Chapter 21, Problem 1CP

Summary Introduction

To review:

The function of smooth muscles and elastic fibers in the arteries of tunica media.

Introduction:

The blood vessels, which transports the oxygenated blood from the heart to different body parts are known as arteries. In general, the wall of the blood vessels is composed of three distinct layers. The innermost layer is the tunica interna or intima, while tunica externa or adventitia is the outermost layer. Between these two layers is the tunica media.

Explanation of Solution

The tunica media consists of the smooth muscle cells as well as the elastic fibers. The primary function of the cells of the smooth muscle that sheath the lumen of the vessel is to regulate its diameter in response to external stimuli. An increased sympathetic stimulus causes the smooth muscle cells to contract, which in turn narrows down the lumen.

This reduction in the blood vessel's lumen diameter is termed as vasoconstriction. On the contrary, a decreased sympathetic stimulus causes the cells of smooth muscle to relax leading to an increased lumen diameter. This process is called vasodilation. The cells of the smooth muscle also help in the production of the elastic fibers in the arteria's tunica media. These elastic fibers help increase the stretch or recoil the blood vessel depending on the pressure applied.

Conclusion

Thus, cells of the smooth muscle in tunica media respond to the external stimuli and cause the blood vessels to contract or dilate. The elastic fibers help the blood vessels to stretch or recoil under pressure and prevents their tearing when the pressure increases.