The ascending lumbar vein is an ascending blood vessel that runs alongside the spine. In the right half of the body, it flows into the azygos vein, while on the left it flows into the hemiazygos vein. The ascending lumbar vein may provide a bypass route in cases of inferior vena cava embolism.
What is the ascending lumbar vein?
The ascending lumbar vein is a blood vessel of the systemic circulation. The vein carries deoxygenated blood toward the heart, from where the body pumps the blood into the pulmonary circulation. There, the red blood cells (erythrocytes) take up oxygen and distribute it to the various organs and tissues of the organism. The ascending lumbar vein occurs in both halves of the body. Anatomy distinguishes between the vena lumbalis ascendens dextra (right) and the vena lumbalis ascendens sinistra (left). Because the human body is not completely symmetrical and the heart is displaced to the left in most individuals, the two blood vessels follow a slightly different course.
Anatomy and structure
On both the right and left sides, the ascending lumbar vein passes under the lumbar muscle (psoas major and psoas minor muscles). There it runs even before the costal processes, at the level of the lumbar vertebrae. The vena lumbalis ascendens thereby crosses the regio lumbalis between the iliac crest and the lowest rib. On the right side of the body, the vena lumbalis ascendens flows into the vena azygos, which runs in the region of the thoracic spine. Through the lumbar fissure (pars lumbalis diaphragmatis), the azygos vein passes through the diaphragm and enters the superior vena cava. Prior to this, several other veins flow into the azygos vein, including the hemiazygos vein. This originates in the left side of the body and also receives blood from the left ascending lumbar vein. From the superior vena cava, blood enters the right atrium. The ascending lumbar vein has a wall that consists of three layers in cross-section. The innermost vein wall is the tunica interna, which has a layer of endothelial cells. These line the interior of the blood vessel. The tunica interna also includes the venous valves. Above this is the tunica media, which has a layer of smooth muscle. The tunica externa forms the outer layer of the vein wall and is also known as the tunica adventitia.
Function and Tasks
The ascending lumbar vein has a connection to the lumbar veins. Normally, they drain into the inferior vena cava, which begins in the lumbar spine, passes through the diaphragm, and flows into the right atrium via the sinus venarum cavarum. The ascending lumbar vein carries deoxygenated blood. In the human body, red fluid moves within a closed circuit. Therefore, the proper drainage of blood is of great importance. As the ascending lumbar vein rises in the body, it must transport blood upward against gravity most of the time. It is aided in this by a thin layer of muscle located in the vein wall. Venous valves protrude into the interior of the blood vessel, preventing the blood from flowing back. Blood pressure within a vein is relatively low, typically 0-15 mm Hg. By comparison, arteries have an average blood pressure of 70-120 mm Hg in healthy people. Because of this difference, medicine also refers to the low-pressure system. This part of the cardiovascular system includes the ascending lumbar vein and all other veins, as well as parts of the heart, the pulmonary circulation and the fine capillary bed. The low-pressure system serves to store blood. Its vessels release more blood when the volume in the total circulation decreases. This happens, for example, when blood is lost due to injury. As soon as the body has sufficient blood volume again, it fills up the low-pressure system until it again stores around 85% of the blood within it.
Diseases
The ascending lumbar vein has a connection to the lumbar vein, external iliac vein, and iliolumbar vein on the one hand and to the superior vena cava on the other. As a result, it can contribute to a collateral circulation that bypasses the inferior vena cava. In this case, medicine also speaks of a cavocaval anastomosis, where “anastomosis” refers to a connection and “cavocaval” refers to the vena cava.Such bypass circulation is relevant when blood flow in the inferior vena cava is no longer guaranteed, especially in the event of constriction or occlusion of the blood vessel. The clinical phenomenon is also known as embolism and may be due to various causes. A thrombus consists of clotted blood platelets that clump together in the vessel. The blood components can be deposited, for example, on the venous valves or in protrusions of the vein wall. Lack of exercise, smoking, an unhealthy diet and other risk factors promote the development of a thrombus. If such a clot detaches, it can subsequently get stuck in a smaller blood vessel or become wedged. Another possible cause of venous occlusion is gas embolism, in which gases are released from the blood and obstruct blood flow. Other forms of embolism include foreign bodies and the body’s own tissues that can enter the vein, for example, when injured. Tumors can also restrict blood flow. The ascending lumbar vein can also be directly damaged by injuries to the back. In addition, other vein diseases such as inflammation (phlebitis) are basically possible.