embryology of the heart and the great vessels dr gerrit engelbrecht dept of radiology ufs
TRANSCRIPT
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Embryology of Embryology of the heart and the heart and
the great the great vesselsvessels
Dr Gerrit EngelbrechtDept of Radiology
UFS
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• ESTABLISHMENT OF THE CARDIOGENIC FIELD
• FORMATION AND POSITION OF THE HEART TUBE
• FORMATION OF THE CARDIAC LOOP
• MOLECULAR REGULATION OF CARDIAC DEVELOPMENT
• DEVELOPMENT OF THE SINUS VENOSUS
• FORMATION OF THE CARDIAC SEPTAE
• FORMATION OF THE CONDUCTING SYSTEM OF THE HEART
• VASCULAR DEVELOPMENT
Steps in the Steps in the embryology of the embryology of the vascular systemvascular system
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ESTABLISHMENT OF ESTABLISHMENT OF THE CARDIOGENIC THE CARDIOGENIC
FIELDFIELD
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Dorsal view of a late presomite embryo (approximately 18 days) after removal of the amnion. Prospective myoblasts and hemangioblasts reside in thesplanchnic mesoderm in front of the neural plate and on each side of the embryo after migrating up from the primitivestreak
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• Transverse section through a similar-staged embryo to show the position of the blood islands in the splanchnic mesoderm layer.
• With time, the islands unite and form a horseshoe-shaped endothelial-lined tube surrounded by myoblasts. This region is known as the cardiogenic field
• In addition to the cardiogenic region, other blood islands appear bilaterally, parallel and close to the midline of the embryonic shield. These islands form a pair of longitudinal vessels, the dorsal aortae.
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Cephalocaudal section through a similar staged embryo showing the position of the pericardial cavity and cardiogenic field.
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FORMATION AND POSITION OF FORMATION AND POSITION OF
THE HEART TUBETHE HEART TUBE
2 processes responsible for positioning of the heart
1.Folding of the embryo in a cephalocaudal direction
2.Simultanous folding laterally
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Cephalocaudal folding
Figures showing effects of the rapid growth of the brain on positioningof the heart. Initially the cardiogenic area and the pericardial cavity are in front of the buccopharyngeal membrane. A. 18 days. B. 20 days. C. 21 days. D. 22 days
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Lateral folding of the embryo
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Formation of the Formation of the cardiac loopcardiac loop
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Bulbus cordisBulbus cordis
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Primitive ventriclePrimitive ventricle
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The primitive atrium The primitive atrium and sinus venosusand sinus venosus
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Abnormalities of Abnormalities of cardiac loopingcardiac 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.
Dextrocardia may coincide with situs inversus
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Molecular regulation Molecular regulation of cardiac of cardiac
developmentdevelopment
Dependent on the activation of twotranscription factors
•NKX2.5• Specifies
cardiogenic field
• Septation• Conduction
system•TBX5
• Septation
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Development of the Development of the sinus venosussinus venosus
4th weekreceives blood fromright and left sinus horns
5th week
Obliteration R umbilical veinleft vitelline vein
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Development of the Development of the sinus venosus(2)sinus venosus(2)
10th week left common cardinal vein obliterates
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Development of the Development of the venous valvesvenous valves
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Formation of the Formation of the cardiac septaecardiac septae
The major septae are formed between the 27 and 37th days of development
It is a simultanuous process if the following areas
•Septum formation in the common atrium•Septum formation in the atrioventricular canal•Septum formation in the truncus arteriosus and conus cordis•Septum formation in the ventricles
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Septum formation in Septum formation in the common atriathe common atria
At the end of the fourth week, a sickle-shaped crest grows from the roof of thecommon atrium into the lumen. This crest is the first portion of the septumprimum
A. 30 days (6 mm).B. Same stage as A, viewed from the right.
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Septum formation of Septum formation of the common atria (2)the common atria (2)
C. 33 days (9 mm). D. Same stage asC, viewed from the right
When the lumen of the right atrium expands as a result of incorporation ofthe sinus horn, a new crescent-shaped fold appears. This new fold, the septum secundum never forms a complete partion in the atrial cavity
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Septum formation of Septum formation of the common atria(3)the common atria(3)
E. 37 days (14 mm)F. Newborn.G. The atrial septum from the right; same stage as F.
When the upper part of the septum primum gradually disappears, theremaining part becomes the valve of the oval foramen.
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Further differentiation Further differentiation of the atriaof the atria
Coronal sections through the heart to show development of the smoothwalledportions of the right and left atrium. Both the wall of the right sinus horn (blue)and the pulmonary veins (red) are incorporated into the heart to form the smooth-walledparts of the atria.
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Septum formation of Septum formation of the atrioventricular the atrioventricular
canalcanalAt the end of the fourth week, two mesenchymal cushions, the atrioventricular endocardial cushions, appear at the superior and inferior borders of the atrioventricular canal, two additional lateral cushions appear at the left and right borders.At the end of the fifth week there is complete fusion of the superior and inferior cushions with complete division of the canal into left and right orifices.
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Atrioventricular valvesAtrioventricular valves
Formation of the atrioventricular valves and chordae tendineae. Thevalves are hollowed out from the ventricular side but remain attached to the ventricular wall by the chordae tendineae.
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Clinical correlatesClinical correlatesHeart defectsHeart defects
• Largest category of birth defects• Multifactorial ( viruses, medicines, alchohol,
diabetes, hypertension.• Genetic syndromes: DiGeorge and Downs• TBX5 gene defect: Holt –Oram syndrome( ASD +
pre axial abnormalities.• ASD• Premature closure of the oval foramen• Endocardial cushion defects AV canal( persistent
AV canal)• Tricuspid atresia
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ASDASD
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PersistePersistent nt
common common AV AV
canalcanal
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Tricuspid atresiaTricuspid atresia
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Septum formation of the truncus Septum formation of the truncus
arteriosus and conus cordisarteriosus and conus cordis
Fifth week, pairs of opposing ridges appear in the truncus and conus cordis
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Septum formation of the truncus Septum formation of the truncus
arteriosus and conus cordisarteriosus and conus cordis
Proliferations of the right and left conus cushions, combinedwith proliferation of the inferior endocardial cushion, close the interventricular foramen and form the membranous portion of the interventricular septum.A.6 weeks(12 mm).
B. Beginning of the seventh week (14.5 mm).
C. End of the seventh week(20 mm).
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Septum formation of Septum formation of the ventriclesthe ventricles
End of the fourth week the two primitive ventricles start to expand.The medial walls of the expanding ventricles become apposed and graduallymerge, forming the muscular interventricular septum
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Semilunar valvesSemilunar valvesWhen partitioning of the truncus is almost complete, primordia of the semilunar valves become visible as small tubercles found on the main truncus swellings.
•One of each pair is assigned to the pulmonary and aortic channels, respectively
•A third tubercle appears in both channels opposite the fused truncus swellings.
•Gradually the tubercles hollow out at their upper surface, forming the semilunar valves.
•Recent evidence shows that neural crest cells contribute to formation of these valves.
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Longitudinal section through the semilunar Longitudinal section through the semilunar
valvesvalves
6 weeks seven weeks 9 weeks
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Clinical correlatesClinical correlatesVSD related defectsVSD related defects
• Isolated lesion
• Conotruncal lesions : Tetralogy of Fallot
• Persistent truncus arteriosus
• Transposition of the great vessels
• Pulmonar valvular atresia
• Aorta valvular stenosis and artresia
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Isolated VSDIsolated VSD
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Tetralogy of FallotTetralogy of Fallot
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Persistent truncus Persistent truncus arteriosusarteriosus
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Transportation of the great Transportation of the great
vesselsvessels
Pulmonar valvular atresiaPulmonar valvular atresia
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Aortic valvular Aortic valvular stenosis and atresiastenosis and atresia
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Formation of the conducting Formation of the conducting
system of the heartsystem of the heartSinu atrial node
Initially the pacemaker for the heart lies in the caudal part of the left cardiac tube.Later the sinus venosus assumes this function, and as the sinus is incorporated into the right atrium, pacemaker tissue lies near the opening of the superior vena cava. Thus, the sinuatrial node is formed.
Atrioventricular node
The atrioventricular node and bundle (bundle of His) are derived fromtwo sources: (a)cells in the left wall of the sinus venosus(b) cells from the atrioventricular canal.
Once the sinus venosus is incorporated into the right atrium, these cells lie in their final position at the base of the interatrial septum.
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Vascular developmentVascular development
Arterial system
Venous system
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Arterial systemArterial system
• Aortic arches
• Vitelline and umbilical arteries
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Aortic archesAortic archesKey factsKey facts
• Arise from the aortic sac(truncus arteriosus ) to pharyngeal arches ( 4-5 weeks)
• Terminate in the left and right dorsal aorta
• These arches and vessels appear in a cranial to caudal sequence and not all simultanously
• The aortic sac also forms left and right horns which give rise to the brachiocephalic artery and proximal arch respectively
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Aortic archesAortic arches
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Aortic Aortic archesarches
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Ductus Ductus
arteriosusarteriosus
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Vitelline and umbilical Vitelline and umbilical arteriesarteries
Vitelline arteries fuse and form the Coeliac, SMA and IMA
Umbilical arteries
•Initially paired ventral branches of the aorta•Fourth week acquire a secondary connection with the aorta the common iliac artery•After birth the proximal part persist as the internal iliac and internal iliac and superior vesical and the distal part obliterate to form the medial umbilical ligaments.
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Clinical correlatesClinical correlatesArterial system Arterial system
defectsdefects• Patent ductus arteriosus
• Coarctation of the aorta ( preductal and post ductal)
• Abnormal origin of the right subclavian artery
• Right aortic arch
• Interrupted aortic arch
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Coarctation of the Coarctation of the aortaaorta
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Abnormal origin of the Abnormal origin of the right subclavian arteryright subclavian artery
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Double aortic archDouble aortic arch
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Interrupted aortic Interrupted aortic archarch
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Venous systemVenous system
• Vitelline veins
• Umbilical veins
• Cardinal veins
End of fourth week
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Vitelline veinsVitelline veins• Forms a plexus
around the duodenum, forms the portal vein.
• Pass through the septum transversum
• Hepatic cords grow into the septum and form the hepatic sinusoids
• Connects to the sinus venosum
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Vitelline veins (2)Vitelline veins (2)•Enlargement of the right vitelline vein.
•Forms the hepatic cardiac part of the IVC
•The SMV derives from the right vitelline vein
•The left vitelline vein disappears.
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Umbilical veinsUmbilical veins• Proximal and
distal right umbilical vein disappears
• Proximal left umbilical vein disappears
• The left distal umbilical vein remains and carry blood from the placenta
to the liver
• The ductus venosus form between the left umbilical vein and
right hepatic cardiac
channel, it bypasses
the sinusoidal plexus
• Both are obliterated after birth to form the ligamentum teres and venosum respectively
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Anterior cardinal veins, which drain the cephalic part of the embryo
Posterior cardinal veins, which drainthe rest of the embryo.
Common cardinal veins.
During the fourth week this forms a symmetrical system
Cardinal veins
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From the fifth to the seventh week additional veins areformed: a)Subcardinal veins, which mainly drain the kidneys; b) Sacrocardinal veins, which drain the lower extremitiesc)Supracardinal veins, which drain the body wall by way of the intercostal veins, taking over the functions of the posterior cardinal veins
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Formation of the vena cava system is characterized by the appearance ofanastomoses between left and right in such a manner that the blood from theleft is channeled to the right side.
• Anterior cardinal veins -> left brachocephalic vein
• Left posterior cardinal vein terminal portion - > left superior intercostal vein
• Right common cardinal vein + proximal right anterior cardinal vein-> SVC
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• Subcardinal veins - > left renal vein
• Left subcardinal vein distal portion - > left gonadal vein
• Right subcardinal vein - > renal segment of the IVC
• Sacrocardinal veins - > left common iliac vein
• Right sacro cardinal vein - > sacro cardinal segmentWhen the renal segment of the inferior vena cava connects with the
hepatic segment, which is derived from the right vitelline vein, the inferior vena cava, consisting of hepatic, renal, and sacrocardinal segments, is complete.
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Right 4th to 11th intercostal veins -> right supracardinal vein
+ post cardinal vein
- > azygos vena
Left 4th to 7th intercostal veins
-> left supracardinal vein ( hemiazygos vein )
-> Azygos vein
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Clinical correlatesClinical correlatesLeft superior vena cava: Persistence of the left anterior cardinal vein
Obliteration of the common cardinal and anterior cardinal veins on the right
Double superior vena cava: Persistence of the left anterior cardinal vein Failure of the right brachiocephalic vein to form
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Clinical correlatesClinical correlatesDouble inferior vena cava: Left sacrocardinal vein remain connected to the left subcardinal vein
Absence of the inferior cava : The right subcardinal vein fails to make the connection with the liver
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ConclusionConclusion• The cardiovacular system is functionally important in development. It starts working when the embryo is between 200 to 400 microns thick.
• The cardiovascular system is radically remodeled at least four times ( Bilateral, central as a single pump, entire system of veins and some of the arteries regress, splits into two pumps, at birth the placental circulation is shut down and the pulmonary circulation opened up.
• The cardiovascular system is made up of splancnic mesoderm and neural crest cells ( cranial skeleton, adrenals,neurons, glia, ciliary body )
• Three systems of veins empty into the sinus venosus ( vitelline, umbilical and cardinal system)
• The heart starts out with its venous side located caudally
• The heart and arterial trunk are split into the adult compartments by six septae Septum primum, septum secundum, AV septum, interventricular muscular and membranous septums, Aortico pulmonary bulbae or ridges
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ReferencesReferences• Langman’s Medical embryology, Eight edition, p
223• Electronic resources last accessed on 20/02/2012
http://www.embryology.ch/ http://www.indiana.edu/
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