Composition and Dimensions of Alveolo-capillary Tissue Barrier
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The alveolar capillary blood is separated from the alveolar air by a layer of tissue (Fig. 66) which represents a resistance to the diffusion of gases between air and blood. This so-called air-blood barrier is composed of an alveolar epithelium and a capillary endothelium, separated by an interstitial framework of basement membranes and connective tissue elements (Fig. 67). Over large areas this barrier is greatly attenuated so as to form a thin alveolo-capillary “membrane”, while in other regions it may develop considerable thickness (Figs. 66 and 67). Various electron microscopic studies have revealed that each of the three constituent layers1 is continuous throughout the lung (Low, 1953; Karrer, 1956; Bargmann and Knoop, 1956; Schulz, 1957; Policard et al., 1957; and others). The fine structure of their components has been discussed in detail. In the following pages these findings will be briefly reviewed in order to define the morphologic entities we have analyzed quantitatively. The illustrations used for this purpose (Figs. 66 to 70) are taken from rat lungs because better tissue preservation can be achieved in material from experimental animals than in human lungs.
KeywordsBasement Membrane Alveolar Epithelium Intercellular Junction Capillary Endothelium Pinocytotic Vesicle
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