EMBRYOLOGYOF

HEART BY: DR.SHILPA

PRAJAPATI (FIRST YEAR M.PT)

contents1. Introduction 2. 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 cordis

10.Interventricular septum11.Development of the ventricles12. Conducting system of the Heart

13. Congenital anomalies of Heart

INTRODUCTIONVery early in the life of the embryo, mesenchyme differentiates over the yolk sac and in the body of embryo itself to form small masses of angioblastic tissue.

which gives rise to endothelium and blood cells.

The heart is first organ of the body to start functioning, is prominent in 21 to 28 days post conception.

Heart Fusion 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.

Heart

Fusion of endothelial heart tubesBulbus cordis represents arterial end of heart.

conus (bulbus cordis).truncus arteriosus.

continuous with the aortic sac from which right and left pharyngeal arch arteries arise.

Heart

Arterial and venous ends of heart tubeSinsus venosus represents the venous end of the heart.

Horns joins:i. Vitelline vein from yolk sacii. Umbilical vein from placentaiii. Common cardinal vein from body wall

The body and right horn are absorbed into the common atrial chamber, form part of the right atrium.

Heart ….

Subdivisions of the Heart TubeRight 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 ventricular chamber and forms to give rise to the right and left ventricles.And forms outflow tracts

TRUNCUS ARTERIOSUS:Form the ascending aorta and the pulmonary trunk.

Heart …Heart tubes to pericardial cavityEndothelial heart tubes derived from splanchnopleuric mesoderm

After formation of head fold, tube lies dorsal to pericardial cavity and ventral to foregut.

Splanchnopleuric mesoderm, on dorsal side, form a thick layer called myoepicardial mental, After complete invagination, layer completely surrounds the heart tubes.

It gives rise to the cardiac muscle and visceral layer of pericardium(epicardium).

Parietal layer derived from somatopleuric mesoderm.

Anomalies

Poor development of myocardium(hypoplasia).

Exterior of the heartThe heart tube is for sometime suspended from the dorsal wall of the pericardial cavity, Mesocardium soon disappears

It 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 by deep bulbo-ventricular sulcus, After these changes exterior of the heart assumes its definitive shape.

Exterior of the heart…sinus venosusSinus venosus and atrial chamber are at first in open communication.

They become partially separated by grooves at the junction of these 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 and appears 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 and left venous valves.

Upper ends of the two valves fuse to form structure called septum spurium.

Exterior of the heart…Atrio-ventricular canal

At first rounded aperture, soon comes to be transverse canal.

On its dorsal and ventral walls Atrio-ventricular cushions appears.

This grow and fuse with each other to divide the Atrio-ventricular canal in right and left halves.

This is called septum intermedium.

Anomalies Atrio-ventricular canal defect or persistent Atrio-ventricular canal :Defective formation of AV cushions may leads the interatrial and interventricular septa are in complete.

Formation of interatrial septum Atrial 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 septum

b) A second septum to the right of the septum primum, btw septum primum and septum spurium.•It grows and overlaps the foramen secundum.•Right and left atria communicate through foramen ovale.•Lower edge of septum secundum (crista dividends)is thick and firm.•Edge of the septum primum forms the lower boundary of foramen secundum is thin and flap.

Formation of interatrial septum

Blood flows from right to left atrium through this foramen.When blood flows left to right, flap comes into apposition with the septum secundum and close the opening.After birth, left atrium begins to receive blood and the pressure becomes greater than right atrium.Causes closer of foramen ovale, permanently fusion of two flaps.In adult anatomy, annulus ovalis represent septum secundum.Fossa ovalis represents septum primum.

Congenital anomaliesDefective formation of septa A). 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 atrium

Right and left venous valves separates.Left valve and the septum spurium fuse with the interatrial septum.Right valve becomes greatly stretched out and subdivided into three parts:

i. Crista terminalisii. Valve of the IVCiii. Valve of coronary sinus

Development of the right atriumDerived from

a)Right half of the primitive atriumb)Sinus venosusc)Right half of the atrio ventricular canal

Absorption of the pulmonary veins

At the time when septum primum beginning, a single pulmonary vein open into the left half of the atrium.

Vein divides into right and left branch.Gradually veins nearest to the left atrium are absorbed into the atrium, four separate veins come to open 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 cordis

Divisible into a proximal part; conus Distal part; truncus arteriosus

Pulmonary and aortic valves, derived from endocardial cushion.

Grows and fuse with each other in wall of conus.

Aortic and pulmonary openings each have 3 cushions; forms 3 cusps of valve.

Congenital anomalies

Atresia or stenosisany of the orifice may have too narrow an opening (stenosis),or non at all(atresia).Types :

1. Valvular2. Supravalvular3. Infravalvular

Abnormal growth 4. Accessory cusps in the valves.

Defects of the spiral septum:septum may not be formed at all also called patent truncus arteriosus.

Interventricular septum

Bulbo-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 atriumb) 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 ridgesArises 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 edge of bulbar septum, field by proliferation of tissue from A.V cushions.Membranous part of the interventricular septum: Divisible into anterior and posterior part separated by A.V septum.

Interventricular septumThe membranous part of the interventricular septum is made up

1) of the original AV cushion btw the attachment of the interatrial and interventricular septa.

2) of the endocardial proliferation from these cushions.

First part separates the left ventricle from the right atrium while the lower part separates two ventricles.

The tricuspid valve is attached to the membranous septum at the junction of these parts.

Anomalies

Interventricular septum defect : may seen in membranous or in muscular part of septum

Development of the ventriclesDerive from:

a).primitive ventricular chamberb).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 the junction of conus and truncus arteriosus.

Mitral and tricuspid valves formed by proliferation of connective tissue of A.V canal.

Conducting system of the HeartWhen there are two heart tubes, pacemaker lies in the caudal part of the left tube.

After fusion , lies in the sinus venosus.

When the sinus venous is incorporated into the right ventricle ,it lies near the opening of the SVC.

The A.V node and A.V bundle form in the left wall of the sinus venosus, and In the A.V canal.

After the sinus venosus is absorbed, A.V node lie near the 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 of the chest, and can be seen from the outside , due to defective development of the chest wall.

Abnormal growth1. Tumors

Congenital anomalies of Heart

Combine defects :two or more of the above defects may consist , 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 stenosisIV. 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 pulmonary artery to descending thoracic aorta just beyond the origin of the left subclavian artery, should have contracted, closed and fibrosed into the ligamentum arteriosum in a few days from birth.

It persist and blood will flow from the aorta into the pulmonary circulation

References •Text book of medical physiology ( Guyton and hall, 9th Edition)

•Human embryology( Inderbir Singh)

•Human embryology(Hamilton, body and Mossman's)

•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 circulation

4. From the Rt ventricle, deoxygenated blood enters the pulmonary 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 receivesa) Oxygenated blood from Rt atriumb) 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 circulation

6. Much of blood of the aorta is carried by the umbilical arteries to the placenta.

Changes in circulation at birth

1) 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 birth

Vessels 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

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