What is the primary site for gas exchange in the respiratory system?

What is the primary site for gas exchange in the respiratory system?

• A. Alveoli
• B. Dead space
• C. Ventilation
• D. Respiration

Answer: (A)

Gas exchange happens where air meets blood most intimately: the alveoli. These tiny air sacs in the lungs have walls that are exceedingly thin and surround a dense network of capillaries, giving a very large surface area for diffusion. Oxygen in the alveolar air diffuses across the alveolar–capillary membrane into the blood, while carbon dioxide diffuses from the blood into the alveolar air to be exhaled. This efficient exchange is aided by a thin barrier formed by the alveolar epithelium and the capillary endothelium, plus surfactant that keeps the alveoli open so diffusion can happen readily. Dead space refers to portions of the airways where no exchange occurs, ventilation is the process of moving air in and out, and respiration can refer to cellular processes or the broader act of gas exchange, but the actual site of gas exchange is the alveoli.

Gas exchange happens where air meets blood most intimately: the alveoli. These tiny air sacs in the lungs have walls that are exceedingly thin and surround a dense network of capillaries, giving a very large surface area for diffusion. Oxygen in the alveolar air diffuses across the alveolar–capillary membrane into the blood, while carbon dioxide diffuses from the blood into the alveolar air to be exhaled. This efficient exchange is aided by a thin barrier formed by the alveolar epithelium and the capillary endothelium, plus surfactant that keeps the alveoli open so diffusion can happen readily. Dead space refers to portions of the airways where no exchange occurs, ventilation is the process of moving air in and out, and respiration can refer to cellular processes or the broader act of gas exchange, but the actual site of gas exchange is the alveoli.