Structure and Physiology

Diseases of the peripheral arterial system cause ischemia of the extremities. When the body is at rest, collateral blood vessels may be able to provide adequate circulation. During exercise, when oxygen demand increases, this circulation may not be sufficient for the actively contracting muscles, and ischemia may result.

The venous system consists of a series of low-pressure capacitance vessels. Nearly 70% of the blood volume is contained in this system. Although offering little resistance, the veins are controlled by a variety of neural and humoral stimuli that enhance venous return to the right side of the heart. In addition, valves aid in the return of blood.

When an individual is in the upright posture, the venous pressure in the lower extremity is the highest. Over many years, the veins dilate as a result of weakening of their walls. As the walls dilate, the veins are unable to close adequately, and reflux of blood occurs. In addition, the venous pump becomes less efficient in returning blood to the heart. Both of these factors are responsible for the venous stasis seen in patients with chronic venous insufficiency. Complications from venous stasis include pigmentation, dermatitis, cellulitis, ulceration, and thrombus formation.

The lymphatic system is an extensive vascular network and is responsible for returning tissue fluid (lymph) back to the venous system. The extremities are richly supplied with lymphatic tissue. Lymph nodes, many of which are located between major proximal joints, aid in filtering the lymphatic fluid before it enters the blood. The most important clinical symptoms of lymphatic obstruction are lymphedema and lymphangitis.

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