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Differences in vascular permeability between normal tissue and a tumor. Vascular permeability, often in the form of capillary permeability or microvascular permeability, characterizes the capacity of a blood vessel wall to allow for the flow of small molecules (drugs, nutrients, water, ions) or even whole cells (lymphocytes on their way to the site of inflammation) in and out of the vessel.
Capillary permeability can be increased by the release of certain cytokines, anaphylatoxins, or other mediators (such as leukotrienes, prostaglandins, histamine, bradykinin, etc.) highly influenced by the immune system.
Overexpression of VEGF causes increased permeability in blood vessels in addition to stimulating angiogenesis. In wet macular degeneration , VEGF causes proliferation of capillaries into the retina. Since the increase in angiogenesis also causes edema , blood and other retinal fluids leak into the retina , causing loss of vision.
The decrease in surface tension increases the wettability of the capillary walls, making it easier for the fluid to flow through the capillary. Heat also effects the viscosity of a fluid inside a capillary. An increase in heat decreases the viscosity of the lumenal fluid. A good example of this action can be observed in the human body during ...
Diffusion through the capillary walls depends on the permeability of the endothelial cells forming the capillary walls, which may be continuous, discontinuous, and fenestrated. [4] The Starling equation describes the roles of hydrostatic and osmotic pressures (the so-called Starling forces ) in the movement of fluid across capillary endothelium .
Staverman's reflection coefficient, σ, is a unitless constant that is specific to the permeability of a membrane to a given solute. [ 4 ] The Starling equation, written without σ , describes the flow of a solvent across a membrane that is impermeable to the solutes contained within the solution.
Bradykinin (BK) (from Greek brady-'slow' + -kinin, kīn(eîn) 'to move') is a peptide that promotes inflammation.It causes arterioles to dilate (enlarge) via the release of prostacyclin, nitric oxide, and endothelium-derived hyperpolarizing factor and makes veins constrict, via prostaglandin F2, thereby leading to leakage into capillary beds, due to the increased pressure in the capillaries.
Specific gravity is used to measure the protein content of the fluid. The higher the specific gravity, the greater the likelihood of capillary permeability changes in relation to body cavities. For example, the specific gravity of the transudate is usually less than 1.012 and a protein content of less than 2 g/100 mL (2 g%).