The azygos vein is formed from the right lumbar vein up through the right phrenic foot and into the posterior mediastinumaortaThe right rear of the thorax and esophagothorax runs along the right front of the spine, collecting most of the right posterior intercostal veins, semiazygos veins, accessory semiazygos veins, and the veins of the esophagothorax, pericardium, and main bronchus.At the height of the fourth thoracic vertebra, the azygos vein bends forward to form an azygos vein arch and flows into the superior vena cava above the right pulmonary root.
Since the superior vena cava and inferior vena cava are separated by the heart, there is no vein trunk in the chest that is equivalent to and accompanies the thoracic aorta. Therefore, the venous blood of the chest wall and most organs in the chest all flows into a special vein, called azygos vein.This vein starts from the right lumbar ascending vein at the right foot of the diaphragm, rises along the right side of the thoracic spine, turns to the height of the fourth thoracic vertebral body, hooks forward above the right lung root, enters the pericardial cavity, and injects into the superior vena cava.The azygos vein collects the venous blood of the right intercostal vein, esophageal vein, bronchial vein and semiazygos vein. The semiazygos vein starts from the left lumbar ascending vein, about the height of the 9th or 10th thoracic vertebral body and flows right across the spine into the azygos vein.It mainly collects venous blood from right intercostal vein, esophageal vein and bronchial vein.
The upper end of the azygos vein flows into the superior vena cava, while the lower end starts from the ascending lumbar vein of the inferior vena cava system.Therefore, azygos vein is one of the important channels to communicate with superior and inferior vena cava.When the return of superior vena cava or inferior vena cava is obstructed, the above channels become one of the important lateral collateral circulation pathways.
2. Veins:
The blood vessels that carry blood back to the atrium are called veins.According to the size of pipe diameter, it can also be divided into four levels: large, medium, small and micro.The structure of the tube wall is basically similar to that of the artery, and it is composed of three layers of membrane: inner, middle and outer.The boundary of the three-layer membrane is not very clear. The membrane is thinner than the corresponding artery, and the elastic tissue and smooth muscle are not as developed as the artery. Therefore, the elasticity and contractility are small.But the adventitia is relatively developed.The veins are divided into superficial veins and deep veins, which are connected with each other.The superficial vein is located under the skin, so it is also called skin vein or subcutaneous vein.The deep vein is located on the deep surface of the deep fascia or in the body cavity, and is accompanied by the artery of the same name.Generally, there are two accompanying veins of middle and small arteries.Therefore, there are many veins. Compared with the corresponding artery, the vein has a large diameter, thin wall, small elasticity, and a vein valve formed from the endothelium to the lumen, which can prevent blood reflux.In addition, the variation of veins is greater than that of arteries, and even different sections of the same vein often have greater differences.
A vein with a diameter of more than 10 mm is generally called a great vein.As above, inferior vena cava, innominate vein, subclavian vein, internal jugular vein and femoral vein;Those with a diameter of less than 10 mm and more than 2 mm are called middle veins;Those below 2 mm and above 300 μ m are called venules.Veins migrate from venules.
The function of veins is to guide blood from all parts of the body back to the heart.The driving force of venous blood return is the pressure difference in the venous tube, rather than the contraction of the tube wall itself.There are many factors that affect the venous pressure difference, such as cardiac contractility, gravity, body position, respiratory movement, muscle contraction around the vein, squeezing and arterial pulsation in the corresponding part.
Tissue structure and surrounding structure of azygos vein:
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Azygos vein is a branch of superior vena cava.The azygos vein starts from the right lumbar ascending vein, goes up along the right side of the thoracic vertebra, bends slightly forward at the level of the fourth or fifth thoracic vertebra, and flows around the right lung root to the superior vena cava.The azygos vein receives blood from the right intercostal vein, esophageal vein and semiazygos vein.The azygos vein passes through the middle branch, collects the venous blood of the rear thoracic organs from the front, and collects the venous blood of the venous plexus from the rear, anastomoses with the vein of the rear abdominal wall downward, and connects with the intercostal vein on both sides.Therefore, it is the pathway to communicate the superior and inferior vena cava. These extensive communication and anastomosis relationships are of clinical significance.
The azygos vein is a longitudinal vein that extends from the right ascending lumbar vein to the chest. It mainly receives the venous return of the chest wall and the posterior mediastinal organs, and is one of the important connecting channels between the superior and inferior vena cava.The azygos vein starts from the junction of the right ascending lumbar vein and the right inferior costal vein, and sometimes there are small branches from the inferior vena cava (at the level of the renal vein) or the venous plexus in front of the upper lumbar body. These small branches are called the lumbar azygos vein.Ascending through the middle leg of the diaphragm and between the medial leg of the diaphragm (or aortic hiatus) to enter the posterior mediastinum, then ascending along the thoracic aorta at the rear of the esophagus, and on the right side of the thoracic duct, when reaching the level of the fourth thoracic vertebra, the arch goes forward to bypass the upper right lung root, into the superior vena cava, and occasionally into the right cephalbrachial vein or the right internal thoracic vein.During its journey, azygos vein receives its branches along the way, including esophageal vein, bronchial vein, pericardial vein, etc. in front;The right side receives all intercostal veins except the first intercostal vein, and the left side is between the 8th and 10th thoracic vertebrae, with half azygos vein confluence.The semiazygos vein is formed by the confluence of the left lower intercostal vein and the accessory semiazygos vein, and the accessory semiazygos vein collects the left middle upper intercostal vein;The accessory semiazygos vein can also be directly injected into the azygos vein.The posterior azygos vein receives veins from the vertebral and external venous plexus;The azygos vein and semiazygos vein can be connected to the common iliac vein (belonging to the inferior vena cava system) through the ascending lumbar vein, which is one of the important channels for communicating the superior and inferior vena cava.These extensive anastomoses have important clinical significance. When the blood flow of superior vena cava or inferior vena cava is blocked, the above anastomotic channels become important ways of collateral circulation.Since the azygos vein communicates with the vertebral and external venous plexus, and these two plexuses communicate with the intracranial venous sinus, the infection of the thorax and abdomen can spread to the intracranial, and vice versa.
There are many variations in azygos vein, semiazygos vein and accessory semiazygos vein, which can be divided into four types according to their existence and deficiency: ① the most common one is that all three veins exist, accounting for about 66%; ②The absence of accessory semiazygos vein accounted for 27%; ③The absence of semiazygos vein accounts for about 5%; ④Only 2% of the patients lacked both semiazygos vein and accessory semiazygos vein.
In addition, the azygos vein may also form on the left side, and then bypass the rear of the left lobe of the liver and finally the coronary sinus.
