Describe the process of breathing

Breathing begins with inhalation when the contraction of the diaphragm flattens on contraction, pulling the lungs down. The contraction of these muscles increases the volume of the lungs. This reduces the air pressure in the lung to below that of the external air. This pressure difference forces air to move into the lungs where gas exchange occurs. The relaxation of the diaphragm and intercostals reduces the volume of the lungs, which then increases the air pressure inside the lung to that above the external air. This forces air out of the lungs. The cycle goes on and on. Hope this helped!