Discontinuous capillaries

Discontinuous capillaries are present in the liver, bone marrow, and spleen. These capillaries have relatively large gaps between the endothelial cells (30-500 nm), and have incomplete basement membranes, which make them best suited for extravasation of macromolecules. 

Capillary structure Capillary structure varies widely in terms of the fraction of the basement membrane that is exposed by slit (tight) junctions between endothelial cells. In the brain, the capillary structure is continuous, and there are no slit junctions (Figure 1.8). This contrasts with the liver and spleen, where a large part of the basement membrane is exposed due to large discontinuous capillaries, through which large plasma proteins can pass. 

If a pressure measuring device were run inside the capillary, an oil gradient would be measured in the oil column. A pressure discontinuity would be apparent across the interface (the difference being the capillary pressure), and a water gradient would be measured below the interface. If the device also measured resistivity, a contact would be determined at this interface, and would be described as the oil-water contact (OWC). Note that if oil and water pressure measurements alone were used to construct a pressure-depth plot, and the gradient intercept technigue was used to determine an interface, it is the free water level which would be determined, not the OWC. 

In summary, equation (13) accurately describes longitudinal dispersion in the stationary phase of capillary columns, but it will only be significant compared with other dispersion mechanisms in LC capillary columns, should they ever become generally practical and available. Dispersion due to longitudinal diffusion in the stationary phase in packed columns is not significant due to the discontinuous nature of the stationary phase and, compared to other dispersion processes, can be ignored in practice. 

There are also numerous important variations in the microvasculature bed (i.e., arterioles, capillaries, and venules) that affect permeability. For example, venular portions of the capillaries have thin endothelial cells (170 nm), with frequent interendothelial discontinuities. About 30% of venular junctions are believed to have gaps of about 6 nm. Arterioles, in contrast, have endothelial cells that are linked by the tight junctions and communicating junctions, whereas the capillary endothelium contains... 

Saturation (v) is the volume fraction of the total void volume occupied by a specific fluid at a point. Saturation values can vary from zero to 1 with the saturation of all fluids equal to 1. Residual saturation (Sr) is the saturation at which the NAPL becomes discontinuous and immobile due to capillary forces. Residual saturation is dependent upon many factors, including pore size distribution, wettability, fluid viscosity and density ratios, interfacial surface tension, gravity and buoyancy forces, and hydraulic gradients. 

The capillary-rise method was employed to measure the surface tension of aqueous solutions of disodlum alkyl phosphate at 25 °C. The cmc values of the solutions were obtained from the discontinuity in the surface tension - concentration curves(7). 

Although the two growth factors have similar effects on neutrophil counts, G-CSF is used more frequently because it is better tolerated. G-CSF can cause bone pain, which clears when the drug is discontinued. GM-CSF can cause more severe side effects, particularly at higher doses. These include fevers, malaise, arthralgias, myalgias, and a capillary leak syndrome characterized by peripheral edema and pleural or pericardial effusions. Allergic reactions may occur but are infrequent. Splenic rupture is a rare but serious complication of the use of G-CSF for PBSC. 

Capillaries are the exchange vessels of the body. They have structural variations to allow different levels of metabolic exchange (of exogenous and endogenous substances) between blood and the surrounding tissues. The structure of the walls varies depending on their resident tissue. There are three major types of blood capillaries continuous fenestrated and sinusoidal (discontinuous) [1] ... 

FIGURE 3.29 A schematic view from above the disk of a passive capillary burst valve. A liquid flows in a channel or capillary and is pinned at the discontinuity where the channel meets a chamber or a wider channel. Sufficient fluidic pressure must be exerted by the centrifugal pump to overcome the pressure of curved liquid surfaces and to wet the walls of the chamber with liquid. This pressure is achieved at a characteristic rate of rotation or burst frequency, C0c, above which the liquid exits the channel and enters the chamber. CO, depends on the hydraulic diameter (dH) of the capillary and the amount of liquid in the channel and therefore provides a means of gating the flow of liquid [1042]. Reprinted with permission from the American Chemical Society. 

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