摘要：

This chapter discusses the ultrastructural basis of capillary permeability. Capillaries possess an enormous total area for interchange between blood and tissue spaces. The endothelium shows permeability to fluid many times greater than that of certain cell membranes. The endothelium demonstrates the physical characteristics of an inert (in the sense of non-secreting) membrane permeable to water and crystalloids but relatively impermeable to plasma proteins. Factors important to capillary permeability relate to the two components involved—the vascular and tissue spaces and the barriers. The chapter presents capillary permeability related to the capillary itself—that is, to the capillary as a barrier. Factors influencing the spaces are intravascular pressure or tissue pressures, both of which are distant or gross effects, and changes in protein content that are a systemic effect. The endothelium is necessary for the immediate or short-term passage of fluid across the capillary wall and not merely for the long-term maintenance of otherwise passive structures.

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