Chapter 29: Structure and Function of the Respiratory System

The system is organized into conducting airways, which filter and warm inspired air, and respiratory airways within the alveoli where gas exchange actually occurs. The larynx serves dual roles as a protective valve and reflex center, with its vocal folds capable of sealing the airway and initiating forceful expulsion of foreign materials through the cough reflex. Gas exchange obeys physicochemical principles centered on partial pressure gradients; calculating alveolar oxygen partial pressure requires integrating atmospheric pressure with the constant water vapor pressure in the respiratory tract. Once oxygen crosses the alveolar-capillary membrane, its transport and delivery depend critically on hemoglobin binding characteristics described by the oxygen-hemoglobin dissociation curve, which demonstrates that oxygen affinity changes based on metabolic conditions—rightward shifts driven by increased carbon dioxide tension, elevated temperature, or decreased pH promote oxygen unloading at the tissue level, while leftward shifts enhance pulmonary uptake. Clinical conditions like anemia compromise oxygen-carrying capacity independent of saturation status. Effective gas exchange requires precise matching between ventilation rates and blood perfusion in lung regions; ventilation-perfusion mismatch represents a major pathophysiological problem occurring as either shunt conditions where blood perfuses non-ventilated alveoli or dead space where ventilation occurs without corresponding perfusion. Pulmonary embolism exemplifies how disrupted perfusion creates severe V-Q mismatch. The chapter addresses developmental physiology, noting that newborns initially exhibit lower oxygen saturation due to fetal circulatory patterns, typically requiring approximately one hour to achieve normal saturation levels around 88 percent as respiratory and circulatory adaptations complete.