The mediastinum is a collection of organs, nerves, lymph nodes and vessels that are in the same space. In front, it is limited by the sternum, on the sides - by the pleura (the membrane surrounding the lungs), behind - by the thoracic spine. From below, the mediastinum is separated from the abdominal cavity by the largest respiratory muscle - the diaphragm. There is no border from above, the chest smoothly passes into the space of the neck.
Classification
For greater convenience of studying the organs of the chest, all its space was divided into two large parts:
- anterior mediastinum;
- posterior mediastinum.
The front, in turn, is divided into upper and lower. The border between them is the base of the heart.
Also in the mediastinum allocate spaces filled with fatty tissue. They are located between the sheaths of vessels and organs. These include:
- retrosternal or retrotracheal(superficial and deep) - between the sternum and the esophagus;
- pretracheal - between the trachea and the aortic arch;
- left and right tracheobronchial.
Borders and major organs
The border of the posterior mediastinum in front is the pericardium and trachea, behind - the anterior surface of the bodies of the thoracic vertebrae.
The following organs are located within the anterior mediastinum:
- heart with a bag surrounding it (pericardium);
- upper airways: trachea and bronchi;
- thymus or thymus;
- lymph nodes;
- phrenic nerve;
- initial part of vagus nerves;
- two sections of the largest vessel of the body - the aorta (ascending part and arch).
The posterior mediastinum includes the following organs:
- descending aorta and vessels extending from it;
- upper gastrointestinal tract - esophagus;
- part of the vagus nerves below the roots of the lungs;
- thoracic lymphatic duct;
- unpaired vein;
- semi-unpaired vein;
- sympathetic stem;
- lymph nodes;
- abdominal nerves.
Features and anomalies of the structure of the esophagus
The esophagus is one of the largest organs of the mediastinum, namely its posterior part. Its upper border corresponds to the VI thoracic vertebra, and the lower one corresponds to the XI thoracic vertebra. This is a tubular organ that has a wall consisting of three layers:
- mucousshell inside;
- muscle layer with circular and longitudinal fibers in the middle;
- serosa outside.
The esophagus is divided into cervical, thoracic and abdominal parts. The longest of them is the chest. Its dimensions are approximately 20 cm. At the same time, the cervical region is about 4 cm long, and the abdominal region is only 1-1.5 cm.
Among the malformations of the organ, the most common is esophageal atresia. This is a condition in which the named part of the alimentary canal does not pass into the stomach, but ends blindly. Sometimes atresia forms a connection between the esophagus and the trachea, which is called a fistula.
Fistula formation is possible without atresia. These passages can occur with the respiratory organs, pleural cavity, mediastinum, and even directly with the surrounding space. In addition to congenital etiology, fistulas are formed after injuries, surgical interventions, cancerous and infectious processes.
Features of the structure of the descending aorta
Considering the anatomy of the chest, you should disassemble the structure of the aorta - the largest vessel in the body. In the back of the mediastinum is its descending section. This is the third part of the aorta.
The whole vessel is subdivided into two large sections: thoracic and abdominal. The first of them is located in the mediastinum from the IV thoracic vertebra to the XII. To the right of it is the unpaired vein and the thoracic duct, on the left side is the semi-unpaired vein, in front is the bronchus and the heart sac.
Thoracic aorta gives two groups of branches to internalorgans and tissues of the body: visceral and parietal. The second group includes 20 intercostal arteries, 10 on each side. Internal, in turn, include:
- bronchial arteries - most often there are 3 of them that carry blood to the bronchi and lungs;
- esophageal arteries - there are from 4 to 7 pieces that supply blood to the esophagus;
- vessels supplying blood to the pericardium;
- mediastinal branches - carry blood to mediastinal lymph nodes and adipose tissue.
Features of the structure of the unpaired and semi-unpaired vein
The unpaired vein is a continuation of the right ascending lumbar artery. It enters the posterior mediastinum between the legs of the main respiratory organ - the diaphragm. There, on the left side of the vein is the aorta, spine and thoracic lymphatic duct. 9 intercostal veins flow into it on the right side, bronchial and esophageal veins. The continuation of the unpaired is the inferior vena cava, which carries blood from the whole body directly to the heart. This transition is located at the level of IV-V thoracic vertebrae.
The semi-unpaired vein is also formed from the ascending lumbar artery, only located on the left. In the mediastinum, it is located behind the aorta. After it comes to the left side of the spine. Almost all intercostal veins on the left flow into it.
Features of the structure of the thoracic duct
Considering the anatomy of the chest, it is worth mentioning the thoracic part of the lymphatic duct. This section originates in the aortic orifice.diaphragm. And it ends at the level of the upper thoracic aperture. First, the duct is covered by the aorta, then by the wall of the esophagus. Intercostal lymphatic vessels flow into it from both sides, which carry lymph from the back of the chest cavity. It also includes the broncho-mediastinal trunk, which collects lymph from the left side of the chest.
At the level of the II-V thoracic vertebrae, the lymphatic duct turns sharply to the left and then approaches the VII cervical vertebra. On average, its length is 40 cm, and the width of the gap is 0.5-1.5 cm.
There are different variants of the structure of the thoracic duct: with one or two trunks, with a single trunk that bifurcates, straight or with loops.
Blood enters the duct through the intercostal vessels and esophageal arteries.
Features of the structure of the vagus nerves
The left and right vagus nerves of the posterior mediastinum are isolated. The left nerve trunk enters the space of the chest between two arteries: the left subclavian and the common carotid. The left recurrent nerve departs from it, enveloping the aorta and tending to the neck. Further, the vagus nerve goes behind the left bronchus, and even lower - in front of the esophagus.
The right vagus nerve is first placed between the subclavian artery and vein. The right recurrent nerve departs from it, which, like the left one, approaches the space of the neck.
The thoracic nerve gives off four main branches:
- anterior bronchial - are part of the anterior pulmonary plexus along with branchessympathetic trunk;
- posterior bronchial - are part of the posterior pulmonary plexus;
- to the heart sac - small branches carry a nerve impulse to the pericardium;
- esophageal - form the anterior and posterior esophageal plexuses.
Mediastinal lymph nodes
All lymph nodes located in this space are divided into two systems: parietal and visceral.
The visceral system of lymph nodes includes the following formations:
- anterior lymph nodes: right and left anterior mediastinal, transverse;
- posterior mediastinal;
- tracheobronchial.
Studying what is in the posterior mediastinum, it is necessary to pay special attention to the lymph nodes. Since the presence of changes in them is a characteristic sign of an infectious or cancerous process. The generalized increase is called lymphadenopathy. For a long time it can proceed without any symptoms. But a prolonged enlargement of the lymph nodes eventually makes itself felt with such disorders:
- weight loss;
- lack of appetite;
- excessive sweating;
- high body temperature;
- angina or pharyngitis;
- enlarged liver and spleen.
Not only medical workers, but also ordinary people should have an idea about the structure of the posterior mediastinum and the organs that are in it. After all, this is a very important anatomical formation. Violation of its structure can lead to severeconsequences requiring professional assistance.
