Vein Obstruction

Excerpt

The circulatory system can be divided based on blood vessels types. The venous system comprises blood vessels which carry blood from tissue and organs allowing a return to the heart. The majority of veins carry deoxygenated blood with the exceptions of the umbilical vein which is patent during fetal development, growth and closes after birth and the pulmonary vein. The 3 layers which constitute the structure of a vein are the outer connective tissue layer (tunica adventitia or tunica externa); the middle smooth muscle layer (tunica media); and the inner endothelial cell layer (tunica intima). The middle, smooth muscle layer is less muscular in veins compared to arteries allowing for increased capacitance; however, valves are needed to provide unidirectional flow.

Venous obstruction is partial or complete occlusion of the lumen and can be related to decreased flow and increased pooling. The most commonly seen is a deep vein thrombosis in the lower extremities — venous stasis results in increased viscosity and the formation of microthrombi. This is due to any factor which slows or obstructs the flow of venous blood. One of the most common causes is endothelial (intimal) damage secondary to intrinsic or secondary to external trauma. In a hypercoagulable state, a biochemical imbalance between procoagulant and anticoagulant factors occur. Chronic venous insufficiency is a manifestation of decreased vein wall contractility and vein valve dysfunction.

Other areas affected by venous obstruction include portal vein obstruction which is primary thrombosis of the portal vein.