Mediastinum
/ heart
Pg. 184-202
The mediastinum is the visceral compartment between the two lungs
and includes the mediastinal part of the parietal pleura. It is commonly
defined as the region between the two pleural sacs, bounded laterally
by the mediastinal parietal pleura, anteriorly by the sternum and
posteriorly by the thoracic vertebral column, and extending vertically
from the superior thoracic inlet to the respiratory diaphragm
The mediastinum is divided
into superior and inferior
mediastinum by the sternal
plane , which passes
horizontally from the
manubriosternal joint to
intersect the vertebral column
from the fourth to the superior
half of the fifth thoracic
vertebral body.
Superior mediastinum
Boundaries:
Anteriorly : manubrium of the sternum
Posteriorly: first 4 thoracic vertebra and intervertebral discs
Superiorly: superior thoracic aperture,
The superior mediastinum contains the
trachea, oesophagus, aortic arch,
brachiocephalic trunk, left common carotid
And subclavian arteries ,the internal
thoracic arteries, the supreme intercostal,
left superior intercostal, accessory
hemiazygos, internal thoracic and inferior
thyroid veins, and numerous lymph nodes,
including the para-aortic, upper
paratracheal, Retrotracheal and prevascular
groups.
the major structure in the anterior
mediastinum is an inferior extension of the
thymus gland. Also fat, connective tissue,
lymph nodes , mediastinal branches of the
internal thoracis vessels and
stertnopericardial ligaments.
Anterior mediastinum
• The anterior mediastinum is posterior to the
body of the sternum and anterior to the
pericardial sac
• Its superior boundary is a transverse plane
passing from the sternal angle to the
intervertebral disc between vertebra TIV and
TV, separating it from the superior
mediastinum
• Its inferior boundary is the diaphragm.
• Laterally, it is bordered by the mediastinal
part of parietal pleura on either side.
• Major structure in the anterior mediastinum
is an inferior extension of the thymus gland,
also fat, connective tissue, lymph nodes, and
sternopericardial ligaments.
Middle mediastinum
• Is centrally located in the thoracic cavity.
Contains pericardium, heart, origins of the
great vassels, nerves, and smaller vassels
• The pericardium is a fibroserous sac
surrounding the heart and the roots of the
great vessels. It consists of two components,
the fibrous pericardium and the serous
pericardium
• The fibrous pericardium is a tough connective
tissue outer layer that defines the boundaries
of the middle mediastinum.
• The serous pericardium is thin and consists of
two parts: The parietal layer of serous
pericardium lines the inner surface of the
fibrous pericardium. The visceral layer
(epicardium) of serous pericardium adheres
to the heart and forms its outer covering
• The space between
the two layers of
serous pericardium ,
containing small
amount of fluid is
the pericardial
cavity.
HEART
• The shape and the orientation of
the heart are that of the pyramid
that has fallen over and is resting
on one of its sides. It is placed in
the thoracic cavity, the apex of this
pyramid projects forward,
downward and to the left.
• The base of the pyramid is opposite
the apex and faces in the posterior
direction
• Consists of diaphragmic )inferior)
surface; anterior (sternocostal)
surface) ; right and left pulmonary
surfaces.
The base of the heart
• The left atrium
• Small portion of the right atrium
• Proximal parts of the great veins
( superior and inferior vena cava
and the pulmonary veins)
Apex of the heart
• From the base of the heart to
forward , downward and the
lefts ending in the apex of the
heart. Formed by:
• The inferolateral part of the left
ventricle and is positioned deep
to the left fifth intercostal space,
8-9 cm from the mediastinal line
Surfaces of the heart
• Anterior surface: right ventricle, part
of the right atrium on the right and
some of the left ventricle on the left.
• Diaphragmic surface : left ventricle
and small portion of the right ventricle
separated by the posterior
interventricular groove.
• Left pulmonary surface faces the left
lung is broad and convex and consists
of the left ventricle and a portion of
the left atrium
• Right pulmonary surface faces the
right lung is broad and convex and
consists of the right atrium.
External sulci
• Internal partitions divide the
heart into four chambers and
produce surface or external
grooves referred to as sulci
• The coronary sulcus circles the
heart, separating the atria from
the ventricle, contains right
coronary artery, the small
cardiac vein, the coronary sinus
and the circumflex branch of the
left coronary artery.
• Anterior and posterior
interventricular sulci: separates
the two ventricles the anterior
interventricular sulcus is on the
anterior surface of the heart and
contains anterior interventricular
artery and the great cardiac vein
• and the posterior interventricular
sulcus is on the diaphragmic
surface of the heart and contains
the posterior interventricular
artery and the middle cardiac vein
Cardiac chambers
• The heart has 2 pumps separated by a
partition.
• The right pump receives
deoxygenated blood from the body
and sends it to the lungs.
• The left pump receives oxygenated
blood from the lungs and sends it to
the body..
• Each pump consists of the atrium and
ventricle separated by valves
• The thin walled atria receive blood
coming into the heart, thick walled
ventricles pump blood out of the
heart
Right atrium
• Right border of the heart
• Blood returning to the right
atrium enters through one of
three vessels: the superior and
inferior vena cava( deliver blood
to the heart from the body) ,
coronary sinus( returns blood
from the walls of the heart itself)
• The superior vena cava enters the upper
posterior portion of the right atrium and the
inferior vena cava and coronary sinus enter
the lower posterior portion of the right
atrium
• From the right atrium, blood passes into the
right ventricle through the right
atrioventricular orifice.
• The interior of the right atrium is divided
into 2 continuous spaces. Externally this
separation is indicated by shallow , vertical
groove (sulcus terminalis cordis) which
extend from the right side of the opening of
superior vena cava from the right side of the
opening of the inferior vena cava
• This division is indicated by the crista
terminalis .
• Separating the right atrium from the left atrium is
the interatrial septum. Which faces forward and to
the right because the left atrium lies posteriorly
and to the left of the right atrium.
• A depression is clearly visible in the septum above
the orifice of the inferior vena cava . This is the
fossa ovalis(oval fossa)
• Fossa ovalis marks the location of the embryonic
foramen ovale which his the important part of fetal
circulation.
Rigth ventricle
• Forms most of the anterior surface of the
heart and a portion of the diaphragmic
surface .
• The outflow tract of the right ventricle which
leads to the pulmonary trunk is the conus
arteriosus. This area has smooth walls
• The walls of the inflow portion of the right
ventricle have numerous muscular , irregular
surfaces called tuberculae carneae.
• A few tubercula carneae (pupillary muscles)
have only one end attached to the ventricular
surface, other end serves as a point of the
attachment for tendon like fibrous cordschordae tendineae, which connect to the free
edged of the cusps of the tricuspid valve
There are 3 papillary muscles in the right
ventricle
• Anterior papillary muscle
• Posterior papillary muscle
• Septal papillary muscle
Tricuspid valve
• The right atrioventricular orifice is
closed during ventricular
contraction by tricuspid valve (
consist of 3 cusps or leaflets)
• The base of each cusp is secured to
the fibrous ring that surrounds the
atrioventricular orifice.
• That helps to maintain the shape of
the opening.
• The cusps are continuous with each
other near their bases at sites
termed commissures
• During the filling of the right ventricle
the tricuspid valve is open and the three
cusps project into the right ventricle
• Necrosis of the papillary muscle
following myocardial infarction (heart
attack) may result in prolapse of the
related valve
Pulmonary valve
• The apex of the infundibulum,
the outflow tract of the right
ventricle the opening into the
pulmonary trunk is closed by the
pulmonary valve.
• Consists of three semilunar
cusps with free edges projecting
upward into the lumen of the
pulmonary trunk
• Cusps are named left, right and
anterior semilunar cusps,
Left atrium
• Forms most of the base or posterior
surface of the heart
• Is derived embryologically from 2
structures : the posterior half or inflow
portion receives the four pulmonary
veins. Has smooth walls and derives from
the proximal parts of the pulmonary veins
. The anterior half is continuous with the
left auricle. Contains musculi pectinate
and derives from embryologic primitive
atrium.
• During development the valve of the
foramen ovale prevents blood from
passing from the left atrium to the right
atrium.
Left ventricle
• Lies anterior to the left atrium
• Contributes to the anterior,
diaphragmic and left pulmonary
surfaces of the heart and forms the
apex
• Blood enters the ventricle through
the left atrioventricular orifice and
flows in a forward direction to the
apex.
• It is conical, larger than the right
ventricle, has thicker layer of
myocardium.
Mitral valve
• The left atrioventricular orifice
opens into the posterior right
side of the superior part of the
left ventricle.
• It is closed during ventricular
contraction by mitral
valve(bicuspid valve)
• Anterior and posterior cuspc
Aortic valve
• The aortic vestibule Is continuous superiorly with
the ascending aorta
• The opening from the left ventricle to the aorta is
closed by the aortic valve
• Structure is similar to the pulmonary valve.
Contains 3 semilunar cusps
• Between the semilunar cusps and the wall of the
ascending aorta is pocket like sinuses the right, left
and posterior aortic sinuses . The right and left
coronary arteries originate from the right and left
aortic sinuses .
• Function of the aortic valve is similar to the
pulmonary valve with one additional process : as
blood recoils after ventricular contraction and fills
the aortic sinuses it is automatically forced into the
coronary arteries because these vessels originate
from the right and left aortic sinuses.
https://www.youtube.com/watch?v=heSsAreO_y0