ChapterSummary
•The chest wall is formed by 1 2 thoracic vertebrae, 1 2 pairs of ribs, and the sternum. An important landmark on the anterior chest wall is the sternal angle found where the 2nd rib articulates with the sternum.
•The respiratory system develops as an endodermal outgrowth ofthe foregut. The tracheoesophageal septum separates the lung buds from the foregut. Improper development ofthis 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 ofthe thoracic cavity, and the visceral pleura that is attached to the surface ofthe lung. Between these 2 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 ofthe 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 ofthe heart tube will develop into the coronary sinus and the smooth part ofthe right atrium. The primitive atrial and ventricle chambers divide into right and left chambers following development of interatrial and interventricular septae. Ventricular septal defects result from failure of the membranous septum
to develop. Failure ofthe foramen ovale to close at birth results in atrial septal defects. Fetal circulation involves 3 shunts: ductus venosus, ductus arteriosum, and the foramen ovale. After birth these shunts shut down following changes in the circulatory system.
•The thoracic cavity is divided into the superior mediastinum above the plane of the sternal angle and the inferior mediastinum (anterior, middle, and posterior mediastina) below that sternal plane. The superior mediastinum contains the superiorvena 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 ofthe thymus. The middle mediastinum contains the heart and great vessels and the posterior mediastinum containing the thoracic aorta, esophagus, thoracic duct, azygos veins, and vagus nerve. The inferiorvena cava passes through the diaphragm atthe caval hiatus at the level ofthe 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 ofthe 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 pericardia! cavity is located between these 2 serous layers and includes the transverse and oblique pericardiaI sinuses.
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