DEVELOPMENT OF THE CARDIOVASCULAR SYSTEM 1Lufukuja G.

2 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. Lufukuja G.

3 PRIMITIVE CVS…  Areas of angiogenesis begin in the extraembryonic mesoderm of the yolk sac on day 17.  Hemoangioblasts, myoblast Lufukuja G.

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. 4Lufukuja G.

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 5Lufukuja G.

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10 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 ). Lufukuja G.

2/27/ 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.heart tube  With further development, the dorsal mesocardium disappears, creating the transverse pericardial sinus, which connects both sides of the pericardial cavity.

2/27/ 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.

13 PRIMITIVE CVS… Lufukuja G.

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Lufukuja G.15 PRIMITIVE CVS…

Lufukuja G.16 PRIMITIVE CVS…

2/27/ 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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2/27/ 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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2/27/ 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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23 Sinus venosus Left atrium Left ventricle Bulbus cordis Conus cordis Truncus arteriosus Aortic sac Right atrium

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2/27/ 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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2/27/ 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.

28 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. Lufukuja G.

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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 Lufukuja G.30

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Development of the coronary Sinus Lufukuja G.32

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 Lufukuja G.33

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36 …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 Lufukuja G.

2/27/ …coronary Sinus

Lufukuja G.38 …coronary Sinus

 The remainder of the left sinus horn is the coronary sinus and the oblique vein (of Marshall) in the adult heart. Lufukuja G.39 …Definitive right Atrium

 The major septa of the heart are formed between the 27th and 37th days of development Lufukuja G.40 Formation of the Cardiac Septa

Lufukuja G.41 Atrioventricular Canal

2/27/ 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.

43 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 Lufukuja G.

44 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). Lufukuja G.

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49 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. Lufukuja G.

50 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. Lufukuja G.

51 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. Lufukuja G.

52 T.of Fallot (Pulmonary infundibular stenosis)

Lufukuja G.53 T. Of Fallot Overriding aorta & Ventricular septal defect

Lufukuja G.54 T.of Fallot Right ventricular hypertrophy

55 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 defectsaortaductus arteriosusligamentum arteriosum Lufukuja G.

56 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. Lufukuja G.

2/27/ 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.

2/27/ Thank you