygen from that air so that it can be transported around the body. At the same time, carbon dioxide is transferred from the organism's blood to the lungs or gills so that it can be removed from the body. This is called breathing and is the primary function of the respiratory system.

While all animals have some form of respiratory system, this lesson will focus on the human animal. As seen in the diagram below, the respiratory system starts with the nose (A) and mouth (B), where air is inspired. From here, it travels through a network of tubes, the first of which is called the pharynx (G). It then travels through the larynx (C), which is where the voice box is located. It then moves through branching tubes called bronchi (E) and bronchioles (J), until it reaches deep within the lungs (D). In the lungs, there are tiny structures called alveoli (K) that contain a large network of capillaries. It is through these capillaries that gas exchange takes place.

Capillaries are also connected to the circulatory system. This is a good thing because the body needs the blood in it to transport the oxygen and carbon dioxide around the body.

The inspiration and exhalation of air is due to pressure gradients between the lungs and the external environment. To drive this pressure, there is also another thin tissue called the diaphragm (F) that moves up and down to cause the lungs to expand or contract. Professional singers practice controlling their diaphragms so they will have better airflow to hit high notes or hold notes longer.

Directions for this Lesson: Answer the practice questions and then watch the videos to learn more about the respiratory system.