Chapter 18, Problem 1CYU

Which branch of the autonomic nervous system innervates blood vessels? Which layer of the blood vessel wall do these nerves innervate? What are the effectors (cells that carry out the response)?

Summary Introduction

To review:

The branch of the autonomic nervous system that innervates blood vessels and the layer of blood vessel walls innervated by these nerves. Also, the cells that carry out the response.

Introduction:

The blood vessels form a closed circulatory system that begins and ends at the heart. The three major types of blood vessels are arteries, veins, and capillaries. Majority of the blood vessels have three distinct layers, which are tunica intima (innermost layer), tunica media (middle layer) and tunica externa (outermost layer).

Explanation of Solution

The inner layer of blood vessels, tunica intima, mainly contains the simple squamous epithelial cells called the endothelium. These cells form the lining of the lumen in all the blood vessels. The middle tunica media layer has sheets of elastin and smooth muscle cells arranged in a circular manner. Outer tunica externa contains loosely woven collagen fibers, nerve fibers, and lymphatic vessels.

The sympathetic vasomotor nerve fibers of the autonomic nervous system usually regulate the activity of the smooth muscle in the middle tunic or tunica media. These nerve fibers act along with chemicals and their activity depends upon the needs of the body. The nerve fibers can cause vasoconstriction or vasodilation of smooth muscles in the arteries. Vasoconstriction causes a decrease in diameter whereas vasodilation increases the diameter. Such regulation helps in maintaining the blood pressure and circulation.

Conclusion

Therefore, it can be concluded that it is the sympathetic nervous system that innervates the blood vessels. The layer innervated by the fibers is tunica media. Smooth muscle cells in arteries are the effectors that carry out the response.