Download MEDIASTINUM OVERVIEW Contains all structures except the lungs

MEDIASTINUM
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OVERVIEW
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Contains all structures except the lungs
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Superior mediastinum extends from superior thoracic aperture to the horizontal plane that
includes the sternal angle anteriorly and passes through T4/T5
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inferior mediastinum is subdivided by the pericardium into anterior, middle, and posterior parts
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heart and great vessels lie in the pericardium, which constitutes the middle mediastinum
PERICARDIUM
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Ascending aorta, pulmonary trunk, and superior vena cava pass to and from the heart and lie in
the middle mediastinum
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Has two layers fibrous pericardium—continuous with central tendon of the diaphragm
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Internal surface of the fibrous layer is lined with serous membraneparietal layer of
serous pericardium
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This layer is reflected onto the heart and great vessels, making the visceral layer
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Fibrous pericardium is continuous superiorly with the pretracheal layer of cervical fascia
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Is attached anteriorly via sternopericardial ligaments to the sternum
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Is bound posteriorly by loose connective tissue to structure in the posterior mediastinum
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Is continuous inferiorly with the central tendon of the diaphragmpericardiacophrenic ligament
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Fibrous pericardium protects the heart from overfilling suddenly
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Pericardial cavity is between the parietal and visceral layers of the serous pericardium, allowing
the heart to beat in a frictionless environment.
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ARTERIAL SUPPLY
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From a branch of the internal thoracic artery the pericardiacophrenic artery, that
accompanies or parallels the phrenic nerve in the diaphragm
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Also the musculophrenic artery a terminal branch of the internal thoracic artery
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Bronchial, esophageal, and superior phrenic arteries branches off thoracic aorta
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Coronary arteries (visceral layer of serous pericardium only) first branches off of the
aorta
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VENOUS DRAINAGE
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Pericardiacophrenic veins tributaries off of the braciocephalic veins/internal thoracic
veins
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Azygos venous system
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NERVE SUPPLY
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Phrenic nerves sensory is referred along the C3-5 dermatomes of the ipsilateral
supraclavicular region
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Vagus nerves function uncertain
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Sympathetic nerves vasomotor
BLUE BOXES PAGE 132
HEART
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Is a double, self-adjusting pressure pump
Right heart receives poorly oxygenated blood (venous) from the body through the superior and inferior
vena cavae and pumps it through the pulmonary trunk and arteries to the lungs for oxygenation
The left heart receives well oxygenated blood from the lungs, through the pulmonary veins and pumps it
into the aorta for distribution to the body
Has 4 chambersright and left atria and right and left ventricles
Heart cycle begins with diastole and ends with systole
Heart sounds
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Lub (1st) as the blood is transferred from the atria into the ventricles
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Dub (2nd) as the ventricles expel blood from the heart
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They are produced by the snapping shut of the one way valves that keep blood from flowing
backward during contractions of the heart
Heart wall
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Endocardiumendothelium and subendothelial connective tissuealso covers the valves
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Myocardium cardiac muscle
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Epicardium mesothelium formed by the visceral layer of the serous pericardium
Muscle fibers are anchored to the fibrous skeleton of the heartforms four fibrous rings that surround the
orifices of the valves
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Right and left fibrous trigone are formed by connections of the rings
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Fibrous skeleton keeps the valves patent and allows the leaflets and cusps to attach
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Allows the myocardium to attach to something
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Myocardium forms a continuous ventricular myocardial band that originates from the
fibrous ring of the pulmonary valve and inserts on the fibrous ring of the aortic valve
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Forms an electrical insulator
Atria are separated from ventricles by coronary sulcus (atrioventricular groove) and the right and left
ventricles are separated by the anterior and posterior interventricular sulci (grooves)
Apex of the heart is directed anteriorly and to the left, while the base is directed posteriorly
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The apex is the inferior point of the heart, while the base is the superior portion
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Heart has four sides, like a pyramid
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Apex is formed by the inferolateral part of the left ventricle and lies posterior to the 5th intercostal
space in adults
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Remains motionless throughout the cardiac cycle
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Is where the sounds of the mitral valve closure are maximal (apex beat)
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The apex underlies the site where the heartbeat may be auscultated on the thoracic wall
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base of the heart is formed mainly by the left atrium, and small part of the right atrium
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receives pulmonary veins on the right and left sides of its left atrial portion and the superior and
inferior venae cavae at the superior and inferior ends of its right atrial portion
HEART HAS FOUR SURFACES
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Anterior (sternocostal) surface right ventricle
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Diaphragmatic (inferior) surface left ventricle and partly by right ventricle; is related mainly to
the central tendon of the diaphragm
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Right pulmonary surface formed mainly by the right atrium
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Left pulmonary surface formed mainly by the left ventricle; it forms the cardiac impression of
the left lung
HEART HAS FOUR BORDERS
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Right border formed by the right atrium and extending between the SVC and the IVC
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Inferior border formed mainly by the right ventricle and slightly by the left ventricle
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Left border formed mainly by the left ventricle and slightly by the left auricle
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Superior border formed by the right and left atria and auricles in an anterior view
RIGHT ATRIUM
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Forms the right border of the heart, receives venous blood from the SVC, IVC, and coronary sinus
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Right auricle is a conical muscular pouch that projects from thischamber, increasing the capacity
of the atrium as it overlaps the ascending aorta
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INTERIOR
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Smooth, thin walled posterior part (sinus venarum) is where venae cavae and coronary
sinus dump
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Muscular anterior wall composed of pectinate muscles
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Right AV orifice where right atrium dumps to right ventricle (poorly oxygenated blood)
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Smooth and rough parts are separated by the sulcus terminalis (external) and the crista
terminalis (internal)
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SVC opens into right atrium at the level of the right 3 rd costal cartilage
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IVC opens at the level of the 5th costal cartilage
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The interatrial septum has an oval fossa, which is the remnant of the foramen ovale and its valve
in the fetus
RIGHT VENTRICLE
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Largest part of the anterior surface of the heart, small part of diaphragmatic surface, and inferior
border of the heart
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Tapers superiorly into an arterial cone, the conus arteriosus, which leads into the pulmonary
trunk
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INTERIOR
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Irregular muscular elevations trabeculae carneae
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Thick muscular ridge supraventricular crest
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Separates the ridged muscular wall of the inflow part of the chamber from the
smooth wall of the conus arteriosus, or outflow part
inflow of the ventricle receives blood from the right AV (tricuspid) orifice (4-5th
intercostal spaces)
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this is surrounded by a ring from the fibrous skeleton
TRICUSPID VALVE
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Guards the right AV orifice
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Bases of the cusps are attached to the fibrous ring around the orifice
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They contact eachother the same way with each beat
TENDINOUS CORDS
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Attach to the anterior, posterior, and septal cusps (like cords on a parachute)
PAPILLARY MUSCLES
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Anterior papillary muscle
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Largest and most prominent of the three
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From anterior wall of the right ventricle to the anterior and posterior
cusps of the tricuspid valve (through tendinous cords
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Posterior papillary muscle
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Smaller than the anterior
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Arises from inferior wall of the right ventricle and its cords attach to
the posterior and septal cusps of the tricuspid valve
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Septal papillary muscle
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From interventricular septum and its cords attach to anterior and
septal cusps of the tricuspid valve
INTERVENTRICULAR SEPTUM
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Partitions the right and left ventricles
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MUSCULAR PART OF IVS
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Bulges into the cavity of the right ventricle b/c of how thick it is due to
the pressure needed to pump blood through the body through the left
ventricle.
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MEMBRANOUS PART OF IVS
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From part of the fibrous skeleton of the heart
SEPTOMARGINAL TRABECULA (MODERATOR BAND)
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Traverses the right ventricular chamber from the inferior part of IVS to the
base of anterior papillary muscle
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Carries right branch of the AV bundle
SUPRAVENTRICULAR CREST
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Deflects the incoming flow of blood into the main cavity of the right ventricle,
and outgoing flow into the conus arteriosus towards the pulmonary orifice
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Pulmonary valve and apex of conus arteriosus is at the level of the 3rd costal
cartilage
LEFT ATRIUM
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Forms most of the base of the heart
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LEFT AURICLE
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Wall is trabeculated with pectinate muscles
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Forms superior part of left border of heart and overlaps the root of the pulmonary trunk
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Semilunar depression in the interatrial septum indicates the floor of the oval fossa
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INTERIOR
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Larger smooth walled part and smaller muscular auricle containing pectinate muscles
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4 pulmonary veins (2 superior/2 inferior) enter posterior wall
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Thicker wall than that of the right atrium
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Interatrial septum that slopes posteriorly and to the right
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Left AV orifice going to the left ventricle
LEFT VENTRICLE
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Forms apex of heart, nearly all of its left surface and border, and most of the diaphragmatic
surface
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INTERIOR
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Thick walls
Mesh of trabeculae carneae that are finer and more numerous than those of the right
ventricle
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Anterior and posterior papillary muscles (larger)
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Aortic vestibule (smooth walled outflow part leading to aortic valve)
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Double – leaflet mitral valve that guards the AV orifice and aortic valve
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Aortic orifice surrounded by fibrous ring – ascending aorta begins here
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MITRAL VALVE
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Has anterior and posterior cusps
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Located posterior to sternum at 4th costal cartilage level
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Cusps receive cords from more than one papillary muscle
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AORTIC VALVE
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Semilunar valve between left ventricle and ascending aorta is located posterior to the
left side of the sternum at the level of the 3rd intercostal space
SEMILUNAR VALVES
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3 semilunar cusps of the pulmonary valve (anterior, right, and left), like the semilunar cusps of
the aortic valve (posterior, right, and left) si concave when viewed superiorly
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Purpose is to prevent blood from returning to the ventricle
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Edge of cusps are thick, forming the lunule
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Apex of the angulated free edge is called the nodule
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Immediately superior to each semilunar cusp, the pulmonary trunk and aorta form sinuses
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The mouth of the RIGHT CORONARY ARTERY is in the right aortic sinus
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The mouth of the LEFT CORONARY ARTERY is in the left aortic sinus
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No artery arises from the posterior aortic (non-coronary) sinus
VASCULATURE OF HEART
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Arterial supply of the heart
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CORONARY ARTERIES, first arteries off the aorta, supply the myocardium and the
epicardium
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Right and left coronary arteries arise from corresponding aortic sinuses at the
proximal part of the ascending aorta, and pass around opposite sides of the
pulmonary trunk
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They supply both the atria and the ventricles
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RIGHT CORONARY ARTERY
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Passes to the right side of the pulmonary trunk, running in coronary
sulcus
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Near its origin, it gives off an ascending sinuatrial nodal branch, which
supplies the SA node
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Then it goes into the coronary sulcus and gives off the right marginal
branch, which supplies the right border of the heart
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Then it runs to the posterior aspect of the heart
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At the posterior aspect (crux) of the heart, the junction of the
interatrial and interventricular septa between the four heart chambers,
it gives rise to the AV nodal branch which supplies the AV node
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SA and AV nodes are part of the conducting system of the heart
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Dominance of the right coronary artery is typical
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Gives rise to the large posterior interventricular branch
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Supplies both ventricles and gives off interventricular septal
branches into the IV septum
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The RCA usually supplies, therefore, the diaphragmatic surface of the
heart
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SUPPLIES
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Right atrium, right ventricle (most), part of IV septum, SA
node, AV node
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LEFT CORONARY ARTERY
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Passes between the left auricle and the left side of the pulmonary
trunk, runs in coronary sulcus
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Can have an SA NODAL BRANCH
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Divides into anterior IV branch and the circumflex branch
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Anterior IV branch passes to apex of heart and anastomoses
with the posterior IV branch of the right coronary artery and
supplies ventricles
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Gives rise to a lateral branch (diagonal artery) which
descends on anterior surface of heart
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Circumflex branch goes to posterior surface
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Left marginal branch of this supplies the left ventricle
SUPPLIES
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Left atrium, most of the left ventricle, part of the right
ventricle, most of the IVS (AV bundle), SA node (in 40% of
people)
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VARIATIONS
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Some arteries are more dominant than others in some people, but typically RCA and LCA
supply about 50% of heart each
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Some people only have one coronary artery
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Some people have an accessory coronary artery
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CORONARY COLLATERAL CIRCULATION
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Branches of coronary arteries are considered functional end arteries
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Anastomoses exist between terminations of RCA and LCA and between the IV branches
around the apex in approximately 10%
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Collateral circulation can develop in most if not all normal hearts
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GOOD PICTURES/CHART 146
VENOUS DRAINAGE
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Some small veins dump into the right atrium here
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CORONARY SINUS is the main vein of the heart
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Receives great cardiac vein at its left and middle cardiac vein and small cardiac veins at
its right end
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Left posterior ventricular and left marginal veins also open into coronary sinus
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GREAT CARDIAC VEIN is the main tributary for the coronary sinus
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First part is ANTERIOR INTERVENTRICULAR VEIN
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MIDDLE CARDIAC VEIN
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Accompanies the posterior interventricular branch (from RCA, usually)
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SMALL CARDIAC VEIN
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Accompanies the right marginal branch of the RCA
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OBLIQUE VEIN OF THE LEFT ATRIUM (OF MARSHALL)
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Is the remnant of the embryonic left superior vena cava
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ANTERIOR CARDIAC VEINS begin over the right ventricle and end in the right atrium directly
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SMALLEST CARDIAC VEINS begin in capillary beds of the myocardium and open into the
chambers of the heart directly (mostly the atria)
LYMPHATIC DRAINAGE
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Subepicardial lymphatic plexus pass to coronary sulcus and follow coronary arteries
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Ends in the inferior tracheobronchial lymph nodes, usually on the right side
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STIMULATING, CONDUCTING, AND REGULATING SYSTEMS OF THE HEART
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STIMULATING AND CONDUCTING SYSTEM OF THE HEART
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CONDUCTING SYSTEM generates and transmits the impulses that produce the coordinated
contractions of the cardiac cycle
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Consists of nodal tissue with conducting fibers
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Impulses are propagated by the striated muscle cells so that the chamber walls contract
simultaneously
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SA NODE located anterolaterally just deep to epicardium at junction of SVC and right atrium
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Pacemaker of heart
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Supplied by sinuatrial node artery, which arises as atrial branch of RCA, but sometimes
LCA in 40% of people
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AV NODE smaller collection of nodal tissue than the SA node
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Located on posteroinferior regioin of interatrial septum near the opening of coronary
sinus
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AV node distributes signal to the ventricles via the AV bundle
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Sympathetic speeds up conduction, while parasympathetic slows it down
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AV BUNDLE
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Branches to right and left bundles at the membranous and muscular parts of IVS
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Branches go to subendocardial branches (PURKINJE FIBERS)
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RIGHT BUNDLE
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Stimulates muscle of IVS, anterior papillary muscle through the septomarginal
trabecular (moderator band), and the wall of the right ventricle
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LEFT BUNDLE
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IVS, anterior and posterior papillary muscles, and wall of left ventricle
stimulated
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AV NODE is supplied by AV nodal artery, usually branch of RCA
INNERVATION OF HEART
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Supplied by autonomic nerve fibers from cardiac plexus
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Lies on anterior surface of bifurcation of trachea and posterior side of ascending aorta
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Formed by both parasympathetic and sympathetic fibers, and visceral afferents.
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SYMPATHETIC SUPPLY
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From presynaptic fibers with cell bodies in intermediolateral cell columns of T5-6 and
postsynaptic sympathetic fibers with cell bodies in cervical and superior thoracic
paravertebral ganglia of the sympathetic chains
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Postsynaptic fibers traverse cardiopulmonary splanchnic nerves and end in SA and AV
nodes
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Causes INCREASED HEART RATE, IMPULSE CONDUCTION, FORCE OF CONTRACTION,
AND INCREASED BLOOD FLOW THROUGH CORONARY VESSELS, INCREASED
CONTRACTILITY
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Most adrenergic receptors on the CORONARY VESSELS are BETA 2  relaxation of
vascular smooth muscle  DILATION
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PARASYMPATHETIC SUPPLY
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From presynaptic fibers of vagus nerves
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Ganglia are located in atrial wall and interatrial septum near SA and AV nodes and along
coronary arteries
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SLOWS HEART RATE, REDUCES FORCE OF CONTRACTION, CONSTRICTS CORONARY
ARTERIES, which saves energy between periods of increased demand
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Ach is released; DECREASES ATRIAL CONTRACTILITY
149 CONDUCTION OF HEART, 151 blue boxes
SUPERIOR MEDIASTINUM
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Superior to the transverse thoracic plane, passing through sternal angle and the junction of T4-5
From anterior to posterior the CONTENTS OF SUPERIOR MEDIASTINUM:
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Thymus
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Great vessels, with the veins (brachiocephalic veins and SVC) anterior to the arteries (arch of
aorta and roots of major branches—brachiocephalic trunk, left common carotid artery, left
subclavian artery) with nerves (vagus and phrenic and cardiac plexus of nerves)
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Inferior continuation of cervical viscera (trachea anteriorly and esophagus posteriorly) and
related nerves (left recurrent laryngeal nerves)
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Thoracic duct and lymphatic trunks
THYMUS
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Arterial supply comes from anterior intercostal, anterior mediastinal branches of the internal
thoracic arteries
GREAT VESSELS
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Right and left brachiocephalic veins formed from internal jugular and subclavian veins
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At level of inferior border of 1st costal cartilage, brachiocephalics unite to form the SVC
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Left brachiocephalic vein crosses over to the right to become the SVC, so it’s twice as long as the
right.
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Veins are ANTERIOR here
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SVC returns blood from all structures superior to the diaphragm, EXCEPT THE LUNGS AND HEART
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Ends at level of 3rd costal cartilage, where it enters the right atrium
Is anterior to the trachea and posterior to the ascending aorta
RIGHT PHRENIC NERVE lies between the SVC and the mediastinal pleura
Terminal half of the SVC is in the middle mediastinum, where it forms the posterior
boundary of the transverse pericardial sinus
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ASCENDING AORTA
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Its only branches are the coronary arteries
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Is considered a content of the MIDDLE MEDIASTINUM
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ARCH OF AORTA
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Begins posterior to the 2nd right sternocostal joint at the level of the sternal angle
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Ascends anterior to right pulmonary artery and bifurcation of trachea
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Reaches apex at left side of trachea and esophagus as it passes over the root of the left
lung
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Descends posterior to the left root of the lung beside the T4 vertebra
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Ends by becoming the DESCENDING AORTA
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BRANCHES
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IN ORDER: (1) Brachiocephalic trunk,(2) left common carotid, (3) left
subclavian
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Brachiocephalic trunk divides to right subclavian and right common carotid
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Arises posterior to the manubrium
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ARCH OF AZYGOS VEIN
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Corresponds to aorta on right side over the root of the right lung
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LIGAMENTUM ARTERIOSUM
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Remnant of fetal ductus arteriosus, passes from root of left pulmonary arteryto the
inferior surface of the arch of the aorta
NERVES OF SUPERIOR MEDIASTINUM
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VAGUS NERVES—PAGE 164
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RIGHT VAGUS NERVE
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Enters thorax anterior to right subclavian artery, where it gives rise to right
recurrent laryngeal nerve hooks around the right subclavian artery and
ascends between the trachea and esophagus to supply the LARYNX
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Runs posteroinferiorly through the superior mediastinum on the right side of
the trachea, then passes posterior to the right brachiocephalic vein, SVC, and
root of the right lung
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Then it divides and contributes to right pulmonary plexus
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Leaves plexus as single nerve and passes to esophageal nerve plexus
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Also gives rise to nerves contributing to cardiac plexus
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LEFT VAGUS NERVE
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Descends posterior to left common carotid artery
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Reaches left side of aortic arch, diverges posteriorly from left phrenic nerve
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Gives off LEFT RECURRENT LARYNGEAL NERVE
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Passes inferior to aortic arch, ascends to larynx
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LVN passes posterior to the root of the left lung, contributing to left pulmonary
plexus
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Leaves this as a single trunk and goes to esophageal nerve plexus
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PHRENIC NERVES
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Supply diaphragm with motor and sensory
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Sensory only 1/3rd of the fibers
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Also supply sensory to pericardium and mediastinal pleura
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Pass ANTERIOR TO ROOTS OF LUNGS how to differentiate from vagus, which pass
POSTERIOR
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RIGHT PHRENIC NERVE
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Passes over the right atrium
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Descends on right side of IVC to diaphragm, where it pierces near the caval
opening
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LEFT PHRENIC NERVE
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Descends anterior to the root of the left lung and runs along fibrous
pericardium, superficial to left atrium
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Pierces the diaphragm to left of pericardium
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Most branching occurs on the diaphragm’s abdominal surface
TRACHEA
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Anterior to esophagus
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Is NOT a component of the POSTERIOR MEDIASTINUM
ESOPHAGUS
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From pharynx to stomach
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Lies anterior to T1-4
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Thoracic duct usually lies on its left side, deep to arch of aorta
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Passes through esophageal hiatus in the diaphragm
POSTERIOR MEDIASTINUM
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Located inferior to transverse thoracic plane, anterior to T5-T12, posterior to pericardium and diaphragm,
and between parietal pleura of the two lungs
CONTAINS
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Thoracic aorta, thoracic duct, lymphatic trunks, posterior mediastinal lymph nodes, azygos and
hemiaxygos veins, esophagus, and esophageal nerve plexus
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Some include the sympathetic trunks and thoracic splanchnic nerves, but they don’t lie within the
posterior mediastinum per se.
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THORACIC AORTA
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Is a continuation of the arch of the aorta
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Begins at the left side of the inferior border of the body of the T4 vertebra and descends
in the posterior mediastinum on the left sides of the T5-T12 vertebrae
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Displaces the esophagus to the right
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Thoracic aortic plexus, an autonomic nerve network, surrounds it
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Lies posterior to the root of the left lung, pericardium and esophagus
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Terminates with a name change (abdominal aorta) at T12 and enters abdomen through
aortic hiatus in the diaphragm
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Thoracic duct and azygos vein ascend on its right side and accompany it through the
hiatus
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BRANCHES
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Anterior, midline plane of unpaired visceral branches to the gut and its
derivatives
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Esophageal arteries (usually 2)
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Lateral planes of paired visceral branches serving viscera other than the gut
and its derivatives
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Bronchial arteries (only the paired left bronchial arteries usually)
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Right bronchial arteries arise indirectly as branches of a right posterior
intercostal artery (usually the 3rd)
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Posterolateral planes of paired (segmental) parietal branches to the body wall
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Nine posterior intercostal arteries that supply all but the upper two
intercostal spaces and subcostal arteries, which course below the
diaphragm
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SUPERIOR PHRENIC ARTERIES
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These paired parietal branches pass anterolaterally to the superior
surface of the diaphragm, where they anastomose with the
musculophrenic and pericardiacophrenic branches of the internal
thoracic artery
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PERICARDIAL BRANCHES
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Unpaired branches arising anteriorlysend twigs to pericardium
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MEDIASTINAL ARTERIES
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Supply LNs and other tissues of posterior mediastinum
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ESOPHAGUS
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Descends into posterior mediastinum
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Posterior to and to the right of the arch of the aorta
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Posterior to pericardium and left atrium
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Passes through esophageal hiatus at the level of the T10 vertebra, anterior to the aorta
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It is compressed in 3 places
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Arch of aorta
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Left main bronchus
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The diaphragm
THORACIC DUCT AND LYMPHATIC TRUNKS
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Thoracic duct is the largest lymphatic channel in the body
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Lies anterior to the inferior 7 thoracic vertebrae
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Drains lower limbs, pelvic cavity, abdominal cavity, left upper limb, left side of the
thorax, left side of head and neck
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All lymph EXCEPT that from the right superior quadrant
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Originates from the chyle cistern in the abdomen and ascends through the aortic hiatus
in the diaphragm with azygos to its right, esophagus anteriorly, and vertebrae
posteriorly
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Crosses left at T4,5, or 6, posterior to esophagus, ascends in superior mediastinum
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Thoracic duct empties into the venous sytem near the union of the left internal jugular
and subclavian veins – venous angle or origin of the left brachiocephalic vein
VESSELS AND LYMPH NODES
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Posterior mediastinal lymph nodes lie posterior to the pericardium
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Receive lymph from esophagus, posterior aspect of pericardium and diaphragm,
and middle posterior intercostal spaces
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AZYGOS SYSTEM OF VEINS
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Drains back and thoracoabdominal walls and mediastinal viscera

Exhibits much variation

AZYGOS VEIN is the main tributary
o
Forms a collateral pathway between the SVC and IVC, and drains
blood from the thorax and abdomen
o
Ascends in the posterior mediastinum, passing close to the inferior 8
vertebrae
o
Arches over superior aspect of right lung to join the SVC
o
Communicates with posterior intercostal veins and vertebral venous
plexus that drain the back, vertebrae, and vertebral canal
o
Also receives mediastinal, esophageal, and bronchial veins

HEMIAZYGOS VEIN usually arise from roots arising from the posterior aspect of
the IVC or renal vein
o
Ascends on the left side of the vertebral column, posterior to thoracic
aorta as far as T9
o
Crosses to the right, posterior to aorta, thoracic duct, and esophagus,
and joins the AZYGOS VEIN
o
Receives inferior 3 posterior intercostal veins, the inferior esophageal
veins, and mediastinal veins

ACCESSORY HEMIAZYGOS VEIN
o
Begins at 5th or 5th intercostal space and descends on the left from T58
o
Receives veins from 4th-8th intercostal spaces
o
Crosses over at T7 or T8, posterior to thoracic aorta and thoracic duct,
where it joins AZYGOS VEIN
NERVES OF POSTERIOR MEDIASTINUM

Thoracic sympathetic trunks

Lower thoracic splanchnic nerves—greater, lesser, and least

Supply viscera inferior to diaphragm

Presynaptic fibers from 5th – 12th ganglia (sympathetic), which synapse in
prevertebral ganglia in the abdomen

Sympathetics to most of abdominal viscera
ANTERIOR MEDIASTINUM


Smallest, lies between the body of the sternum and the transversus thoracis muscles anteriorly and the
pericardium posteriorly
Is continuous with superior mediastinum at the sternal angle and is limited inferiorly by diaphragm


Consists of loose connective tissue (sternopericardial ligaments), fat, lymphatics, nodes, branches of
internal thoracic vessels
Contains inferior part of thymus in children
SURFACE ANATOMY—HEART BORDERS






Superior border line connecting the inferior border of the 2nd left costal cartilage to the superior border
of the 3rd right costal cartilage
Right border line draw from 3rd right costal cartilage to the 6th right costal cartilage—slightly convex to
the right
Inferior border line drawn from the inferior end of the right border to a point in the 5 th intercostal space
close to the left MCL
o
Left end of this line corresponds to the location of the apex of the heart and the apex beat
o
Apex beat is the impulse that results from the apex of the hart being forced against the anterior
thoracic wall when the left ventricle contracts—can be found in the 4th-5th intercostal spaces, 6-10
cm from the anterior median line
Left border
o
Corresponds to a line connecting the left ends of the lines representing superior and inferior
borders
VALVES
o
Are located posterior to sternum
o
Sounds are projected lateral to sternumpg. 173
o
Important to know these points are far enough away so that the valve sounds can be
distinguished individually AUSCULTATION
Blue boxes 174