Back there is the spine: 12 thoracic vertebrae, 5 lumbar, increasing in height from top to bottom. The dorsal spine is concave in front, the lumbar is behind. The most anterior vertebra is L3. In front of the thorax, the sternum has two parts: the sternal manubrium and the body of the sternum. The upper edge of the manubrium is at level Th2. The manubrium / body junction (Louis’ angle) is at level Th4. The sternum extends from the anterior part of the trunk to Th10. At its lower part, it ends with the xiphoid process, often bituberculée and pierced, palpable.
The abdominal and thoracic cavities are separated by the diaphragm muscle. This is inserted over the entire lower orifice of the thorax : sternum in front, costal ends laterally, the spine behind. It is a dome with a fibrous center. The periphery is muscular.
The thoracic cavity is located above the diaphragm, it consists of three regions: the two right and left hemithorax, which contain the right and left lungs respectively covered by the pleura which pass between the lungs and on the lateral sides of the cavity, and the mediastinum which contains the heart and some vessels.
The diaphragm creates a straight hemi-dome which rises higher because it is raised by the liver.
Projection on the thorax: the right part of the diaphragm corresponds to the fourth intercostal space, the left part at the level of the fifth.
The bony thorax is closed by 12 pairs of ribs, behind by the spine and in front by the sternum. The manubrium narrows from top to bottom, then the body widens from top to bottom. At the level of the xiphoid process, the body shrinks. The body receives insertions from all ribs through the costal cartilages. The first rib limits the upper orifice of the thorax outside. It is marked by the Lisfranc tubercle where the tendon of the anterior scalene muscle is inserted. The second rib is a little wider. It ends at the corner of Louis. The thorax widens up to the level of the fifth rib, then it will gradually reduce in width. The eighth, ninth and tenth ribs will end on a common costal cartilage, that of the seventh rib. These are therefore false ribs. The eleventh and twelfth are floating ribs because they do not end on the sternum. The end of the twelfth rib is at L1.
The trunk consists of two cavities, the thoracic cavity at the top and the abdominal cavity at the bottom. They are separated by a muscle: the diaphragm. The trunk is connected to the upper limbs by the shoulder joints and to the lower limbs by the coxofemoral joints.
The trunk is delimited by:
the spine back,
the ribs on the sides for the thorax,
the muscles of the abdominal wall for the abdomen
the first rib which forms with the collarbones the upper opening
The muscles of the perineum that close the abdomen down, in the hip bones.
2. The Coasts
They are even bones. They consist of a head which is articulated with two thoracic vertebrae. The head is carried by the collar. At the junction between the neck and the posterior arch, there is a tuberosity which rests on the transverse process of the lower vertebra. The posterior articulation is solid, it is done in two points. Then, 3 arches: posterior, middle, anterior. So 2 angles: posterior and anterior.
Anteriorly, the rib is followed by a costal cartilage which unites it to the sternum.
Each side has two faces: one external, one internal and two edges: upper and lower. The bottom edge is hollowed out, a bit like a gutter. So between 2 ribs, there is the intercostal space. There are muscles organized on three planes : external, medium and internal and between them, a fairly thick fibrous sheet which constitutes the intercostal fascia, ie from top to bottom: vein, artery, intercostal nerve. This provision is constant.
Clinical application : pleural puncture. It is taken at the level of the upper base of the coast.
The thoracic fascia is attached to the pleura in the thoracic cavity.
Pneumothorax = gas effusion, hemothorax = blood effusion, pleurisy = infected effusion.
3. The Diaphragm
It is a muscle that closes the chest cavity below. It is also a respiratory muscle.
It is formed by a muscular periphery and a fibrous center in the shape of a clover with three leaflets: anterior, right and left. This clover is the intersection of several fibrous planes :
• upper strip: fibers that start from the anterior leaflet, concentrate towards the rear of the phrenic center and flare at the level of the right part of the phrenic center.
• lower strip: fibers of the left leaflet which concentrate towards the front of the phrenic center, cross from below the fibers of the upper strip to regroup in the anterior part of the phrenic center and flare out in the right part.
The criss-cross delimits an orifice where the IVC engages which rises from the abdominal cavity to engage in the thoracic cavity. In the phrenic center, there is no risk of it being compressed.
The diaphragm is inserted around the entire periphery of the lower orifice of the thorax. At Th12, there is an important orifice, the one where the Aorta passes : the Thoracic aorta becomes Abdominal aorta. There is therefore a fibrous orifice between the pillars, undeformable. The pillars of the diaphragm are arches for inserting the diaphragm between the vertebral body and the transverse process. The right pillar is inserted on L1, L2, L3 and the left pillar on L1 and L2. The two pillars meet in front of Th12 to form the orifice of the Aorta. At Th10, the fibers intersect to form the esophageal orifice.
Another important opening is the esophageal opening in the thickness of the muscle, in front of and outside the Aorta. The esophagus can be compressed and the diaphragm can be used for swallowing.
Finals, There are perforations : the hiatus.
• the 2 cost diaphragmatic hiatus, behind : the diaphragm is crossed There by nervous elements: the sympathetic chains.
• the 2 sternocostodiaphragmatic hiatuses, in front : they give way to the vascularization vessels of the wall: the median thoracic artery with one or two veins.
The esophagus is accompanied by two nerves : the right and left pneumogastric nerves or Xth cranial nerves. The left became anterior, and the right posterior.
With the Aorta, the central lymphatic collector of the abdomen travels: the Pecquet cistern. It converges the lymphatic channels towards the thoracic cavity.
On each side of the pillars, along the first lumbar vertebrae insert the accessory pillars. There is also the arch of the psoas, which connects the transverse process and the body, surrounding the upper part of the psoas, it belongs to the posterior insertions of the diaphragm. These fibers continue until the twelfth rib and cover the origin of the lumbar muscle, and this line continues on the ends of the different ribs.
The diaphragm has a long insertion line.
Another report: the splanchnic nerves, nerves of the viscera, located between the lateral and anterior pillars.
4. Respiratory Mechanics
Inspiration = contraction of the diaphragm, separation of the thorax laterally and forward. Air inspiration rich in O2.
Innervation of the diaphragm: vagus nerve (pneumogastric), 10th cranial nerve. This nerve originates at the medullary level of C4. It bypasses the anterior scalene muscle and descends into the mediastinum. There are two phrenic nerves: right and left.
Vascularization of the diaphragm: the median thoracic artery which crosses it, the inferior and postero-inferior diaphragmatic arteries which arise from the abdominal aorta, they vascularize the diaphragm by its underside.