Anatomy & Physiology

Anatomy & Physiology Study Guide Pulmonary ventilation—the exchange of air between the atmosphere and the lungs—involves pressure changes, muscle movement, and respiratory rates and volumes: • Pulmonary ventilation is the physical movement of air into and out of the respiratory tract. • As pressure on a gas decreases, its volume expands; as pressure increases, gas volume contracts. This inverse relationship is Boyle's law. • Lung volume is directly affected by the movement of the diaphragm and ribs. • The relationship between intrapulmonary pressure (the pressure inside the respiratory tract) and atmospheric pressure determines the direction of airflow. Intrapleural pressure is the pressure in the space between the parietal and visceral pleurae. • A single cycle of inhalation and exhalation is known as the respiratory cycle, and the amount of air moved in one respiratory cycle is the tidal volume. • External and internal intercostal muscles and the diaphragm are involved in regular/quiet breathing or eupnea. During the active inspiratory and expiratory movements of forced breathing, or hyperpnea the accessory muscles become active. • Alveolar ventilation is the amount of air reaching the alveoli each minute. The vital capacity includes the tidal volume plus the expiratory and inspiratory reserve volumes. Residual volume is the measurement of the amount of air left in the lungs after maximum exhalation. Gas exchange depends on the partial pressures of gases and the diffusion of molecules: • In a heterogeneous gas mixture, the individual gases exert a pressure (known as partial pressure) proportional to their abundance in the mix (Dalton's law). • The partial pressure of the gas in a solution is directly proportionate to the amount of gas in a solution (Henry's law). • Alveolar air and atmospheric air differ in composition. Gas exchange across the respiratory membrane is efficient due to differences in partial pressures, the short diffusion distance, lipid-soluble gases, the large surface area of all the alveoli combined, and the coordination of blood flow and airflow. Most oxygen is transported bound to hemoglobin; and carbon dioxide is transported in three ways: as carbonic acid, bound to hemoglobin, or dissolved in plasma: • Carbon dioxide is absorbed and oxygen is delivered as blood enters the peripheral capillaries. • The transport of oxygen and carbon dioxide in blood involves reactions that are reversible. • Oxygen is carried mainly by RBCs, reversibly bound to hemoglobin. At alveolar, PO2 hemoglobin is almost entirely saturated; at the PO2 of peripheral tissues, it retains a substantial oxygen reserve. The Bohr effect explains how the pH of the hemoglobin effects the saturation curve. When low plasma PO2 continues for extended periods, it reduces the hemoglobin's affinity for oxygen as the red blood cells generate more 2,3-bisphosphoglycerate (BPG).

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