CAPILLARY PERMEABILITY
1973; Elsevier BV; Linguagem: Inglês
10.1016/b978-0-12-783402-3.50010-x
Autores Tópico(s)Hemoglobin structure and function
ResumoThis chapter discusses the physiological considerations of capillary permeability. The function of the capillaries is to permit close contact between two compartments of the extracellular space: (1) a stirred compartment, the plasma, and (2) an unstirred compartment, the interstitial fluid. The system must be designed to make this contact as efficient as possible, while at the same time securing a constant partition of the extracellular spaces between the two sides of the capillary membrane. Many influences contribute to the net transfer of fluid between the two compartments, and it is clear that pressure-regulating mechanisms operate at the level of the small vessels to ensure constant fractional distribution of the extracellular fluid. The net transcapillary pressure gradient determines bulk fluid movement across the capillary wall, while the transcapillary concentration gradient determines net transport of solutes. One of the goals of capillary physiology is to obtain reliable measurements of these parameters in various tissues under physiological circumstances. Difficulties arise because of major experimental shortcomings when attempts are made to describe the events in capillaries in strict physicochemical terms. First, the structure is extremely delicate, and only in a few instances has it been possible to perform experiments on single capillaries, although considerable progress is being made. Second, even when information is obtained from single capillaries, it is not always useful with respect to transport in a whole organ under physiological circumstances.
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