Final answer:
The alveolar walls consist of type I alveolar cells, type II alveolar cells, and alveolar macrophages, supported by connective tissue and elastic fibers. These structures facilitate gas exchange by providing a large surface area and a thin respiratory membrane for simple diffusion of oxygen into the blood and carbon dioxide out of the blood.
Step-by-step explanation:
The composition of the alveolar walls and the surrounding connective tissue is crucial for gas exchange in the lungs. The alveolar wall primarily comprises three types of cells: type I alveolar cells, type II alveolar cells, and alveolar macrophages. Type I alveolar cells are squamous epithelial cells covering about 97% of the alveolar surface area and are essential for gas permeability due to their thinness at approximately 25 nm.
Additionally, the alveoli are surrounded by a network of connective tissue that includes elastic fibers and a smooth muscle lining known as the alveolar ducts. This connective tissue provides structural support and is crucial for maintaining the shape and function of the alveoli during the breathing process. The alveoli themselves are tiny sacs, each approximately 200 µm in diameter, with elastic walls that stretch during air intake to increase the surface area for gas exchange. They are interconnected through alveolar pores, ensuring equal air pressure throughout the lungs.
The respiratory membrane, formed by the alveolar and capillary walls, is approximately 0.5 µm thick and enables simple diffusion of gases. This proximity of capillaries to the alveoli allows oxygen from the air to be absorbed into the bloodstream and permits carbon dioxide to be expelled from the blood into the alveoli, to be exhaled out of the body.