Which of the following provide the greatest surface area for gas exchange?
A respiratory bronchioles.
B terminal bronchioles.
C alveolar ducts.
D alveoli.
The correct answer and explanation is:
The correct answer is D. alveoli.
Alveoli are the primary sites of gas exchange in the lungs. These small, sac-like structures are located at the ends of the respiratory tree and have a vast surface area. They provide the greatest surface area for gas exchange due to their large number and structure. The total surface area for gas exchange in the lungs is estimated to be around 70-100 square meters in an adult, which is roughly the size of a tennis court.
Alveoli are lined with a thin layer of epithelial cells that are only one cell thick. This facilitates the efficient diffusion of gases such as oxygen and carbon dioxide between the alveolar air and the capillaries surrounding them. The large surface area of the alveoli ensures that a substantial amount of gas can be exchanged quickly, meeting the body’s oxygen demands.
The alveoli are also covered by a network of capillaries, which are the smallest blood vessels in the body. The close proximity of alveolar walls to the capillary walls creates a short diffusion distance for gases. Oxygen moves from the alveolar air into the blood, while carbon dioxide moves from the blood into the alveoli to be exhaled.
In comparison, structures like respiratory bronchioles, terminal bronchioles, and alveolar ducts, although involved in the passage of air, do not provide as large a surface area for gas exchange as the alveoli. These structures are more involved in the conduction of air, and their surfaces are either too thick or not designed for gas exchange in the same way that alveoli are. Thus, alveoli are the most specialized and efficient for the function of gas exchange in the lungs.