Explain in what ways the structure of an alveolar type 1 cell is adapted to its function.
Alveolar type 2 cells secrete pulmonary surfactant into the watery fluid that lines the alveolus. The surfactant lowers the fluid’s surface tension so that the alveolus does not collapse. Pulmonary surfactant is a mixture of phospholipids and proteins. The phospholipids make a monolayer at the surface of the fluid. Explain how phospholipids interact with water so that a monolayer forms on the surface of the fluid.
Describe the function of macrophages in the lungs.
Neutrophils leave the blood and release the extracellular enzyme elastase. Suggest why neutrophils secrete elastase.
The protein alpha-1 antitrypsin is made in liver cells and carried to the lungs, where it inhibits elastase. Some people produce an alternative form of this protein that stays inside liver cells. These people have a higher risk of developing emphysema, in which the alveolar walls break down. Emphysema is one of the conditions linked with chronic obstructive pulmonary disease (COPD). Explain why these people are at increased risk of developing emphysema.