Role of the endothelium and nitric oxide (NO) in regulating vascular tone and blood flow
The endothelium is the innermost membrane that covers the lumen of blood arteries and the heart. Cells that make a single layer of endothelial membrane produce chemicals that regulate vasoconstriction and vasodilation. Also, these cells secrete enzymes that regulate the clotting of the blood. Therefore, the vascular tone is essential in keeping blood flowing efficiently. The degree of constriction of a blood artery in relation to its maximal diameter in the dilated condition is known as a vascular tone (Jackson et al., 2000). Vascular tone is achieved by intrinsic and extrinsic factors leading to constriction or dilation of blood vessels. Extrinsic factors come from outside the organ or tissue where the blood vessel is located, while intrinsic factors come from the vessel itself or the surrounding tissue. Extrinsic factors regulate arterial blood pressure by modulating systemic vascular resistance, whereas intrinsic mechanisms are responsible for regulating local blood flow within an organ (Marieb et al., 2018, p.725). Also, extrinsic control uses the nervous and endocrine systems to control the environment and keep the blood pressure from dropping too low. In contrast, intrinsic control through dilation of skeletal muscles during intense exercise brings more blood to muscle tissue since they are in high demand for blood. NO is indirectly synthesized by the protein arginine, which is recognized as the most essential vasoprotective factor in the body (Oak et al., 2018, p.162). Arginine is a non-essential amino acid, and our body can synthesize it on its own. However, we can also obtain it from varieties of products, such as animal or plant domains (Winter et al., 2015).
The function of the endothelium.
The endothelium functionality is very diverse because it is a dynamic tissue. The endothelial is responsible for exchanging oxygen with the carbon dioxide between the tissue and blood vessels, the same goes for the nutrient and waste exchange. The endothelial maintains constriction and relaxation of blood vessels due to internal or external stimuli via the nervous or the endocrine system. Fluid balance is by far a significant functionality of the endothelium to maintain the system's homeostasis. This tissue is also responsible for monitoring blood viscosity by secreting clotting factors. The actual exchange between gasses and nutrients happens on a capillary level, and the vascular tone is determined by the smooth muscle layer of tunica media. Chemicals that are released by the endothelium may regulate both vasodilation and vasoconstriction of the vessel. Nitric oxide (NO) and prostaglandin chemicals regulate dilation, and endothelin controls the constriction of the vessel (Oak et al., 2018). Another important endothelium function is the immune protection against the invading pathogens through the production of adhesive molecules, which in turn help to attach the leukocytes to the endothelium and wait for the invasion (Marieb et al., 2018, p.711).
Jackson W. F. (2000). Ion channels and vascular tone. Hypertension (Dallas, Tex. : 1979), 35(1 Pt 2), 173–178. https://doi.org/10.1161/01.hyp.35.1.173
Oak, Auger, C., Belcastro, E., Park, S.-H., Lee, H.-H., & Schini-Kerth, V. B. (2018). Potential mechanisms underlying cardiovascular protection by polyphenols: Role of the endothelium. Free Radical Biology & Medicine, 122, 161–170. https://doi.org/10.1016/j.freeradbiomed.2018.03.018
Marieb, E. N. (2018). The function of blood and its constituents. In Human Anatomy and Physiology (pp. 699-730). Pearson.
Sandoo, A., van Zanten, J. J., Metsios, G. S., Carroll, D., & Kitas, G. D. (2010). The endothelium and its role in regulating vascular tone. The open cardiovascular medicine journal, 4, 302–312. https://doi.org/10.2174/1874192401004010302
Winter, G., Todd, C. D., Trovato, M., Forlani, G., & Funck, D. (2015). Physiological implications of arginine metabolism in plants. Frontiers in plant science, 6, 534. https://doi.org/10.3389/fpls.2015.00534
