Which of these veins returns blood to the superior vena cava
Anatomical PositionThe superior vena cava is classified as a large vein, with a wide diameter of up to 2cm and a length of approximately 7cm. Show
It arises from the union of the left and right brachiocephalic veins, posterior to the first right costal cartilage. It descends vertically through the superior mediastinum, behind the intercostal spaces and to the right of the aorta and trachea. At the level of the second costal cartilage, the SVC enters the middle mediastinum and becomes surrounded by the fibrous pericardium. It terminates by emptying into the superior aspect of the right atrium at the level of the third costal cartilage.  Fig 1 – Anterior view of the superior vena cava. Clinical Relevance: Jugular Venous PressureThe superior vena cava is a valveless structure. This allows the pressure in the right atrium to be conducted upwards into the right internal jugular vein. Visualisation of the right internal jugular vein is an indicator of the jugular venous pressure – which in turn represents the pressure in the right atrium. To examine, the patient should be at a 45° angle with their head turned slightly to the left. The JVP can be identified as a pulsation between the two heads of the sternocleidomastoid muscle. Causes of a raised JVP include right-sided heart failure, pulmonary hypertension, and SVC obstruction. TributariesThe superior vena cava contains venous blood from the head, neck, both upper limbs and from structures within the thorax It is formed by the union of the right and left brachiocephalic veins – which provide venous drainage of the head, neck, and upper limbs. At the level of T4, the superior vena cava receives the azygous vein, which drains the upper lumbar region and thoracic wall. The SVC receives tributaries from several minor vein groups:
Clinical Relevance: Superior Vena Cava ObstructionThe superior vena cava is a thin-walled, low pressure vessel which makes it vulnerable to compression. Superior vena cava obstruction can occur either due to external compression or from an occlusion within the vessel lumen itself. The most common cause of SVC obstruction is malignancy, typically from lung cancer, lymphoma, or metastatic disease. Vessel obstruction interrupts venous return and can lead to swelling in the neck, face, and upper limbs. Clinical features include shortness of breath and distension of the veins of the face and upper limb. SVC obstruction can be assessed clinically by performing Pemberton’s test. The patient is asked to raise both arms above their head – a positive test is indicated if facial oedema or cyanosis occurs after approximately 1 minute.
SPRINGER MEDIZIN/Getty Images The venae cavae are the two largest veins in the body. These blood vessels carry oxygen-depleted blood from various regions of the body to the right atrium of the heart. The superior vena cava delivers blood from the head and chest area to the heart, while the inferior vena cava returns blood from the lower body regions to the heart. As blood is circulated along the pulmonary and systemic circuits, oxygen-depleted blood returning to the heart is pumped to the lungs by way of the pulmonary artery. After picking up oxygen in the lungs, the blood is returned to the heart and is pumped out to the rest of the body via the aorta. The oxygen-rich blood is transported to cells and tissues where it is exchanged for carbon dioxide. The newly oxygen-depleted blood is returned to the heart again via the venae cavae. Function of the Venae CavaeMedicalRF.com/Getty ImagesThe superior and inferior venae cavae play a vital role in blood circulation as they return oxygen-poor blood to the heart for re-oxygenation and recirculation.
The superior vena cava is located in the upper chest region and is formed by the joining of the brachiocephalic veins. These veins drain blood from the upper body regions including the head, neck, and chest. It is bordered by heart structures such as the aorta and pulmonary artery. The inferior vena cava is formed by the joining of the common iliac veins which meet a little below the small of the back. The inferior vena cava travels along the spine, parallel to the aorta, and transports blood from the lower extremities of the body to the posterior region of the right atrium. Superior and Inferior Vena Cava LocationMedicalRF.com/Getty Images Like arteries and medium-sized veins, the walls of the superior and inferior venae cavae are composed of three layers of tissue. The outer layer is the tunica adventitia or tunica externa. It is composed of collagen and elastic fiber connective tissues. This layer allows the vena cava to be strong and flexible. The middle layer is composed of smooth muscle and is called the tunica media. Smooth muscle in this layer allows the venae cavae to receive input from the nervous system. The inner layer is the tunica initima. This layer has an endothelium lining which secretes molecules that prevent platelets from clumping together and helps blood to move smoothly. Veins in the legs and arms also have valves in the innermost layer that are formed from the infolding of the tunica intima. The valves are similar in function to heart valves, which prevent blood from flowing backwards. Blood within veins flows under low pressure and often against gravity. Blood is forced through the valves and toward the heart when skeletal muscles in the arms and legs contract. This blood is eventually returned to the heart by the superior and inferior venae cavae. Venae Cavae ProblemsScience Photo Library - PIXOLOGICSTUDIO/Getty Images Due to the important role that the superior and inferior venae cavae play in circulation, problems arising with these large veins can have serious consequences. Since veins have relatively thin walls and the venous system is a low-pressure system, both venae cavae are subject to compression by surrounding tissues that swell. This compression inhibits blood flow and impacts proper heart function. The development of blood clots within the venae cavae can also impede or block blood from returning to the heart. Superior vena cava syndrome is a serious condition that arises from the constriction or obstruction of this vein. The superior vena cava may become constricted due to enlargement of surrounding tissue or vessels such as the thyroid, thymus, aorta, lymph nodes, and cancerous tissue in the area of the chest and lungs. The swelling may slow or obstruct blood flow to the heart. Superior vena cava syndrome is most often caused by lung cancer and lymphoma. Inferior vena cava syndrome is caused by the obstruction or compression of the inferior vena cava. This condition results most often from tumors, deep vein thrombosis, congestive heart failure, kidney disease, and pregnancy. Sources "Obstruction of the Veins to the Heart (Superior Vena Cava Syndrome)." UNM Comprehensive Cancer Center, UNM Health Sciences Center, 2016, New Mexico. Tucker, William D. "Anatomy, Abdomen and Pelvis, Inferior Vena Cava." Bracken Burns, National Center for Biotechnology Information, U.S. National Library of Medicine, April 3, 2019, Bethesda MD. Watch Now: What Is the Circulatory System?What supplies blood to the superior vena cava?Embryologically, the SVC is formed by the left and right brachiocephalic veins (also known as the innominate veins) that also receive blood from the upper limbs, certain parts of the head, one being the eyes, and neck.
How does blood return to the superior vena cava?Venous return from the lower half, below the diaphragm, flows through the inferior vena cava. The SVC is located in the anterior right superior mediastinum.
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. Where does the superior vena cava receive blood from?In addition to the innominate veins, the superior vena cava receives blood from the azygous vein and small veins from the mediastinum (the region between the two lungs) and the pericardium.
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