Download 17- interior of heart

Borders of the heart
The right border: It is formed by right atrium
The left border: It is formed by the L. ventricle & L. auricle.
The lower border : It is formed mainly by the R. ventricle & by R. atrium.
The apex is formed by the left ventricle.
The walls of the heart are composed of cardiac muscle ( myocardium ) which is
covered externally by the visceral layer of the serous pericardium ( epicardium )
The heart is lined internally with a layer of endothelium ( endocardium ).
Chambers
It has 2 atria & 2 ventricles. The superior atria are receiving chambers. They are not
important in pumping activity. Blood flow into them under low pressure from the veins of
the body then to the ventricles.
The longitudinal septum which divides the heart is called the interventricular or the
interatrial septum.
The left ventricle’s walls are thicker than the right & more powerful pump. It is the
systemic pump.
Right Atrium
It consists of a main cavity & outpouching ( the auricle ). Externally at their junction,
there is a vertical groove ( the sulcus terminalis ) which on the inside forms a ridge
( the crista terminalis ).
The main part of the atrium that lies posterior to the ridge is smooth walled which is
derived from the sinus venosus.
The part in front of the ridge is roughened or trabeculated by bundles of muscle fibers
( the musculi pectinati ) which is derived from the primitive atrium.
Openings into the Right Atrium
1-The Superior Vena Cava opens into the upper part. It has no valve. It returns blood
from the upper half of the body.
2- The inferior vena cava opens into the lower part. It guarded by a rudimentary, nonfunctioning valve. It returns the blood from the lower half of the body.
3- The coronary Sinus. It drains most of the blood from the heart wall. It opens
between the I.V.C. and the atrioventricular orifice. It is guarded by a rudimentary,
nonfunctioning valve.
4- The right
atrioventricular
orifice. It lies
anterior to the I.V.C.
opening and is
guarded by the
tricuspid valve.
5- Many small orifices
of small veins which
drain the wall of the
heart, open directly
into the right atrium.
Right Ventricle
As the cavity approaches the pulmonary orifice it becomes funnel shaped
( infundibulum)
The trabeculae carneae are the projecting ridges that gives the ventricular wall a
sponge like appearance. They are composed of 3 types.
The 1st comprises the papillary muscles which project inward, being attached by their
bases to the ventricular wall & their apices are connected by fibrous cords
( chordae tendineae ) to the cusps of the tricuspid valve.
The 2nd are attached at their ends to the ventricular wall being free in the middle. One
of these ( moderator band ). It crosses the ventricular cavity from the septal to the
anterior wall. It conveys the right branch of the atrioventricular bundle.
The 3rd type is composed of prominent ridges.
Tricuspid valve
Guards the right atrioventricular orifice
and consists of 3 cusps formed by a
fold of endocardium with some
connective tissue enclosed.
The anterior cusp lies anteriorly – The
septal cusp lies against the ventricular
septum – the posterior or the inferior
lies inferiorly.
The bases of the cusps are attached
to the fibrous ring of the skeleton of
the heart, whereas their free edges
and ventricular surfaces are attached
to the chordae tendineae which
connect the cusps to the papillary
muscles.
The chordae tendineae of one
papillary muscle are connected to the
adjacent parts of the 2 cusps.
When the ventricle contracts, the
papillary muscles contract to
prevent the cusps from being forced
into the atrium.
Pulmonary Valve
It guards the pulmonary
orifice. It consists of 3
semilunar cusps formed
by folds of endocardium
with connective tissue
enclosed. The curved lower
margins and the sides of
each cusp are attached to
the arterial wall to prevent
The cusps from prolapsing into ventricle.The
open mouths of the cusps are directed upward
into the pulmonary
trunk.
At the root of the pulmonary trunk are 3
dilatations called sinuses.
The 3 semilunar cusps are arranged with one
posterior and 2 anterior.
During ventricular systole ( 1 ).
During ventricular diastole ( 2 ).
N.B. No chordae or papillary muscles are
1-1
2-
Left atrium
It consists of a main cavity and a left auricle. It is situated behind the right atrium and
forms the greater pert of the base or posterior surface.
Behind it lies the oblique sinus of the serous pericardium and the fibrous pericardium
separates it from the esophagus.
Its interior is smooth but the auricle have muscular ridges.
The 4 pulmonary veins, 2 from each lung open through its posterior wall and have
no valves. The left atrioventricular orifice is guarded by the mitral valve.
left ventricle
Its walls are 3 times thicker than those of the right ventricle. The left ventricular blood
pressure is 6 times higher than that inside the right ventricle.
In cross section, the left ventricle is circular, the right is crescentic because of the
bulging of the ventricular septum into the cavity of the right ventricle.
There are well - developed trabeculae carneae, 2 large papillary muscles, but no
moderator band. The part below the aortic orifice is called the aortic vestibule.
The mitral valve consists of 2 cusps, one anterior & one posterior. The anterior is the
larger and intervenes between the atrioventricular & aortic orifices.
The aortic valve has one cusp is situated on the anterior wall ( right ) and 2 cusps are
located on the posterior wall ( left & posterior ). Behind each cusp the aortic wall
bulges to form an aortic sinus. The anterior aortic sinus gives origin to the right
coronary artery, the left posterior sinus gives origin to the left coronary artery.
Structure of the Heart
The atria has thin wall and is divided by the atrial septum. The septum runs from the
anterior wall of the heart backward and to the right.
The interventricular septum is placed obliquely with one surface facing forward and
to the right and the other facing backward and to the left. Its position is indicated on
the surface of the heart by the anterior & posterior intervetricular grooves.
The lower part of the septum is thick and formed of muscle. The smaller part of the
septum is thin and membranous and attached to the fibrous skeleton.
The skeleton of the Heart
It consists of fibrous rings that surround the 1-atrioventricular orifices
2-pulmonary orifice
3- Aortic orifice and are continuous with the membranous upper part of the
ventricular septum.
The fibrous rings around the atrioventricular orifices separate the muscular walls of the
atria from those of the ventricle but provide attachment for the muscle fibers.
The fibrous rings support the bases of the valve cusps and prevent the valves from
stretching and becoming incompetent.
Conducting system
The heart contract at about 70 to 90 beats
per minute in the resting adult.
The atria contract first and together, to be
followed later by the contractions of both
ventricles together.
It consists of specialized cardiac muscle
pressent in the:
1- Sinuatrial node:It located in the wall of
the right atrium in the upper part of the
sulcus terminalis just to the right of the
opening of the S.V.C. The node
spontaneously gives origin to rhythmical
electrical impulses that spread in all
directions through the cardiac muscle of
the atria and cause the muscle to contract.
2- Atrioventricular node: It is placed on the
lower part of the atrial septum just
above the attachment of the septal cusp
of the tricuspid valve. From it, the
cardiac impulse is conducted to the
ventricles by atrioventricular bundle.
Conducting system
The speed of conduction of the cardiac impulse
through the atrioventricular node (0.11 second )
allows sufficient time for atria to empty their blood
into the ventricles before the ventricles start to
contract.
3- Atrioventricular Bundle ( of His
It is the only pathway of cardiac muscle
that connects the myocardium of the atria
and the myocardium of the ventricles.
The bundle descends through the fibrous
skeleton of the heart
It then descends behind the septal cusp of
the tricuspid valve to reach the inferior
border of the membranous part of the
ventricular septum.
At the upper border of the muscular part of
the septum it divides into 2 branches, one for
each ventricle.
The right bundle branch (RBB) passes
down on the right side of the ventricular
septum to reach the moderator band,
where it crosses to the anterior wall of the
right ventricle. Here it becomes continuous
with the fibers of the Purkinje plexus.
Conducting system
The left bundle branch (LBB) pierces the
septum and passes down on its left side
beneath the endocardium. It divides into 2
branches ( anterior & posterior) which
become continuous with the fibers of the
Purkinje plexus of the left ventricle.
Internodal Conduction Paths
Impulses from the sinuatrial node have been
shown to travel to the atrioventricular node
more rapidly than they can travel by passing
along the ordinary myocardium.
The anterior internodal pathway leaves the
anterior end of the sinuatrial node and
passes anterior to the SVC opening. It
descends on the atrial septum and ends in
the atrioventricular node.
The middle internodal pathway leaves the
posterior end of the sinuatrial node and
passes posterior to the SVC opening. It
descends on the atrial septum to the
atrioventricular node.
The posterior internodal pathway leaves the posterior part of the sinuatrial node and
descends through the crista terminalis and valve of the inferior vena cava to the
atrioventricular node.
Arterial supply to the Conducting System
It is supplied by the right but sometimes by the left coronary artery.
The atrioventricular node and the atrioventricular bundle are supplied by the
right coronary artery.
The RBB of the atrioventricular bundle is supplied by the left coronary artery.
The LBB is supplied by the right & left coronary arteries.
Surface Anatomy of the Heart Valves
1- The tricuspid valve lies behind the right half of the sternum opposite the 4th intercostal
space.
2- The mitral valve lies behind the left half of the sternum opposite the 4th intercostal
space.
3- The pulmonary valve lies behind the medial end of the 3rd left costal cartilage and the
adjoining part of the sternum.
4- The aortic valve lies behind the left half of the sternum opposite the 3rd intercostal
space.
Auscultation of the Heart Valves
On listening to the heart with a stethoscope, one can hear 2 sounds: lub- dup. the first sound is
produced by the contraction of the ventricles and the closure of the tricuspid and mitral valves. The
second sound is produced by the sharp closure of the aortic and pulmonary valves.
1- The tricuspid valve is best heard over the right half of the lower end of the body of the sternum.
2- The mitral valve is best heard over the apex beat, that is at the level of the 5th left intercostal
space, 3.5 inch (9 cm ) from the midline.
3- The pulmonary valve is heard over the medial end of the 2nd left intercostal space.
4- The aortic valve is heard over the medial end of the 2nd right intercostal space.
Innervation of the Heart
Postganglionic fibers reach the heart by way of the
superior , middle, and inferior cardiac branches of
the cervical portion of the sympathetic trunk and a
number of cardiac branches from the thoracic
portion of the sympathetic trunk.
The efferent preganglionic fibers arise in the upper
4 or 5 thoracic segments of the spinal cord ; pass
by white rami communicantes to synapse about cells
in the upper thoracic ganglia or travel up the trunk to
synapse in the cervical ganglia.
The postganglionic fibers pass through the cardiac
plexuses and terminate on the sinoatrial and
atrioventricular nodes, on cardiac muscle fibers
and on coronary arteries.
Activation of these nerves results in cardiac
acceleration, increased force of contraction of the
cardiac muscle and dilatation of the coronary
arteries. So, more oxygen and nutrients supply to
myocardium.
The coronary dilatation is mainly produced in
response to local metabolic needs rather than by
direct nerve stimulation of the coronary arteries.
The parasympathetic preganglionic fibers
originate in the dorsal nucleus of the vagus
and from cells near the nucleus ambiguus and
descend into the thorax in the cardiac branches
of the vagus nerves .
The fibers terminate by synapsing with
postganglionic neurone in the cardiac plexuses
and in the walls of the atria.
Postganglionic fibers terminate on the sinoatrial
and atrioventricular nodes and on the coronary
arteries.
Activation pf these nerve results in a reduction
in the rate and force of contraction of the
myocardium and a constriction of the coronary
arteries.
Also, the coronary constriction is mainly
produced by the reduction in local metabolic
needs rather than by neural effects.
Ischemia and accumulation of metabolic products
stimulate pain ending in the myocardium.
Afferent fibers running with the vagus nerves take
place in cardiovascular reflexes.
Cardiac Pain
Pain originating in the heart is assumed to be caused by oxygen deficiency and
the accumulation of metabolites, which stimulate the sensory nerve endings in
the myocardium.
The afferent nerve fibers ascend to the central nervous system through the
cardiac branches of the sympathetic trunk and enter the spinal cord through
the posterior roots of the upper 4 thoracic nerves .
The pain is not felt in the heart but is referred to the skin areas supplied by
the corresponding spinal nerves. The axons of the primary sensory neurons
enter spinal cord segments T1 toT4 or T5 on the left side. The pain varies
from a severe crushing pain to a mild discomfort.
The skin areas supplied by the upper 4 intercostal nerves and by the
intercostobrachial nerve ( T2 ) are therefore affected. The intercostobrachial
nerve communicates with the medial cutaneous nerve of the arm and is
distributed to skin on the medial side of the upper part of the arm. The pain
radiates from the substernal region and left pectoral to the left shoulder and
medial aspect of the left arm. The pain is sometimes felt in the neck and jaw.
Myocardial infarction involving the inferior wall or diaphragmatic surface of
the heart often gives rise to discomfort in the epigastrium.
The afferent pain fibers from the heart
ascend in the sympathetic nerves
and enter the spinal cord in the
posterior roots of the 7th ; 8th and 9th
thoracic spinal nerves dermatomes in
the epigastrium.
The heart and the thoracic part of the
esophagus have similar afferent pain
pathway. So, painful acute esophagitis
can mimic the pain of myocardial
infarction.
The heart is insensitive to touch,
cutting, cold and heat.
N.B.
Synaptic contacts may also be made
with commissural neurons
( connector neurons ) that conduct
impulses to neurons on the right side of
comparable areas of the cord. This is
the cause of radiating pain to the right
side or both sides.