AP BIOLOGY

Detailed explanation-1: -Type I pneumocytes cover 70% of the internal surface of each alveolus. These cells are thin and squamous, ideal for gas exchange. They share a basement membrane with pulmonary capillary endothelium, forming the air-blood barrier where gas exchange occurs.

Detailed explanation-2: -The type I cell is a complex branched cell with multiple cytoplasmic plates that are greatly attenuated and relatively devoid of organelles; these plates represent the gas exchange surface in the alveolus. On the other hand, the type II cell acts as the “caretaker” of the alveolar compartment.

Detailed explanation-3: -Type 1 pneumocytes are alveolar cells that line the alveolar surface. Type 2 pneumocytes are alveolar cells that secrete surfactant proteins to reduce surface tension.

Detailed explanation-4: -The alveolar sacs are lined by the squamous type alveolar type I cells (or type I pneumocytes) and cuboidal alveolar type II (or type II pneumocytes) cells.

Detailed explanation-5: -The alveolus is composed of alveolar epithelial type 1 cells, alveolar epithelial type 2 cells and capillary cells. Type 1 cells are large, squamous epithelial cells that cover  95% of the alveolar surface area. Type 2 cells produce surfactant and play a role in maintenance of lung fluid balance.