reduction in the lumen diameter of a blood vessel as the smooth muscle contracts is known as __________.
1. 3 Layers in arterial walls (are also known as tunics): a. Tunica interna-innermost layer. Also known as the tunica intima. 1) Surrounds a central blood-containing space known as the lumen. 2) Lined with endothelium (simple squamous epithelium). This tissue. reduces friction as blood moves through the lumen. b. Tunica media-composed primarily of smooth muscle tissue and elastic tissue. 1) This smooth muscle is regulated by the autonomic nervous system. and various chemicals. 2) Vasoconstriction (reduction in lumen diameter due to smooth muscle. contraction) and Vasodilation (widening of the lumen due to smooth. muscle relaxation) both occur in the tunica media.