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3 PRIMITIVE CVS… Areas of angiogenesis begin in the extraembryonic mesoderm of the yolk sac on day 17. Hemoangioblasts, myoblast Lufukuja G.
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DEVELOPMENTOF 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 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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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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Sinu
s ven
osus
Left atrium
Left
vent
ricle
Bulbus cordis
Conus cordis
Truncus arteriosus
Aortic sac
Right atrium
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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
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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…Definitive right Atrium
The major septa of the heart are formed between the 27th and 37th days of development
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Formation of the Cardiac Septa
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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 aorta3. Ventricular septal defect (VSD), 4. Right ventricular hypertrophy.
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T.of Fallot(Pulmonary infundibular
stenosis)
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T. Of FallotOverriding aorta & Ventricular
septal defect
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T.of FallotRight 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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