Our body systems work together in a coordinated way to get oxygen into the body and deliver it to tissues, while removing carbon dioxide, a waste product. Here’s how this process occurs step-by-step:
1. Respiratory System: Bringing Oxygen In and Removing Carbon Dioxide
- When you breathe in, air enters through the nose or mouth, travels down the trachea, and into the lungs via the bronchi and smaller bronchioles until it reaches tiny air sacs called alveoli
- The diaphragm and rib muscles expand the chest cavity to pull air into the lungs
- In the alveoli, oxygen from the air diffuses across a very thin barrier into the surrounding capillaries (tiny blood vessels), while carbon dioxide diffuses from the blood into the alveoli to be exhaled
- This gas exchange occurs because oxygen moves from an area of higher concentration in the alveoli to lower concentration in the blood, and carbon dioxide moves in the opposite direction
2. Cardiovascular System: Transporting Oxygenated Blood
- Oxygen binds primarily to hemoglobin molecules inside red blood cells, which carry about 98% of the oxygen in blood; a small amount dissolves in plasma
- Oxygen-rich blood travels from the lungs to the left side of the heart via the pulmonary veins
- The heart pumps this oxygenated blood through arteries to tissues throughout the body
3. Cellular Level: Oxygen Delivery and Carbon Dioxide Removal
- In body tissues, oxygen is released from hemoglobin and diffuses into cells where it is used for metabolism, producing energy (ATP) through oxidative phosphorylation
- Cells produce carbon dioxide as a waste product, which diffuses into the blood
- Carbon dioxide is mostly converted into bicarbonate inside red blood cells, which helps transport it back to the lungs
4. Return of Deoxygenated Blood and Carbon Dioxide to the Lungs
- Carbon dioxide-rich, oxygen-poor blood returns to the right side of the heart through veins
- The heart pumps this blood through the pulmonary artery back to the lungs
- In the lungs, carbon dioxide is converted back from bicarbonate and expelled during exhalation
5. Additional Supportive Mechanisms
- The kidneys produce erythropoietin (EPO) in response to low oxygen levels, stimulating the bone marrow to produce more red blood cells to increase oxygen-carrying capacity
In summary, the respiratory system brings oxygen into the lungs and removes carbon dioxide, the cardiovascular system transports oxygenated blood to tissues and returns deoxygenated blood to the lungs, and the cellular processes use oxygen for energy and produce carbon dioxide as waste. These systems work seamlessly to ensure oxygen is continuously delivered and carbon dioxide removed, sustaining life
