โ Scribed by R.E. Gosselin; W.O. Berndt
No coin nor oath required. For personal study only.
Equations are derived to represent the permeability of a barrier composed of either two or three distinct layers through which solutes diffuse in sequence. In mesentery and peritoneum the thickest layer consists of areolar connective tissue, but it probably offers little more resistance to diffusion than an equal volume of extracellular fluid. The mesothelium is judged to present a more formidable barrier. The ions 8SRb+ and s~p_ orthophosphate migrate independently through excised pieces of rabbit mesentery and peritoneum in the absence of hydrostatic and electrochemical gradients (tracer-ion diffusion). This transport can be described by experimental values of the permeability constant K. If one assumes that S6Rb+ diffuses freely within pores that lie between mesothelial cells, experimentally determined values of K require that these pores occupy in the aggregate o'6% of the macroscopic area of the mesentery. For the peritoneum, which is less permeable than mesentery to both rubidium and phosphate, the corresponding pore area is o'2%. These values are comparable to Pappenheimer's estimate of o'2% for capillary endothelium, representing one more of the many similarities between mesothelium and endothelium in both structure and function. It is believed that these inferences about the pore area of mesothelium are not inconsistent with morphological evidence.
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