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Harrison's Principles of Internal Medicine, 18e
| Part 11. Disorders of the Respiratory System > Section 1. Diagnosis of Respiratory Disorders > |
Chapter 252. Disturbances of Respiratory Function
Sections: Introduction, Ventilation, Gas Exchange, Clinical Correlations: Typical Examples, Acknowledgement, Further Readings.
Topics Discussed: abnormal respiratory function.
Excerpt:"The primary function of the respiratory system is to oxygenate blood and eliminate carbon dioxide, which requires that blood come into virtual contact with fresh air to facilitate diffusion of respiratory gases between blood and gas. This process occurs in the lung alveoli, where blood flowing through alveolar wall capillaries is separated from alveolar gas by an extremely thin membrane of flattened endothelial and epithelial cells, across which respiratory gases diffuse and equilibrate. Blood flow through the lung is unidirectional via a continuous vascular path, along which venous blood absorbs oxygen from and loses CO2 to inspired gas. The path for airflow, in contrast, reaches a dead end at the alveolar walls; as such, the alveolar space must be ventilated tidally, with inflow of fresh gas and outflow of alveolar gas alternating periodically at the respiratory rate (RR). To achieve an enormous alveolar surface area (typically 70 m2) for blood-gas diffusion within the modest volume of a thoracic cavity (typically 7 L), nature has distributed both blood flow and ventilation among millions of tiny alveoli through multigenerational branching of both pulmonary arteries and bronchial airways. As a consequence of variations in tube lengths and calibers along these..."
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