Note

Structures that pass through the diaphragm without a specific hiatus include the sympathetic trunk, the thoracic splanchnic nerves, the hemiazygos vein, and most branches of the phrenic nerves.

Clinical Correlate

Pain Referral

8ecause the innervation to the diaphragm (motor and sensory) is primarily from G through G spinal nerves, pain arising from the diaphragm (e.g.; subphrenic access) is referred to these dermatomes in the shoulder region.

Figure lll-2-20.The Diaphragm

Figure lll-2-20.The Diaphragm

Interior vena cava Esophagus Aorta

Interior vena cava Esophagus Aorta

Table III-2-4. Important Landmarks in the Thorax

Level

Landmark

T2

Jugular notch

T3

Base of scapular spine

Top of aortic arch

T4

Sternal angle (manubriosternal junction)

Second costal cartilage

Tracheal bifurcation

Upper end of ascending aorta

Beginning of descending aorta

Arch of azygos vein and its entrance into superior vena cava

Fusion of right and left mediastinal pleurae in anterior midline

T7

Inferior angle of scapula

T8

Caval hiatus

T9

Xiphoid process

TIO

Esophageal hiatus

T12

Aortic hiatus

Bracheocephahc

Trunk

Left Common

Bracheocephallc Manubrium

Carotid Artery

Esophagus

Subclavian

Artery

J2 Vertebra Scapula

Bracheocephahc

Trunk

Left Common

Bracheocephallc Manubrium

Carotid Artery

Esophagus

Subclavian

Artery

J2 Vertebra Scapula

Superior

Aortic

Trachea

Vena Cava

Esophagus

Ribs t3 Vertebra Scapula

Superior

Aortic

Trachea

Vena Cava

Esophagus

Ribs t3 Vertebra Scapula

Figure III-2-24. Chest: CT, T3

Superior Vena Cava

Ascending Aorta

Bifurcation of Trachea

Descending Aorta

Superior Vena Cava

Ascending Aorta

Bifurcation of Trachea

Descending Aorta

Ribs

T4 Vertebra

Scapula

Ribs

T4 Vertebra

Scapula

Figure III-2-25. Chest: CT, T4

Ri9ht Body of Pulmonary

Pulmonary Superior sternum Ascending Trunk Artery Vena Cava / Aorta

Ri9ht Body of Pulmonary

Pulmonary Superior sternum Ascending Trunk Artery Vena Cava / Aorta

Descending Aorta

T5 Vertebra Spinal Cord

Figure 111-2-26. Chest: CT,TS

Descending Aorta

T5 Vertebra Spinal Cord

Figure 111-2-26. Chest: CT,TS

R>9ht Right Left

Atrium Ventricle Ventricle

R>9ht Right Left

Atrium Ventricle Ventricle

T6 Vertebra Spinal I Descending Left

Cord 1 Aorta Atrium

Esophagus

T6 Vertebra Spinal I Descending Left

Cord 1 Aorta Atrium

Esophagus

Figure 111-2-27. Chest: CT,Te

Superior Ascending Pulmonary

Vena Cava Aorta Trunk

Superior Ascending Pulmonary

Vena Cava Aorta Trunk

Esophagus Descending

Aorta

Figure 111-2-28. Chest: MRI, Axial T4

Esophagus Descending

Aorta

Figure 111-2-28. Chest: MRI, Axial T4

kapun.. , medical 159

Right Left

Ventricle Ventricle

Right Atrium

Figure 1(1-2-29. Chest: MRI, AxlalT6

Esophagus Descending

Aorta

Len Atrium

Right Left

Ventricle Ventricle

Figure 1(1-2-29. Chest: MRI, AxlalT6

Right Atrium

Esophagus Descending

Aorta

Len Atrium

Figure III-2-30. Chest: MRI, Coronal

Brachiocephalic Trunk -

Pulmonary Left Common Trunk Carotid Artery

Left

Ventricle

Right Ascending

Atrium Aorta

Superior Vena Cava

Chapter Summary

The chest wall is formed by 12 thoracic vertebrae, 12 pairs of ribs, and the sternum. An important landmark on the anterior chest wall is the sternal angle found where the second rib articulates with the sternum.

The respiratory system develops as an endodermal outgrowth of the foregut. The tracheoesophageal septum separates the lung buds from the foregut. Improper development of this septum will produce an abnormal communication between the trachea and esophagus, a tracheoesophageal fistula.

The lungs are surrounded by the pleura, which is divided into the parietal pleura lining, the inner surface of the thoracic cavity, and the visceral pleura that is attached to the surface of the lung. Between these two layers is the pleural cavity containing a small amount of serous fluid. The lungs demonstrate costal, mediastinal, and diaphragmatic surfaces and an apex that projects through the thoracic inlet into the root of the neck Oblique and horizontal fissures divide the lungs into lobes.

Heart development begins with the formation of a primitive heart tube, which develops from the lateral plate mesoderm in the third week. The arterial end of the heart tube is called the truncus arteriosus and will develop into the aorta and pulmonary trunk. The sinus venosus at the venous end of the heart tube will develop into the coronary sinus and the smooth part of the right atrium. The primitive atrial and ventricle chambers divide into right and left chambers following development of j interatrial and interventricular septae. Ventricular septal defects result from failure of the membranous j septum to develop. Failure of the foramen ovale to close at birth results in atrial septal defects. Fetal j circulation involves three shunts: ductus venosus, ductus arteriosum, and the foramen ovale. After j birth these shunts shut down following changes in the circulatory system. j

The thoracic cavity is divided into the superior mediastinum above the plane of the sternal angle and j the inferior mediastinum (anterior, middle, and posterior mediastina) below that sternal plane. The superior mediastinum contains the superior vena cava, aortic arch and its branches, trachea, esophagus, thoracic duct, and the vagus and phrenic nerves. The anterior mediastinum is anterior to the heart and contains remnants of the thymus. The middle mediastinum contains the heart and great vessels and the posterior mediastinum containing the thoracic aorta, esophagus, thoracic duct, azygos veins, and the vagus nerve. The inferior vena cava passes through the diaphragm at the caval hiatus at the level of the 8th thoracic vertebra, the esophagus through the esophageal hiatus at the 10th thoracic vertebra, and the aorta course through the aortic hiatus at the level of the 12th thoracic vertebra.

Covering the heart is the pericardium formed by an outer, tough fibrous layer and a doubled-layered serous membrane divided into parietal and visceral layers. The pericardial cavity is located between these two serous layers and includes the transverse and oblique pericardial sinuses.

The external surface of the heart consists of several borders: the right border formed by the right atrium, the left border formed by the left ventricle, the base formed by the two atria, and the apex at the tip of the left ventricle. The anterior surface is formed by the right ventricle, the posterior surface formed mainly by the left atrium, and a diaphragmatic surface is formed primarily by the left ventricle.

Arterial supply to the heart muscle is provided by the right and left coronary arteries, which are branches of the ascending aorta. The right coronary artery supplies the right atrium, the right ventricle, the sinoatrial and atrioventricular nodes, and parts of the left atrium and left ventricle, The distal branch of the right coronary artery is the posterior interventricular artery that supplies, in part, the posterior aspect of the interventricular septum.

Chapter Summary (continued)

The left coronary artery supplies most of the left ventride, the left atrium, and the anterior part of the interventricular septum. The two main branches of the left coronary artery are the anterior interventricular artery and the circumflex artery,

Venous drainage of the heart is provided primarily by the great cardiac and middle cardiac veins and the coronary sinus, which drains into the right atrium.

Sympathetic innervation increases the heart rate while the parasympathetics slows the heart rate. These autonomic fibers fire upon the conducting system of the heart The sinoatrial node initiates the impulse for cardiac contraction. The atrioventricular node receives the impulse from the sinoatrial node and transmfts that impulse to the ventricles through the bundle of His. The bundle divides into the right and left bundle branches and Purkinje fibers to the two ventricles.

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