DEVELOPMENT OF THE HEART

By: Gan Quan Fu

CONTENT1. Introduction2. Fusion of Heart Tube3. The Bulbus Cordis4. The Sinus venosus5. Formation of Atria6. Separation of Aorta & Pulmonary

Trunk)7. The Ventricles8. The Exterior of Heart9. Development of Heart Valve10. Development of the Heart

conducting system11. Timeline12. Congenital Anomalies of Heart

By: Gan Quan Fu

By: Gan Quan Fu

By: Gan Quan Fu

INTRODUCTION Mesodermal origin Formed from angioblastic tissues that arise from

Splanchnopleuric Mesoderm (Cardiogenic area). After formation of the head fold, this tube lies dorsal to

pericardial cavity & ventral to foregut. Tube invaginates pericardial sac from dorsal side,

splanchnopleuric mesoderm lining the dorsal side of pericardial cavity proliferates to form a thick layer (myoepicardial mantle).

When invagination complete, myoepicardial mantle completely surrounds the heart tube and give rise to myocardium and also the epicardium.

Parietal layer of pericardium is derived from somatopleuric mesoderm.

By: Gan Quan Fu

By: Gan Quan Fu

HEART TUBE 1st seen in form of right and left

endothelial heart tube. Fuse and form single tube.

(Cranial to Caudal) The single tube shows series of

dilatation: Bulbus Cordis Primitive Ventricle Primitive Atrium Sinus Venosus

Primitive Ventricle and Atrium connected by a narrow atrioventricular canal/ atrioventricular sulcus.

By: Gan Quan Fu

BULBUS CORDIS

Lies at arterial end of heart Divisible into:

Proximal Part = Conus Distal Part = Truncus arteriosus

Truncus arteriosus continuous distally with aortic sac.

Aortic Sac is continuous distally with right and left pharyngeal arch arteries.

Arteries arch backwards to become continuous with right and left dorsal aortae.

By: Gan Quan Fu

HEART TUBES IN RELATION TO RIGHT AND LEFT DORSAL AORTA

By: Gan Quan Fu

SINUS VENOSUS

Lies at venous end of heart It has right and left horns

(prolongations of sinus venosus)

Each Horns are joined by: One vitelline vein (from the

yolk sac) One umbilical vein (from the

placenta) One common cardinal vein

(from the body wall)

By: Gan Quan Fu

By: Gan Quan Fu

FORMATION OF ATRIA (SINU-ATRIAL ORIFICE) Sinus venosus and

primitive atrial chamber are 1st connected by wide opening.

Gradually opening becomes narrow & shifts to right.

Finally becomes a narrow slit. (The slit has right & left margins known as right & left venous valves).

Cranially these 2 valve fuse to form septum spurium.

By: Gan Quan Fu

FORMATION OF ATRIA (ATRIOVENTRICULAR CANAL)

2 thickenings (atrioventricular cushions) appear on dorsal and ventral walls.

Grow towards each other and fuse to form septum intermedium.

By: Gan Quan Fu

FORMATION OF ATRIA (INTERATRIAL SEPTUM)

Atrial chamber undergoes division into right and left by formation of 2 septa.

1. Septum Primum 2. Septa Secundum

By: Gan Quan Fu

FORMATION OF ATRIA (SEPTUM PRIMUM)

Arises from roof of atrium towards atrioventricular canal and form foramen primum.

Before foramen primum close (Septum primum fuse with septum intermedium), a new gap (foramen secundum) is form on upper part of foramen primum by breaking down of upper part of septum primum.

Septum primum now has a free upper edge.

This is to ensure communication between left and right atria.

By: Gan Quan Fu

FORMATION OF ATRIA (SEPTUM SECUNDUM)

Arises downwards from roof of atrial chamber at the right of septum primum.

Overlap with free edge of septum primum and form foramen ovale (valvular aperture that allows blood to flow from right to left).

After birth, foramen ovale is obliterated by fusion of septum primum and septum secundum.

Annulus ovalis Lower free edge of septum secundum

Fossa Ovalis Septum primum

By: Gan Quan Fu

DEVELOPMENT OF RIGHT ATRIUM Sinus venosus is absorbed into right atrium by

great enlargement of sinu-artrial orifice. Left horn Part of coronary sinus Right common cardinal Part of superior vena cava Right vitelline vein Terminal part of inferior vena

cava Right margin of original sinu-atrial orifice (right & left

venous valve) expands and divide into: Crista terminalis Valve of inferior vena cava Valve of coronary sinus

Right half of atrioventricular canal is also absorbed into right atrium.

By: Gan Quan Fu

DEVELOPMENT OF LEFT ATRIUM

During the beginning of formation of septum primum, single pulmonary vein open into left half of atrium.

This pulmonary vein divide into left and right branches.

Gradually the parts of pulmonary veins nearest to left atrium are absorbed into the atrium resulting in 4 separate veins (2 each side).

By: Gan Quan Fu

SEPARATION OF AORTA AND PULMONARY TRUNK

Spiral Septum appears within truncus arteriosus and subdivides it into ascending aorta and pulmonary arteries.

They fuse along the axis of the cylinder extending down towards the ventricles.

Interventricular foramen obliterated by mass of endocardial tissues from interventricular septum, endocardial cushions & Spiral Septum.

By: Gan Quan Fu

DEVELOPMENT OF VENTRICLES (INTERVENTRICULAR SEPTUM)

Conus of bulbus cordis merge with cavity of primitive ventricle.

Interventricular septum grows upwards from the floor of bulbo-ventricular cavity & divide it into right & left halves.

2 ridges (right & Left bulbar ridges) from the wall of the conical part of bulbar cavity (Spiral septum), grows towards each other and fuse form bulbar septum.

The gap between upper edge of interventricular septum and lower edge of bulbar septum, is filled by proliferation of tissues from atrioventricular cushions.

By: Gan Quan Fu

EXTERIOR OF HEART

Heart tube is suspended from the dorsal wall of the pericardial cavity by 2 layers of percardium which constitude dorsal mesocardium.

Mesocardium disappears and heart tube lies within the pericardial sac.

Caudal part of the heart tube (atrium, sinus venosus) is embedded within the septum transversum

By: Gan Quan Fu

EXTERIOR OF HEART Bulbus cordis and ventricle in pericardial cavity grows

rapidly & becomes folded to form U-shape Bulbo-ventricular loop.

The atrium and sinus venosus freed from septum transversum. (Lie behind and above the ventricle and the heart tube is now S shaped)

Arterial and venous ends come closer to each other and the space between them becomes the transverse sinus of pericardium.

By: Gan Quan Fu

EXTERIOR OF THE HEART

Till now, bulbus cordis (conus) & ventricle are separated by deep bulboventricular sulcus.

Sulcus gradually becomes narrow, bulbus cordis & ventricle come to form 1 chamber which communicates with truncus arteriosus.

The atrial chamber which lies behind the upper part of ventricle expands and projects forwards on either side of the truncus.

Finally heart assumes its definitive shape.

By: Gan Quan Fu

VALVES OF HEART (MITRAL & TRICUSPID) Formed by proliferation of connective

tissue under endocardium of left and right atrio-ventricular canals.

By: Gan Quan Fu

VALVES OF HEART (PULMONARY & AORTIC) Derived from endocardial cushions formed at

junction of truncus arteriosus and the conus which grows and fuse with each other.

With separation of aortic and pulmonary trunk each cushions are subdivided into 2 parts (each in each orifice).

2 more cushions (anterior and posterior) appear. 3 cushions in each opening which the 3 cusps of the corresponding valve develops.

Pulmonary valve is initially ventral to aortic valve,. Subsequently rotation happens and pulmonary valve lie ventral to left aortic valve.

By: Gan Quan Fu

DEVELOPMENT OF CONDUCTING SYSTEM OF HEART

When there are 2 heart tubes, a pacemaker (which later forms sinu-atrial node) lies in caudal part of left tube.

After fusion of 2 tubes it lies in sinus venosus. Comes to lie near to opening of superior vena cava

when sinus venosus is incorporated into right ventricle.

Atrio-ventricular node and atrio-ventricular bundle form in left wall of sinus venosus and in atrio-ventricular canal.

After sinus venosus is absorbed into right atrium, atrio-ventricular node comes to lie near the interatrial septum.

By: Gan Quan Fu

TIMELINE ON FORMATION OF HEART Early 4th week

The pair of lateral endocardial tubes fuse 5th to 6th week

A pair of septa, Septum Primum & Septum Secundum separates right & left atria

Development of bicuspid and tricuspid atrioventricular valve 6th week

Muscular ventricular septum partially separates the ventricles

7th & 8th week Spiral septum separates ascending aorta & pulmonary trunk Swellings within truncus arteriosus give rise to semilunar

valves of aorta & pulmonary trunk Complete ventricular septation

By: Gan Quan Fu

CONGENITAL ANOMALIES OF HEART

Anomalies of Position Atresia or Stenosis Abnormal Growth Defective Formation of Septa Anomalies of Relationship of Chambers

to Great Vessels

By: Gan Quan Fu

ANOMALIES OF POSITION

Dextrocardia Chambers and blood vessels of heart are reversed

from side to side (i.e. all structures that normally lie on right side are on left and vice versa)

Maybe a part of the condition called situs inversus (Organs are transposed)

If not part of situs inversus, usually accompanied by anomalies of heart chambers and great vessels.

Ectopia Cordis Heart lies exposed, on front of the chest and can

be seen from outside, due to defective development of chest wall.

By: Gan Quan Fu

ATRESIA OR STENOSIS

Too narrow opening (stenosis) or no opening (atresia) of the orifices of heart.

Aortic and pulmonary passages may also show supravalvular or subvalvular stenosis.

Alternately, the openings may be too large and valves becomes incompetent.

In pulmonary stenosis foramen ovale and ductus arteriosus remain patent.

In aortic stenosis ductus arteriosus is patent and blood flows into aorta through it.

By: Gan Quan Fu

ABNORMAL GROWTH

There maybe acessory cusps in the valves

Congenital tumors may be formed Left atrium may be partially subdivided

by a transverse septum. Myocardium may be poorly developed

(hypoplasia).

By: Gan Quan Fu

DEFECTIVE FORMATION OF SEPTA

1. INTERATRIAL SEPTAL DEFECTS Osteum Primum Defect (image A)

Septum primum fail to reach atrio-ventricular endocardial cushions Foramen primum persist.

Osteum Secundum Defect (image B) Septum secundum fail to develop foramen

secundum remains wide open. Patent Foramen Ovale (image C)

Septum Primum and Secundum may develop normally but the Oblique valvular passage between them may remain patent.

By: Gan Quan Fu

DEFECTIVE FORMATION OF SEPTA Interventricular Septal Defects (image D)

Maybe seen either in the membranous or muscular part of the septum

Most common congenital anomalies of the heart. Patent Truncus Arteriosus

Defects of the spiral septum Spiral Septum may not be formed at all. Partial

absence of the septum leads to communications(shunts)between the aorta and pulmonary trunk.

Atrio-ventricular canal defect / Persistent atrio-ventricular canal

Defective formation of AV cushions, 4 chambers of heart may intercommunicate.

By: Gan Quan Fu

COMBINED DEFECTS

Tetralogy of Fallot Interventricular septal Defect Aorta overriding the free upper edge of

ventricular septum Pulmonary Stenosis Hypertrophy of the Right Ventricle

By: Gan Quan Fu

ANOMALIES OF RELATIONSHIP OF CHAMBERS TO GREAT VESSELS

Transposition of Great Vessels The aorta arises from the right ventricle and the

pulmonary trunk from the left ventricle. Taussig-Bing Syndrome

The aorta arises from the right ventricle and pulmonary trunk overrides both the right and left ventricle.

Interventricular defect The Superior Vena Cava may end in the Left

Atrium Pulmonary Veins may end in the Right Atrium or

one of it’s tributaries.

By: Gan Quan Fu

SUMMARY Heart primodium forms in a horseshoe-shape

region of splanchnopleuric mesoderm at cranial end of germ disc (Cardiogenic Region).

In response to signals from underlying endoderm, angioblastic cords in this region coalesce to form a pair of lateral heart tube.

Early of 4th week, they fuse to form primitive heart tube.

Between weeks 5 and 8, primitive heart tube undergoes process of looping, remodelling, and septation that transform it’s single lumen into 4 chambers, thus laying down the basis for separation of pulmonary and systemic circulation

By: Gan Quan Fu

REFERENCES

Larsen, W.J. (1997) Human Embryology, 2nd edn. Hong Kong; Churchill Livingstone.

Singh, I. & Pal, G.P. (1976) Human Embryology, 7th edn. India; Macmillan.

By: Gan Quan Fu

Q&A SESSION !!!!

By: Gan Quan Fu

THANK YOU!!!!!