Human respiratory system: 1 Parietal pleura – 2 Visceral pleura – 3 Primary bronchus – 4 Secondary bronchi – 5 Tertiary bronchi – 6 Bronchiole – 7 Pleural space – 8 Terminal bronchiole – 9 Pulmonary vein – 10 Alveolar sac – 11 Nasal cavity – 12 Pharynx – 13 Larynx – 14 Trachea – 15 Hilum – 16 Mediastinal surface – 17 Capillary – 18 Red blood cell – 19 Pulmonary artery – 20 Alveolar duct – 21 Alveolus.

1. Anatomy of the trachea

It is an irregular tube which penetrates at the level of the upper orifice of the thorax and which will divide into two main bronchi. It has 2 portions:

  • cervical following the larynx;
  • thoracic which runs in the mediastinum and which will be divided into right main bronchus and left main bronchus;

The origin of the trachea at the cervical level is at level C6. The cervical / thoracic trachea junction is made just behind the upper edge of the sternum at level Th2.

 The tracheal bifurcation is done at level Th5.

The trachea allows gas exchange between the ambient air and the pulmonary cavity.

The tube is formed by a stack of cartilage rings, they are present in front and on the lateral faces, hence the crenellated appearance.

Under this stack of 16 to 20 rings, there is the bifurcation.

The two main bronchi located, on the right and on the left, also present a rather resistant cartilaginous framework.

The posterior part is closed by a membrane, it is the transverse blade of the trachea. This membrane is lined on its deep side by a layer of smooth muscle cells, this is the tracheal muscle. By its contraction, it allows the caliber of the trachea to be reduced. The trachea is surrounded by a thin serous membrane that covers the rings and ligaments, this is the adventitia, which lines the trachea over its entire length.

1.1. Dimensions

Moyenne average length: 12 cm (including 6 cm for the thoracic portion)

  • diameter: 12 mm

The size allows gas exchange.

At the bifurcation, the two main bronchi are not symmetrical, there is an angle of 70 °.

The right main bronchus is more vertical than the left.

We find the annular structure.

The rings are closed behind by the transverse blade of the trachea.

On the deep side, we find the tracheal muscles.

At the bifurcation, there is cartilage in the middle portion that divides the lumen of the trachea in two. This cartilage is the Carina. It is a spur that separates the lumen from the trachea into two parts. In the trachea, the mucosa has hair cells which, by their permanent upward beating, cause dust to rise. There are also serous glands.

1.2. Reports

These are essentially vascular reports.

There are the large vessels from the heart:

  • The Aorta, called the aortic arch, formed of three parts:

– ascending, following the aortic orifice, rises in front of the right main bronchus and the trachea; horizontal which crosses the anterior surface of the lower portion of the trachea;

– descending which is a ratio of the left flank of the trachea.

There are large arterial trunks born from the butt:

  • arterial trunk cephalic brachio antero-lateral right ratio of the trachea;
  • the left primary carotid artery in front and left;
  • the left subclavian artery a little further out;
  • The pulmonary artery arises at the level of the pulmonary orifice of the right ventricle. It has a short trunk that divides into two branches; the right pulmonary artery covered by the arch of the aorta opposite the right main bronchus; and the left pulmonary artery which wraps around the left main bronchus, it is an anterior report of the tracheal bifurcation and the origin of the left bronchus;
  • Remainder of the arterial canal, it is a small ligament between the underside of the arch of the aorta and in general the upper part of the pulmonary artery
  • a venous trunk, this is the VCS which is a confluence of the internal jugular vein and the right subclavian vein which will receive the brachio cephalic venous trunk. The VCS is placed in front of the previous elements and ends at the right atrium extended by the right auricle which covers the origin of the aortic arch.

The biggest report of the left main bronchus is the aortic arch. It winds from the aortic orifice of the left ventricle around the left pulmonary pedicle and is placed successively in front on the left then behind compared to the trachea then compared to the main left bronchus.

The brachio cephalic arterial trunk is a little masked. It divides into the right primary carotid and right subclavian artery.

The second most visible trunk is the left primary carotid artery. It rises along the left flank of the trachea. The left subclavian artery goes to the upper edge of the first rib to follow up on the axillary artery.

The pulmonary artery, underlying, covered by the arch of the aorta, follows the right ventricle and will lead to the lungs, by its two branches, the blood which will have to be purified.

The venous elements are located in front of the trachea, it is the confluence of the subclavian vein and the jugular vein behind the sterno-costo-clavicular joint. The VCS ends in the right atrium.

1.3. Nervous elements

  • the 10th left cranial nerve, left pneumogastric nerve, also called left vagus nerve. It accompanies the jugular and the carotid inside the jugulo-carotid package. He walks in front of the butt then goes below. It is a left lateral report of the trachea.

Under the arch, the Xth cranial nerve gives its recurrent: the lower left laryngeal nerve which will go up along the left side of the trachea in the tracheoesophageal angle to the larynx where it will innervate the vocal cords on the left side.

Xth right cranial nerve passes in front of the right subclavian artery and gives its recurrent around the right subclavian artery and it goes up in the tracheoesophageal angle to the larynx where it will innervate the vocal cords on the right side.

There are also the nerves of the heart: plexuses on the anterior portion of the heart which receive branches of the two Xth cranial nerve and parasympathetic chains.

There is another large ganglion on the underside of the arch of the aorta: the Wrisberg ganglion.

The main posterior report is the esophagus.

 It descends vertically behind the trachea; and in the lower part of the posterior mediastinum, it is deflected to the right by the aorta. The arch straddles the left main bronchus and gives way to the descending aorta which runs along the left flank of the spine to the aortic orifice of the diaphragm.

The VCS receives a venous arch back, this is the arch of the azygos vein. It runs along the right flank of the spine and drains all of the venous blood from the chest wall and all of the venous blood from the spine. Its butt ends at the same level as the th4 aortic butt.

Hence the name of cross section for a Th4 cut: we go through the arch of the aorta and the butt of the azygos vein.

The azygos receives venous blood from the left side of the spine through the hemi azygos vein, which most often flows into the Th8 azygos, behind the esophagus and in front of the spine.

The thoracic duct drains all the lymphatic fluid which comes from the lower limbs, it travels between the spine and the esophagus then curves to the left to reach the posterior surface of the left subclavian vein where it is touched.

The trachea is very much forward at the level of the neck. It is separated from the sternum by the remnants of the thymus.

Main report: the esophagus which runs along the anterior concavity of the thoracic spine to the esophageal orifice of the diaphragm.

The two layers of pericardium are reflected around the large vessels. The mediastinal pleura is reflected at the level of the pulmonary pedicles, it follows the whole of the pulmonary cavity by surrounding the two hemithoraxes.

 The two bronchi are surrounded by lymph nodes which are the two retro bronchial nodes, a pre bronchial and a large inter tracheobronchial node, the crossroads of the other nodes.

Copyrigth photo : Par USGOV — file:poumons2.jpg, Public Domain

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