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Ministry of Health of Ukraine

Bukovinian State Medical University


APPROVED”


on methodical meeting of the Department of Anatomy, Topographical anatomy and Operative Surgery

…………………………….2008 р. (Protocol №……….)

The chief of department


professor ……………………….……Yu.T.Achtemiichuk

…………………………….2008 р.


METHODICAL GUIDELINES



for the 2nd-year foreign students of English-spoken groups of the Medical Faculty

(speciality “General medicine”)

for independent work during the preparation to practical studies



the Theme of studies

Topographical anatomy and operative surgery of the heart”


MODULE I

Topographical Anatomy and Operative Surgery

of the Head, Neck, Thorax and Abdomen


Semantic module

Topographical Anatomy and Operative Surgery of the Thorax”


Chernivtsi – 2008

1. Actuality of theme:

The topographical anatomy and operative surgery of the thorax are very importance, because without the knowledge about peculiarities and variants of structure, form, location and mutual location of their anatomical structures, their age-specific it is impossible to diagnose in a proper time and correctly and to prescribe a necessary treatment to the patient. Surgeons usually pay much attention to the topographo-anatomic basis of surgical operations on the thorax.


^ 2. Duration of studies: 2 working hours.


3. Objectives (concrete purposes):

To know the definition of regions of the thorax.

To know classification of surgical operations on the thorax.

To know the topographical anatomy and operative surgery of the organs of the thoracic cavity.


^ 4. Basic knowledges, abilities, skills, that necessary for the study themes (interdisciplinary integration):


The names of previous disciplines

The got skills

1. Normal anatomy

2. Physiology

3. Biophysics


To describe the structure and function of the different organs of the human body, to determine projectors and landmarks of the anatomical structures. To understand the basic physical principles of using medical equipment and instruments.


^ 5. Advices to the student.

5.1. Table of contents of the theme:


Heart

The heart is a hollow muscular organ that is somewhat pyramid shaped and lies within the pericardium in the mediastinum. It is connected at its base to the great blood vessels but otherwise lies free within the pericardium.

Surfaces of the Heart

The heart has three surfaces: sternocostal (anterior), diaphragmatic (inferior), and a base (posterior). It also has an apex, which is directed downward, forward, and to the left.

The sternocostal surface is formed mainly by the right atrium and the right ventricle, which are separated from each other by the vertical atrioventricular groove. The right border is formed by the right atrium and the left border, by the left ventricle and part of the left auricle. The right ventricle is separated from the left ventricle by the anterior interventricular groove.

The diaphragmatic surface of the heart is formed mainly by the right and left ventricles separated by the posterior interventricular groove. The inferior surface of the right atrium, into which the inferior vena cava opens, also forms part of this surface.

The base of the heart, or the posterior surface, is formed mainly by the left atrium, into which open the four pulmonary veins. The base of the heart lies opposite the apex.

The apex of the heart, formed by the left ventricle, is directed downward, forward, and to the left. It lies at the level of the fifth left intercostal space, 9 cm from the midline. In the region of the apex, the apex beat can usually be seen and palpated in the living patient.

Borders of the Heart

The right border is formed by the right atrium, the left border by the left auricle, and below by the left ventricle. The lower border is formed mainly by the right ventricle but also by the right atrium and the apex by the left ventricle. These borders are important when examining a radiograph of the heart.

Chambers of the Heart

The heart is divided by vertical septa into four chambers: the right and left atria and the right and left ventricles. The right atrium lies anterior to the left atrium and the right ventricle lies anterior to the left ventricle.

Right Atrium

The right atrium consists of a main cavity and a small outpouching, the auricle. On the outside of the heart at the junction between the right atrium and the right auricle is a vertical groove, the sulcus terminalis, which on the inside forms a ridge, the crista terminalis.

The main part of the atrium that lies posterior to the ridge is smooth walled and is derived embryologically from the sinus venosus. The part of the atrium in front of the ridge is roughened or trabeculated by bundles of muscle fibers, the musculi pectinati, which run from the crista terminalis to the auricle. This anterior part is derived embryologically from the primitive atrium.

Openings Into the Right Atrium

The superior vena cava opens into the upper part of the right atrium; it has no valve. It returns the blood to the heart from the upper half of the body. The inferior vena cava (larger than the superior vena cava) opens into the lower part of the right atrium; it is guarded by a rudimentary, nonfunctioning valve. It returns the blood to the heart from the lower half of the body.

The coronary sinus, which drains most of the blood from the heart wall, opens into the right atrium between the inferior vena cava and the atrioventricular orifice; it is guarded by a rudimentary, nonfunctioning valve.

The right atrioventricular orifice lies anterior to the inferior vena caval opening and is guarded by the tricuspid valve.

Many small orifices of small veins also drain the wall of the heart and open directly into the right atrium.

Fetal Remnants

In addition to the rudimentary valve of the inferior vena cava are the fossa ovalis and anulus ovalis. These latter structures lie on the atrial septum that separates the right atrium from the left atrium. The fossa ovalis is a shallow depression, which is the site of the foramen ovale in the fetus. The anulus ovalis forms the upper margin of the fossa. The floor of the fossa represents the persistent septum primum of the heart of the embryo, and the anulus is formed from the lower edge of the septum secundum.

Right Ventricle

The right ventricle communicates with the right atrium through the atrioventricular orifice and with the pulmonary trunk through the pulmonary orifice. As the cavity approaches the pulmonary orifice it becomes funnel shaped, at which point it is referred to as the infundibulum.

The walls of the right ventricle are much thicker than those of the right atrium and show several internal projecting ridges formed of muscle bundles. The projecting ridges give the ventricular wall a spongelike appearance and are known as trabeculae carneae. The trabeculae carneae are composed of three types. The first type comprises the papillary muscles, which project inward, being attached by their bases to the ventricular wall; their apices are connected by fibrous chords (the chordae tendineae) to the cusps of the tricuspid valve. The second type are attached at their ends to the ventricular wall, being free in the middle. One of these, the moderator band, crosses the ventricular cavity from the septal to the anterior wall. It conveys the right branch of the atrioventricular bundle, which is part of the conducting system of the heart. The third type is simply composed of prominent ridges.

The tricuspid valve guards the atrioventricular orifice and consists of three cusps formed by a fold of endocardium with some connective tissue enclosed: anterior, septal, and inferior (posterior) cusps. The anterior cusp lies anteriorly, the septal cusp lies against the ventricular septum, and the inferior or posterior cusp lies inferiorly.

The bases of the cusps are attached to the fibrous ring of the skeleton of the heart (see below), whereas their free edges and ventricular surfaces are attached to the chordae tendineae. The chordae tendineae connect the cusps to the papillary muscles. When the ventricle contracts, the papillary muscles contract and prevent the cusps from being forced into the atrium and turning inside out as the intraventricular pressure rises. To assist in this process, the chordae tendineae of one papillary muscle are connected to the adjacent parts of two cusps.

The pulmonary valve guards the pulmonary orifice and consists of three semilunar cusps formed by folds of endocardium with some connective tissue enclosed.

The curved lower margins and sides of each cusp are attached to the arterial wall. The open mouths of the cusps are directed upward into the pulmonary trunk. No chordae or papillary muscles are associated with these valve cusps; the attachments of the sides of the cusps to the arterial wall prevent the cusps from prolapsing into the ventricle.

At the root of the pulmonary trunk are three dilatations called the sinuses, and one is situated external to each cusp (see aortic valve).

The three semilunar cusps are arranged with one posterior (left cusp) and two anterior (anterior and right cusps).

The cusps of the pulmonary and aortic valves are named according to their position in the fetus before the heart has rotated to the left. This unfortunately causes a great deal of unnecessary confusion.) During ventricular systole, the cusps of the valve are pressed against the wall of the pulmonary trunk by the outrushing blood. During diastole, blood flows back toward the heart and enters the sinuses; the valve cusps fill, come into apposition in the center of the lumen, and close the pulmonary orifice.

Left Atrium

Similar to the right atrium, the left atrium consists of a main cavity and a left auricle. The left atrium is situated behind the right atrium and forms the greater part of the base or the posterior surface of the heart. Behind it lies the oblique sinus of the serous pericardium, and the fibrous pericardium separates it from the esophagus.

The interior of the left atrium is smooth, but the left auricle possesses muscular ridges as in the right auricle.

Openings into the Left Atrium

The four pulmonary veins, two from each lung, open through the posterior wall and have no valves. The left atrioventricular orifice is guarded by the mitral valve.

Left Ventricle

The left ventricle communicates with the left atrium through the atrioventricular orifice and with the aorta through the aortic orifice. The walls of the left ventricle are three times thicker than those of the right ventricle. (The left intraventricular blood pressure is six times higher than that inside the right ventricle.) In cross section, the left ventricle is circular; the right is crescentic because of the bulging of the ventricular septum into the cavity of the right ventricle. There are well-developed trabeculae carneae, two large papillary muscles, but no moderator band. The part of the ventricle below the aortic orifice is called the aortic vestibule.

The mitral valve guards the atrioventricular orifice. It consists of two cusps, one anterior and one posterior, which have a structure similar to that of the cusps of the tricuspid valve. The anterior cusp is the larger and intervenes between the atrioventricular and the aortic orifices.

The attachment of the chordae tendineae to the cusps and the papillary muscles is similar to that of the tricuspid valve. The aortic valve guards the aortic orifice and is precisely similar in structure to the pulmonary valve.

One cusp is situated on the anterior wall (right cusp) and two are located on the posterior wall (left and posterior cusps). Behind each cusp the aortic wall bulges to form an aortic sinus. The anterior aortic sinus gives origin to the right coronary artery, and the left posterior sinus gives origin to the left coronary artery.

Structure of the Heart

The walls of the heart are composed of a thick layer of cardiac muscle, the myocardium, covered externally by the epicardium and lined internally by the endocardium. The atrial portion of the heart has relatively thin walls and is divided by the atrial (interatrial) septum into the right and left atria. The septum runs from the anterior wall of the heart backward and to the right. The ventricular portion of the heart has thick walls and is divided by the ventricular (interventricular) septum into the right and left ventricles.

The septum is placed obliquely, with one surface facing forward and to the right and the other facing backward and to the left. Its position is indicated on the surface of the heart by the anterior and posterior interventricular grooves. The lower part of the septum is thick and formed of muscle. The smaller upper part of the septum is thin and membranous and attached to the fibrous skeleton.

The so-called skeleton of the heart consists of fibrous rings that surround the atrioventricular, pulmonary, and aortic orifices and are continuous with the membranous upper part of the ventricular septum. The fibrous rings around the atrioventricular orifices separate the muscular walls of the atria from those of the ventricles but provide attachment for the muscle fibers. The fibrous rings support the bases of the valve cusps and prevent the valves from stretching and becoming incompetent.

Conducting System of the Heart

The normal heart contracts rhythmically at about 70 to 90 beats per minute in the resting adult. The rhythmic contractile process originates spontaneously in the conducting system and the impulse travels to different regions of the heart, so the atria contract first and together, to be followed later by the contractions of both ventricles together. The slight delay in the passage of the impulse from the atria to the ventricles allows time for the atria to empty their blood into the ventricles before the ventricles contract.

The conducting system of the heart consists of specialized cardiac muscle present in the sinoatrial node, the atrioventricular node, the atrioventricular bundle and its right and left terminal branches, and the subendocardial plexus of Purkinje fibers. (The specialized cardiac muscle fibers that form the conducting system of the heart are known as Purkinje fibers.)

Sinoatrial Node

The sinoatrial node is located in the wall of the right atrium in the upper part of the sulcus terminalis just to the right of the opening of the superior vena cava.

The node spontaneously gives origin to rhythmical electrical impulses that spread in all directions through the cardiac muscle of the atria and cause the muscle to contract.

Atrioventricular Node

The atrioventricular node is strategically placed on the lower part of the atrial septum just above the attachment of the septal cusp of the tricuspid valve.

From it, the cardiac impulse is conducted to the ventricles by the atrioventricular bundle. The atrioventricular node is stimulated by the excitation wave as it passes through the atrial myocardium.

The speed of conduction of the cardiac impulse through the atrioventricular node (about 0.11 sec) allows sufficient time for the atria to empty their blood into the ventricles before the ventricles start to contract.

Atrioventricular Bundle

The atrioventricular bundle (bundle of His) is the only pathway of cardiac muscle that connects the myocardium of the atria and the myocardium of the ventricles and is thus the only route along which the cardiac impulse can travel from the atria to the ventricles. The bundle descends through the fibrous skeleton of the heart.

The atrioventricular bundle then descends behind the septal cusp of the tricuspid valve to reach the inferior border of the membranous part of the ventricular septum. At the upper border of the muscular part of the septum it divides into two branches, one for each ventricle. The right bundle branch (RBB) passes down on the right side of the ventricular septum to reach the moderator band, where it crosses to the anterior wall of the right ventricle. Here it becomes continuous with the fibers of the Purkinje plexus. The left bundle branch (LBB) pierces the septum and passes down on its left side beneath the endocardium. It usually divides into two branches (anterior and posterior), which eventually become continuous with the fibers of the Purkinje plexus of the left ventricle.

It is thus seen that the conducting system of the heart is responsible not only for generating rhythmical cardiac impulses but also for conducting these impulses rapidly throughout the myocardium of the heart so that the different chambers contract in a coordinated and efficient manner.

The activities of the conducting system can be influenced by the autonomic nerve supply to the heart. The parasympathetic nerves slow the rhythm and diminish the rate of conduction of the impulse; the sympathetic nerves have the opposite effect.

Internodal Conduction Paths

Impulses from the sinoatrial node have been shown to travel to the atrioventricular node more rapidly than they can travel by passing along the ordinary myocardium. This phenomenon has been explained by the description of special pathways in the atrial wall, having a structure consisting of a mixture of Purkinje fibers and ordinary cardiac muscle cells. The anterior internodal pathway leaves the anterior end of the sinoatrial node and passes anterior to the superior vena caval opening. It descends on the atrial septum and ends in the atrioventricular node. The middle internodal pathway leaves the posterior end of the sinoatrial node and passes posterior to the superior vena caval opening. It descends on the atrial septum to the atrioventricular node. The posterior internodal pathway leaves the posterior part of the sinoatrial node and descends through the crista terminalis and the valve of the inferior vena cava to the atrioventricular node.

Arterial supply of the Heart

The arterial supply of the heart is provided by the right and left coronary arteries, which arise from the ascending aorta immediately above the aortic valve. The coronary arteries and their major branches are distributed over the surface of the heart lying within subepicardial connective tissue.

The right coronary artery arises from the anterior aortic sinus of the ascending aorta and runs forward between the pulmonary trunk and the right auricle. It descends almost vertically in the right atrioventricular groove, and at the inferior border of the heart it continues posteriorly along the atrioventricular groove to anastomose with the left coronary artery in the posterior interventricular groove. The following branches from the right coronary artery supply the right atrium and right ventricle and parts of the left atrium and left ventricle and the atrioventricular septum.

Branches

1. Right conus artery. This supplies the anterior surface of the pulmonary conus (infundibulum of the right ventricle) and the upper part of the anterior wall of the right ventricle.

2. Anterior ventricular branches. Two or three in number, they supply the anterior surface of the right ventricle. The marginal branch is the largest and runs along the lower margin of the costal surface to reach the apex.

3. Posterior ventricular branches. Usually two in number, they supply the diaphragmatic surface of the right ventricle.

4. Posterior interventricular (descending) artery. This artery runs toward the apex in the posterior interventricular groove. It gives off branches to the right and left ventricles, including its inferior wall. It supplies branches to the posterior part of the ventricular septum but not to the apical part, which receives its supply from the anterior interventricular branch of the left coronary artery. A large septal branch supplies the atrioventricular node. In 10% of individuals the posterior interventricular artery is replaced by a branch from the left coronary artery.

5. Atrial branches. Several branches supply the anterior and lateral surfaces of the right atrium. One branch supplies the posterior surface of both the right and left atria.

The artery of the sinoatrial node supplies the node and the right and left atria; in 35% of individuals it arises from the left coronary artery.

The left coronary artery, which is usually larger than the right coronary artery, supplies the major part of the heart, including the greater part of the left atrium, left ventricle, and ventricular septum. It arises from the left posterior aortic sinus of the ascending aorta and passes forward between the pulmonary trunk and the left auricle. It then enters the atrioventricular groove and divides into an anterior interventricular branch and a circumflex branch.

Branches

1. The anterior interventricular (descending) branch runs downward in the anterior interventricular groove to the apex of the heart. In most individuals it then passes around the apex of the heart to enter the posterior interventricular groove and anastomoses with the terminal branches of the right coronary artery. In onethird of individuals it ends at the apex of the heart. The anterior interventricular branch supplies the right and left ventricles with numerous branches that also supply the anterior part of the ventricular septum. One of these ventricular branches (left diagonal artery) may arise directly from the trunk of the left coronary artery. A small left conus artery supplies the pulmonary conus.

2. The circumflex artery is the same size as the anterior interventricular artery. It winds around the left margin of the heart in the atrioventricular groove. A left marginal artery is a large branch that supplies the left margin of the left ventricle down to the apex. Anterior ventricular and posterior ventricular branches supply the left ventricle. Atrial branches supply the left atrium.

Variations in the Coronary Arteries

Variations in the blood supply to the heart do occur, and the most common variations affect the blood supply to the diaphragmatic surface of both ventricles. Here the origin, size, and distribution of the posterior interventricular artery are variable. In right dominance the posterior interventricular artery is a large branch of the right coronary artery. Right dominance is present in most individuals (90%). In left dominance the posterior interventricular artery is a branch of the circumflex branch of the left coronary artery (10%).

Coronary Artery Anastomoses

Anastomoses between the terminal branches of the right and left coronary arteries (collateral circulation) exist, but they are usually not large enough to provide an adequate blood supply to the cardiac muscle should one of the large branches become blocked by disease. A sudden block of one of the larger branches of either coronary artery usually leads to myocardial death (myocardial infarction), although sometimes the collateral circulation is enough to sustain the muscle.

Summary of the Overall Arterial Supply to the Heart in Most Individuals

The right coronary artery supplies all of the right ventricle (except for the small area to the right of the anterior interventricular groove), the variable part of the diaphragmatic surface of the left ventricle, the posteroinferior third of the ventricular septum, the right atrium and part of the left atrium, and the sinoatrial node and the atrioventricular node and bundle. The LBB also receives small branches.

The left coronary artery supplies most of the left ventricle, a small area of the right ventricle to the right of the interventricular groove, the anterior two-thirds of the ventricular septum, most of the left atrium, the RBB, and the LBB.

Arterial Supply to the Conducting System

The sinoatrial node is usually supplied by the right but sometimes the left coronary artery. The atrioventricular node and the atrioventricular bundle are supplied by the right coronary artery. The RBB of the atrioventricular bundle is supplied by the left coronary artery; the LBB is supplied by the right and left coronary arteries.

Venous drainage of the Heart

Most blood from the heart wall drains into the right atrium through the coronary sinus, which lies in the posterior part of the atrioventricular groove and is a continuation of the great cardiac vein. It opens into the right atriurn to the left of the inferior vena cava. The small and middle cardiac veins are tributaries of the coronary sinus. The remainder of the blood is returned to the right atrium by the anterior cardiac vein and by small veins that open directly into the heart chambers.

Nerve supply of the Heart

The heart is innervated by sympathetic and parasympathetic fibers of the autonomic nervous system via the cardiac plexuses situated below the arch of the aorta. The sympathetic supply arises from the cervical and upper thoracic portions of the sympathetic trunks, and the parasympathetic supply comes from the vagus nerves.

The postganglionic sympathetic fibers terminate on the sinoatrial and atrioventricular nodes, on cardiac muscle fibers, and on the coronary arteries. Activation of these nerves results in cardiac acceleration, increased force of contraction of the cardiac muscle, and dilatation of the coronary arteries.

The postganglionic parasympathetic fibers terminate on the sinoatrial and atrioventricular nodes and on the coronary arteries. Activation of the parasympathetic nerves results in a reduction in the rate and force of contraction of the heart and a constriction of the coronary arteries.

Afferent fibers running with the sympathetic nerves carry nervous impulses that normally do not reach consciousness.

However, should the blood supply to the myocardium become impaired, pain impulses reach consciousness via this pathway. Afferent fibers running with the vagus nerves take part in cardiovascular reflexes.

Action of the Heart

The heart is a muscular pump. The series of changes that take place within it as it fills with blood and empties is referred to as the cardiac cycle. The normal heart beats about 70 to 90 times per minute in the resting adult and about 130 to 150 times a minute in the newborn child.

Blood is continuously returning to the heart, and during ventricular systole (contraction), when the atrioventricular valves are closed, the blood is temporarily accommodated in the large veins and atria. Once ventricular diastole (relaxation) occurs, the atrioventricular valves open, and blood passively flows from the atria to the ventricles. When the ventricles are nearly full, atrial systole occurs and forces the remainder of the blood in the atria into the ventricles. The sinoatrial node initiates the wave of contraction in the atria, which commences around the openings of the large veins and "milks" the blood toward the ventricles. By this means blood does not reflux into the veins.

The cardiac impulse, having reached the atrioventricular node, is conducted to the papillary muscles by the atrioventricular bundle and its branches. The papillary muscles then begin to contract and take up the slack of the chordae tendineae. Meanwhile, the ventricles start contracting and the atrioventricular valves close. The spread of the cardiac impulse along the atrioventricular bundle and its terminal branches, including the Purkinje fibers, ensures that myocardial contraction occurs at almost the same time throughout the ventricles.

Once the intraventricular blood pressure exceeds that present in the large arteries (aorta and pulmonary trunk), the semilunar valve cusps are pushed aside, and the blood is ejected from the heart. At the conclusion of ventricular systole, blood begins to move back toward the ventricles and immediately fills the pockets of the semilunar valves.

The cusps float into apposition and completely close the aortic and pulmonary orifices.

Surface Anatomy of the Heart Valves

The surface projection of the heart has already been described at the beginning of the chapter. The surface markings of the heart valves are as follows.

• The tricuspid valve lies behind the right half of the sternum opposite the fourth intercostal space.

• The mitral valve lies behind the left half of the sternum opposite the fourth costal cartilage.

• The pulmonary valve lies behind the medial end of the third left costal cartilage and the adjoining part of the sternum.

• The aortic valve lies behind the left half of the sternum opposite the third intercostal space.

Auscultation of the Heart Valves

On listening to the heart with a stethoscope, one can hear two sounds: lub-dup. The first sound is produced by the contraction of the ventricles and the closure of the tricuspid and mitral valves. The second sound is produced by the sharp closure of the aortic and pulmonary valves. It is important for a physician to know where to place the stethoscope on the chest wall so that he or she will be able to hear sounds produced at each valve with the minimum of distraction or interference.

• The tricuspid valve is best heard over the right half of the lower end of the body of the sternum.

• The mitral valve is best heard over the apex beat, that is, at the level of the fifth left intercostal space, 9 cm from the midline.

• The pulmonary valve is heard with least interference over the medial end of the second left intercostal space.

• The aortic valve is best heard over the medial end of the second right intercostal space.


??? CONGENITAL ANOMALIES OF THE HEART

Of the many congenital anomalies that can occur in the heart and large arteries, four common varieties are illustrated in Figure ____.


Esophagus

The esophagus is a tubular structure about 25 cm long that is continuous above with the laryngeal part of the pharynx opposite the 7th cervical vertebra. It passes through the diaphragm at the level of the 10th thoracic vertebra to join the stomach.

In the neck, the esophagus lies in front of the vertebral column; laterally, it is related to the lobes of the thyroid gland; and anteriorly, it is in contact with the trachea and the recurrent laryngeal nerves.

In the thorax, it passes downward and to the left through the superior and then the posterior mediastinum. At the level of the sternal angle the aortic arch pushes the esophagus over to the midline.

The relations of the thoracic part of the esophagus from above downward are as follows:

• Anteriorly: The trachea and the left recurrent laryngeal nerve; the left principal bronchus, which constricts it; and the pericardium, which separates the esophagus from the left atrium.

• Posteriorly: The bodies of the thoracic vertebrae; the thoracic duct; the azygos veins; the right posterior intercostal arteries; and, at its lower end, the descending thoracic aorta.

• Right side: The mediastinal pleura and the terminal part of the azygos vein.

• Left side: The left subclavian artery, the aortic arch, the thoracic duct, and the mediastinal pleura.

Inferiorly to the level of the roots of the lungs, the vagus nerves leave the pulmonary plexus and join with sympathetic nerves to form the esophageal plexus. The left vagus lies anterior to the esophagus and the right vagus lies posterior.

At the opening in the diaphragm the esophagus is accompanied by the two vagi, branches of the left gastric blood vessels, and lymphatic vessels. Fibers from the right crus of the diaphragm pass around the esophagus in the form of a sling.

In the abdomen the esophagus descends for about 1.3 cm and then enters the stomach. It is related to the left lobe of the liver anteriorly and to the left crus of the diaphragm posteriorly.

Blood supply of the Esophagus

The upper third of the esophagus is supplied by the inferior thyroid artery, the middle third by branches from the descending thoracic aorta, and the lower third by branches from the left gastric artery. The veins from the upper third drain into the inferior thyroid veins, from the middle third into the azygos veins, and from the lower third into the left gastric vein, a tributary of the portal vein.

Lymph drainage of the Esophagus

Lymph vessels from the upper third of the esophagus drain into the deep cervical nodes, from the middle third into the superior and posterior mediastinal nodes, and from the lower third into nodes along the left gastric blood vessels and the celiac nodes.

Nerve supply of the Esophagus

The esophagus is supplied by parasympathetic and sympathetic efferent and afferent fibers via the vagi and sympathetic trunks. In the lower part of its thoracic course, the esophagus is surrounded by the esophageal nerve plexus.


Thymus

The thymus is a flattened, bilobed structure lying between the sternum and the pericardium in the anterior mediastinum. In the newborn infant it reaches its largest size relative to the size of the body, at which time it may extend up through the superior mediastinum in front of the great vessels into the root of the neck. The thymus continues to grow until puberty, but thereafter undergoes involution. It has a pink, lobulated appearance and is the site for development of T (thymic) lymphocytes.

Blood supply

The blood supply of the thymus is from the inferior thyroid and internal thoracic arteries.


Large Arteries of the Thorax

Aorta

The aorta is the main arterial trunk that delivers oxygenated blood from the left ventricle of the heart to the tissues of the body. It is divided for purposes of description into the following parts: ascending aorta, arch of the aorta, descending thoracic aorta, and abdominal aorta.

Ascending Aorta

The ascending aorta begins at the base of the left ventricle and runs upward and forward to come to lie behind the right half of the sternum at the level of the sternal angle, where it becomes continuous with the arch of the aorta.

The ascending aorta lies within the fibrous pericardium and is enclosed with the pulmonary trunk in a sheath of serous pericardium. At its root it possesses three bulges, the sinuses of the aorta, one behind each aortic valve cusp.

Branches

The right coronary artery arises from the anterior aortic sinus, and the left coronary artery arises from the left posterior aortic sinusArch of the Aorta

The arch of the aorta is a continuation of the ascending aorta. It lies behind the manubrium sterni and arches upward, backward, and to the left in front of the trachea (its main direction is backward). It then passes downward to the left of the trachea, and at the level of the sternal angle becomes continuous with the descending aorta.

Branches

The brachiocephalic artery arises from the convex surface of the aortic arch. It passes upward and to the right of the trachea and divides into the right subclavian and right common carotid arteries behind the right sternoclavicular joint.

The left common carotid artery arises from the convex surface of the aortic arch on the left side of the brachiocephalic artery. It runs upward and to the left of the trachea and enters the neck behind the left sternoclavicular joint.

The left subclavian artery arises from the aortic arch behind the left common carotid artery. It runs upward along the left side of the trachea and the esophagus to enter the root of the neck. It arches over the apex of the left lung.

Descending Thoracic Aorta

The descending thoracic aorta lies in the posterior mediastinum and begins as a continuation of the arch of the aorta on the left side of the lower border of the body of the fourth thoracic vertebra (i.e., opposite the sternal angle). It runs downward in the posterior mediastinum, inclining forward and medially to reach the anterior surface of the vertebral column. At the level of the twelfth thoracic vertebra it passes behind the diaphragm (through the aortic opening) in the midline and becomes continuous with the abdominal aorta.

Branches

Posterior intercostal arteries are given off to the lower nine intercostal spaces on each side. Subcostal arteries are given off on each side and run along the lower border of the twelfth rib to enter the abdominal wall.

Pericardial, esophageal, and bronchial arteries are small branches that are distributed to these organs.

Pulmonary Trunk

The pulmonary trunk conveys deoxygenated blood from the right ventricle of the heart to the lungs. It leaves the upper part of the right ventricle and runs upward, backward, and to the left. It is about 5 cm long and terminates in the concavity of the aortic arch by dividing into right and left pulmonary arteries. Together with the ascending aorta, it is enclosed in the fibrous pericardium and a sheath of serous pericardium.

Branches

The right pulmonary artery runs to the right behind the ascending aorta and superior vena cava to enter the root of the right lung.

The left pulmonary artery runs to the left in front of the descending aorta to enter the root of the left lung.

The ligamentum arteriosum is a fibrous band that connects the bifurcation of the pulmonary trunk to the lower concave surface of the aortic arch. The ligamentum arteriosum is the remains of the ductus arteriosus, which in the fetus conducts blood from the pulmonary trunk to the aorta, thus bypassing the lungs. The left recurrent laryngeal nerve hooks around the lower border of this structure. Following birth, the ductus closes. Should it remain patent, aortic blood will enter the pulmonary circulation, producing pulmonary hypertension and hypertrophy of the right ventricle. Surgical ligation of the ductus is then necessary.

Large Veins of the Thorax

Brachiocephalic Veins

The right brachiocephalic vein is formed at the root of the neck by the union of the right subclavian and the right internal jugular veins. The left brachiocephalic vein has a similar origin. It passes obliquely downward and to the right behind the manubrium sterni and in front of the large branches of the aortic arch. It joins the right brachiocephalic vein to form the superior vena cava.

Superior Vena Cava

The superior vena cava contains all the venous blood from the head and neck and both upper limbs and is formed by the union of the two brachiocephalic veins. It passes downward to end in the right atrium of the heart. The vena azygos joins the posterior aspect of the superior vena cava just before it enters the pericardium.

Azygos Veins

The azygos veins consist of the main azygos vein, the inferior hemiazygos vein, and the superior hemiazygos vein. They drain blood from the posterior parts of the intercostal spaces, the posterior abdominal wall, the pericardium, the diaphragm, the bronchi, and the esophagus.

Azygos Vein

The origin of this vein is variable. It is often formed by the union of the right ascending lumbar vein and the right subcostal vein. It ascends through the aortic opening in the diaphragm on the right side of the aorta to the level of the 5th thoracic vertebra (Fig. 4-30). Here it arches forward above the root of the right lung to empty into the posterior surface of the superior vena cava.

The azygos vein has numerous tributaries that include the eight lower intercostal veins, the right superior intercostal vein, the superior and inferior hemiazygos veins, and numerous mediastinal veins.

Inferior Hemiazygos Vein

This vein is often formed by the union of the left ascending lumbar vein and the left subcostal vein. It ascends through the left crus of the diaphragm, and at about the level of the eighth thoracic vertebra turns to the right and joins the azygos vein. It receives as tributaries some lower left intercostal veins and mediastinal veins.

Superior Hemiazygos Vein

This vein is formed by the union of the fourth to the eighth intercostal veins. It joins the azygos vein at the level of the seventh thoracic vertebra.

Inferior Vena Cava

The inferior vena cava pierces the central tendon of the diaphragm opposite the eighth thoracic vertebra and almost immediately enters the lowest part of the right atrium.

Pulmonary Veins

Two pulmonary veins leave each lung carrying oxygenated blood to the left atrium of the heart.


Mediastinum

In addition to the nodes draining the lungs, other nodes are found scattered through the mediastinum. They drain lymph from mediastinal structures and empty into the bronchomediastinal trunks and thoracic duct. Disease and enlargement of these nodes may exert pressure on important neighboring mediastinal structures, such as the trachea and superior vena cava.

Thoracic duct

The thoracic duct begins below in the abdomen as a dilated sac, the cisterna chyli. It ascends through the aortic opening in the diaphragm, on the right side of the descending aorta. It gradually crosses the median plane behind the esophagus and reaches the left border of the esophagus at the level of the lower border of the body of the fourth thoracic vertebra (sternal angle). It then runs upward along the left edge of the esophagus to enter the root of the neck. Here, it bends laterally behind the carotid sheath and in front of the vertebral vessels. It turns downward in front of the left phrenic nerve and crosses the subclavian artery to enter the beginning of the left brachiocephalic vein.

At the root of the neck the thoracic duct receives the left jugular, subclavian, and bronchomediastinal lymph trunks, although they may drain directly into the adjacent large veins.

The thoracic duct thus conveys to the blood all lymph from the lower limbs, pelvic cavity, abdominal cavity, left side of the thorax, and left side of the head, neck, and left arm.

Right Lymphatic Duct

The right jugular, subclavian, and bronchomediastinal trunks, which drain the right side of the head and neck, the right upper limb, and the right side of the thorax, respectively, may join to form the right lymphatic duct. This common duct, if present, is about 1.3 cm long and opens into the beginning of the right brachiocephalic vein.

Alternatively, the trunks open independently into the great veins at the root of the neck.

Nerves of the Thorax

Vagus nerves

The right vagus nerve descends in the thorax, first lying posterolateral to the brachiocephalic artery, then lateral to the trachea and medial to the terminal part of the azygos vein. It passes behind the root of the right lung and assists in the formation of the pulmonary plexus. On leaving the plexus, the vagus passes onto the posterior surface of the esophagus and takes part in the formation of the esophageal plexus. It then passes through the esophageal opening of the diaphragm behind the esophagus to reach the posterior surface of the stomach.

The left vagus nerve descends in the thorax between the left common carotid and left subclavian arteries. It then crosses the left side of the aortic arch and is itself crossed by the left phrenic nerve. The vagus then turns backward behind the root of the left lung and assists in the formation of the pulmonary plexus. On leaving the plexus, the vagus passes onto the anterior surface of the esophagus and takes part in the formation of the esophageal plexus. It then passes through the esophageal opening in the diaphragm in front of the esophagus to reach the anterior surface of the stomach.

Branches

Both vagi supply the lungs and esophagus. The right vagus gives off cardiac branches, and the left vagus gives origin to the left recurrent laryngeal nerve. (The right recurrent laryngeal nerve arises from the right vagus in the neck and hooks around the subclavian artery and ascends between the trachea and esophagus.)

The left recurrent laryngeal nerve arises from the left vagus trunk as the nerve crosses the arch of the aorta. It hooks around the ligamentum arteriosum and ascends in the groove between the trachea and the esophagus on the left side. It supplies all the muscles acting on the left vocal cord (except the cricothyroid muscle, a tensor of the cord, which is supplied by the external laryngeal branch of the vagus).

Phrenic Nerves

The phrenic nerves arise from the neck from the anterior rami of the third, fourth, and fifth cervical nerves.

The right phrenic nerve descends in the thorax along the right side of the right brachiocephalic vein and the superior vena cava. It passes in front of the root of the right lung and runs along the right side of the pericardium, which separates the nerve from the right atrium. It then descends on the right side of the inferior vena cava to the diaphragm. Its terminal branches pass through the caval opening in the diaphragm to supply the central part of the peritoneum on its underaspect.

The left phrenic nerve descends in the thorax along the left side of the left subclavian artery. It crosses the left side of the aortic arch and here crosses the left side of the left vagus nerve. It passes in front of the root of the left lung and then descends over the left surface of the pericardium, which separates the nerve from the left ventricle. On reaching the diaphragm, the terminal branches pierce the muscle and supply the central part of the peritoneum on its underaspect.

The phrenic nerves possess efferent and afferent fibers.

The efferent fibers are the sole nerve supply to the muscle of the diaphragm.

The afferent fibers carry sensation to the central nervous system from (a) the peritoneum covering the central region of the undersurface of the diaphragm, (b) the pleura covering the central region of the upper surface of the diaphragm, and (c) the pericardium and mediastinal parietal pleura.

Thoracic part of the Sympathetic Trunk

The thoracic part of the sympathetic trunk is continuous above with the cervical and below with the lumbar parts of the sympathetic trunk. It is the most laterally placed structure in the mediastinum and runs downward on the heads of the ribs. It leaves the thorax on the side of the body of the twelfth thoracic vertebra by passing behind the medial arcuate ligament.

The sympathetic trunk has 12 (often only 11) segmentally arranged ganglia, each with a white and gray ramus communicans passing to the corresponding spinal nerve. The first ganglion is often fused with the inferior cervical ganglion to form the stellate ganglion.

Branches

1. Gray rami communicantes go to all the thoracic spinal nerves. The postganglionic fibers are distributed through the branches of the spinal nerves to the blood vessels, sweat glands, and arrector pili muscles of the skin.

2. The first five ganglia give postganglionic fibers to the heart, aorta, lungs, and esophagus.

3. The lower eight ganglia mainly give preganglionic fibers, which are grouped together to form the splanchnic nerves and supply the abdominal viscera. They enter the abdomen by piercing the crura of the diaphragm. The greater splanchnic nerve arises from ganglia 5-9, the lesser spanchnic nerve arises from ganglia 10 and 11, and the lowest splanchnic nerve arises from ganglion 12. For details of the distribution of these nerves in the abdomen.

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