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Pulmonary Vascular Mechanobiology
Published in Jiro Nagatomi, Eno Essien Ebong, Mechanobiology Handbook, 2018
Diana M. Tabima Martinez, Naomi C. Chesler
All vessels except the capillaries have three layers, which are the tunica intima, tunica media, and tunica adventitia. The innermost layer, the tunica intima, consists of a monolayer of endothelial cells and subendothelial layer of connective tissue. The tunica media is mainly composed of elastin, collagen, and vascular smooth muscle cells (vSMCs). The vSMCs are typically circumferentially oriented and arranged in layers separated by elastic fibers and an ECM rich in collagen. The outermost layer, the tunica adventitia, is composed of fibroblasts (10%) and connective tissue which consists mainly of the ECM proteins: collagen (63%), ground substances (25%) and elastin (2%).45 Unlike in the tunica media where collagen fibers are oriented circumferentially, in the tunica adventitia rope-like bundles of collagen are oriented longitudinally.
Cardiovascular System:
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
The blood vessel wall is made up of three layers: the tunica intima, the tunica media, and the tunica externa (Figure 1.7). The innermost layer, the tunica intima, is made up of a basement membrane and endothelium, which is in contact with the blood as the blood moves through the blood vessel lumen. The endothelial cells secrete chemicals such as endothelin and nitric oxide, which can trigger a local vasoconstriction or vasodilation. The endothelium also provides a smooth surface that minimizes the friction at the wall. The basement membrane and the internal elastic lamina make up the rest of the tunica intima. The network of collagen fibers within the basement membrane and the layers of elastic fibers within the lamina provide tensile strength to the wall while also allowing for stretching and recoiling.
The response of endothelial cells to endogenous bioelectric fields
Published in Ze Zhang, Mahmoud Rouabhia, Simon E. Moulton, Conductive Polymers, 2018
The primary capillary networks that develop via vasculogenesis in the embryo are modified, extended, and pruned by angiogenesis so that the functional requirements for each tissue in terms of energy, material and oxygen delivery, and waste removal are provided. In the normal mature state, no cell will be more than 50–100 microns away from a blood vessel (Alberts et al. 2002). The physical processes by which nutrient and waste exchange occurs in the vascular system require an intricate balance between large-diameter vessels under high pressure, smaller low-pressure capillary networks, and the control of blood flow as the demand of various tissues varies on a minute-to-minute basis. The mature organism develops a rich array of vessels, all of which are modifications of the basic vessel developed during vasculogenesis. With the exception of the capillary networks, virtually all blood vessels, including arteries and veins, end up comprising three layers: The tunica intima, which is the endothelial cell layer surrounded by its basal lamina. In the small capillaries, there may be pericytes included in an inconsistent pattern.The tunica media is formed by SMCs that are recruited by the endothelial cells to surround the intima. These SMCs produce an extracellular matrix (ECM) composed of glycosaminoglycans and the connective proteins elastin and collagen, which provide elastic compliance and tensile strength to the vessel. The SMCs both provide the structural integrity needed by any vessel larger than a capillary and impart the capacity of the vessel to constrict and dilate in response to endothelial stimuli such as nitric oxide (NO), and also to neurogenic stimuli and hormonal stimuli such as epinephrine.Finally, the outer layer of the vessel is a connective tissue layer, the tunica externa.
Medical textiles
Published in Textile Progress, 2020
There are three types of vessels: arteries, veins and capillaries. Arteries and veins are composed of three distinct layers; tunica intima, tunica media and tunica adventitia. In arteries, the intima is composed of a single layer of epithelial cells (endothelium) supported by a basement membrane and elastic lamina. The media contains circular smooth muscle cells and an elastin-rich cellular matrix whereas the adventitia is composed of loose connective tissue, fibroblasts, nerve endings and vasa vasorum (blood supply to the vessel) [335]. Arteries can be divided into large elastic arteries, medium muscular arteries and small arteries. Veins are capacitance vessels that operate under low-pressure conditions and are larger and thinner-walled than arteries. There are fewer smooth muscle cells in the tunica media. The basic structural components allow for the vasculature to regulate blood flow by changing luminal area and wall thickness. As the vessels are living tissues, damage to them or the introduction of foreign material results in endothelial dysfunction leading to an inflammatory response resulting in atherosclerosis.
Boundary layer considerations in a multi-layer model for LDL accumulation
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2018
Marcello Iasiello, Kambiz Vafai, Assunta Andreozzi, Nicola Bianco
Predicting Low-Density Lipoprotein (LDL) deposition in an artery is of primary importance, due to the role that it has in the atherosclerotic plaque genesis. Due to difficulties for experimental studies in this area, accurate modeling efforts have a primary role in understanding how the particles deposit through the wall. Modeling efforts in analyzing the arterial wall have been based on wall-free, single-layer and multi-layer model approaches (Prosi et al. 2005). For the first approach, the wall is replaced by velocity and mass flux boundary conditions (Wada and Karino 2000). This approach saves computational time; however, it does not provide a correct physical boundary condition. For the single-layer model approach, the wall is modeled by means of a homogenous layer with average properties (Stangeby and Ethier 2002a). The single layer model has been also employed by assuming that the mass transport through the wall is purely diffusive, thus no solution for the velocity field is required (Hansen et al. 2014). While this approach provides a better alternative than the wall-free model, it is still not possible to obtain accurate results. Analyzing the LDL deposition within the arterial wall is of primary importance, since the particles deposit within each heterogeneous layer. The tunica intima is an important layer, since it is where the atherosclerotic plaque grows. The multilayer model is the most accurate approach, since it enables us to analyze the concentration distributions within each layer of an artery. Both analytical and numerical approaches have been utilized. Analytical solutions were derived for straight arteries (Khakpour and Vafai 2008; Wang and Vafai 2013), curved arteries (Wang and Vafai 2015) as well as taking into account hypertension and hyperthermia conditions (Iasiello et al. 2016a). When the geometry is more complex, such as multiple bends (Wada and Karino 2002), stenosed arteries (Ai and Vafai 2006; Nematollahi et al 2012; Iasiello et al. 2015) or bifurcations (Kenjereš and de Loor 2014; Iasiello et al. 2016b), a numerical approach is necessary.