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No. 14
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1. Introduction of the Cardiovascular
System
2. Heart (1)
The location of heart
The external features of heart
The chambers of heart
The Structure of heart
PART Ⅳ ANGIOLOGY
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Introduction:
Physico-chemical properties and
composition of the micro-environment of
the cells comprising the various tissues of
the body remain relatively constant, by
the operation of a complex series of
homeostatic control mechanisms, which
depend for effectiveness upon adequate
circulatory system
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The circulatory system can be
separated into two divisions: the
cardiovascular system consisting
the heart and blood vessels through
which the blood circulates, and the
lymphatic system consisting of
lymph nodes and vessels which
conduct the lymph fluid.
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The cardiovascular system includes the
heart, which serves as a pump for the
blood, and the blood vessels, which
transport the blood throughout the body.
The lymphatic system consists of organs
that play a role in specific immune
responses (tonsils, thymus, spleen, lymph
nodes, and lymphatic nodules) and
vessels that collect tissue fluid from
between the cells of the body and
transport it to the cardiovascular system.
Chapter 1 The
Cardiovascular System
Section 1 Introduction
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The cardiovascular system is a closed circular
system. Confined to the heart and the numerous
vessels, blood continuously travels a circular
route through the heart, into arteries, then to
capillaries, into veins, and back to the heart.
Normally, blood does not leave this system,
although some of the fluid part of the blood does
pass through the walls of the capillaries to join
the tissue fluid between the cells. However, even
this fluid is returned to the cardiovascular system
directly or by way of the lymphatic system
Ⅰ. Organization of the
Cardiovascular System
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The Cardiovascular system
comprises the heart and blood
vessels. The blood vessels consist of
arteries, veins and capillaries.
Ⅰ) Heart
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The heart is a hollow, muscular
organ situated within the thorax. Its
contraction expels blood to all parts
of the body through a complicated
series of tubes, termed arteries.
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In order to function as a pump, the heart must
have both receiving and delivery chambers,
valves to direct the flow of blood through the
heart, a wall that is strongly compressible and
thus provides the force to propel blood, and
vessels to deliver blood to and from the heart.
The heart consists of four chambers: right and
left atria and right and left ventricles, of which
two are receiving and two are distributing
chambers. The right and left atria receive the
blood from the great veins and expel it into the
right and left ventricles. From the ventricles the
blood is pumped into the arterial system and
carried to the various organs of the body.
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Each atrium communicates with the
corresponding ventricle through
atrioventricular orifices, but the right
and left chambers of the heart are
separated from one another by
partitions, called septa.
Ⅱ) Arteries
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The arteries carry blood away from the
heart. They transport blood to the various
body tissues under high pressure exerted
by the pumping action of the heart. It is,
therefore, imperative that they possess
strong, elastic walls to insure fast, efficient
blood flow to the tissues. Compared to the
other types of blood vessels, arteries must
be able to withstand the greatest internal
pressrue.
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Arteries are classified according to size as
large, medium, and small ones.
The wall of an artery consists of three
layers, which are named from within
outwards: the tunica intima, the tunica
media, and the tunica adventitia.
The arteries ramify extensively in their
course throughout the body, and end in
minute vessels, called arterioles, which
open into a close-meshed network,
capillaries.
Ⅲ) Capillary
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They are simply thin endothelial tubes with a
layer of basement membrane.
They have an average diameter of 7～8μ.
They have extremely thin walls. As a
consequence, they are sites at which the
exchange of materials between the blood and the
interstitial fluid takes place. Across their walls the
fluids, oxygen, carbon dioxide, nutrients,
vitamins, hormones, metabolic products and
immune substances are exchanged between the
blood and tissue fluid. In the body they
anastomose with each other to form capillary
networks except for in the cartilage, hair, cornea
and lens.
Ⅳ) Veins
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After the blood has passed through the capillaries, it is
collected into a series of minute vessels, called venules,
which join with one another to form veins. The major veins
return blood to the atria of the heart. The veins unite with
one another, and ultimately two large venous trunks,
named the superior and inferior venae cavae, are formed,
which convey the blood to the heart. After the blood leaves
the capillaries, its pressure continues to drop; it is lowest
near the right atrium of the heart in the superior and
inferior venae cavae. With the progressive change from
capillaries to venules to veins, the diameters of individual
vessels and the thickness of their walls steadily increase,
whereas the total cross-sectional area of parallel vessels
decreases. Venous pressure is always lower than arterial
pressure, and the walls of the veins are never as thick as
the walls of the corresponding arteries.
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The walls of veins, like those of the
arteries, are composed of three coats:
the internal being endothelial, the
middle muscular and the external
connective tissue.
Ⅱ. The Cardiovascular Circuits
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The superior and inferior venae cavae bring to
the right atrium the blood which has become
deoxygenated and taken up carbon dioxide
during its circulation through the tissues of the
body. From the right atrium this venous blood
passes into the right ventricle, by which it is
expelled into the pulmonary trunk to be conveyed
to the lungs. As it circulates through the
pulmonary capillaries the blood is brought into
close relationship with the inspired air and it
gives off some of its carbon dioxide and acquires
a fresh supply of oxygen. This oxygenated blood
is returned by the pulmonary veins to the left
atrium and thence passes into left ventricle. With
each beat of the heart the left ventricle pumps its
contents into the aorta, which distributes blood
through its numerous branches to all the tissues
and organs of the body.
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Greater or systemic circulation and lesser
or pulmonary circulation:
The course of the blood from the left
ventricle through the whole body finally to
the right atrium of the heart constitutes
the greater or systemic circulation.
While the passage from the right ventricle
through the lung to the left atrium of the
heart is termed the lesser or pulmonary
circulation.
Ⅲ Anastomoses
1. Anastomoses between arteries:
 Arteries do not always end in
capillaries; in many cases they unite
with one another, forming what are
called anastomoses.
 Anastomosis between arterial trunks
of nearly equal size is found in the
brain and in the abdomen.
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In the limbs, the anastomoses are
largest and most numerous around
the joints; these anastomoses may
be so numerous that they constitute
a close network. Arteries often join
end to end, forming the arterial
arch (e.g. the palmar and plantar
arches).
2. Anastomoses between veins:
 Veins join with one another to from
the venous plexus or network.
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3. Anastomoses between arteries and
veins:
In a number of situations in the body
direct connections exist between the small
arteries and corresponding veins, they are
called the arteriovenous anastomoses.
The connecting vessel can conduct blood
directly from the artery to the vein and so
partially or completely exclude the
capillary bed from the circulation for the
time being.
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Arteriovenous anastomoses are
found in the skin of the nose, lips,
hands and feet.
They function to regulate the local
blood flow and temperature.
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4. Collateral anastomoses:
Each region or organ of the body is
usually supplied by several vessels.
One of them, the largest in diameter,
is called the main vessel, while the
smaller ones are called the accessory
or collateral vessels; they
communicate with one another
through anastomotic channels.
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If a vessel is occluded by thrombosis,
embolism or by ligation, the flow of
blood through the collateral and
anastomotic channels will increase.
The anastomotic channels may
become so enlarged as to replace the
normal and constitute an aberrant
supply to a part.
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The blood circulation is thus partially
restored and the collateral circulation is
established.
Sudden occlusion of a vessel may be
followed in some situations by necrosis of
the part supplied, while gradual occlusion
may allow time for the dilatation of the
anastomosing channels and the
establishment of the collateral circulation.
Section 2 The Heart
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The heart is the pump that provides
the force necessary to keep the
blood flowing through the system of
vessels.
It is a hollow, muscular organ of a
somewhat conical form, about the
size of a person’s fist and weighs
about 260g in Chinese adult.
Ⅰ. The Location of Heart
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The heart is located in the middle
mediastinum between the lungs, and
is enclosed in the pericardium.
It is obliquely in the chest behind the
body of the sternum and adjoining
parts of the costal cartilages, onethird of it on the right of the median
plane and two-thirds on the left.
Ⅱ. The External Features of Heart
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The heart is described as having a
base, an apex, two surfaces
(diaphragmatic and sternocostal
surfaces), three borders and four
grooves.
Ⅰ) Cardiac base
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The cardiac base faces backwards and to
the right.
It consists mainly of the left atrium, part
of the right atrium. The four pulmonary
veins, two on each side, open into the left
atrium, while the superior vena cava
opens into the upper part, and the inferior
vena cava into the lower part, of the right
atrium.
Ⅱ) The cardiac apex
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The cardiac apex, formed by the left
ventricle, is directed downwards,
forwards and to the left, and is
overlapped by left lung and pleura.
It is situated in the 5th left
intercostal space 1～2 cm to the right
of the left mid-clavicular plane. Here
the apex beat is palpable.
Ⅲ) The two surfaces
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1. The sternocostal surface, or called
the anterior surface, is directed forwards,
upwards and to the left.
It consists of an atrial and a ventricular
portion.
2. The diaphragmatic surface
The diaphragmatic surface, or called the
inferior surface, is directed downwards
and slightly backwards.
It is formed by the ventricles (chiefly by
the left ventricle), and rests upon the
diaphragm.
Ⅳ) Three borders
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1. The right border
The right border of the heart, formed by
the right atrium, is almost vertical.
2. The left border
The left border, formed mainly by the
left ventricle, is rounded.
3. The inferior border
The inferior border, formed almost
entirely by the right ventricle and the
cardiac apex, is nearly horizontal.
Ⅴ) Four grooves
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1. The coronary groove
The coronary groove separates the atria
from the ventricles and contains the
trunks of the coronary vessels of the heart.
It is deficient in front, where it is crossed
by the root of the pulmonary trunk.
2. The anterior interventricular groove
On the sternocostal surface, the line of
separation between the ventricles being
marked by the anterior interventricular
groove.
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3. The posterior interventricular groove
The diaphragmatic surface is traversed
obliquely by the posterior
interventricular groove.
4. The posterior interatrial groove
On the diaphragmatic surface, the sulcus
between the right atrium and the right
superior and inferior pulmonary veins.
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Cardiac apical incisure:
The anterior and posterior interventricular
grooves extend from the base of the
ventricular portion to a notch, termed the
cardiac apical incisure, situated a little
to right of the apex of the heart.
Crux:
The crossing point of the posterior
interatrial groove, the posterior
interventricular groove and the coronary
groove is the crux.
Ⅲ. The Chambers of Heart
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The heart is divided into right and left
halves, each half is subdivided into two
chambers. The upper chambers, the atria,
are separated by the interatrial septum;
the lower chambers, the ventricles, are
separated by the interventricular
septum.
The atria serve as receiving chambers for
blood from the various parts of the body,
the ventricles as pumping chambers.
Ⅰ) The Right Atrium
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It constitutes the right superior portion of the
heart.
Right auricle: a small, conical, muscular pouch,
termed the right auricle, projects towards the left
from its upper and anterior part and overlaps the
right side of the ascending aorta.
The cavity of right atrium is divided into two
portions, an anterior (atrium proper) and a
posterior (sinus venarum cavarum), by the crista
terminalis, a smooth, muscular ridge, which
extends from the orifice of the superior vena cava
to the orifice of the inferior vena cava.
1. The atrium proper
 The anterior portion, called the
atrium proper, has rough walls. Many
nearly parallel muscular ridges,
termed the pectinate muscles, run
forwards from the crista terminalis
towards the auricle. In the auricle
they are connected to one another so
as to form a muscular network.
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2. The sinus venarum cavarum
The posterior portion, termed the sinus venarum
cavarum, has smooth walls. There are three
orifices opens into it:
① Orifice of superior vena cava
The superior vena cava returns the blood from
the upper half of the body, and opens into the
upper part of the sinus venarum cavarum.
② Orifice of inferior vena cava
The inferior vena cava returns the blood from the
lower half of the body, and opens into the lowest
part of the sinus venarum cavarum.
The valve of inferior vena cava (Eustachian
valve) lies anterior lip of the orifice of inferior
vena cava.
③ Orifices of coronary sinus
 The coronary sinus returns the
greater part of the blood from the
substance of the heart. Its opening,
the orifice of coronary sinus, is
placed between the orifice of inferior
vena cava and the right
atrioventricular orifice.
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Fossa ovalis:
On the lower part of the septal wall of the
atrium there is an oval depression, called
the fossa ovalis, which is the remnant of
the oval foramen of the fetal heart.
The anterior inferior part of the right
atrium is the right atrioventricular
orifice. Blood from the right atrium goes
into the right ventricle through this orifice.
Ⅱ) The Right Ventricle
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It constitutes the right inferior portion of
the heart. Its anterosuperior surface forms
a large part of the sternocostal surface of
the heart. The wall of the right ventricle is
thinner than that of the left, the
proportion between them being as 1:3.
The interior of the right ventricle is
separated into the inflow and outflow
tracts by a muscular ridge, the
supraventricular crest, situated
between the atrioventricular and
pulmonary orifices.
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1. Inflow tract of the right ventricle
The inflow tract has rough walls due to the
presence of trabeculae carneae. It
receives the blood from the right atrium
through the right atrioventricular
orifice.
The right atrioventricular (tricuspid) valve
guards the right atrioventricular orifice,
and consists of three somewhat triangular
cusps, named anterior, posterior,
medial or septal cusps.
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A number of delicate, tendinous cords, termed
the chordae tendineae, are attached to the
apices, margins and ventricular surfaces of the
cusps.
The trabeculae carneae are irregular muscular
columns which project from the whole of the
inner surface of the ventricle. Some of them are
merely elevated ridges, others form conical
projections, the papillary muscles, which give
origin to the chordae tendineae. The chordae
tendineae of each papillary muscle are connected
with the contiguous margins of two cusps, hence,
there are 3 papillary muscles on th eright side.
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A muscular band termed the moderator
band or septomarginal trabecula,
which extends from the interventricular
septum to the base of the aterior papillary
muscle. It serves to convey the right
bundle branch of the atrioventricular
bundle.
Tricuspid valve complex: The rings and
apexes of tricuspid valve, chordae
tendineae, and papillary muscles
constitute the tricuspid valve complex.
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2. Outflow tract of the right ventricle,
conus arteriosus or infundibulum
It has smooth walls and leads upwards to
the opening of the pulmonary trunk,
termed the pulmonary orifice. The
pulmonary valve consists of three
semilunar cusps, which are attached to
the pulmonary orifice, their free borders
being directed upwards into the lumen of
the vessel. The semilunar valves are
constructed to permit the flow of blood in
only one direction.
Ⅲ) The Left Atrium
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It constitutes the most part of the
base of the heart.
It is divided into two portions, an
anterior part (the left auricle), and a
posterior part (left atrial sinus or
atrium proper).
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1. Left auricle
A small somewhat conical pouch, termed
the left auricle, projects forwards from
its upper left corner and overlaps the root
of the pulmonary trunk. The pectinate
muscles, fewer and smaller than those in
the right atrium, are confined to the inner
surface of the auricle.
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2. left atrial sinus or atrium proper
The interior side of left atrial sinus is
smooth.
The pulmonary veins, four in number,
open into the upper part of the posterior
surface of the left atrium, two on each
side; their orifices are not provided with
valves.
The left atrioventricular orifice is the
aperture between the left atrium and
ventricle.
Ⅳ) The Left Vertricle
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It constitutes the left inferior portion
and the apex of the heart. Inferiorly,
it forms a large part of the
diaphragmatic surface of the heart.
Inflow tract.
Left atrioventricular (or bicuspid,
mitral) valve
Anterior cusp.
Poterior cusp.
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Mitral valve complex: The rings
and apexes of bicuspid valve,
chordae tendineae, and papillary
muscles constitute the tricuspid valve
complex.
Outflow tract.
Aortic vestibule.
Aortic orifice.
Aortic sinuses.
Ⅳ. The Structure of Heart
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The wall of the heart comprises three layers,
named from within outwards endocardium,
myocardium and epicardium.
(1) The endocardium is a thin, smooth,
glistening membrane which lines the chambers of
the heart, and is continuous with the lining of the
large blood vessels.
The valves are formed by duplications of the
lining endocardium of the heart, strengthened by
intervening layer of fibrous tissue.
(2) The myocardium consists of the ordinary
cardiac muscle and specially differentiated
cardiac muscle (the conduction system).
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(3) The epicardium is the visceral layer
of the serous pericardium.
It consists of a layer of the mesothelium
and a delicate layer of connective tissue.
The interatrial septum and interventricular
septum:
The interatrial septum is placed so
obliquely that the right atrium lies in front
and to the right of the left atrium. It is
formed by two layers of the endocardium,
strengthened by fibrous tissue and
containing a few muscular fibers.
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The interventricular septum slops
obliquely from before backwards and
towards the right, and is curved with the
convexity towards the right ventricle. Its
margins correspond with the anterior and
posterior interventricular grooves on the
surface of the heart, it is so called the
muscular part of the interventricular
septum. In its upper part, there is a thin,
fibrous area, which is termed the
membranous part.