title: Heart, lungs, and blood as an integrated system: the alveolar-capillary barrier and the cardiorespiratory apparatus.
abstract: The living organism is complex and depends on information transfer for its effective operation. One way to regard the organism is as a biological hierarchy in which each level not only serves a particular, circumscribed function but also contributes in an important way to the integrated performance of the organism as a whole. Two levels in the organization of biological functions are discussed to illustrate the principle of biological hierarchy: a subsidiary role, as exemplified by the role of the lungs in water and macromolecular exchange, and a primary function, as typified by the integrated performance of the cardiorespiratory apparatus in accord with the metabolic needs of the whole body. This hierarchical approach not only preserves the perspective for appreciating the coordinated behavior of the normal individual but also provides a vantage for assessing derangements produced by disease at any level in the biological hierarchy.
mesh_terms: D001769:Blood; D002196:Capillaries / Q000502:physiology; D002199:Capillary Permeability; D006321:Heart / Q000502:physiology*; D006801:Humans; D008168:Lung / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000502:physiology; D012119:Respiration