Blood boundary layer permeability

Figure 38 Correlations between appearance permeability coefficients for a related series of peptides measured in mesenteric blood draining perfused rat ileal segments and Caco-2 cell monolayers in the Transwell system. See Table 14 for identification of the peptides. The Pe for the rat ileum was not corrected for the aqueous boundary layer and blood flow effects. [Redrawn from Kim et al. (1993) with permission from the publisher.]...

The second generation of nonporous membranes was silicon based which displayed increased CO2 permeabilities. In 1965, Bramson et al. commercialized the first nonporous membrane BO [18]. Since the diffusion coefficient of oxygen and carbon dioxide in air is about four orders of magnitude higher than in blood, the gas side mass-transfer resistance was negligible. The major resistance to respiratory gas transfer was due to the membrane and the liquid side concentration boundary layer [19]. Though nonporous membrane BOs reduced blood damage, up to 5.5 m membrane surface area was often required to ensure adequate gas transfer rates. 

When the permeabilities of the aqueous boundary layer and membrane are relatively large, reduced blood flow becomes the rate-limiting step. For example, the apparent permeability coefficient is approximately 85% controlled by blood flow when Pgq and Pmembrane are each approxi-mately 10 times greater than Pbiood-... 

Assuming no significant aqueous boundary layer on the blood side, the apparent permeability coefficient (Papp) in Eq. (1) is expressed by ... 

The blood gas cell can be modified to optimize either the measurements of partial pressures or contents. Decreasing the permeability of the membrane by an order of magnitude will effectively reduce all boundary layer effects, allowing a linear calibration for P02. At the other extreme, increasing the membrane permeability (e.g., silicone rubber membranes) would permit a rapid depletion of the blood gases, facilitating content measurements. 

In postmenopausal women, the incidence of mitosis in the basal and parabasal layers and the number of small blood vessels decreases. The vaginal epithelium becomes extremely thin, cell boundaries in the surface are less distinct, the micro-ridges of the cells are dramatically reduced, and the vagina is often invaded with leukocytes. Naturally, this thinning of the epithelium leads to a substantial increase in the permeability of this tissue. 

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