The Human Respiratory System

by Karthik Gurumurthy

To blow up a balloon, sing a song or chase a butterfly, humans rely on the help of their lungs.

Your lungs sit inside your rib cage. They expand as they fill with air and contract as they expel it. The movement of your diaphragm, a large, dome-shaped muscle under your lungs, helps you breathe. This muscle pulls down downward to create the extra space the lungs need to expand and fill with air. Then the diaphragm relaxes and moves back up, shoving the air out of the lungs and making them smaller again.

As air enters your mouth and nose, it goes down a tube called the trachea, or windpipe. Inside your rib cage, the trachea splits into two tubes called bronchi- one for each lung. These branch into smaller and smaller tubes, filling all parts of the lung with air. At their very ends are thin air sacs called alveoli that look like tiny bunches of grapes. Oxygen passes through these sacs and catches a ride to all parts of the body in the bloodstream, the main liquid transportation system of the body. Red blood cells take oxygen from the alveoli and drop off carbon dioxide picked up from the cells. When you exhale, you push out unused air and carbon dioxide through the same tubes the oxygen used to come in.

Some animals are efficient breathers. They take in a lot of oxygen each time they inhale. A wolf can run for miles without having to stop and “catch its breath.” Other animals are less efficient. The lion, although fast, gets easily “out of breath” because its body does not take in enough oxygen with each breath to maintain its pace for long.