Question

Short / long answer type questions.
Oxygen enters the blood from the alveolar air but carbon dioxide leaves the blood to enter the alveolar air. Explain.

Answer 1

• Gaseous exchange at alveoli essentially occurs as a result of diffusion down a concentration gradient.
  
• Inhaled oxygen is able to diffuse into the capillaries from the alveoli while carbon dioxide from the blood diffuses in the opposite direction into the alveoli. Differences in partial pressure of oxygen create a gradient that causes oxygen to move from the alveoli to the capillaries and into the tissues.
  
• Oxygen and carbon dioxide move independently of each other.