I know that the diaphragm expands causing the air to leave the lungs. But what happens when the diaphragm contracts? How does this draw air in to the lungs?
In: Biology
When muscles contract they get shorter. The diaphragm is like an umbrella with the curve cavity on the lower side (facing your internal organs like liver and stomach). If it shortens, it gets flatter, which means the dome part will get lower into your abdomen, this means the space inside your rib cage becomes larger. Your lungs are surrounded by thin layer of fluid that has no access to air or other large movement of fluid. If the thoracic wall is pulled away (bigger cavity in it), the fluid between the wall and the lungs cannot expand, and so the lungs get stretched in many directions too. At the same time, your ribs are like stacked circles that are not horizontal but declined, and when you inhale you flex some muscles that cause the ribs to get more horizontal, so this pulls the ribcage outwards also expanding the space inside it. When you expand the space of any gas filled cavity, the pressure in it drops, and since your lungs are open to the atmosphere when you inhale, dropping the pressure in them forms a pressure gradient so the air rushes from the outside to the lungs. Then you relax the diaphragm and rib cage muscles, ribs fall back to their declined position and the diaphragm dome rises again as that’s it’s physical shape. This decreases the space again, increasing pressure and expelling air out. You can also forcefully exhale by flexing some muscles in your rib cage to force the ribs down stronger and quicker. In general, exhalation is passive, but when you are running and need quick gas exchange for example, you begin to recruit muscles like these.
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