The Respiratory System
Start with the complete respiratory system and learn what the airways, lungs, and breathing muscles are doing together.
What makes up the system?
The respiratory system consists of the airways, the lungs, and the muscles of breathing. Together they move air into and out of the body and exchange oxygen and carbon dioxide with the blood.
The respiratory system as a network
Air moves through the airways into the lungs, where gas exchange connects breathing to the bloodstream.
The pathway
The nose, pharynx, larynx, trachea, and bronchi carry air to and from the lungs.
The gas-exchange organs
The lungs contain millions of alveoli where oxygen and carbon dioxide are exchanged with the blood.
The pump
The diaphragm and intercostal muscles change the volume of the chest cavity to move air in and out.
The transport link
The circulatory system carries oxygen from the lungs to the body's tissues and returns carbon dioxide for exhalation.
Breathing connects two systems.
The respiratory and circulatory systems work together: one moves air, the other moves the gases air carries.
Two phases of breathing
Breathing is usually described in two phases: inhalation, when air moves into the lungs, and exhalation, when air moves out. Together they form the breathing cycle.
Follow the breath
A useful way to understand the system is to follow one breath. Air enters through the airways, reaches the alveoli in the lungs, and oxygen crosses into the blood while carbon dioxide crosses out to be exhaled.
Breathing is a continuous cycle, not a single event.
The respiratory system continuously cycles air in and out to keep gas exchange going as long as the body is alive.