1. Inspiration: During inspiration, we breathe in air from the atmosphere, which contains approximately 0.04% carbon dioxide. This air enters the lungs through the nose or mouth, and it travels down the trachea and into the bronchi. The bronchi divide into smaller branches called bronchioles, which lead to the alveoli, which are tiny air sacs where gas exchange takes place.
2. Expiration: Once the air reaches the alveoli, oxygen from the air passes into the bloodstream through the capillaries that surround the alveoli. At the same time, carbon dioxide from the bloodstream moves into the alveoli to be expelled from the body. The concentration of carbon dioxide in the alveoli is higher than that in the atmosphere, so the carbon dioxide moves down its concentration gradient and diffuses from the alveoli into the air in the lungs.
When we exhale, the air that we breathe out contains a higher concentration of carbon dioxide (approximately 4%) and a lower concentration of oxygen (approximately 15%) compared to the air that we breathe in. This difference in gas concentrations is due to the process of respiration, where oxygen is taken up by the body and carbon dioxide is released as a waste product.
