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DEVELOPMENT
OF THE
CARDIOVASCULAR SYSTEM
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FROM SIMPLE DIFFUSION TO THE
PRIMITIVE CVS
 From the formation of the zygote up until the
beginning of third week of development the
embryo’s demand for Oxygen and nutrients is
met by simple diffusion.
 During the third week of development however,
Oxygen cannot reach all cells in the embryo by
diffusion.
 So, during the third week the cardiovascular
system begins to develop in order to meet this
increased demand for Oxygen and nutrients.
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PRIMITIVE CVS…
 Areas of angiogenesis
begin in the
extraembryonic
mesoderm of the yolk
sac on day 17.
 Hemoangioblasts,
myoblast
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PRIMITIVE CVS…
 Isolated masses and cords of mesenchymal cells
in the area proliferates and form blood islands.
 These blood islands begin to anastamose forming
the initial vascular network.
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PRIMITIVE CVS…
 Some clusters of angiogenetic cells
(angioblasts) appear bilaterally,
parallel and near the midline of the
embryo. These clusters canalize into
the paired dorsal aortae.
 Extraembryonic vessels soon
establish communication with those in
the developing embryonic
vasculature to create a primitive
circulatory system, permitting stem
blood cells formed in the yolk sac to
circulate in the embryonic body
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Development of the Heart tube
 Late in the third week, embryonic folding begins
to move the endocardial tubes from their initial
cranial and lateral position to a midline position, in
what will become the thoracic region.
 Once the endocardial tubes have reached this
midline position they fuse and form a primitive
heart tube (day 21 ).
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Heart Tube
 The newly formed heart
tube bulges into the
pericardial cavity and is
attached to the dorsal wall
by a fold of tissue, the
dorsal mesocardium.
 With further development,
the dorsal mesocardium
disappears, creating the
transverse pericardial
sinus, which connects both
sides of the pericardial
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cavity.
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Heart Tube…
 Eventually the heart tube is now suspended in the pericardial
cavity anchored cranially by the dorsal aortae and
caudally by the vitelloumbilical veins.
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PRIMITIVE CVS…
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PRIMITIVE CVS…
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PRIMITIVE CVS…
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Heart Tube…
 The heart tube now consists
of
three
layers:
the
endocardium, forming the
internal endothelial lining of
the
heart;
the
myocardium, forming the
muscular wall; and the
epicardium or visceral
pericardium, covering the
outside of the tube. This
outer layer is responsible for
formation of the coronary
arteries,
including
their
endothelial
lining
and
smooth
muscle.
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Heart Tube…
 The heart elongates as the embryo grows, and it
acquires dilatations and constrictions.
 These regional divisions, which are in the order
followed by circulating blood, are the sinus
venosus, primitive atrium, P.ventricle, bulbus
cordis, and truncus arteriosus.
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Heart Tube…
 Formation of the Cardiac Loop
 The heart tube continues to elongate and bend on day 23.
The cephalic portion of the tube bends ventrally,
caudally, and to the right and the atrial (caudal) portion
shifts dorsocranially and to the left. It is complete by
day 28.
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Aortic sac
Truncus arteriosus
Right atrium
Conus cordis
Left atrium
Bulbus cordis
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Heart Tube…
 The atrioventricular junction remains narrow
and forms the atrioventricular canal, which
connects the common atrium and the early
embryonic ventricle
 The midportion, the conus cordis, will form the
outflow tracts of both ventricles. The distal part of
the bulbus, the truncus arteriosus, will form the
roots and proximal portion of the aorta and
pulmonary artery
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C l i n i c a l notes
 Abnormalities of Cardiac Looping
 Dextrocardia, in which the heart lies on the right
side of the thorax instead of the left, is caused
because the heart loops to the left instead of the
right.
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Partition of the
Atrioventricular
Canal
 The opening between
the primitive atrium
and the primitive
ventricle is at first a
single channel,
atrioventricular canal.
 Toward the end of the
fourth week, dorsal and
ventral endocardial
cushions develop in the
walls of the
atrioventricular canal.
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Development of the Sinus
Venosus
 In the middle of the
fourth week, the sinus
venosus
receives
venous blood from the
right and left sinus
horns
 At first communication
between the sinus and
the atrium is wide. Soon,
however, the entrance
of the sinus shifts to
the right
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Development of the coronary
Sinus
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Development of the
coronary Sinus
 With obliteration of the right umbilical vein and the left
vitelline vein during the fifth week, the left sinus horn
rapidly loses its importance. When the left common
cardinal vein is obliterated at 10 weeks, all that remains of
the left sinus horn is the oblique vein of the left atrium
and the coronary sinus
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…coronary Sinus
 The right anterior cardinal
vein becomes the superior
vena cava.
 The right vitelline vein
becomes the inferior vena
cava
 The right umbilical vein is
obliterated, the Lt
umbilical Vein shunts the
liver through the ductus
venosus to enter the sinus
venosus
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…coronary Sinus
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…coronary Sinus
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…Definitive right Atrium
 The remainder of the left
sinus horn is the coronary
sinus and the oblique vein
(of Marshall) in the adult
heart.
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Formation of the Cardiac
Septa
 The major septa of the heart are formed between
the 27th and 37th days of development
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Atrioventricular
Canal
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C l i n i c a l notes
 Endocardial Cushions and Heart Defects
 Because of their key location, abnormalities in endocardial
cushion formation contribute to many cardiac malformations,
including atrial and ventricular septal defects and defects
involving the great vessels (i.e., transposition of the
great vessels and tetralogy of Fallot). Since cells
populating the conotruncal cushions include neural crest
cells and since crest cells also contribute extensively to
development of the head and neck, abnormalities in these
cells,produced by teratogenic agents or genetic causes, often
produce both heart and craniofacial defects in the same
individual.
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SEPTUM FORMATION IN THE COMMON
ATRIUM
 At the end of the fourth week, a sickle-shaped crest
grows from the roof of the common atrium into the
lumen. This crest is the first portion of the septum
primum
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Partition of the Atrium
 The foramen primum obliterates when the septum
primum meets the fused endocardial cushions (but
after another foramen the foramen secundum
has appeared).
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Anomalies of the Heart
 Atrial Septal Defects
 Atrial Septal Defects
(ASD) are a group of
common (1% of cardiac)
congenital anomolies
defects occuring in a
number of different forms
and more often in
females.
 Patent foramen ovale allows a continuation
mixing of the atrial blood.
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Anomalies of the Heart
 Patent Ductus Arteriosus
 The operation is always
recommended even in the
absence of cardiac failure and
can often be deferred until
early childhood.
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Tetralogy of Fallot
 Named after Etienne-Louis Arthur Fallot (1888)
who described it first.
 The 4 features typical of tetralogy of Fallot
include
1. Pulmonary infundibular stenosis,
2. Overriding aorta
3. Ventricular septal defect (VSD),
4. Right ventricular hypertrophy.
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T.of Fallot
(Pulmonary infundibular
stenosis)
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T. Of Fallot
Overriding aorta & Ventricular
septal defect
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T.of Fallot
Right ventricular hypertrophy
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Coarctation of Aorta
 is a congenital condition whereby the aorta narrows in
the area where the ductus arteriosus (ligamentum
arteriosum after regression) inserts. Prevalence ranges
from 5% to 8% of all congenital heart defects
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Hypoplastic
Left ventricle
 Characterized by
hypoplasia
(underdevelopment or
absence) of the left
ventricle,
obstructive valvular
and vascular lesion
of the left side of the
heart.
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Transposition of Great Vessels
 Characterized by aorta
arising from right
ventricle and pulmonary
artery from the left
ventricle and often
associated with other
cardiac abnormalities (e.g.
ventricular septal defect).
 Most neonates with
transposed great arteries
die without an arterial
switch operation, first
carried
out in 1975.
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Thank you
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