EMBRYOLOGY OF HEART BY: DR.SHILPA PRAJAPATI (FIRST YEAR M.PT)
1. Introduction contents2. Heart3. Exterior of the heart4. Formation of interatrial septum5. Absorption of sinus venosus into right atrium6. Development of the right atrium7. Absorption of the pulmonary veins8. Development of left atrium9. Bulbus cordis10.Interventricular septum11.Development of the ventricles12.Conducting system of the Heart13. Congenital anomalies of Heart
INTRODUCTIONVery early in the life of the embryo, mesenchymedifferentiates over the yolk sac and in the body ofembryo itself to form small masses of angioblastictissue.which gives rise toendothelium and blood cells.The heart is first organ of the body to startfunctioning, is prominent in 21 to 28 days post conception.
HeartFusion of endothelial heart tubes Heart is in form of two endothelial heart tubes, fuse with one another, shows series of dilatation.Cranial to caudal end are Ventricle and atrium, connected by A.V. canal. Fusion in the heart tube in sinus venosus is partial.
HeartFusion of endothelial heart tubesBulbus cordis represents arterial end of heart. conus (bulbus cordis). truncus arteriosus.continuous with the aortic sac from which right andleft pharyngeal arch arteries arise.
HeartArterial and venous ends of heart tubeSinsus venosus represents the venous end of the heart.Horns joins: i. Vitelline vein from yolk sac ii. Umbilical vein from placenta iii. Common cardinal vein from body wall The body and right horn are absorbed into the commonatrial chamber, form part of the right atrium.
Heart ….Subdivisions of the Heart Tube Right CCV forms terminal part of SVC. Rt Vitelline vein forms terminal part of IVC Left horn forms part of the coronary sinus.They open into the atrium.ATRIUM:Right and left atria.A.V.CANAL:Forms right and left halves, take part in the formation of atria.
Heart ….Subdivisions of the Heart TubeVENTRICLE:Bulbus cordis is absorbed into the ventricularchamber and forms to give rise to the right and leftventricles.And forms outflow tractsTRUNCUS ARTERIOSUS:Form the ascending aorta and the pulmonary trunk.
Heart …Heart tubes to pericardial cavityEndothelial heart tubes derived from splanchnopleuric mesodermAfter formation of head fold, tube lies dorsal to pericardial cavityand ventral to foregut.Splanchnopleuric mesoderm, on dorsal side, form a thick layercalled myoepicardial mental, After complete invagination, layercompletely surrounds the heart tubes.It gives rise to the cardiac muscle and visceral layer ofpericardium(epicardium).Parietal layer derived from somatopleuric mesoderm.
AnomaliesPoor development of myocardium(hypoplasia).
Exterior of the heartThe heart tube is for sometime suspended from the dorsalwall of the pericardial cavity, Mesocardium soon disappearsIt folded to form ‘U’ shaped bulbo-ventricular loop.Atrium and sinus venosus come behind and above the ventricle form ‘S’ shaped.At that stage, bulbus cordis and ventricle are separated bydeep bulbo-ventricular sulcus, After these changes exterior ofthe heart assumes its definitive shape.
Exterior of the heart…sinus venosusSinus venosus and atrial chamber are at first in opencommunication.They become partially separated by grooves at the junction ofthese two chambers.Right groove remains shallow, left one becomes very deep.left part become completely separated from atrial chamber.The left horn and its tributaries much reduce in size andappears as tributary of the right half.
Exterior of the heart…Retrogression of left horn of sinus venosusCentrally placed sinu-atrial orifice shifts to the right.Orifice at first transversely orientated becomes vertical.Margins of orifice come to be bounded by the right andleft venous valves.Upper ends of the two valves fuse to form structurecalled septum spurium.
Exterior of the heart…Atrio-ventricular canalAt first rounded aperture, soon comes to be transversecanal.On its dorsal and ventral walls Atrio-ventricular cushionsappears.This grow and fuse with each other to divide the Atrio-ventricular canal in right and left halves.This is called septum intermedium.
AnomaliesAtrio-ventricular canal defect or persistent Atrio-ventricular canal :Defective formation of AV cushions may leads theinteratrial and interventricular septa are in complete.
Formation of interatrial septumAtrial chamber communicates: •Posteriorly with sinus venosus •Anteroinferiorly with ventricle.Divided into right and left halves: a) Septum arises from the roof of the atrial chamber is septum primum (ostium primum). •Grows downwards towards the septum intermedium of AV canal. •Only for sometime foramen primum is present. •Septum primum fuse with septum intermedium, closing the foramen primum. •upper part of septum primum form foramen secundum (ostium secundum)
Formation of interatrial septumb) A second septum to the right of the septumprimum, btw septum primum and septum spurium.•It grows and overlaps the foramen secundum.•Right and left atria communicate through foramenovale.•Lower edge of septum secundum (crista dividends)isthick and firm.•Edge of the septum primum forms the lowerboundary of foramen secundum is thin and flap.
Formation of interatrial septumBlood flows from right to left atrium through thisforamen.When blood flows left to right, flap comes intoapposition with the septum secundum and close theopening.After birth, left atrium begins to receive blood and thepressure becomes greater than right atrium.Causes closer of foramen ovale, permanently fusion oftwo flaps.In adult anatomy, annulus ovalis represent septumsecundum.Fossa ovalis represents septum primum.
Congenital anomaliesDefective formation of septaA). Interatrial septal defects I. septum primum defect: septum may fail to reach the AV endocardial cushions. II. septum secundum defect : may fail to develop as a foramen secundum remains wide open. III. Patent foramen ovale : the oblique valvular passage between septum primum and secundum remain patent. IV. Occasionally , premature closer of the foramen ovale.
Absorption of sinus venosus into right atriumRight and left venous valves separates.Left valve and the septum spurium fuse with theinteratrial septum.Right valve becomes greatly stretched out andsubdivided into three parts: i. Crista terminalis ii. Valve of the IVC iii. Valve of coronary sinus
Development of the right atriumDerived froma)Right half of the primitive atriumb)Sinus venosusc)Right half of the atrio ventricular canal
Absorption of the pulmonary veinsAt the time when septum primum beginning, asingle pulmonary vein open into the left half of theatrium.Vein divides into right andleft branch.Gradually veins nearest to the left atrium areabsorbed into the atrium, four separate veins come toopen it.
Development of left atriumDerived from:a) left half of the primitive atrial chamberb) left half of the AV canalc) absorbed proximal parts of the pulmonary veins
Bulbus cordisDivisible into a proximal part; conus Distal part; truncus arteriosusPulmonary and aortic valves, derived fromendocardial cushion.Grows and fuse with each other in wall of conus.Aortic and pulmonary openings each have 3cushions; forms 3 cusps of valve.
Congenital anomaliesAtresia or stenosisany of the orifice may have too narrow an opening(stenosis),or non at all(atresia).Types : 1. Valvular 2. Supravalvular 3. InfravalvularAbnormal growth 1. Accessory cusps in the valves.Defects of the spiral septum: septum may not be formed at all also called patent truncus arteriosus.
Interventricular septumBulbo-ventricular cavity consists of: a)Primitive ventricle communicates Posteriorly with atria through bilateral A.V canals. b) Conical upper part communicating with truncus arteriosus.
Interventricular septumCavity subdivided in to right and left halves: a) Each half communicates with corresponding atrium b) right ventricle opens into pulmonary trunk and left ventricle into the aorta. Subdivision takes place as:1) A septum – called interventricular septum, grows upwards from the floor of bulbo-ventricular cavity and fused with atrio-ventricular cushions(septum intermedium)2) Two ridges –right and left bulbar ridges Arises in the wall of bulbo-ventricular cavity continuous with the right and left endocardial cushions fuse to form bulbar septum(conus septum).
Interventricular septum3) The gap btw upper edge of interventricular septum and lower edgeof bulbar septum, field by proliferation of tissue from A.V cushions.Membranous part of the interventricular septum: Divisible intoanterior and posterior part separated by A.V septum.
Interventricular septumThe membranous part of the interventricular septum ismade up 1) of the original AV cushion btw the attachment of the interatrial and interventricular septa. 2) of the endocardial proliferation from thesecushions. First part separates the left ventricle from the rightatrium while the lower part separates two ventricles.The tricuspid valve is attached to the membranousseptum at the junction of these parts.
AnomaliesInterventricular septum defect : may seen in membranous or in muscular part of septum
Development of the ventriclesDerive from: a).primitive ventricular chamber b).proximal part of the bulbus cordis (conus)Gives rise to infundibulum of right ventricle, And to the aortic vestibule of the left ventricle.Aortic and pulmonary valves are formed at thejunction of conus and truncus arteriosus.Mitral and tricuspid valves formed by proliferation ofconnective tissue of A.V canal.
Conducting system of the HeartWhen there are two heart tubes, pacemaker lies in thecaudal part of the left tube.After fusion , lies in the sinus venosus.When the sinus venous is incorporated into the rightventricle ,it lies near the opening of the SVC.The A.V node and A.V bundle form in the left wall of thesinus venosus, and In the A.V canal.After the sinus venosus is absorbed, A.V node lie nearthe interatrial septum.
Congenital anomalies of HeartAnomalies of position a).Dextrocardia :chambers and blood vessels are reversed from side to side.b).Ectopia cordis : heart lies exposed on the front ofthe chest, and can be seen from the outside , due todefective development of the chest wall.Abnormal growth 1. Tumors
Congenital anomalies of HeartCombine defects :two or more of the above defects mayconsist , condition of this type known as fallot’s tetrology I. interventricular septal defect : II. Aorta over riding the free upper edge of the ventricular septum. III. Pulmonary stenosis IV. Hypertrophy of the right ventricular
Congenital anomalies of HeartOther defects : a).pericardium may be partially or completely absent. b).Congenital defects in conducting systems c).Transposition of great vessels d).Taussing – bing syndrome e).superior or inferior vana cava end in the left atrium. f).pulmonary veins end in the right atrium or in one of its tributaries.
Patent ductus arteriosusThe ductus arteriosus, connects the left pulmonaryartery to descending thoracic aorta just beyond theorigin of the left subclavian artery, should havecontracted, closed and fibrosed into the ligamentumarteriosum in a few days from birth.It persist and blood will flow from the aorta into thepulmonary circulation
References•Text book of medical physiology ( Guyton and hall,9th Edition)•Human embryology( Inderbir Singh)•Human embryology(Hamilton, body and Mossmans)•Text book of obstetrics( D.C.Dutta)
Fetal circulation1. Source of oxygenated blood is placenta.2. Through the umbilical vein; a small portion of blood passes through the substances of liver to IVC, but the greater part passes direct through ductus venosus to IVC.3. Through the IVC blood reaching the right atrium. a. most of passes through the foramen ovale into the left atrium. b. The rest of it get mixed up with the blood returning through the SVC to the Rt atrium, passes in to the Rt ventricle.
Fetal circulation4. From the Rt ventricle, deoxygenated blood enters thepulmonary trunk. a) only a small portion of blood reaches the lungs, passes to Lt atrium. b) the greater part is sort circuited by the ductus arteriosus into the aorta.5. Lt atrium receives a) Oxygenated blood from Rt atrium b) A small amount of deoxygenated blood from lungs This oxygenated blood passes into the left ventricle and then into aorta. some of this passes into carotid and subclavian arteries. And rest of it mixed with deoxygenated blood from ductus arteriosus.
Fetal circulation6. Much of blood of the aorta is carried by theumbilical arteries to the placenta.
Changes in circulation at birth1) Muscle in the wall of the umbilical arteries contracts immediately after birth, this prevent loss of fetal blood into the placenta.2) Lumen of the umbilical veins and ductus venosus is occluded.3) Ductus arteriosus is occluded, so all blood from Rt ventricle goes to the lungs, is caused by contraction of muscle in the vessel wall.4) Through pulmonary vessels much larger volume of blood reaches the Lt atrium, causing the valve of foramen ovale to close.5) When the new born cries, rise of pressure in the Rt atrium leading to a temporary shunt to the left. This can cause cynosis.
Changes in circulation at birthVessels occluded soon after birth are: •Umbilical artery medial Umbilical ligament •Left Umbilical vein ligamentum teres of the liver •Ductus venosus ligamentum venosum •Ductus arteriosus ligamentum arteriosum