Cystic Fibrosis Physiology of How Breathing Works By Lori Alma Lori Alma Lori Alma, RN, is a registered nurse and cystic fibrosis expert who assists families in a Florida Department of Health program for special needs children. Learn about our editorial process Medically reviewed by Sanja Jelic, MD Medically reviewed by Sanja Jelic, MD on April 18, 2020 Sanja Jelic, MD, is board-certified in sleep medicine, critical care medicine, pulmonary disease, and internal medicine. Learn about our Medical Review Board on April 18, 2020 Print The first stage of breathing, inhaling air into your lungs, is called inspiration or inhalation. Inspiration happens because of a large breathing muscle called the diaphragm, which is located underneath the lungs in the ribcage. 1 The Breathing Muscles Matthias Tunger/Getty Images When you inhale, the diaphragm and muscles between your ribs contract, creating a negative pressure—or vacuum—inside your chest cavity. The negative pressure draws the air that you breathe into your lungs. 2 Inflation of the Lungs ZEPHYR/SCIENCE PHOTO LIBRARY/Getty Images Lungs are not hollow like balloons but are made of spongy, flexible tissue that inflates when filled with air. So, how does the air get in there? Where does it go? Let’s follow a breath of air from start to finish. 3 Taking a Breath Westend61/Getty Images When you take a breath, the air goes in through your nose and mouth and travels down your throat, through your voice box and into the trachea, which is also known as the windpipe. 4 Entering the Lungs ALFRED PASIEKA/SCIENCE PHOTO LIBRARY/Getty Images The end of your trachea splits into an upside down Y-shape and forms the bronchi. Air passes through either the right or left bronchus into both sides of the lungs. 5 Entering the Bronchial Tree PIXOLOGICSTUDIO/SCIENCE PHOTO LIBRARY/Getty Images Inside of the lungs, the bronchi branch off into bronchioles, which look similar to branches of a tree. Read what paradoxical breathing is and how to treat it. 6 Branching out Into Bronchioles MedicalRF.com/Getty Images The air flows through the bronchioles, which keep getting smaller until the air reaches the ends of the branches. 7 Filling up Air Pockets PIXOLOGICSTUDIO/Getty Images At the ends of the bronchioles are clusters of little pockets that collect the air, called alveoli. 8 Gas Exchange Dorling Kindersley/Getty Images When the air reaches the alveoli, oxygen diffuses through the membrane into small blood vessels called capillaries, and carbon dioxide diffuses from the blood in the capillaries into the alveoli. 9 Blowing It All Out Mark Bolton/Getty Images The second stage of breathing, blowing air out of the lungs, is called expiration or exhalation. After the oxygen and carbon dioxide trade places in the alveoli, the diaphragm relaxes and positive pressure is restored to the chest cavity. This forces the used air out of the lungs, following the reverse of the path that it used to get in the lungs. The entire breathing process is repeated 10 to 20 times per minute in a healthy adult. Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Cleveland Clinic. Vital Signs. Updated January 23, 2019.