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In addition, the tunica adventitiaanchors blood vessels to the adjacent tissues ( Figure 1). The tunica adventitia, that is, the exterior part of a blood vessel (also referred to as tunica externa), contains fibroblasts, nerves and, in bigger vessels, also small blood vessels supplying the vascular wall, called vasa vasorum.
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The tunica intima(also referred to as tunica interna) contains a semipermeable monolayer of endothelial cells and forms the luminal part of a blood vessel, contacting the blood. As the medium part of the blood vessel wall, the tunica mediais located between the tunica intimaand tunica adventitia, and is separated from these parts by the lamina elastica internaand the lamina elastica externa, respectively. In medium vessels, there are up to 40 layers of VSMCs, and in large vessels, there are up to 60 layers. The cells are located in the medium part of a blood vessel, that is, tunica media, where they are oriented in a circle around the vascular lumen and form numerous layers. Vascular smooth muscle cells (VSMCs) are an important component of blood vessels. *Address all correspondence to: Introduction Clinic of Plastic Surgery, Faculty Hospital Na Bulovce, Czech Republic.Biotechnology and Biomedicine Center of the Academy of Sciences and Charles University in Vestec (BIOCEV), Czech Republic.Department of Biomaterials and Tissue Engineering, Institute of Physiology of the Czech Academy of Sciences, Czech Republic.These features can lead to stenosis or to obliteration of the vascular lumen and impaired blood supply to various tissues and organs. However, after blood vessel injury, surgery or explantation in vitro, VSMCs undergo a phenotypic modulation to synthetic phenotype, which endows them with high activity in migration, growth and proteosynthesis. In a healthy adult organism, VSMCs have a quiescent and differentiated contractile phenotype characterized by early markers (e.g., SM α-actin, SM22-α), intermediate markers (h-caldesmon, calponin) and late markers (SM myosins, smoothelin) of VSMC differentiation. The origin, location in the vascular tree, gender, species, strain and age influence the phenotype of VSMCs and their propensity to migration and growth. VSMCs of neuroectodermal origin are implicated in defects of cardiovascular morphogenesis, such as bicuspid aortic valve, coarctation of the aorta, patent ductus arteriosus and tetralogy of Fallot. VSMCs are mostly of mesodermal origin, although some are of neuroectodermal origin, for example, VSMCs present in the aorta and in blood vessels arising from the aortic arch. Vascular smooth muscle cells (VSMCs) play important roles not only in the physiological functions of the blood vessels, such as vasoconstriction, vasodilatation and extracellular matrix production, but also in the pathogenesis of vascular diseases, particularly atherosclerosis and hypertension.