The lungs are one of the most vital components of the human body. They are used every second of the day and without them, we would die in 4-6 minutes. The lungs are located in the thoracic cavity behind your pectoral muscles and behind your ribs. Within the Thoracic cavity, there are two pleural cavities. Each pleural cavity contains one lung. The pleural cavity is created by two membranes and a fluid called pleural fluid. Combined, these structures make it easier for the lungs to expand and contract during inhalation and exhalation.
Within the lungs, there is a combination of many structures that carry air from your oral and nasal airways. These include the bronchi, bronchioles, and alveoli (the major ones). The bronchi is one major airway that brings air to both lungs. The bronchioles are tree-like structures that branch from the bronchi. Finally, the alveoli are the tiny ball-like structures at the end of the bronchioles that oxygen and carbon dioxide transfer through its membrane.
So, we all know how to breathe but, do you know what is actually going on in your body? Breathing is a combination of multiple muscles contracting and relaxing. When breathing in your diaphragm will contract. This increases the volume of the thoracic cavity and thus decreases the pressure of the lungs. When this occurs, the pressure outside of your mouth is higher than in your body. The difference in pressures causes a rush of air through your nasal and oral cavities and into your lungs to try and make the pressures the same. Other muscles that aid in this decrease of pressure include the ribs and intercostal muscles.
When exhaling, the same muscles relaxed and the muscles between the ribs contract, making the volume of the thoracic cavity decrease. This decreased volume causes an increase in pressure and for the same reason air enters your lungs, it will now leave your lungs.