الفهرس 
Endothelial ontogneyOnly 14 pages are availabe for public view
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Abstract
The endothelium is composed of specialized epithelial cells that line the vasculature, the lymph vessels, and the heart, considerable heterogeneity exists among different organs and even within vessels. During development, the endothelial cells are specified before they migrate to their final destination, and then they commit to an arterial or venous fate. from the venous endothelial cell population, a subset of cells is further specified as lymphatic end othelium.
The endothelium is a major player in the control of blood fluidity, platelet aggregation and vascular tone, a major actor in the regulation of immunology, inflammation and angiogenesis, and an important metabolizing and an endocrine organ.
The endothelium of arteries and veins forms a continuous uninterrupted layer of cells, held together by tight junctions. The endothelium of capillaries may be continuous, fenestrated, or discontinuous, according to the needs of the underlying tissue. Fenestrated endothelium is characteristic of organs involved in filtration or secretion, including exocrine and endocrine glands, gastric and intestinal mucosa, choroid plexus, glomeruli, and a subpopulation of renal tubules. Discontinuous endothelium is similar to fenestrated endothelium, with the exception that the fenestrations are larger in diameter (they may manifest as gaps in the cell) and they lack a diaphragm.
The endothelium in traversing the body must provide a broad menu of functions that are adapted to the diverse needs of the underlying tissues.
Each EC is analogous to a miniature adaptive nonlinear input/output device. Input arises from the extracellular environment and consists of biomechanical (eg, shear stress) and biochemical forces (eg, growth factors, cytokines, chemokines, hormones, complement, nitric oxide, oxygen, and reactive oxygen species). Output represents the cellular phenotype and may be measured as cell shape, calcium flux, protein expression, mRNA expression, migration, proliferation, survival/apoptosis, vasomotor tone, hemostatic balance, release of inflammatory mediators. Input is coupled to output by signaling pathways that typically begin at the cell surface and end at the level of transcription or posttranscriptional modification.
At any point in time, the net input of biomechanical and biochemical signals varies across the vasculature. Because signal input varies in space and time, and because ECs are capable of sensing and responding to the microenvironment, EC phenotypes display marked spatial and temporal heterogeneity. in fact the endothelium is a spatially distributed organ system. Like a chameleon, it molds itself to the needs of the underlying tissue.
Each vascular bed has its own ―story to tell.‖ ECs from different organs demonstrate unique structural and functional properties, as well as distinct developmental programs, roles in pathophysiology, and potential for targeted therapy.
Endothelial dysfunction appears to play a critical role in a variety of human disorders, including peripheral vascular disease, stroke, heart disease, diabetes, insulin resistance, chronic kidney failure, tumor growth, metastasis, venous thrombosis, SLE, rheumatoid arthritis & vasculitis.