Chapter 1

### INTRODUCTION

Along with an exponential increase in awareness of venous disease has come a concomitant increase in its evaluation and treatment. Innovation from new drugs and novel devices specifically designed for the treatment of patients with venous disease has also driven this large increase in care that can be offered. Thus, a firm foundation in the knowledge of venous anatomy and physiology remains paramount to understanding what kinds of questions to ask throughout the evaluation process as well as to optimally apply proper treatment algorithms.

This chapter represents a brief overview of venous anatomy and physiology to give clinicians a solid foundation to apply to their everyday practice. The evolution of knowledge on this topic since Hippocrates' first descriptions of venous ulcers around 400 BC has been vast.1 Interestingly, although the facts of venous anatomy have come to a pinnacle in understanding, the topic often remains poorly misquoted, even by some of the most accomplished venous specialists. In contrast, knowledge of venous physiology and flow dynamics remains rudimentary at best despite the many advances in the treatment of patients with venous disease. Nevertheless, increased interest continues, and new discoveries are being made every day that will further the health of millions of individuals who are affected by acute and chronic diseases of the veins.

### ANATOMY

#### Basics

Three distinct layers make up the tubular structure of the vein wall. These are the tunica intima, the tunica media, and the tunica adventitia.2 A single layer of endothelial cells lines the tunica intima. Depending on the type, location, and size of the vein, the tunica media varies considerably in the amount of smooth muscle and elastic fibers. The largest veins that include the superior and inferior vena cavae are almost completely void of smooth muscle fibers. Large veins such as the femoral or axillary veins have slightly more smooth muscle fibers. Medium-sized veins have a thicker layer of elastic fibers in association with circumferential smooth muscle fibers. These veins also have a thick layer of elastic fibers called the internal elastic lamina at the base of the tunica intima. Venules as well as most superficial veins such as the great saphenous vein have large amounts of smooth muscle fibers. These veins also lack an internal elastic lamina. There is little demarcation between the tunica media and the tunica adventitia. The tunica adventitia contains adrenergic nerve fibers and vasa vasorum in a bed of loose connective tissue. Figure 1-1 illustrates a cross-section of a medium-sized vein.

###### FIGURE 1-1.

Cross-section of a medium-sized vein. Note the large amount of smooth muscle fibers within its wall.

Unique to the anatomy of veins is the presence of one-way valves to assist in directing blood flow back to the heart. Venous valves are made up of ...

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