How do the body's lungs work? Get a brief overview of how our lungs do their job. The explanations are accompanied by diagrams.

What do you know about the circulatory system? This site features several links to help you increase your knowledge of this fascinating human body system.

This lesson goes over the parts of the human respiratory system and the gas exchange process that occurs in the lungs. It also covers changes in the respiratory system that occur during spaceflight, such as decreased lung capacity.

This feature from the NOVA: "Cut to the Heart" highlights facts about the heart, including its size and placement, and will help you to understand the importance of this wondrous organ in our bodies.

This article, written for younger readers, explains cystic fibrosis (CF), an inherited disease that causes the body to produce mucus that's extremely thick and sticky.