CHAPTER 18 – RESPIRATORY SYSTEM

Publisher Summary This chapter discusses the respiratory system and the organs involved. The respiratory system consists of a series of passages connecting the essential respiratory organs, that is, the lungs with the exterior. As the lungs are in free communication with the outside air, they are especially liable to damage from inhaled dust, to bacterial infection, and to the spread of such infection. Several defensive mechanisms normally keep the alveoli free from damage and infection, namely, the presence of diffuse lymphoid masses immediately beneath the epithehum throughout the tract, the presence of mucin combined with the activity of the ciliated epithelium driving all foreign particles outward, and the presence in the alveoli of phagocytic cells. The surface of the lungs is covered by the visceral pleura, which is reflected upon the inner surface of the chest wall as the parietal pleura. The septa of connective tissue pass from the visceral pleura into the organ dividing it into lobules. A functional pulmonary unit can be regarded as consisting of the respiratory bronchiole with its alveolar ducts leading into the atria with their air sacs studded with terminal alveoli, together with the blood vessels, lymphatics, nerves, and connective tissue that supply them. The lungs receive a double blood supply, the bronchial system carrying blood for the nutrition of the bronchial tubes and lung tissue and the pulmonary system carrying blood for the respiratory exchanges in the lungs.