How does inhaled oxygen go out as carbon dioxide from our body while breathing?
PAVITHRA
Chennai
While we breathe, we inhale oxygen along with nitrogen and carbon dioxide which co-exist in air. The inhaled air reaches lungs and enters alveoli where oxygen diffuses out from alveoli into blood, which enters into lungs via pulmonary capillaries, and carbon dioxide diffuses into alveoli from blood. This simple diffusion happens because of partial pressure difference between oxygen and carbon dioxide in blood and alveoli.
In alveoli, partial pressure of oxygen is relatively higher than carbon dioxide whereas, in the blood which enters in to the lungs, partial pressure of carbon dioxide is higher than oxygen.
Carbon dioxide entered into the alveoli by diffusion will be exhaled by lungs while we breathe. Blood leaving the pulmonary capillaries is rich in oxygen and it goes to the left atrium and pumped by heart into the systemic circulation of our body.
For our body cells to perform various functions, they need energy, and this energy is generated by producing ATP molecules via burning fuel molecules such as carbohydrates using oxygen.
The side product of this reaction is carbon dioxide. So in the body cells, partial pressure of carbon dioxide is higher than oxygen.
Hence, when oxygen rich blood reaches body cells by systemic circulation, because of partial pressure gradient, oxygen will diffuse into the body cells and carbon dioxide will diffuse into blood.
Now the carbon dioxide rich blood will return to the heart (right atrium) and then pumped into lungs. In the lungs, carbon dioxide will be exhaled as explained in the beginning. This process is a cycle and oxygen is taken up and carbon dioxide is released out continuously in our body.
Dr. K. K. CHERALATHAN
Associate Professor
Materials Chemistry Division
School of Advanced Sciences
VIT University, Vellore
