Transport properties of blood vessels

Under transmural pressures, fluid or plasma will flow across the walls of blood vessels. On one hand, convective fluid motion through the blood vessel wall plays a very important role in nourishing the vessel walls, on the other hand, it is involved in atherogenesis by promoting the transport of macromolecules such as lipoproteins into the arterial wall [55-58], possibly through leaky endothelial cell junctions in regions of hi endothelial cell turnover [59]. Table B6.21 lists the filtration properties of excised, presumably normal, human iliac blood vessels. 

Several studies have shown that the water content of human, rat and dog arteries is increased in hypertension, and this increased water content may be associated with an increased wall thickness [64, 65]. Due to the limitations in studying samples from human subjects, animal models (mainly rats) have been employed. Mallov [66] found that the aorta from hypertensive rats had more smooth muscle than normal aorta. Greenwald and Berry [67] reported increased elastin and decreased collagen content in the aorta from spontaneous hypertensive rats when compared with the normal aorta. Wolinsky [25] observed an increase in the absolute amounts of both medial elastin and collagen contents in hypertensive rats. However, the relative percentage of these elements remained essentially constant. Experimental studies [67-69] showed an increase in vessel stiffness with the development of hypertension. This increase in vessel stiffiiess results in a smaller vessel diameter for a given distending pressure, i.e. a decrease in the distensibility [70]. 

It is generally accepted that substantial changes in the arterial wall occur with atherosclerosis in man. In human atherosclerotic arteries, it appears that there may be an absolute increase in collagen and a decrease in muscle fibers when compared with normal arteries [28]. In canine iliac 

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Blood and lymphatic vessels are soft tissues with densities which exhibit nonlinear stress-strain relationships [1]. The walls of blood and lymphatic vessels show not only elastic [2, 3] or pseudoelastic [4] behavior, but also possess distinctive inelastic character [5, 6] as well, including viscosity, creep, stress relaxation and pressure-diameter hysteresis. The mechanical properties of these vessels depend largely on the constituents of their walls, especially the collagen, elastin, and vascular smooth muscle content. In general, the walls of blood and lymphatic vessels are anisotropic. Moreover, their properties are affected by age and disease state. This section presents the data concerning the characteristic dimensions of arterial tree and venous system the constituents and mechanical properties of the vessel walls. Water permeability or hydraulic conductivity of blood vessel walls have been also included, because this transport property of blood vessel wall is believed to be important both in nourishing the vessel walls and in affecting development of atherosclerosis [7-9]. 

Another field of application of fluorinated biomaterials is connected to lesions or evolving disease pathology of blood vessels. In particular, arteries may become unable to insure an adequate transport of the blood to organs and tissues. Polytetrafluoroethylene (PTFE) and expanded e-PTFE are the preferred materials for vascular prostheses. The interactions of blood cells and blood plasma macromolecules with both natural and artificial vessel walls are discussed in terms of the mechanical properties of the vascular conduit, the morphology, and the physical and chemical characteristics of the blood contacting surface. 

The colligative properties, described in Section 3.4.1 to Section 3.4.3, have been used to determine the molar mass of unknown chemical compounds. Pharmaceutical scientists and pharmacists may apply this concept in the preparation of isotonic (meaning of equal tone) solution dosage forms. These solution dosage forms can be applied to sensitive and delicate organs such as the eye, nose, or ear or directly injected into the body (i.e., blood vessels, muscles, lesions, etc.). They should have, when administered, the same osmotic pressure as body fluids. Otherwise, transport of body fluids inside and outside the cell tissues will occur, causing discomfort and damage to the tissue. Osmolarity of body fluids is approximately 0.307 osmol/L or 307 mosmol/L. 

HA is an unsulfated glycosaminoglycane composed of repeating disaccharide units of D-glucuronic acid and A-acetylglucosaminc linked a-( 1 —4) and p-( 1—3), respectively. HA has special importance because it is a component of the ECM [53] in the soft tissues of mammals, where it mainly ensures water retention [54], This enables the transport of nutrients to, and removal of waste from, cells that do not have a direct blood supply, such a cartilage cells. Moreover, HA is present in the synovial joint fluid, the vitreous humor of the eye, cartilage, blood vessels, and the unbilical cord. More detailed information about the biological functions and physicochemical properties of HA can be found elsewhere [55, 56],... 

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