The breath passes through the nose and trachea into the lungs. This is where gas exchange takes place. Oxygen is absorbed into the blood from the alveoli. Carbon dioxide is discharged from the blood to the lungs and then exhaled. Oxygen is necessary as it produces energy in our body cells via combustion. Carbon dioxide is produced here as a waste product.
Our most important respiratory muscle is the diaphragm. It separates the chest, which is where the lungs and heart are, from the abdominal cavity and the digestive organs. It is dome-shaped. During inhalation, the diaphragm contracts, which lowers the dome. The abdominal organs are pressed into the pelvis and against the abdominal walls, which are thus widened. Because a vacuum is created in the lungs, air is drawn. The lungs fill up. When exhaling, the abdominal walls and diaphragm return to their previous state. The lungs empty.
In addition, muscles contract between the ribs, causing the chest to rise and expand. This helps inhalation. When exhaling, the chest relaxes again.
This means that when we breathe, we alternate between wide and narrow. We see how our whole body vibrates when we breathe.