Middle Mediastinum: Anatomy and Function of the Heart
Pulmonary Valve Location
2nd left intercostal space at sternal border.
Aortic Valve Location
2nd right intercostal space at sternal border.
Mitral Valve Location
5th left intercostal space at midclavicular line.
Tricuspid Valve Location
5th left intercostal space at sternal border.
fibrous rings (annulus fibrosus)
A major part of the fibrous skeleton is four fibrous rings, one surrounding each of the openings housing the major heart valves.
Anterior Interventricular Branch
Also known as left anterior descending (LAD).
Triangle of Koch
Area containing the AV node in the heart.
Diagonal Branch
Arises from LAD, supplies left ventricle.
Right Marginal Artery
Arises from RCA, supplies right ventricle margin.
Middle Cardiac Vein
Ascends in posterior groove, drains into coronary sinus.
Oblique Pericardial Sinus
Blind-ended space posterior to heart's base.
Coronary Circulation
Blood supply to the heart muscle itself.
Coronary arteries
Blood vessels supplying the heart muscle.
Sinuatrial Nodal Artery
Branches from RCA, supplies SA node.
End of Ventricular Systole
Closure of semilunar valves, producing 'Dub' sound.
Coronary Artery Variations
Common variations in coronary artery anatomy.
Atrioventricular bundle
Conducting fibers from AV node to interventricular septum.
Pain fibers
Conductors for heart pain information.
Parasympathetic innervation
Decreases heart rate and contraction strength.
Posterior Interventricular Branch
Descends in groove, supplies ventricles.
Bundle branches
Divisions of AV bundle towards ventricular apices.
Great Cardiac Vein
Drains both ventricles and left atrium.
Anterior Cardiac Veins
Empty directly into right atrium from right ventricle.
Pericardial Effusion
Excess fluid in pericardial cavity, may compress heart.
Pericardium
Fibroserous sac enclosing the heart and vessels.
Coronary Arteries
First branches off the ascending aorta.
Coronary Sulcus
Groove encircling heart, separates atria from ventricles.
Anterior Interventricular Sulcus
Groove marking anterior interventricular septum.
Posterior Interventricular Sulcus
Groove marking posterior interventricular septum.
Sulci
Grooves on heart surface, separate chambers.
Myogenic conduction
Impulse spread through atria via specialized pathways.
Sympathetic innervation
Increases heart rate and contraction strength.
Pericarditis
Inflammation of serous pericardium, restricts heart function.
Phrenic Nerve
Innervates fibrous and parietal pericardium.
limbus fossa ovalis
Its prominent rim of tissue is termed the limbus of the fossa ovalis.
Bicuspid Valve
Left atrioventricular valve, two cusps.
Parietal Pericardium
Lines inner side of fibrous pericardium.
Endocardium
Lines the inside of the heart and formed endothelium and subendothelial connective tissue.
Dorsal root ganglia
Location of sensory neuron cell bodies for pain.
Auscultation Sites
Locations for listening to heart sounds.
Serous Fluid
Lubricates heart, reduces friction during beating.
Vagus nerve
Main parasympathetic nerve influencing heart function.
Pericardiacophrenic Artery
Major arterial supply to fibrous and parietal pericardium.
Coronary Sinus
Major venous channel draining heart into right atrium.
Oblique Vein of Left Atrium
Merges with great cardiac vein, forms coronary sinus.
Cardiac myocytes
Muscle cells responsible for heart contraction.
Cardiac plexus
Nerve fiber network influencing heart rate and force.
Visceral afferent fibers
Nerve fibers carrying sensory information from organs.
Sympathetic pathways
Nerve pathways transmitting pain signals from heart.
Cardiac Plexus
Network of nerves supplying the heart.
Conducting System
Network of nodes and fibers controlling heart rhythm.
AV node
Nodal tissue above coronary sinus in interatrial septum.
Left Coronary Artery (LCA)
Originates from left aortic sinus.
Right Coronary Artery (RCA)
Originates from right aortic sinus.
Epicardium
Outer layer of heart wall, synonymous with visceral pericardium.
Fibrous Pericardium
Outer layer of pericardium, dense connective tissue.
SA node
Pacemaker located in right atrium near SVC.
Cardiac referred pain
Pain perceived in other body parts from heart.
LCA Course
Passes left, divides into anterior and circumflex branches.
RCA Course
Passes right between auricle and pulmonary trunk.
Bachmann's bundle
Pathway facilitating impulse conduction between atria.
Thoracic sympathetic trunk
Pathway for sympathetic fibers to the heart.
Interventricular Septal Arteries
Penetrate septum from posterior interventricular branch.
Aortic Valve
Prevents backflow from aorta to left ventricle.
Pulmonary Valve
Prevents backflow from pulmonary artery to right ventricle.
Ventricles
Pumping chambers of the heart, thick-walled.
Atria
Receiving chambers of the heart, thin-walled.
Ischemia
Reduced blood flow causing metabolic product accumulation.
Cardiac reflexes
Responses involving baroreceptors and chemoreceptors.
Tricuspid Valve
Right atrioventricular valve, three cusps.
Small Cardiac Vein
Runs with right marginal artery, drains into coronary sinus.
Baroreceptors
Sensors detecting changes in blood pressure.
Chemoreceptors
Sensors monitoring CO2 and O2 levels.
Cardiac Cycle
Sequence of heart events during one heartbeat.
Venae cordis minimae
Smallest cardiac veins emptying into heart chambers.
Purkinje fibers
Smallest conducting branches located under endocardium.
Transverse Pericardial Sinus
Space behind pulmonary arteries and aorta.
Pericardial Cavity
Space between parietal and visceral pericardium.
Nodal Tissue
Specialized cardiac tissue for electrical conduction.
Nodal tissue
Specialized cardiac tissue for impulse generation.
Dorsal horn
Spinal cord region for sensory neuron synapse.
Ventricular contraction
Strong contraction starting at ventricular apices.
Left Marginal Branch
Supplies left ventricle along its margin.
Visceral Pericardium
Synonymous with epicardium, covers heart surface.
Circumflex Branch
Terminal branch of LCA, courses left and posterior.
Sinuses
The aortic (and pulmonary) sinuses are the slightly dilated regions between the wall of the vessel and the semilunar valves.
aortic orifice, valve, and sinuses
The aortic orifice lies to the right and posterosuperior to the left AV orifice.
membranous septum
The connective tissue that forms the membranous septum, with both interventricular and atrioventricular parts, is connected to the rest of the fibrous skeleton.
sites of auscultation
The heart valves are best auscultated at spots different from their location, but closer to the point where blood is directed after passing through the valve.
fibrous trigone
There are two trigones, a right and a left one, which are formed by the connective tissue collections between the aortic ring and the rings for the right and left AV orifices.
Myocardium
Thick middle layer formed by the heart muscle itself.
Atrioventricular Nodal Artery
Usually branches from RCA, supplies AV node.
Atrioventricular Valves
Valves between atria and ventricles, prevent backflow.
Interatrial septum
Wall separating the left and right atria.
right auricle
a blind-ended muscular pouch at the superior part of the right atrium lined with pectinate muscles - lies against the root of the aorta.
fibrous skeleton of the heart
a collection of dense connective tissue located at the level of the coronary sulcus between the atria and the ventricles.
crista terminalis
a smooth muscular ridge of tissue extending from anterior to the opening of the SVC, along the lateral wall of the right atrium, to the anterior part of the opening of the IVC - separates the smooth-walled sinus venarum from the ridged-walled rest of the atrium.
septomarginal trabecula (moderator band)
a specific elevated trabeculae carneae that passes between the interventricular septum and the base of the anterior papillary muscle - contains part of the conducting system of the heart.
fossa ovalis
a thumbprint-sized depression in the interatrial septum above the opening of the inferior vena cava.
Ventricular diastole
all chambers are relaxed, semilunar valves are closed, atrioventricular valves open, and blood enters the four chambers passively.
heart boundaries
as visualized on the chest wall - superior right point is ̴ 1 cm from the right margin of the sternum on the 3rd costal cartilage - superior left point is ̴ 2 cm from the left margin of the sternum on the upper border of the left 3rd costal cartilage or slightly above this. The apex point is at about the midclavicular line in the left 5th intercostal space. The last point is at the sternocostal joint of the right 6th rib. Slightly curved lines connect these points.
AV valve closure
av valves close, atria then relax, and ventricular systole begins.
Atrial systole
both atria contract to force additional blood into the ventricles.
cusps of tricuspid (right atrioventricular) valve
each of the three cusps of this valve (anterior, septal, and posterior) is formed by a thin layer of fibrous tissue covered on both sides by endocardium.
sulcus terminalis
external groove demarcating the location of the internal crista terminalis - lying on the right side - extending from anterior part of where SVC enters the heart to the anterior part where the IVC enters the heart.
location (Base)
faces posteriorly towards the mid-thoracic vertebral bodies (T6 → T9 vertebra when erect and T5 → T8 when recumbent).
chordae tendineae
fibrous cords that attach parts of the free edges of the tricuspid leaflets to the tips of papillary muscles.
right border
formed by slightly convex right atrium.
superior border
formed by the right and left atria and their auricles.
interatrial septum
formed by the tissue between the right and left atria - faces anteriorly and to the right because the left atrium lies posterior to the right atrium.
pulmonary valve
formed by three semilunar cusps with free margins that come together, closing the pulmonary orifice when the ventricle is relaxed (diastole).
diaphragmatic surface
formed mainly by left ventricle (with some right ventricle) - related mainly to central tendon of diaphragm - extends from base to apex - coronary sinus separates this surface from the base.
left pulmonary surface
formed mainly by left ventricle - occupies cardiac impression of left lung.
right pulmonary surface
formed mainly by right atrium - faces the right lung.
left border (obtuse margin)
formed mostly by the left ventricle with a little of the left atrium - lies vertically.
sternocostal surface
formed mostly by the right ventricle (with some right atrium and left ventricle).
inferior border (acute margin)
formed mostly by the right ventricle with a little of the left ventricle - lies horizontally.
interventricular septum
forms the anterior and right wall of the left ventricle.
Pulmonary valve auscultation
in left 2nd intercostal space near sternum.
Tricuspid valve auscultation
in left 5th intercostal space near sternum.
Aortic valve auscultation
in right 2nd intercostal space near sternum.
chamber involved (Apex)
inferolateral part of left ventricle.
pectinate muscles
irregular ridges of muscles in the wall of the atrium anterior and medial to the crista terminalis.
valve of foramen ovale
is a ridge of tissue inferior to the thinned, depressed area of the interatrial septum.
aortic vestibule
is the smooth-walled outflow tract of the left ventricle.
right atrioventricular orifice
large opening between right atrium and ventricle that is closed by the tricuspid valve during ventricular systole.
left atrioventricular orifice
large opening between the left atrium and left ventricle maintained by the Bicuspid valve (Mitral valve).
chambers involved (Base)
mostly the left atrium, with a lesser amount of the right atrium.
supraventricular crest
muscular ridge that separates the conus arteriosus from the rest of the right ventricle - may help direct flow of blood which changes direction between inflow and outflow parts of the cycle.
left auricle
narrowed, conical structure extending anteriorly and to the right, overlying the root of the pulmonary trunk.
Mitral valve auscultation
over apex of heart in left 5th intercostal space near midclavicular line.
Ventricular Systole
overlaps with step 3, contraction of ventricles closes AV valves and opens semilunar valves (aortic and pulmonary valves).
location (Apex)
posterior to the left 5th intercostal space at about the midclavicular line.
functions of fibrous skeleton
provides the site of attachment for the AV and semilunar valves and keeps these openings correctly sized and patent.
Left ventricle
pumps the oxygen-rich blood out the aorta to the systemic circulation - has a thicker wall than the right ventricle because it needs to pump blood out with a greater force.
Right atrium
receives deoxygenated blood returning from the systemic circulation (including the heart).
Right ventricle
receives oxygen-poor blood from the right atrium and pumps it out the pulmonary trunk to the lungs.
Left atrium
receives oxygen-rich blood from the lungs.
trabeculae carneae (left ventricle)
similar to those in the right ventricle except finer and more intricate.
opening of coronary sinus
small but distinct opening for the coronary sinus which carries most of the venous blood from the heart itself - located between the openings for the inferior vena cava and the right atrioventricular orifice.
Apex of heart
the blunted tip of the heart which is directed inferiorly, anteriorly, and to the left.
Lunule
the free edge of each cusp towards the lumen.
Base of heart
the part of the heart opposite the apex. It is here that the great veins enter the heart.
posterior interventricular sulcus
the posterior indentation produced by the deeper lying interventricular septum.
sinus venarum
the posteriorly located, smooth-walled portion of the right atrium that receives the blood from the vena cavae and coronary sinus.
conus arteriosus (infundibulum)
the smooth-walled outflow portion of the right ventricle leading towards the pulmonary orifice.
trabeculae carneae
thick, crisscrossing and anastomosing muscular ridges.
Nodule
thickening of the lunule at the center of the free edge.
papillary muscles
three conical projections of muscles (anterior, posterior, and septal) from the wall of the ventricle that anchor the chordae tendineae.
mitral (bicuspid, left atrioventricular) valve
two cusps - the name 'mitral' reflects its resemblance to a bishop's miter.
papillary muscles (left ventricle)
two of these (anterior and posterior) that generally are larger than those in the right ventricle.
openings for pulmonary veins
typically 4 pulmonary veins (2 right and 2 left) enter the posterior, smooth wall of the left atrium.
opening of inferior vena cava
wide opening with a rudimentary valve - located at inferior part of right atrium - blood passing through this opening is directed towards the interatrial septum where opening to left atrium (foramen ovale) once was in the fetus.
opening of superior vena cava
wide opening with no valve - located in the superoposterior part of atrium - blood passing through this opening is directed towards the right atrioventricular orifice.
