Файл: Kaplan USMLE-1 (2013) - Anatomy.pdf

Section Ill • Gross Anatomy

•The circumflex artery courses around the left border of the heart in the coronary sulcus and supplies ( 1) the left border ofthe heart via the marginal branch and (2) ends on the posterior aspect of the left ven­ tricle and supplies the posterior-inferior left ventricular wall.

Venous Drainage ofthe Heart

The major cardiac veins (Figure IIl-2-34) draining the heart course in the sulci and accompany the arteries but do not carry the same names. The major veins are the following:

•Coronarysinus

The coronary sinus is the main vein of the coronary circulation; it lies in the posterior coronary sulcus. It drains to an opening in the right atrium (Figure III-2-34). It develops from the left sinus venosus.

•Great cardiacvein

The great cardiac vein lies in the anterior interventricular sulcus with the LAD artery. It is the main tributary of the coronary sinus.

•Middle cardiac vein

The middle cardiac vein lies in the posterior interventricular sulcus with the posterior interventricular artery. It joins the coronary sinus.

•Venae cordis minimae (thebesian veins) and anterior cardiac veins

The venae cordis minimae and anterior cardiac veins open directly to the chambers of the heart.

Coronary

sinus

Great

vein

Figure 111-2-34. Venous Drainage of the Heart

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Chapter 2 • Thorax

Conducting System ofthe Heart

SA node

The SA node initiates the impulse for contraction ofheart muscle (and is therefore termed the "pacemaker" of the heart). It is located at the superior end of the crista terminalis, where the superior vena cava enters the right atrium (Figure IIl-2-35).

The SA node is supplied bythe SA nodal branch ofthe right coronary artery.

Impulse production is speeded up by sympathetic nervous stimulation; it is slowed by parasympathetic (vagal) stimulation.

AVnode

The AV node receives impulses from the SA node. The AV node is located in the interatrial septum near the opening ofthe coronary sinus. The AV node slows the impulse so that it reaches the ventricles after it has reached the atria.

The AV node is supplied by the rightcoronaryartery.

Bundle ofHis

The bundle ofHis originates in the AV node. It conducts impulses to the right and left ventricles. It is supplied by the LAD artery.

In the right ventricle, the moderator band (septomarginal trabecula) contains the right bundle branch.

Impulses pass from the right and left bundle branches to the papillary muscles and ventricular myocardium.

Innervation

The cardiac plexus is a combination of sympathetic and parasympathetic (vagal) fibers.

•Sympathetic stimulation increases the heart rate. Nerves that sense pain associated with coronary artery ischemia (angina) follow the sympa­ thetic pathways back into spinal cord segments Tl-TS.

•Parasympathetic stimulation slows the heart rate. Sensory nerves that carry the afferent limb of cardiac reflexes travel with the vagus nerve.

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Section Ill • Gross Anatomy

Figure 111-2-42. Chest: CT, T5

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Chapter 2 • Thorax

PA= pulmonary artery

RA = right atrium

AA= ascending aorta

LA= left atrium

E = esophagus

DA= descending aorta

Esophagus

Figure 111-2-44. Chest: CT, T6

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Section Ill • Gross Anatomy

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.

(Continued)

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