Respiration

When we breathe in our diaphragm contracts, our chest expands and air is drawn in through our mouth and nose. An adult breathes in and out around 12-20 times per minute on average.

This air travels down through our trachea and enters each lung through the bronchi, which are two tubes that split from the trachea, one for each of our lungs.

The bronchi then continue to split into smaller and smaller tubes in much the same way a tree’s branches expand from the trunk and the air we breathe in continues to fill each of these tubes. These smaller tubes are called bronchioles.

At the end of each bronchiole are spongy, air-filled sacs called alveoli and each adult lung contains around 600 million of these. The alveoli are surrounded by extremely small capillaries which transport blood in and out of the lungs with each heart beat. Oxygen from the air that we breathe in passes from the alveoli into the capillaries and is then taken to the heart and transported around the body for use through our arteries. Approximately 25% of the available oxygen is used by our bodies due to our lungs only being able to process so much with each breath.

In reverse, waste carbon dioxide from our bodies is returned in our blood back to the lungs through our veins, passed back into our alveoli and then exhaled when we breathe out.