Quick Facts
The tunica media is the middle coat of a blood or lymph vessel, made up of transverse elastic fibers and smooth muscle cells (Dorland, 2011).
Structure and/or Key Feature(s)
The tunica media is the middle layer of a typical blood vessel and extends from the internal to the external elastic membrane. It consists mainly of smooth muscle cells arranged circumferentially around the vessel. Depending on the size of the arteriole, there are varying amounts of elastic and reticular (collagen) fibers and proteoglycans between the smooth muscle cells. Smooth muscle cells of afferent arteriole supplying blood to the glomerulus, and sometimes the efferent arteriole taking blood away from the glomerulus, exhibit spherical nuclei and their cytoplasm contain secretory granules.
Anatomical Relations
An arteriole has three layers (or tunics). The tunica adventitia of an arteriole is the outermost layer of a blood vessel that merges with surrounding loose connective tissue. The tunica media is adjacent to the outer adventitia layer as the middle layer of a blood vessel. The layer adjacent to the blood vessel lumen (or inner layer) is the tunica intima.
Function
The tunica media is responsible for vasoconstriction and vasodilation of the artery or arteriole as a result of the smooth muscle contracting and relaxing, respectively. This regulates blood pressure and blood flow (Ross and Pawlina, 2016).
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Ross, M. H. and Pawlina, W. (2016) Histology: A Text and Atlas. Wolters Kluwer Health.
