The vena hemiazygos is a venous continuation of one of the longest veins in the body. It runs cranially to the diaphragm. Its functions include transporting venous blood to the azygos vein.
What is the hemiazygos vein?
The blood that is in the body circulates in the systemic circulation and is transported by blood vessels. These blood vessels are veins. In them, blood flows back to the heart. Venous blood is characterized by the fact that it is particularly low in oxygen. Some veins have to transport blood against the force of gravity. The vena hemiazygos is also oriented cranially, i.e. upward, in the region of the thoracic spine. The vena hemiazygos is a branch of the venae lumbales ascendentes. These are veins that run along the trunk of the spine. They are particularly long compared to other veins of the human body. The vena hemiazygos runs as a branch along the thoracic spine and through the thoracic cavity. Almost all human organs are located there. In the area of the thoracic cavity, the vena hemiazygos takes in other veins and then flows into the vena azygos. This carries the venous blood cranial to the diaphragm to the superior vena cava. This is one of the largest veins in the human body. Its blood pathway runs from the head and neck to the heart via the upper extremities.
Anatomy and structure
Beginning in the thoracic vertebral region, the vena hemiazygos travels along the left side of the thoracic vertebral bodies. It then runs to the diaphragm. It takes its route there through the medial lumbar fissure. At this point it passes from the abdominal cavity to the thoracic cavity of the human organism. From the thoracic cavity, the hemiazygos vein runs into the posterior thoracic cavity. The thoracic cavity is called the mediastinum. It contains all organs with the exception of the lungs. The vena hemiazygos continues from the thoracic cavity into the area of the thoracic vertebral bodies. There are twelve numbered thoracic vertebrae along the thoracic spine. The vena hemiazygos moves to the ninth thoracic vertebral body. The direction at this point of the vein is cranial. This means that it is anatomically oriented in the direction of the head or “upward.” At the level of the ninth thoracic vertebral body, the vena hemiazygos receives the venae bronchiales. In addition, the venae intercostales posteriores and the venae oesophageae also flow into it. It then crosses to the opposite side in the region between the seventh and ninth thoracic vertebrae. Here the vena hemiazygos joins the vena azygos.
Function and tasks
The blood is essential for oxygen supply to the tissues and CO2 removal. In addition, nutrients and hormones are transported through it to their destination. The body’s thermoregulation takes place via the blood. All these functions are carried out by the venous blood of the vena hemiazygos. Veins of all types are ideal for infusion. Through a parenteral supply of fluids as well as medications, they quickly enter the blood and through the bloodstream they are transported to the appropriate locations in a short time. There they can develop their effect. The wall of veins is thinner than that of arteries, as their layers are less distinct. For this reason, they are readily used for the supply as well as the withdrawal of blood. Even though the vena hemiazygos is less suitable for infusions or the supply of blood, it is directly and essentially involved in the rapid transport of the absorbed messenger substances, since it runs in the thoracic cavity along all organs except the lungs. The vena hemiazygos is a branch of a bypass circulation. It is connected to the azygos vein and the venae lumbales ascendentes. The latter, in turn, is connected to the inferior and superior vena cava. All together they can form a circulation between the two vena cavae. This is called the collateral circulation and is a bypass circulation. It is also called a cavocaval anastomosis. In this case, the collateral circulation arises physiologically, but it can also develop in acute or chronic circulatory disturbance by use of collateral vessels.
Diseases
The wall of the veins is thin. This makes it susceptible to lesions and disease. If the vena hemiazygos is damaged, the supply to important organs as well as the lumbar spine is restricted. Common diseases of the veins are venous thrombosis or thrombophlebitis. Thrombophlebitis is an inflammation of the veins. This is accompanied by the formation of a blood clot.The patient feels pulling pain and tightness in the affected region. When pressure is applied to the vein, a sharp pain occurs. If the blood clot detaches from the vein, for example, it is transported directly to the heart with the venous blood flow. It then travels to the lungs. There, the thrombus clogs a blood vessel and causes a life-threatening pulmonary embolism. In the healing process of inflammation of the vein wall, persistent occlusion can occur as well as permanent damage to the vein valves. This leads to an overall dysfunction of the venous system. In diseases such as cancer, the veins play an important role. Cancer cells that detach from the original tumor are transported via the bloodstream to other locations in the body. Metastases then develop there and the cancer spreads. The vena hemiazygos is involved in a bypass circulation. Cancer cells can be transported through it to organs within the chest.
