Question

*in the lungs , the diffusing particles are oxygen and carbon dioxide and the compartmants involved are the air sacs (alveoli) of the lungs and the capillaries of the pulmonary circulation . the body uses oxygen and produces carbon dioxide as waste material . in which directions , relative to the blood and air sac compartmants will each of these substance move? why ?

Answer 1

When we fill our lungs with air, the oxygen present in the inhaled air will flow down from alveoli into the blood and then it enters the interstitial fluid and reaches the body cells and fulfills their oxygen need.

When it comes to carbon dioxide, it will diffuses in the opposite directions, from the cells of the body, it gains access into the interstitial fluid, from there to blood and reaches the alveoli and all occurs following the concentration gradient. And the movement of these gases is based on Dalton's law (as each gas present in the mixture will try to exert own pressure irrespective of the presence of other gases). Partial pressure of oxygen will keep it diffusing all the time into the body cells as the oxygen cannot reach equilibrium because of its continuous usage by the cells. The carbon dioxide will try to move in the opposite direction along a partial pressure gradient and gets eliminated from the body.