Anatomy & Physiology

Anatomy & Physiology Study Guide of the airway. By adjusting the resistance to airflow, bronchodilation and bronchoconstriction direct airflow toward or away from specific portions of the respiratory exchange surfaces. Alveolar Ducts and Alveoli Respiratory bronchioles are connected to individual alveoli and to multiple alveoli along regions called alveolar ducts. Alveolar ducts end at alveolar sacs , common chambers connected to numerous individual alveoli. About 150 million alveoli are contained within each lung, and their abundance gives the lung an open, spongy appearance. An extensive network of capillaries is associated with each alveolus. A web of elastic fibers surround the capillaries. These structures help maintain the relative positions of the alveoli and respiratory bronchioles. The recoil of these fibers during exhalation reduces the size of the alveoli and helps push air out of the lungs. The Pleural Cavities and Pl ural Membranes The thoracic cavity resembles a broad-based cone in appearance. Its floor is the diaphragm, and the rib cage forms the walls. The mediastinum separates the two pleural cavities . Each lung occupies a single pleural cavity, which is lined by a serous membrane called the pleura . The pleura consists of two layers: the visceral pleura and parietal pleura. Extended over the diaphragm and the mediastinum the parietal pleura covers the inner surface of the thoracic wall. The visceral pleura covers the outer surfaces of the lungs, extending into the fissures between the lobes. Pleural fluid forms a moist, slippery coating that provides lubrication, thereby reducing friction between the parietal and visceral surfaces. Samples of pleural fluid, obtained through a long needle inserted between the ribs, are sometimes obtained for diagnostic purposes. This sampling procedure is called thoracentesis . 22.5 Respiration The general term respiration refers to two integrated processes: external respiration and internal respiration. External respiration includes all the processes involved in the exchange of oxygen and carbon dioxide between the body's bloodstream and the lung, which is the external environment. The purpose of external respiration and the primary function of the respiratory system is meeting the respiratory (primary oxygen) demands of cells. Internal respiration is the absorption of oxygen and the release of carbon dioxide by those cells. There are three integrated steps involved in external respiration: • Step 1: Pulmonary ventilation, or breathing, which involves the physical movement of air into and out of the lungs • Step 2: Gas diffusion across the respiratory membrane between alveolar air spaces and alveolar capillaries and across capillary walls between blood and other tissues • Step 3: The transport of oxygen and carbon dioxide between alveolar capillaries and capillary beds in other tissues The physical movement of air into and out of the lungs and the rest of the respiratory tract is pulmonary ventilation . Maintaining adequate alveolar ventilation is the primary function of Achieve Page 302 of 368 ©2018