(5) Middle Mediastinum & Heart

Mediastinum

middle section of thoracic cavity containing esophagus, trachea, heart, and great vessels

transverse thoracic plane

imaginary horizontal Plane that anteriorly passes through the sternal angle and posteriorly passes through the T4/T5 vertebral junction to divide the mediastinum

Superior mediastinum

mediastinal area above TTP. The superior-most border is formed by the top of the manubrium, the 1st rib, and the spinous process of T1

middle mediastinum

mediastinal area below TTP & medial. The inferior border is formed by the diaphragm. Contains the heart.

posterior mediastinum

mediastinal area below TTP & posterior. Posterior-most border is formed by the bodies of vertebra T1-T12.

anterior mediastinum

mediastinal area below TTP & anterior. Anterior-most border is formed by the manubrium, body of sternum, and xiphoid process.

azygous vein

Empties into superior vena cava. Ascends on right side of posterior thoracic wall

phrenic nerves & pericardiacophrenic vessels

sandwiched between pericardium & mediastinal border

Pericardium

membranous sac enclosing the heart

fibrous pericardium

outer layer of the pericardium that protects heart, prevents the heart from overfilling, & helps attach heart within chest/neighboring structures

serous pericardium

Inner double layer of pericardium composed of parietal and visceral layers. Produces serous fluid

parietal pericardium

outer layer of the pericardium that provides a lining

visceral pericardium (epicardium)

inner layer of the pericardium that touches the heart & forms its outer layer

Myocardium

muscular, middle layer of the heart

endocardium

inner lining of the heart that is internal to the chambers & in contact with blood

heart development in the embryo

Heart begins unpaired & centrally placed in the pericardial sac. As heart grows, it pushes against the back/posterior wall of pericardial sac

location of superior border of the heart

just inferior to level of manubriosternal joint

location of upper right corner of the heart

1 fingers breadth lateral to sternal margin on superior surface of 3rd costal cartilage

location of lower right corner of the heart

1 fingers breadth lateral to sternal margin near xiphoid process on 6th costal cartilage

location of upper left corner of the heart

1 fingers breadth lateral to sternal margin on 2nd costal cartilage

location of lower left corner of the heart

1 hands breath from midline of sternum in left 5th intercostal space

location of inferior border of the heart

at level of xiphisternal joint

superior vena cava

drains blood from areas above the abdominal diaphragm to the right atrium

inferior vena cava

drains blood from areas below the abdominal diaphragm to the right atrium

general circulatory pathway

vena cava → Right Atrium → right ventricle→ pulmonary trunk → Left/Right pulmonary arteries→ Lungs → pulmonary veins → left atrium → left ventricle → aorta → body

the prenatal circulatory pathway differs in that it

bypasses the right half of circulation because a fetus doesn't breath so therefore doesn't use the pulmonary circuit. results in right-to-left shunting.

foramen ovale

fetal right-to-left shunt from right atrium to left atrium. after birth, closes to become fossa ovalis.

fossa ovalis

depression in rear wall of right atrium that is a remnant of the foramen ovale

ductus arteriosus

fetal right-to-left shunt from left pulmonary artery to aorta that allows any blood that didn't make it through the foramen ovale to get to left side of heart. after birth degenerates to become the ligamentum arteriosum

ligamentum arteriosum

depression near curvature of aortic arch that is a remnant of the ductus arteriosus

right auricle

Ear-shaped extension of the right atrium

left auricle

Ear-shaped extension of the left atrium

sulci

grooves that separate chambers of the heart

Coronary sulcus (atrioventricular sulcus)

grooves that separate atria from ventricles

anterior interventricular sulcus

groove that separates left and right ventricles anteriorly

posterior interventricular sulcus

groove that separates left and right ventricles posteriorly

right border of the heart

formed by the right atrium

left border of the heart

formed by the left ventricle

superior border of the heart

formed by the right and left atria, great vessels, and SVC

anterior view of heart is dominated by

right ventricle

posterior view of heart is dominated by

left atrium

aortic arch

the part of the aorta that curves posteriorly & to the left

pulmonary trunk

great vessel that branches into right and left pulmonary arteries

right pulmonary artery

Branch of pulmonary trunk that goes to the right lung. Nestled under the arch of the aorta.

left pulmonary artery

Branch of pulmonary trunk that goes to the left lung

rough parts of atrial walls come from

embryonic right tube

smooth parts of atrial walls come from

smooth muscle that is pulled during embryonic development

direction of blood flow in right atrium

right to left

sources of deoxygenated blood to right atrium

SVC, IVC, coronary sinus

pectinate muscles

rough muscular ridges in right atrial wall

crista terminalis

Part of the right atrial wall where the pectinate muscle stops and smooth surface begins

Right AV (tricuspid) valve

The valve that controls blood flow from the right atrium to the right ventricle. 3 cusps: anterior, septal, posterior.

septal cusp

The tricuspid valve flap that attaches to the ventricular septum.

direction of blood flow in right ventricle

superiorly

Interventricular septum

separates the two ventricles. has a smooth membranous part & a rough muscular part.

trabeculae carneae

muscular ("meaty") ridges on the internal surface of the ventricles

papillary muscle

Small bunches of cardiac muscle responsible for pulling the atrioventricular valves closed by means of the chordae tendinae. 3 in right ventricle (septal, anterior, posterior), 2 in left ventricle (anterior, posterior).

chordae tendineae

"heart strings" ; Tendinous cords that connect the edges of the AV valves to the papillary muscles. Function in preventing the thing & flappy AV valves from being blow back into atria during systole.

moderator band

connects the interventricular septum to the anterior papillary muscle

direction of blood flow in left atrium

down & to the left

Left AV Valve (bicuspid/mitral valve)

The valve that controls blood flow from the left atrium to the left ventricle. 2 cusps: anterior & posterior

direction of blood flow in left ventricle

up & to the right

semilunar valves

pulmonary and aortic valves located between the right ventricle and the pulmonary artery and between the left ventricle and the aorta. Have 3 cusps. Concave upwards. Function in preventing blood from pooling back into the ventricles during diastole.

aortic valve cusps

2 coronary cusps (left & right cusps), 1 non-coronary cusp (posterior cusp)

coronary cusps

cusps of the aortic valve that become left & right coronary arteries

position of heart valves during diastole

AV valves open, semilunar valves closed

position of heart valves during systole

AV valves closed, semilunar valves open

"Lub" sound of heart auscultation

Sound that comes from the closing of the AV valves during ventricular contraction

"dub" sound of heart auscultation

Sound that comes from the closing of semilunar valves after ventricular contraction

auscultation site for aortic valve

right 2nd intercostal space at sternal margin

auscultation site for tricuspid valve

left 5th intercostal space at sternal margin

auscultation site for pulmonary valve

left 2nd intercostal space at sternal margin

auscultation site for mitral valve

left 5th intercostal space at midclavicular line/cardiac apex

aortic sinuses

base of the ascending aorta where blood pools & forces semilunar valves closed during diastole

left coronary artery (LAC)

Artery that runs posterior to the pulmonary trunk & supplies blood to the left side of the heart. Branches into circumflex artery & anterior interventricular artery.

circumflex artery

branch of the left coronary artery that runs along the coronary sulcus. branches into left obtuse marginal branches.

anterior interventricular artery/left anterior descending (LAD) artery

branch of the left coronary artery that runs along the left interventricular sulcus. branches into diagonal branches.

right coronary artery

Artery that runs anterior to the pulmonary trunk along the right coronary sulcus & supplies blood to the right side of the heart. Branches into the right atrial artery, right acute marginal artery, sinu-atrial (SA) nodal artery, & posterior interventricular artery

Atrial branch of RCA

Branch of the RCA that supplies the wall of the right atrium

posterior interventricular artery/posterior descending artery (PDA)

branch of the right coronary artery (where it starts to turn downward) that runs along the posterior portion of the interventricular sulcus

sinu-atrial (SA) nodal artery

branch of the RCA that supplies the SA node

Coronary dominance

determined by which coronary artery is supplying the posterior descending artery (PDA)

right coronary dominance

PDA is supplied by the RCA after it passes the posterior right sulcus. More common type of coronary dominance (75% of individuals)

left coronary dominance

PDA is supplied by the circumflex branch of the LCA. Less common type of coronary dominance (15 % of individuals)

anterior cardiac veins

very small cardiac veins that empty directly into the right atrium

small cardiac vein

cardiac vein that runs alongside the right marginal artery before emptying into the coronary sinus

middle cardiac vein

cardiac vein that runs alongside the posterior interventricular artery before emptying into the coronary sinus

great cardiac vein

cardiac vein that runs alongside the anterior interventricular artery before emptying into the coronary sinus

coronary sinus

enlarged vein on posterior surface of heart that receives blood from cardiac veins & empties into the right atrium

coronary vs cardiac

"coronary" refers specifically to arteries of the heart (besides coronary sinus which is a vein)

sinu-atrial node (SA node)

pacemaker of the heart, located at junction of SVC & right atrium. rapid spontaneous depolarization, waves of which are propagated along atrial wall

atrioventricular (AV) node

a node of specialized heart muscle located in the septal wall of the right atrium that receives impulses from the sinoatrial node and transmits them to the atrioventricular bundle

atrioventricular bundle (bundle of His)

a bundle of modified heart muscle that transmits the cardiac impulse from the atrioventricular node to the IV septa. splits into left and right bundle branches.

right bundle branch

branch of bundle of His that transmits impulses to right ventricle to cause ventricular contraction

moderator band role in conduction

serves as an "off ramp" of right bundle branch that tells anterior papillary muscle to tug on chordae tendineae to prepare for systole

parasympathetic innervation pathway of the heart

vagus nerve -> vagal cardiac branches -> cardiac plexus -> heart

vagal cardiac branches

branches of the vagus nerve that bring info to cardiac plexus

cardiac plexus

Network of nerves supplying the heart that surround the anterior surface of the trachea bifurcation. A mixed autonomic plexus containing both postganglionic sympathetic axons and

preganglionic parasympathetic axons.

location of preganglionic cell bodies in parasympathetic innervation of heart

vagal nuclei in brainstem

location of postganglionic cell bodies in parasympathetic innervation of heart

walls of the heart