Endothelium with red blood cells

What Are Endothelial Cells?    
Endothelial cells from blood vessels  

The endothelial cells form a one-cell thick walled layer called endothelium that lines all of our blood vessels such as arteries, arterioles, venules, veins and capillaries. Smooth muscle cells layer beneath the endothelial cells. The exception to this is the capillaries where endothelium makes up the entire blood vessel wall.



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Functions of Endothelial Cells    
The primary function of endothelium is the maintenance of vessel wall permeability and regulating blood flow. 

Illustration of a blood brain barrier model 

Illustration of blood brain barrier model

Image courtesy of Pharmaceutics 2014, 6(4), 557-583; doi:10.3390/pharmaceutics6040557 http://www.mdpi.com/1999-4923/6/4/557/htm

  Barrier Function: The endothelium acts as a barrier between the blood and the rest of the body tissue while being selectively permeable for certain chemicals and white blood cells to move across from blood to tissue or for waste and carbon-dioxide to move from tissue to blood. This property of endothelial cells is especially investigated in the blood-brain-barrier system. In certain neuro-degenerative diseases, it is difficult to develop drugs that can cross the endothelial barrier efficiently. Research is focused on better mimicking and understanding the functions of blood brain barrier systems to increase the efficacy of drug development. 

Endothelium with blood cells    Regulating blood flow: Endothelial cells generate an anti-thrombotic surface that facilitates transit of plasma and cellular constituents throughout the vasculature. The endothelium is also responsible for maintaining homeostasis and formation of new blood vessels (process referred to as angiogenesis). Angiogenesis has key applications in cancer research. Tumor growth is supported by formation of new blood vessels that provide nutrients for these cells to expand. Current research and drug discovery areas are focused on understanding how inhibiting angiogenesis can have implications on tumor expansion. 



Properties and functions of Endothelial Cells                                 

Image courtesy of Int. J. Mol. Sci. 2012, 13(9), 11288-11311; doi:10.3390/ijms130911288 http://www.mdpi.com/1422-0067/13/9/11288/htm

  Inflammatory response: Endothelial cells are also active participants in and regulators of the inflammatory processes.




Endothelial Cells In Vitro    
Endothelial Cells in Vitro   Many of the endothelial processes are commonly studied in vitro using human umbilical vein endothelial cells (HUVEC), or large vessel and microvascular endothelial cells isolated from various body tissues. Endothelial cells consist of "cobblestone" morphology, stain positive for Factors VIII (an essential blood-clotting protein synthesized by endothelial cells) and take up acetylated low-density lipoprotein. HUVECs stain positive for CD-31. 


Since the circulatory system lines the entire body, endothelial research is tied to many diseases which are top-funded research areas. For instance, dysfunction of endothelial cells has implications in diabetes, pulmonary diseases, inflammatory diseases, cardiovascular diseases and immune diseases to name a few. In addition, blocking angiogenesis has important applications in cancer. Studies are focused on understanding interactions between blood vessel formation and tumor expansion. Endothelial cells also have important applications in tissue engineering studies especially in the development of artificial vascular grafts as alternatives to donor-sourced grafts or supporting organ engineering with a vascular network.



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