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CARDIOVASCULAR
SYSTEM
Cardiovascular
system
Heart
Blood vessels
THE HEART
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It is a muscular hollow organ that pumps the blood to various parts of the
body.
It is located in the mediastinum (the cavity between the lungs).
It is surrounded by the pericardium.
It is formed of 4
chambers; 2 atria
and 2 ventricles,
which are
separated by atrioventricular
(coronary) groove.
The right and left
atria are separated
longitudinally by
the interatrial
septum. The right
and left ventricles
are separated
longitudinally by
the interventricular
septum.
Pericardium
Fibrous
pericardium
Serous
pericardium
Visceral
layer
Parietal
layer
Pericardium
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It is the covering of the heart. It is formed of 2 types:
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Fibrous pericardium: outer tough fibrous conical sac which surrounds
the serous pericardium. The apex (above) surrounds the pulmonary
trunk, ascending aorta and superior vena cava. The base (below) rests
on the central tendon of diaphragm. It protects the heart and prevents its
over distension.
Serous pericardium: a closed serous sac which is formed of:
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Visceral layer: adherent to the heart.
Parietal layer: lines the fibrous pericardium.
The cavity between these 2 layers is called pericardial cavity
which contains a thin film of serous fluid to provide a slippery
surface for the movements of the heart.
NB: Pericardial effusion is accumulation of excessive amount of
fluid in the pericardial cavity leading to compression of the
heart. It is drained by a needle inserted in the 5th or 6th left
intercostal space near the sternum
External features of the heart
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The heart is a cone-shaped.
It has apex, base, 2 surfaces and 4 borders.
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Apex:
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It is directed downwards, forwards and to the left.
 It is formed by the
left ventricle only.
 It lies opposite the
left 5th intercostal
space (3 ½
inches from
midline).
 Base:
 It is directed
upwards,
backwards and to
the right.
 It is formed by the
2 atria (mainly the
left).
 It is lies in front of
middle 4 thoracic
vertebrae
Anterior view
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Sterno-costal surface:
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It is the anterior surface.
It is formed of atrial and ventricular parts, separated by the atrioventricular groove.
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Diaphragmatic surface:
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Atrial part: formed mainly by the right atrium.
Ventricular part: formed by right ventricle (right ⅔) and left ventricle (left ⅓), which are
separated by the anterior interventricular groove.
It is the posterior surface, which rests on the diaphragm.
It is formed of right ventricle (right ⅓) and left ventricle (left ⅔), which are separated by the posterior
interventricular groove.
4 borders:
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Upper border:
formed by the 2
atria (mainly the
left).
Lower border:
formed by the right
ventricle and
apical part of left
ventricle.
Right border:
formed by the right
atrium.
Left border:
formed by the left
ventricle and left
auricle.
Posterior view
Chambers and flow of blood in the heart
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Right atrium:
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Right ventricle:
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It is the right upper chamber of the heart which receives venous
blood (deoxygenated) from whole body (through the superior vena
cava, inferior vena cava, and the coronary sinus). During the interval
when the ventricles are not contracting, blood passes down through
the right atrio-ventricular orifice, guarded by the right atrio-ventricular
(tricuspid) valve into the right ventricle.
It is the right lower chamber of the heart which receives blood from
the right atrium and pumps it to the lungs through the pulmonary
trunk, which divides into two pulmonary arteries, which lead to the left
and right lungs, respectively. The following events occur in the right
ventricle:
When the right ventricle contracts, the tricuspid valve close
and prevent blood from moving back into the right atrium.
When the right ventricle relaxes, the initial backflow of blood
in the pulmonary artery closes the pulmonary (semilunar)
valve and prevents the return of blood to the right ventricle.
Chambers of heart
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Left atrium:
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Left ventricle:
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It is the left upper chamber of the heart which receives oxygenated
blood from the lungs through 4 pulmonary veins (2 from each lung).
The left atrium, like the right atrium, is a holding chamber for blood.
When the left ventricle relaxes, blood passes through the left atrioventricular orifice, guarded by the left atrio-ventricular (mitral) valve
into the left ventricle.
It is the left lower chamber of the heart which receives blood from the
left atrium and pumps it through the aorta into the whole body. The
following events occur in the left ventricle, simultaneously and
analogously with those of the right ventricle:
When the left ventricle contracts, the mitral valve close and
prevent blood from moving back into the left atrium.
When the left ventricle relaxes, the initial backflow of blood
in the aorta closes the aortic (semilunar) valve and prevents
the return of blood to the left ventricle.
Flow of blood
in the heart
Interior of heart
Right atrium
Left atrium
It is formed of:
It is almost smooth except at its auricle
Smooth posterior part: receives the which contains scattered groups of musculi
openings of SVC & IVC & coronary pectinati.
sinus.
Rough anterior part: full of muscular
projections called musculi pectinati.
The 2 parts are separated by a raised band
on the lateral wall called "crista terminalis".
Its septal wall shows oval depression Its septal wall shows nothing.
"fossa ovalis", which has raised crescentic
ridge "limbus of fossa ovalis.
It receives the openings of
SVC: without valve
IVC: with rudimentary valve
Coronary sinus: with well-defined valve
Anterior cardiac veins
It receives the openings of the 4 pulmonary
veins.
Right atrium
Right ventricle
Left ventricle
It is thin- walled
It is thick-walled (3 times as the right ventricle).
Its lumen is large & curved in cross section.
Its lumen is small & circular in cross section.
It is formed of:
 Smooth outflowing part "infundibulum" which
leads to the pulmonary trunk.
 Rough inflowing part due to presence of:
o Trabeculae carnae few
o Papillary muscles 3
 anterior
 posterior
 septal
It is formed of:
 Smooth outflowing part "vestibule" which
leads to the aorta
 Rough inflowing part due to presence of:
o Trabeculae carnae numerous
o Papillary muscles 2
 anterior
 posterior
Moderator band is present (It is a muscular band Moderator band is absent.
which extends from inter-ventricular septum
to base of anterior papillary muscle).
Right ventricle
Left ventricle
Blood supply of heart
Arterial supply:
 Right coronary artery:
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It arises from the beginning of the ascending aorta.
It passes in the coronary groove then curves around the right side of the
heart till the posterior interventricular groove where it ends by
anastomosis with the circumflex branch of left coronary artery.
It gives the following branches:
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Right marginal artery: runs along the lower border of the heart.
Posterior interventricular artery: passes in the posterior interventricular
groove.
Left coronary artery:
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It arises from the beginning of the ascending aorta.
It passes between the pulmonary trunk and left auricle for a short
distance then divides into anterior interventricular artery and circumflex
arteries.
It gives the following branches:
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Anterior interventricular artery: passes in anterior interventricular groove.
Circumflex coronary artery: rotates around left side of the heart at the
coronary groove where it ends by anastomosis with right coronary artery.
Arterial supply of heart
Venous drainage:
 Coronary sinus: a wide short venous channel which
collects the majority of venous drainage of the heart. It
is lodged in the posterior part of the coronary groove
(between the left atrium and left ventricle) and opens
in the right atrium.
 Tributaries:
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Great cardiac vein
Middle cardiac vein
Small cardiac vein
Oblique vein of left atrium
Posterior vein of left ventricle
Anterior cardiac veins: 3-4 small veins draining
anterior surface of right ventricle and ends in right
atrium.
Venae cordis minimi: minute veins which open
directly in all chambers of the heart especially on the
right side.
Venous drainage of heart
Conductive system of the heart
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The conductive system of the heart is concerned with the
initiation and propagation of the cardiac impulse. It consists of
specialized cardiac muscle fibers. It includes the following
components:
Sino-atrial node (SAN):
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It present at the junction of SVC and right atrium.
It is the pacemaker, in which the impulse is initiated.
Atrio-ventricular node (AVN):
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It is present in the lower part of the interatrial septum.
It receives the impulse from SAN by either:
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Spreading through the ordinary atrial myocardium.
Spreading through 3 interatrial tracts (anterior, middle and posterior).
Atrio-ventricular bundle (AVB):
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It starts from the AVN and descends in the interventricular septum till the
apex of the heart and then divides into 2 bundle branches; right and left
branches.
It transmits the impulse from the AVN to the wall of the ventricles.
Conductive
system of
heart
Blood circulations
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The circulation of the blood within the cardiovascular system can be
distinguished into 3 types of circulations, which are communicating together.
These are:
Pulmonary circulation: the deoxygenated blood travels from the right ventricle
to the lungs through the pulmonary trunk. Within the lungs, gaseous exchange
takes place and the oxygenated blood returns from the lungs to the left
ventricle through 4 pulmonary veins.
Right ventricle  pulmonary arteries  lungs  pulmonary veins  left atrium
Systemic circulation: the oxygenated blood travels from the left ventricle via
the aorta which gives branches to the various areas of the body. Gas, nutrient,
and waste exchange occur across the capillary walls. The venous
(deoxygenated) blood is collected to reach to the right atrium via 3 veins; SVC,
IVC and coronary sinus.
Left ventricle  aorta  arteries  arterioles  capillaries  venules  veins
 right atrium
Portal circulation: is the circulation which starts by capillaries and ends in
capillaries (or sinusoids) without entering the systemic or pulmonary
circulation. The most common type is the hepatic portal circulation where the
venous blood from the capillaries of the gastrointestinal tract is collected into
veins that join to form the portal vein. The later enters the liver where it breaks
into the liver sinusoids. The sinusoids are drained by 2 hepatic veins which
open in the IVC.
Veins from gastrointestinal tract  portal vein  liver  2 hepatic veins  IVC
Blood
circulations
THE BLOOD VESSELS
Blood vessels
Arteries
Veins
Capillaries
Arteries
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They are elastic vessels, which carry blood away from the heart.
They are branching so that; a big artery gives medium-sized arteries,
which in turn give small-sized arteries, arterioles, small arterioles and
finally arterial capillaries.
They may communicate together, forming "arterial anastomosis",
through which the blood can find an alternative channels if the main
pathway is obstructed.
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Anastomosis is rich in the regions where movements can interfere with
continuous constant circulation e.g. around knee and elbow.
The arteries which have no communications with the neighbouring arteries
are called "end arteries" e.g. coronary arteries.
Some arteries may have tortuous course, especially those which are
subjected to stretch e.g. lingual, uterine and facial arteries.
There are 3 kinds of arteries (according to size and function):
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Elastic arteries are the largest arteries e.g. aorta and other nearby branches.
They contain a large amount of elastic tissue, which enables them to expand as
blood enters their lumen from the contracting heart.
Muscular arteries are medium-sized arteries e.g. arteries of the limbs. They
contain abundant smooth muscle fibers, which allow them to regulate blood flow
by vasoconstriction or vasodilatation.
Arterioles are small arteries. Most arterioles contain considerable smooth
muscles. The smallest arterioles consist of endothelium surrounded by a single
layer of smooth muscle. Arterioles regulate the flow of blood into capillaries by
vasoconstriction and vasodilatation.
Connections between arteries and veins
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Capillaries:
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Sinusoids:
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Are microscopic blood vessels with extremely thin walls. They are lined
with single layer of endothelium. Capillaries penetrate most body tissues
forming network called capillary beds. The thin walls of the capillaries
allow the diffusion of O2 and nutrients out of the capillaries, while
allowing CO2 and wastes into the capillaries.
Are similar to capillaries in that they are thin-walled blood vessels, but
they have irregular and wider spaces than capillaries. They are seen in
many sites e.g. liver, spleen, bone marrow and suprarenal gland. The
cells lining the sinusoids include phagocytic cells.
Arterio-venous anastomosis (shunts):
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Are direct connections between small arterioles and small venules
without the intervention of the capillaries. They are numerous in the in
the skin of lips, nose, tips of the fingers and toes, intestinal mucosa and
in the cavernous tissues of the sex organs. Their walls are surrounded
by sphincters which open and close controlling the blood supply to the
involved organs.
Connections between arteries and veins
Major
arteries
Major
veins
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