(j)development of the heart (int)

8/10/2019 (j)Development of the Heart (Int)

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ONTOGENI OF THE HEART


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Formation of the heart tube

The primordium of the heart is first evident at18 days and begins to beat at 22 to 23 days.

In the cardiogenic area, splanchnicmesechymal cells aggregate and arrangethemselves side by side to form twolongitudinal, cellular cardiac primordia,angioblastic cords .

The cords become canalized to form twoendocardial heart tubes .


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Mesoderm layer


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As lateral embryonic folding occurs, theendocardial tubes approach each other andfuse to form a single endodardial heart tube .

The heart tube starts to bulge into thepericardial cavity, meanwhile, the endocardialtube becomes surrounded by a thick layermesenchyme, which will differentiate into themyocardium and visceral layer of the serouspericardium.


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The primitive heart has been established, andthe cephalic end is the arterial end , and thecaudal end is the venous end .

The arterial end of the primitive heart iscontinous beyond the pericardium with alarge vessel, the aortic sac . From which theaortic arches arise.


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Concurrently, the tubular heart elongates anddevelops alternate dilatations andconstrictions. These delatatos are called

Truncus arteriosus Bulbus cordis Ventricle Atrium Sinus venosus


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The sinus venosus receives the umbilical,vitelline, and common cardinal veins

Because the bulbus cordis and ventricle growfaster than other regions, the heart bendsupon itself, forming a U-shapedbulboventricular loop ,and then form S shape,with the atrium lying posterior to theventricle; thus the venous and arterial endsare brought close together.


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The sinus venosus has develops laterallyexpansions, the right and left horn of the sinusvenosus.

The passage between the atrium and theventricle narrows to form the atrioventricularcanal.


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Development of the Atria

The primitive atrium becomes divided intotwo atria, the right and the left atria--- in thefollowing manner

First, the atrioventricular canal divided intoright and left by the appearance of ventral anddorsal atrioventricular cushion, which fuseform the septum intermedium.


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Meanwhile, another septum, the septumprimum, develops from the root of theprimitive atrium and grows down to fuse withthe septum intermedium.

Before fusion occurs, the opening betweenthe lower edge of the septum primum and theseptum intermedium is referred to as theforamen primum . The atrium now is dividedinto right and left parts.


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Before the complete obliteration of theforamen primum has taken place, degeneraivechanges occur in the central portion of theseptum primum, a formen appears, theforamen secundum . So that the right and leftatria chambers again communicate.

Another thicker septum grows down from theatrial roof on the right side of the septumprimum called septum secundum .


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Before birth, the foramen ovale allows bloodfrom the right atrium to pass into the leftatrium, However, the lower part of theseptum primum serves as a flap-like valve toprevent blood moving from the left to theright atrium.


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At birth, due to raised blood pressure in theleft atrium, the septum primum is pressedagainst the septum secundum and fuses withit, and the foramen ovale is closed


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Neonatal circulation

Important circulatory adjustments occur atbirth when the circulation of fetal bloodthrough the placenta ceases and the infantslungs expand and begin to function. Threeshunts the permitted much of blood to bypassthe liver and lungs close and cease to

function.


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Adult Derivatives of Fetal vascularstructures

Because of changes in the cardiovascularsystem at birth, certain vessels and structuresare no longer required. Over a period ofmonths, these fetal vessels formnonfunctional ligaments, and fetal structuressuch as the foramen ovale persist as

anatomical vestiges of the prenatal circulatorysystem


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Fetal circulation

Highly oxygenated, nutrient rich blood returns fromthe placenta in the umbilical vein

On approaching the hepar about half of the blood

directly into the ductus venosus, a fetal vesselconnecting the umbilical vein to the Inferior venacava (IVC). The other half of the blood in theumbilical vein flows into sinusoid of the hepar andenter to the IVC through hepatic vein


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Fetal circulation


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Important circulatory adjustments occur atbirth when the circulation of fetal bloodthrough the placenta ceases and the infantslungs expand and begin to function. Threeshunts the permitted much of blood to bypassthe liver and lungs close and cease to

function.


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As soon as the baby is born, The foramen ovale isclosed. Ductus arteriosus, ductus venosus, andumbilical vessels are no longer needed.

Aeration of the lungs at birth is associated with: A dramatic fall in pulmonary vascular resistance A marked increase in pulmonary blood flow A progressive thinning of the walls of the pulmonary

arteries, results mainly from stretching as the lungsincrease in size with the first few breath


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The Change of fetal circulation

Umbilical vein eventually bcomes theligamentum teres Hepatis

Ductus venosus becomes the ligamentumvenosum Arrantii

Framen ovale closed, called fossa ovalis. Closureoccurs by third month after birth

Ductus arteriosus, usually closure compeltelywithin thw first few days after birth


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The Change of fetal circulation

Ductus arteriosus, usually closure compeltelywithin thw first few days after birth. Thesevessel normally close by 12 week after birth

Umbilial arteries,the proximal part becomeof these vessels become superior vesicalarteries, and the distal part become medial

umbilical ligaments.


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Congnital Anomalies

Dextrocardia Ectopic cordis Atrial Septal Defects (ASD), is common

congenital heart anomaly Ventricular Septal Defects is the most

common type CHD

Foramen ovale persistent Patent Ductus Arteriosus, usually closed soon

after birth


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Congnital Anomalies

Persistent Truncus Arteriosus Transposition of the Great Arteries Pulmonary atresia Tetralogy of Fallot

Pulmonary stenosis VSD Overriding Aortae Right ventricular hypertrophy


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Tetralogy of Fallot

(j)development of the heart (int)

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