What role does this layer of smooth muscle play in the regulation of circulation? Why is more muscle found in arteries than in veins? In the tunica media the elastic fibres are secreted by smooth muscle cells, not fibroblasts. The tunica aventitia consists of the connective tissue to the outside of the external elastic lamina. If your slide is stained for elastic fibers note the arrangement of those fibers in each of the tunics. Smaller arteries have about a 1:1 ratio of media to adventitia; however as arteries get smaller the tunica media makes up more than half the width of the wall. The adventitia is mostly collagen fibers, with some elastic fibers, fibroblasts, and clusters of smooth muscle cells. If your slide is not stained for elastic fibers make sure you borrow one so that you clearly see the three tunics and the external elastic lamina.
A. Regulates blood flow; Arteries carry oxygenated blood
B. Regulates blood pressure; Veins carry deoxygenated blood
C. Controls heart rate; Arteries have thicker walls
D. Facilitates gas exchange; Veins have thinner walls