The mediastinum is a collection of organs, nerves, lymph nodes and blood vessels that are in the same space. In front, it is bounded 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 rib cage smoothly passes into the neck space.
Classification
For greater convenience, studying the organs of the chest, its entire space was divided into two large parts:
- anterior mediastinum;
- back mediastinum.
The front, in turn, is divided into upper and lower. The border between them is the base of the heart.
Also, spaces filled with fatty tissue are secreted in the mediastinum. They are placed between the vaginas of blood vessels and organs. These include:
- retrosternal or retrotracheal (superficial and deep) - between the sternum and esophagus;
- pretracheal - between the trachea and the aortic arch;
- left and right tracheobronchial.
Borders and main organs
The border of the posterior mediastinum in front is the pericardium and trachea, behind - the front surface of the bodies of the thoracic vertebrae.
The following organs are located within the anterior mediastinum:
- a heart with a bag surrounding it (pericardium);
- upper respiratory tract: trachea and bronchi;
- thymus gland or thymus;
- The lymph nodes;
- phrenic nerve;
- the initial part of the vagus nerves;
- two sections of the largest vessel of the body - the aorta (ascending part and arch).
The following organs are part of the posterior mediastinum:
- the descending part of the aorta and the vessels extending from it;
- upper part of the gastrointestinal tract - esophagus;
- the part of the vagus nerves located below the roots of the lungs;
- thoracic lymphatic duct;
- unpaired vein;
- semi-unpaired vein;
- sympathetic trunk ;
- The lymph nodes;
- abdominal nerves.
Features and abnormalities 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 - XI thoracic. This is a tubular organ that has a wall consisting of three layers:
- mucous membrane inside;
- muscle layer with ring and longitudinal fibers in the middle;
- serous membrane outside.
In the esophagus, the cervical, thoracic and abdominal parts are distinguished. The longest of them is chest. Its dimensions are approximately 20 cm. At the same time, the cervical region has a length of about 4 cm, and the abdominal region is only 1-1.5 cm.
Among the malformations of the organ, the most common is atresia of the esophagus. This is a condition in which the named part of the digestive canal does not pass into the stomach, but ends blindly. Sometimes, atresia forms a connection between the esophagus and trachea, which is called the fistula.
Fistula formation is possible without atresia. These moves can occur with the respiratory system, pleural cavity, mediastinum, and even directly with the surrounding space. In addition to congenital etiology, fistulas form after injuries, surgical interventions, cancer and infectious processes.
Features of the structure of the descending aorta
Considering the anatomy of the chest, you should analyze the structure of the aorta - the largest vessel in the body. In the posterior part of the mediastinum, its descending section is located. This is the third part of the aorta.
The entire vessel is divided into two large departments: thoracic and abdominal. The first of them is located in the mediastinum from the IV thoracic vertebra to XII. To the right of it is an unpaired vein and a thoracic duct, on the left side there is a semi-unpaired vein, in front - a bronchus and a heart bag.
The thoracic aorta gives two groups of branches to the internal organs and tissues of the body: internal and parietal. The second group includes 20 intercostal arteries, 10 on each side. Internal, in turn, include:
- bronchial arteries - most often there are 3 pieces that carry blood to the bronchi and lungs;
- esophageal arteries - there are from 4 to 7 pieces supplying the esophagus with blood;
- blood vessels supplying the pericardium;
- mediastinal branches - carry blood to the mediastinal lymph nodes and adipose tissue.
Features of the structure of unpaired and semi-unpaired veins
An 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 on the right side, bronchial and esophageal veins flow into it. The unpaired continuation is the inferior vena cava, which carries blood from the whole organism directly to the heart. This transition is located at the level of IV-V thoracic vertebrae.
A 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 she 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 chest part of the lymphatic duct. This department originates in the aortic orifice of the diaphragm. And it ends at the level of the upper thoracic aperture. First, the duct is covered by the aorta, after - by the wall of the esophagus. Intercostal lymphatic vessels, which carry lymph from the back of the chest cavity, flow into it from two sides. It also includes the broncho-mediastinal trunk, collecting lymph from the left side of the chest.
At the level of II-V thoracic vertebrae, the lymphatic duct sharply turns to the left side and then approaches the VII vertebra of the cervical spine. On average, its length is 40 cm, and the lumen width is 0.5-1.5 cm.
There are different options for the structure of the thoracic duct: with one or two trunks, with a single trunk that bifurcates, straight or with loops.
Blood flows to 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 located between the subclavian artery and vein. The right recurrent nerve departs from it, which, like the left, approaches the space of the neck.
The thoracic nerve gives four main branches:
- front bronchial - are part of the anterior pulmonary plexus along with the branches of the sympathetic trunk;
- posterior bronchial - are part of the posterior pulmonary plexus;
- to the heart bag - small branches carry a nerve impulse to the pericardium;
- esophageal - form the anterior and posterior esophageal plexus.
Lymph nodes of the mediastinum
All lymph nodes located in this space are divided into two systems: parietal and visceral.
The visceral system of the lymph nodes includes the following formations:
- front lymph nodes: right and left front 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. A generalized increase is called lymphadenopathy. For a long time, it can occur without any symptoms. But a prolonged increase in lymph nodes ultimately makes itself felt by such disorders:
- weight loss;
- lack of appetite;
- excessive sweating;
- high body temperature;
- tonsillitis 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 grave consequences requiring the help of a specialist.