The Heart

The heart is a hollow muscular organ located in

the anterior (middle) mediastinum within the
pericardial sac. It rests on the central tendon of
the diaphragm and is flanked on either side by
the right and left pulmonary cavities.
The heart has a conical shape. The base,
anchored by the great vessels, is on its
superior and posterior surfaces. The apex,
located approximately at the 5th intercostal
space, left to midclavicular line, projects
anteriorly, inferiorly, and to the left and moves
freely within the pericardial sac. The heart is
covered by the pericardial membrane.
 The Pericardium and Pericardial Cavity
 The pericardium, a double fibroserous membrane, forms the pericardial
sac that surrounds the heart and the origins of the great vessels.
 The pericardium is composed of two layers: an outer fibrous layer and
an inner serous layer.
◦ 1. The outer fibrous pericardium is composed of tough in-elastic connective
tissue. It is attached inferiorly to the diaphragm and is continuous superiorly
with the tunica adventitia (outer layer) of the great vessels.
◦ 2. The thin serous pericardium consists of a parietal part and a visceral part.
 The parietal layer (part) of serous pericardium lines the inner surface of the parietal
pericardium.
 The visceral layer (part) of serous pericardium firmly adheres to the outer surface of the
heart as the epicardium. This layer is continuous with the parietal layer of the serous
pericardium at the root of the great vessels.
 Pericardiacophrenic arteries, branches of the internal thoracic arteries,
provide the main blood supply to the pericardium. Veins that accompany
the arteries drain into the superior vena cava.
 The vagus (CN X) and phrenic nerves (C3–C5) and branches from the
sympathetic trunks innervate the pericardium.
 Pericardial pain is often referred via the phrenic nerve to the skin of the
ipsilateral supraclavicular region (dermatomes C3–C5).
The fibrous pericardium.
 The Pericardial Cavity
The pericardial cavity is the space within
the pericardial sac between the parietal
and visceral layers of the serous
pericardium.
The pericardial cavity is filled with a thin
layer of serous fluid that allows for
frictionless movement of the heart.
 Serous pericardial reflections
 Sagittal section through the mediastinum. Note the continuity of the parietal serous and visceral serous pericardia.
 Heart in
situ
 Anterior
view of the
opened
thorax.
Removed:
Thymus
and
anterior
pericardiu
m.
Revealed:

Heart .
 Posterior pericardial cavity
 Anterior view. The heart has been elevated to partially visualize the
posterior pericardial cavity and the oblique pericardial sinus.
 Pericardium consists of 3 layers (from outer to
inner):
◦ Fibrous pericardium
◦ Parietal layer of serous pericardium
◦ Visceral layer of serous pericardium
 Pericardial cavity lies between parietal and visceral
layers.
 Pericardium innervated by phrenic nerve. Pericarditis
can cause referred pain to the shoulder.
 The Heart
.
 The heart has a conical shape. The base, anchored by the great vessels, is on
its superior and posterior surfaces. The apex, located approximately at the
5th intercostal space, projects anteriorly, inferiorly, and to the left and
moves freely within the pericardial sac.
 Internally, the heart is divided into four chambers: the right and left atria and
the right and left ventricles.
◦ The right and left atria, separated by an interatrial septum, are the inflow chambers
of the heart, receiving blood from the systemic circulation on the right and pulmonary
circulation on the left.
◦ The right and left ventricles, separated by an interventricular septum, are the outflow
chambers of the heart. Blood flows from the right ventricle into the pulmonary
circulation and from the left into the systemic circulation.
◦ Two small appendages, the right and left auricles, are extensions of the atria and are
visible externally.
 The surfaces of the heart are
◦ the sternocostal surface on the anterior side of the heart, formed mostly by the
right ventricle with portions of the right atrium and left ventricle;
◦ the base on the posterior and superior sides of the heart, formed by the left atrium and a
portion of the right atrium; and
◦ the diaphragmatic surface on the inferior side of the heart, formed by the left and
Anterior (sternocostal) surface.
 Posterior surface (base).
Inferior (diaphragmatic) surface.
Three grooves on the external surface of the heart
can be used to determine the position of the
chambers:
◦ 1. The coronary sulcus encircles the heart between the
atria and ventricles. Because the heart has an oblique
orientation, the sulcus is nearly vertical.
◦ 2. The anterior interventricular sulcus is a longitudinal
groove that marks the position of the interventricular
septum on the anterior surface.
◦ 3. The posterior interventricular sulcus is a longitudinal
groove that marks the position of the interventricular
septum on the diaphragmatic surface.
The crux of the heart is a point on the posterior
surface of the heart where the coronary
(atrioventicular) and interventricular sulci meet. It
marks the junction of the four chambers of the heart.
The wall of the heart consists of three
layers:
◦ 1. The epicardium, the thin outermost layer,
formed by the visceral layer of the serous
pericardium
◦ 2. The myocardium, the thick layer of cardiac
muscle, thickest in the walls of the ventricles
◦ 3. The endocardium, the thin internal layer,
which lines the chambers and valves of the
heart
– A cardiac skeleton of dense fibrous connective tissue
forms four fibrous anuli (rings) and intervening trigones
that separate the chambers of the heart, provide anchoring
points for cardiac muscle fibers and cardiac valves, and
insulate electrical impulses of the heart’s conduction
system
 Cardiac skeleton: Superior view. Red dotted circles are attachment sites of
papillary muscles on valves.
Chambers of the heart
A Right ventricle, anterior view.
Right atrium, right lateral view.
Left atrium and ventricle, left lateral view. Note the
irregular trabeculae carneae characteristic of the
ventricular wall.
 The Atria
 The atria are the thin-walled inflow chambers of the heart.
◦ The right atrium receives the superior and inferior venae cavae from the systemic
circulation and the cardiac veins from the heart. The left atrium receives the pulmonary
veins from the lungs.
 Each atrium is associated with an auricle, a small pouch that expands the
capacity of the atrium and whose roughened walls contain pectinate muscles.
 A depression on the right ride of the interatrial septum, the oval fossa (fossa
ovalis), is a remnant of the oval foramen (foramen ovale), an opening
through which blood was shunted from the right to left atria in the prenatal
circulation.
 The right atrium is divided into two parts by a muscular ridge, the terminal
crest (crista terminalis). The two parts of the right atrium are
◦ 1. the venous sinus (sinus venarum), a smooth-walled region on the posterior wall
that contains the openings of the superior vena cava, inferior vena cava, coronary sinus,
and anterior cardiac veins; and
◦ 2. the atrium proper, the anterior muscular portion that, like the right auricle,
contains pectinate muscles.
 The left atrium is smaller but thicker walled than the right atrium and receives
the four to five pulmonary veins from the lungs. The atrial walls are smooth,
with the pectinate muscles confined to the left auricle.
 The Ventricles
 The ventricles are thick-walled chambers that connect to the out-flow channels of the
heart: the right ventricle to the pulmonary artery and the left ventricle to the aorta.
 The walls of the ventricles are marked with a meshwork of thick muscular ridges
known as trabeculae carneae.
 Most of the interventricular septum is muscular, but there is a small membranous part
at the superior end that is a common site of septal defects.
 The right ventricle is the smaller and thinner walled of the two ventricles. A muscular
ridge, the supraventricular crest, separates it into two parts:
◦ 1. The right ventricle proper, the inflow portion of the ventricle that receives blood from the
right atrium
 An anterior and a posterior papillary muscle arise from its floor, and a septal papillary muscle arises
from the interventricular septum.
 A muscular septomarginal trabecula (moderator band) extends from the septum to the base of the
anterior papillary muscle and carries a part of the electrical conduction system (the right branch of the
antrioventricular bundle) that facilitates the coordinated contraction of the papillary muscle.
◦ 2. The conus arteriosus (infundibulum), the smooth-walled outflow channel through which
blood flows into the pulmonary trunk
 The left ventricle, which includes the apex of the heart, is the thickest-walled chamber
of the heart.
 Similar to the right ventricle, the left is divided into inflow and outflow portions:
◦ 1. The left ventricle proper, which receives blood from the left atrium. A large anterior and
small posterior papillary muscle arise from its floor
◦ 2. The aortic vestibule, the smooth-walled outflow channel through which blood flows into
the aorta.
 Valves of the Heart
 Thereare two types of cardiac valves: atrioventricular
and semi-lunar.
◦ 1. Atrioventricular valves separate the atria from the
ventricles and prevent regurgitation of blood into the atria
during contraction of the ventricles.
 The atrioventricular valves are made up of cusps, thin leaflets with
free inner margins and outer margins that are attached to the fibrous
rings of the cardiac skeleton.
 Slender threads called tendinous cords (chordae tendinae) attach
the free edges of the valve leaflets to the papillary muscles in the
ventricles. These cords maintain closure of the valves and prevent
regurgitation of blood during ventricular contraction. Each cusp
attaches to tendinous cords from more than one papillary muscle.
 The atrioventricular valves include
 the tricuspid valve, which separates the right atrium from the right ventricle
and is composed of anterior, posterior, and septal cusps; and
 the bicuspid (or mitral) valve, which separates the left atrium from the left
ventricle and is composed of anterior and posterior cusps. The anterior cusp is
 Valves of the Heart
 Semilunar valves prevent outflow from the ventricles as the
chambers fill and backflow of blood into the ventricles after it has
been expelled.
◦ Each valve is composed of three semilunar cusps with free inner
margins and attached outer margins. A sinus, or pocket, is created
between each cusp and the vessel wall. The thickened free margin of the
cusp, the lunule, is the point of contact of the cusps. A nodule marks the
center of the lunule.
◦ The semilunar valves include the following:
 The pulmonary semilunar valve (pulmonary valve, is located in the pulmonary
trunk at the top of the conus arteriosus, where it moderates blood flow through the
right ventricular outflow channel. Its cusps are in the anterior, right, and left
positions.
 The aortic semilunar valve (aortic valve) is located within the aorta immediately
adjacent to the mitral valve, where it moderates blood flow through the left
ventricular outflow channel. Its cusps are in the posterior, right, and left positions.
The coronary arteries arise from the sinuses above the right and left cusps.
Conduction System of the Heart
 The conduction system of the heart generates and transmits impulses that modulate the
contraction of the cardiac muscle. It consists of nodes, which initiate the impulses, and
conducting fibers, which distribute the impulses to cardiac muscle to effect a coordinated
contraction of the heart chambers.
 The sinoatrial (SA) node, the pacemaker of the heart, located in the wall of right
atriam. it generates impulses which initiates and coordinates the timing of the
contraction of the heart chambers.
◦ At a frequency of 60 to 70 beats per minute, the SA node transmits impulses to both atria and to the
atrioventricular node.
◦ It is subepicardial, located on the external surface of the heart, just within the myocardium of the
right atrium at the junction with the superior vena cava.
◦ A branch of the right coronary artery usually supplies the SA node.
 The atrioventricular (AV) node is stimulated by the SA node and transmits impulses to
the AV bundle.
◦ It is subendocardial, located at the base of the interatrial septum above the septal cusp of the tricuspid
valve.
◦ The AV nodal artery, a branch of the right coronary artery, arises near the origin of the posterior
interventricular artery at the crux of the heart.
 The atrioventricular (AV) bundle (of His) arises from cells of the AV node and transmits
impulses to the walls of the ventricles.
◦ It runs first along the membranous part of the interventricular septum and then divides into right and
left bundle branches that descend to the apex on either side of the muscular part of the septum.
◦ The bundle branches end as Purkinje fibers, modified cardiac fibers, which ascend within the
muscular walls of the ventricles.
Conduction system generates impulses
Sino atrial node which is located ij the wall
of the right atrium, it generates imoulses
which causes contraction of myocardium
of atria and some impulses goes to atrio
ventricular node.
The avn is btw the right atrium and right
ventricle, from here impulses goes to
bundle of his which is divided in to right
and left bundle branches and they end in
the myocardium and cause contraction of
myocardium of the ventricles.
Btw artria and ventricles we have
coronary sulcus
Inside the sulcus we have fibrous tissue/
fibrous rink.
Because we have fibrous tissue
contraction artria does not spread to
ventricles
Neurovasculature of the Heart
 The right and left coronary arteries arise from the
ascending aorta just superior to the right and left cusps of
the aortic valve. In the initial phase of ventricular diastole,
the local surge in aortic pressure caused by the backflow
closes the aortic valve and drives blood into the coronary
arteries. Blood flow in the arteries is greatest during
diastole because of the compression of arteries within the
myocardium during systole.
 The right and left coronary arteries supply the myocardium
and epicardium of the heart.

Coronary arteries start from the bulb of the aorta

Right coronary artery goes to coronary sulcus
 The right coronary artery//RCA
 RCA descends within the coronary sulcus around the
right side of the heart. Its major branches and their
distribution are
◦ the SA nodal artery, which supplies the right atrium and
the SA node;
◦ the right marginal branch, which supplies the apex and
part of the right ventricle; (also the largest)
◦ the posterior interventricular branch, which supplies the
right and left ventricles and posterior third of the
interventricular septum and anastomoses with the
interventricular branch of the left coronary artery near the
apex on the diaphragmatic surface; and
◦ the AV nodal artery, which supplies the AV node.
Thr right coronary artery goes post side in
the coronary sulcus and gives off post
interventricular artery which descends to
the apex and supplies blood to the right
atrium and right ventricle
Rca supplies blood to SA node which
gives of SA nodal atery, right marginal
post interventricular and atriovenntricular
nodal artery
 The left coronary artery
 LCA, typically larger than the right coronary artery, arises
from the aorta posterior to the pulmonary trunk. After a short
but variable course, it divides into two large branches, the
anterior interventricular (left anterior descending//LAD)
artery, which descends in the anterior interventricular
sulcus, and the circumflex artery, which runs around the
left side of the heart in the coronary sulcus. Their branches
and distributions include
◦ the anterior interventricular artery, which supplies the anterior
aspects of the right and left ventricles and the anterior two-thirds of
the interventricular septum, including the AV bundle of the
conducting system; and
◦ the circumflex artery, which supplies the left atrium and, via its left
marginal branch, the left ventricle. In ~40% of the population, an
SA nodal branch arises to supply the SA node.
Lca arises from the left sinus of the aortic bulb
and it is divided into 2 main parts:-
Ant interventricular artey which goes to the ant
interventricular sulcus and left circumflex
coronary artery which goes to coronary sulcus
Lcca gives off left marignal artery
Circumflex artery supplies blood to left atrium
and left ventricle
Aia supplies left atrium and some portion of ant
wall of the right ventricle, 2/3rd of interventricular
septum and bundle of his
 Coronary Veins - LOW-YIELD
 The coronary sinus, which receives most of the venous return from
the heart, runs in the posterior coronary sulcus between the left
atrium and ventricle. The thebesian valve guards the orifice of the
coronary sinus where it drains into the right atrium near the opening
of the inferior vena cava.
 The large veins of the heart are tributaries of the coronary sinus.
◦ The great cardiac vein travels with the anterior interventricular artery and
drains the left atrium and both ventricles.
◦ The posterior left ventricular vein drains the diaphragmatic surface of the
left ventricle.
◦ The posterior interventricular (middle cardiac) vein runs in the posterior
interventricular groove with the posterior interventricular artery and drains
the posterior part of the interventricular septum.
◦ The small cardiac vein, which drains the posterior right atrium and the
right ventricle, accompanies the right coronary artery in the atrioventricular
groove.
◦ The oblique vein of the left atrium drains left atrium.
◦ Anterior cardiac veins drain the anterior surface of the right ventricle and
Veins of the coronary sinus, which is located
in the coronary sulcus, it contains 5 veins
that open into the coronary sinus
Great cardiac vein (ant intreventricular
sulcus of left coronary and great cardiac
starts from this and goes to coronary sulcus,
enters the sinus)
The smallest veins – veneminae r in the
myocardium of all the chnambers of the heart
and they directly open into the chmabers
 Innervation of the Heart
The autonomic nerves of the cardiac plexus innervate
the conduction system of the heart; they therefore
regulate the heart rate but do not initiate the heartbeat.
◦ Sympathetic innervation increases the rate and force of
contractions by increasing the response of the SA and AV
nodes. It also allows dilation of the coronary arteries.
◦ Parasympathetic innervation decreases the rate of
contractions and causes vasoconstriction of the coronary
arteries.
◦ Visceral sensory fibers innervating the baroreceptors
(receptors that measure blood pressure) and chemoreceptors
(receptors that measure blood CO2) in the heart and aortic
arch travel with the parasympathetic fibers of the vagus
nerve.
◦ Visceral sensory fibers carrying pain sensation travel with
sympathetic fibers to the T1–T5 spinal cord.