Final answer:
The alveolus is a small, elastic structure integral to the lungs' gas exchange process. Each alveolus has thin walls and exists in clusters within alveolar sacs, optimized to maximize the surface area for oxygen and carbon dioxide diffusion with the bloodstream.
Step-by-step explanation:
Development, Structure, and Function of the Alveolus
The alveolus is a critical component of the human respiratory system, specifically designed for gas exchange. Each alveolus is approximately 200 to 300 micrometers in diameter and has elastic walls, allowing it to stretch during air intake. This elasticity increases surface area, which is crucial for exchanging oxygen and carbon dioxide effectively. The walls of an alveolus are composed mainly of three types of cells: the type I alveolar cells, which make up most of the alveolar surface area and are extremely thin to facilitate the easy transfer of gases; the type II alveolar cells, which produce pulmonary surfactant to reduce surface tension; and alveolar macrophages, which patrol the alveolar surface to remove debris and pathogens.
Alveoli are grouped into clusters known as alveolar sacs, connected by alveolar ducts to the respiratory bronchioles. The end of each bronchiole leads to these ducts, which then open into clusters of alveoli. Alveoli are directly in contact with the capillaries of the circulatory system, with their thin, one-cell-thick walls being contiguous with the one-cell-thick capillary walls. This arrangement allows for the rapid diffusion of oxygen into the blood and carbon dioxide out of the blood into the alveoli.
The vast number of alveoli, approximately 300 million per lung, and their arrangement into sacs leads to a spongy lung texture and a large surface area—comparable to the size of a tennis court—for gas exchange. The extensive surface area, coupled with the thin barrier between alveolar air and blood, ensures that gas exchange in the lungs is efficient and effective.