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Development of the Development of the Cardiovascular SystemCardiovascular System

Shittu LAJShittu LAJ

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OBJECTIVEOBJECTIVE

1.1. Able to describe the events leading Able to describe the events leading to the formation of the primitive heart to the formation of the primitive heart tube.tube.

2.2. Able to describe the terms looping, Able to describe the terms looping, folding and partitioning of the heart, and folding and partitioning of the heart, and the great vessels.the great vessels.

3. Able to define, aortic arches, 3. Able to define, aortic arches, derivatives and anomalies.derivatives and anomalies.

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OBJECTIVEOBJECTIVE

4.4. Able to eescribe the fetal circulation and Able to eescribe the fetal circulation and circulation changes at birth.circulation changes at birth.

5.5. Able to outline the embryological basis for the Able to outline the embryological basis for the congenital abnormalities of the heart.congenital abnormalities of the heart.

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Development of the Primitive Development of the Primitive HeartHeart

The The Cardiovascular Cardiovascular system is the first system is the first system to system to function in the function in the embryo.embryo.

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Development of the Primitive Development of the Primitive HeartHeart

Occurs around middle of the 3rd Occurs around middle of the 3rd week.week.

In the cardiogenic areaIn the cardiogenic area

Splanchnic mesoderm - Splanchnic mesoderm - splanchnic mesenchymal cellssplanchnic mesenchymal cells

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-- Two angioblastic cordsTwo angioblastic cords - canalized to form 2 endothelial heart - canalized to form 2 endothelial heart

tubes.tubes.-- The Fusion of tubes in midline - A The Fusion of tubes in midline - A

single heart tubesingle heart tube -- Splanchnic mesenchymeSplanchnic mesenchyme - -

Endothelial lining (endocardium)Endothelial lining (endocardium) - Myocardium- Myocardium

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Development of HeartDevelopment of Heart

Two Two endocardial heart tubesendocardial heart tubes arise from arise from cardiogenic mesodermcardiogenic mesoderm . .

As lateral folding occurs, these fuse to form the As lateral folding occurs, these fuse to form the primitive heart tubeprimitive heart tube , which develops into the , which develops into the endocardiumendocardium . .

The The myocardiummyocardium and and epicardiumepicardium develop from develop from mesodermmesoderm surrounding the primitive heart tube. surrounding the primitive heart tube.

Several contractions and dilations soon appear in Several contractions and dilations soon appear in the heart tube, all of which have adult remnants.the heart tube, all of which have adult remnants.

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Heart developmentHeart development

The primitive heart is a single tube with grooves demarcating,

the sinus venosus, atrium, ventricle and bulbus cordis from behind forwards.

As this tube enlarges it kinks so that its caudal end, receiving venous blood,

comes to lie behind its cephalic end with its emerging arteries

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Heart Looping, and FoldingHeart Looping, and Folding -As head folds, the heart elongates-As head folds, the heart elongates

-develops five constrictions and dilatations-develops five constrictions and dilatations a) sinus venosus - caudal, receives all a) sinus venosus - caudal, receives all

venous bloodvenous blood b) primitive atriumb) primitive atrium c) primitive ventriclec) primitive ventricle d) bulbus cordisd) bulbus cordis e) truncus arteriosus - forms the aortic sace) truncus arteriosus - forms the aortic sac

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The sinus venosus later absorbs into the atrium,

the bulbus becomes incorporated into the ventricle so that, in the fully developed heart, the atria and great veins come to lie posterior to the ventricles and the roots of the great arteries.

The boundary tissue between the primitive single atrial cavity and single ventricle grows out as a dorsal and a ventral endocardial cushion

which meet in the midline, thus dividing the common atrio-ventricular orifice into a right (tricuspid) and left (mitral) orifice.

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Formation of septumFormation of septum

A and B. Septum formation by two actively growing ridges that approach each other until they fuse. C. Septum formed by a single actively growing cell mass.D, E, and F. Septum formation by merging of two expanding portions of the wall of theheart. Such a septum never completely separates two cavities

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FIXATIONFIXATION Sinus venous is partly Sinus venous is partly

embedded in septum embedded in septum transversum.transversum.

Truncus Arteriosus is Truncus Arteriosus is connected to aortic connected to aortic arches which enter arches which enter the branchial arches.the branchial arches.

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RAPID GROWTHRAPID GROWTH Bulbus cordis Bulbus cordis

and ventricleand ventricle Heart bends Heart bends

upon itselfupon itself U-shaped bulbo U-shaped bulbo

ventricular loopventricular loop

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Partitioning of the HeartPartitioning of the Heart

During the 4th and 5th During the 4th and 5th weeks the primitive heart is weeks the primitive heart is divided into the typical 4-divided into the typical 4-chambered human organ.chambered human organ.

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Atrial septa at various stages of development. A. 30 days (6 mm).B. Same stage as A, viewed from the right. C. 33 days (9 mm). D. Same stage asC, viewed from the right E. 37 days (14 mm). F. Newborn. G. The atrial septum fromthe right; same stage as F.

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Partit ioning of the Part it ioning of the Atrioventricular CanalAtrioventricular Canal

Dorsal and Ventral Endocardial Dorsal and Ventral Endocardial cushions,cushions,

Divides AV canal into Right and Left AV Divides AV canal into Right and Left AV CanalsCanals

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Development of heart chamberDevelopment of heart chamber

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B.B. Partit ioning of the Primitive AtriumPartit ioning of the Primitive Atrium - Septrum primum (Crescent shaped, or - Septrum primum (Crescent shaped, or

sickle shaped)sickle shaped) - Grows from the Dorsocranial wall- Grows from the Dorsocranial wall - Foramen primum (Ostium Primum)- Foramen primum (Ostium Primum) - Septum secundum (grows from the ventro - Septum secundum (grows from the ventro

cranial wall)cranial wall) - Foramen ovale- Foramen ovale

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Development of heart chamberDevelopment of heart chamber

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A partition, the septum primum, grows downwards from the posterior and superior walls of the primitive common atrium to fuse with the

endocardial cushions.

Before fusion is complete, a hole appears in the upper part of this septum primum, which is termed the foramen secundum in the septum primum.

A second membrane, the septum secundum , then develops to the right of the septum primum but this is never complete; it has a free lower edge which does extend low enough for this new septum

to overlap the foramen secundum in the septum primum and hence to close it.

The two overlapping defects in the septa form the valve-like, which shunts blood from the right to left heart in the fetus.

After birth, this foramen usually becomes completely fused leaving only the fossa ovalis on the septal wall of the right atrium as its memorial.

In about 10% of adult subjects, a probe can still be passed through an anatomically patent, although functionally sealed foramen.

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AV canal 5th wkAV canal 5th wk

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Changes in Sinus VenosusChanges in Sinus Venosus

Right and left horn (Right and left horn (increases and increases and decreases in growth respectively)decreases in growth respectively)

Right becomes incorporated into (Right Right becomes incorporated into (Right Atrium)Atrium)

Left becomes Coronary SinusLeft becomes Coronary Sinus

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sinus venosus The primitive sinus venosus absorbs into the right atrium so

that the venae cavae draining into the sinus come to open separately

into this atrium. The smooth-walled part of the adult atrium represents the

contribution of the sinus venosus, the pectinate part represents the portion derived from the

primitive atrium. NB: the adult left atrium has a double origin: originally, single pulmonary venous trunk entering the left

atrium -donates the smooth-walled part of this chamber with the pulmonary veins entering as four separate openings;

the trabeculated part of the definitive left atrium is the remains of the original atr ial wall .

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development of the sinus venosus at approximately 24 days (A) and 35 days

ACV, anterior cardinal vein; PCV,

posterior cardinal vein; UV, umbilical vein; VIT V, vitelline vein; CCV,

common cardinal vein

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SV-final stageSV-final stage

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Partitioning of the VentriclePartitioning of the Ventricle

Muscular ridge - Muscular ridge - septumseptum

Interventricular Interventricular septumseptum

Interventricular Interventricular foramenforamen

Membranous septumMembranous septum

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Partition of ventriclePartition of ventricle Division of the ventricle is commenced by the up growth of a

fleshy septum from the apex of the heart towards the endocardial cushions.

This stops short of dividing the ventricle completely and thus it has an upper free border, forming a temporary interventricular foramen.

At the same time, the single truncus arteriosus is divided into aorta and pulmonary trunk by a spiral septum (hence the spiral relations of these two vessels),

which grows downwards to the ventricle and fuses accurately with the upper free border of the ventricular septum.

This contributes the small pars membranacea septi, which completes the separation of the ventricle in such a way that blood on the left of the septum flows into the aorta and on the right into the pulmonary trunk.

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Partitioning of the Bulbus Cordis Partitioning of the Bulbus Cordis and Truncus Arteriosusand Truncus Arteriosus

Development and fusion of Development and fusion of truncal and bulbar ridgestruncal and bulbar ridges

Aorticopulmonary SeptumAorticopulmonary Septum

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Formation of aorticopulmonary Formation of aorticopulmonary septumseptum

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Development of the Valves and Development of the Valves and Cardiac Conducting SystemCardiac Conducting System

Endocardial cushionsEndocardial cushions AV (Mitral, Tricuspid), Semilunar (Aorta, AV (Mitral, Tricuspid), Semilunar (Aorta,

Pulmonary A)Pulmonary A) Formation of Aortic Arches and Formation of Aortic Arches and

DerivativesDerivatives Aortic sac gives rise to aortic archesAortic sac gives rise to aortic arches

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Primitive Heart Tube

Embryonic Dilatation

Adult Structure

Sinus venosus Smooth part of right atrium (sinus venarum), coronary sinus, oblique vein of left atrium

Primitive atrium

Trabeculated parts of right and left atria

Primitive ventricle

Trabeculated parts of right and left ventricles

Bulbis cordis Smooth part of right ventricle (conus arteriosus), smooth part of left ventricle (aortic vestibule)

Truncus arteriosus

Aorta, pulmonary trunk

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Formation of Aortic Arches Formation of Aortic Arches and Derivativesand Derivatives

Aortic sac gives rise to aortic archesAortic sac gives rise to aortic arches Six aortic arches corresponding to the 6 Six aortic arches corresponding to the 6

pharyngeal arches.pharyngeal arches. However, one of the aortic arches However, one of the aortic arches

degenerate, i.e, the 5degenerate, i.e, the 5 thth arch. arch.

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Aortic archesAortic arches

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ArchesArches II - Disappear remaining form Maxillary - Disappear remaining form Maxillary

ArteriesArteries IIII - Dorsal persist as stem of stapedial - Dorsal persist as stem of stapedial

arteriesarteries IIIIII - Common Carotid Arteries, Int. cart art - Common Carotid Arteries, Int. cart art

(proximal part)(proximal part) IVIV - (Left): Arch of Aorta= L -subclavian- (Left): Arch of Aorta= L -subclavian

- (Right): Subclavian Artery and - (Right): Subclavian Artery and brachiocephalic VV - Degenerate or never developed- Degenerate or never developed VIVI - Pulmonary Artery (Left and Right only); - Pulmonary Artery (Left and Right only);

L-Ductus Arteriosusl aorta) (connection with L-Ductus Arteriosusl aorta) (connection with dorsal aorta)dorsal aorta)

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Orientation of vagus nerveOrientation of vagus nerve This asymmetrical development of the aortic arches,

elongation of the neck and caudal migration of the heart- accounts for the different course taken by the recurrent laryngeal nerve on each side.

early fetal life- the vagus nerve lies lateral to the primitive pharynx, and separated from it by the aortic arches.

the recurrent laryngeal nerves pass medially, caudal to the aortic arches to supply the developing larynx.

On the right side- the 5th and distal part of the 6th arch are absorbed, leaving the nerve to hook round the 4th arch (i.e. the right subclavian artery).

On the left side- the nerve remains looped around the persisting distal part the 6th arch (the ligamentum arteriosum- which is overlapped and dwarfed by the arch of the aorta).

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Formation of Venous System to Formation of Venous System to the Heartthe Heart

a)a) Vitelline veins - MesentericVitelline veins - Mesenteric b)b) Umbilical veins - Umbilical veins - c)c) Cardinal veins - Vena CavaCardinal veins - Vena Cava

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The 3 embryonic circulationThe 3 embryonic circulation

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Changes in Circulation at BirthChanges in Circulation at Birth

a)a) Lungs expandLungs expand b)b) Ductus Arteriosus and foramen ovale Ductus Arteriosus and foramen ovale

closeclose c)c) Ductus arteriosus - Ligamentum Ductus arteriosus - Ligamentum

arteriosumarteriosum Umbilical vein - ligamentum teresUmbilical vein - ligamentum teres Ductus venosum - ligamentum venosumDuctus venosum - ligamentum venosum Umbilical Artery - medial umbilical ligamentUmbilical Artery - medial umbilical ligament

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Congenital AbnormalitiesCongenital Abnormalities a)a) PositionPosition:: DextrocardiaDextrocardia bb Failure of PartitioningFailure of Partitioning ATRIUMATRIUM - ASD, Patent Foramen Ovale - ASD, Patent Foramen Ovale VENTRICLEVENTRICLE – VSD – VSD Tetralogy of Fallot (Pulmonary Stenosis, VSA, Tetralogy of Fallot (Pulmonary Stenosis, VSA,

overriding Aorta and Hypertrophy of Right overriding Aorta and Hypertrophy of Right ventricleventricle

PDA - Patent Ductus ArteriosusPDA - Patent Ductus Arteriosus Coarctation of AortaCoarctation of Aorta Transposition of great vessels.Transposition of great vessels.

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Dextro-rotation of the heart

means that the heart and its emerging vessels lie as a mirror-image to the normal anatomy.

It may be associated with reversal of all the intra-abdominal organs.

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Septal defectsSeptal defects At birth, closure of the septum primum and

septum secundum with closing of the flap valve of the foramen ovale.

-Fusion usually takes place about 3 months after birth.

-In about 10% of subjects-incomplete fusion However, the two septa overlap and this

patency of the foramen ovale is of no functional significance.

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ASDASDIf the septum secundum is too short to cover the

foramen secundum in the septum primum, an atrial septal defect persists after the septum

primum and septum secundum are pressed together at birth.

This results in an ostium secundum defect , which allows shunting of blood from the left to the right atrium.

This defect lies high up in the atrial wall and is relatively easy to close surgically.

NB: A serious atrial septal defect results if the septum primum fails to fuse with the endocardial cushions.

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ostium primum defect

This lies immediately above the atrioventricular boundary and may be associated with a defect of the pars membranacea septi of the ventricular septum.

In such a case, the child is born with both an atrial and ventricular septal defect.

At times, the ventricular septal defect is so large that the ventricles form a single cavity, giving a tri locular heart.

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Congenital pulmonary stenosis may affect the trunk of the pulmonary artery, its valve

or the infundibulum of the right ventricle. If stenosis occurs in conjunction with a septal defect-

compensatory hypertrophy of the right ventricle (developed to force blood through the pulmonary obstruction),

develops a sufficiently high pressure to shunt blood through the defect into the left heart;

mixing of the deoxygenated right heart blood with the oxygenated left-sided blood results in the

child being cyanosed at birth.

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Tetralogy of fallotTetralogy of fallot

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Tetralogy of fallotTetralogy of fallot The commonest causes of cyanosis is Fallot’s

tetralogy. This results from unequal division of the truncus arteriosus by the spinal septum, resulting

in a stenosed pulmonary trunk a wide aorta which overrides the orifices of both the

ventricles-overriding aorta. The displaced septum is unable to close the

interventricular septum, which results in a ventricular septal defect. Right ventricular hypertrophy

Cyanosis results from the shunting of large amounts of deoxygenated blood from the right ventricle through the ventricular septal defect into the left ventricle and also directly into the aorta.

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PDA & Coartation of AortaPDA & Coartation of Aorta

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A persistent ductus arteriosus is a relatively common congenital defect and If uncorrected, leads to progressive work hypertrophy of the left heart and pulmonary hypertension.

Aortic coarctation is assumed to be due to an abnormality of the obliterative process, which normally occludes the ductus arteriosus.

may be due to an extensive obstruction of the aorta from the left subclavian artery to the ductus, which is widely patent and maintains the circulation to the lower parts of the body; NB: there are often multiple other defects present and such infants affected die at an early age.

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