ABSTRACT
Gas exchange has always been the most extensively studied, vital function of the lung. In recent years, it has become obvious that the lung also plays a central role in several crucial aspects of body metabolism. The lung and other epithelial secretory organ systems in the body are equipped with a secretory immune system which is capable of responding to foreign agents by the production of specific humoral antibodies. The trachea and major branches of the bronchi maintain a rather rigid form during respiration because of their support by rings or islands of cartilage. In addition, these airways are equipped with numerous mucus-producing glands which provide a continuous secretion, containing a variety of glycoproteins which originate both in the serum and in the glands themselves. This chapter discusses several of the macromolecular components of this secretion. The structural, immunologic, and metabolic features of the lung which make it so useful in host defense are also discussed.
