DEVELOPMENT OF ATRIA DEVELOPMENT OF ATRIA & VENTRICLES& VENTRICLES

Dr. Mujahid KhanDr. Mujahid Khan

Fate of Heart TubesFate of Heart Tubes

The tubular heart elongates and develops The tubular heart elongates and develops alternate dilations and constrictions:alternate dilations and constrictions:

Truncus ArteriosusTruncus Arteriosus Bulbus CordisBulbus Cordis VentricleVentricle AtriumAtrium Sinus venosusSinus venosus

Partitioning of HeartPartitioning of Heart

Partitioning of the atrioventricular canal, Partitioning of the atrioventricular canal, primordial atrium, and primordial ventricle primordial atrium, and primordial ventricle begins around 4begins around 4thth week week

Completed by the end of the 5Completed by the end of the 5thth week week

Partitioning of Atrioventricular Partitioning of Atrioventricular CanalCanal

Toward the end of the 4Toward the end of the 4thth week week

Endocardial cushions form on the dorsal and ventral walls Endocardial cushions form on the dorsal and ventral walls of the AV canal of the AV canal

The AV endocardial cushions approach each other and The AV endocardial cushions approach each other and fusefuse

Dividing the AV canal into right & left canalsDividing the AV canal into right & left canals

These canals partially separate the primordial atrium from These canals partially separate the primordial atrium from the ventriclethe ventricle

Endocardial cushion works as AV valvesEndocardial cushion works as AV valves

Endocardial CushionEndocardial Cushion

It develops from a specialized extracellular It develops from a specialized extracellular matrix (ECM) or cardiac jellymatrix (ECM) or cardiac jelly

The transformed endocardial cushions The transformed endocardial cushions contribute to the formation of the valves contribute to the formation of the valves and membranous septa of the heartand membranous septa of the heart

Partitioning of Primordial AtriumPartitioning of Primordial Atrium

Beginning at the end of the 4Beginning at the end of the 4thth week week

Is divided into right & left atria by the Is divided into right & left atria by the formation and subsequent modification formation and subsequent modification and fusion of two septa:and fusion of two septa:

Septum primumSeptum primum Septum secondum Septum secondum

Septum PrimumSeptum Primum

It’s a thin crescent shaped membraneIt’s a thin crescent shaped membrane

Grows from the roof of the primordial Grows from the roof of the primordial atrium towards the fusing endocardial atrium towards the fusing endocardial cushionscushions

Dividing the common atrium into left & Dividing the common atrium into left & right halvesright halves

Foramen PrimumForamen Primum

A large opening forms in the growing septum A large opening forms in the growing septum primum between its crescentic free edge and the primum between its crescentic free edge and the endocardial cushionendocardial cushion

It serves as the shunt, enabling oxygenated It serves as the shunt, enabling oxygenated blood to pass from right to the left atriumblood to pass from right to the left atrium

Becomes progressively smaller and disappears Becomes progressively smaller and disappears as the septum primum fuses with the fused as the septum primum fuses with the fused endocardial cushions to form a primordial AV endocardial cushions to form a primordial AV septumseptum

Foramen SecondumForamen Secondum Perforation appears in the central part of the Perforation appears in the central part of the

septum primum before the foramen primum septum primum before the foramen primum disappears disappears

Perforation coalesce to form another opening, Perforation coalesce to form another opening, the foramen secondumthe foramen secondum

Concurrently, the free edge of the septum Concurrently, the free edge of the septum primum fuses with the left side of the fused primum fuses with the left side of the fused endocardial cushionsendocardial cushions

It ensures a continuous flow of oxygenated It ensures a continuous flow of oxygenated blood from right to the left atriumblood from right to the left atrium

Septum SecondumSeptum Secondum

A crescentic muscular membraneA crescentic muscular membrane

Grows from ventrocranial wall of atriumGrows from ventrocranial wall of atrium

Immediately to the right of the septum primumImmediately to the right of the septum primum

It is thick and grows during 5It is thick and grows during 5 thth & 6 & 6thth weeks weeks

Gradually overlaps the foramen secondum in the Gradually overlaps the foramen secondum in the septum primumseptum primum

Septum SecondumSeptum Secondum

It forms an incomplete partition between the atriaIt forms an incomplete partition between the atria

Consequently an oval foramen formsConsequently an oval foramen forms

Cranial part of the septum primum ( attached to Cranial part of the septum primum ( attached to the roof of left atrium) disappears graduallythe roof of left atrium) disappears gradually

Remaining part of septum primum (attached to Remaining part of septum primum (attached to endocardial cushion) forms a flap like valve of endocardial cushion) forms a flap like valve of oval foramenoval foramen

Oval ForamenOval Foramen

Before birth it allows most of the oxygenated blood Before birth it allows most of the oxygenated blood entering the right atrium from IVC to pass into the entering the right atrium from IVC to pass into the left atriumleft atrium

Prevents the blood flow in opposite directionPrevents the blood flow in opposite direction

After birth it normally closes and the valve of the After birth it normally closes and the valve of the oval foramen fuses with septum primumoval foramen fuses with septum primum

The interatrial septum becomes a complete The interatrial septum becomes a complete partition between the atriapartition between the atria

Oval FossaOval Fossa

An oval depression in the lower part of the An oval depression in the lower part of the interatrial septum of the right atrium known interatrial septum of the right atrium known as oval fossaas oval fossa

It’s a vestige of the oval foramenIt’s a vestige of the oval foramen

Partitioning of Primordial VentriclePartitioning of Primordial Ventricle

Division of primordial ventricle is first Division of primordial ventricle is first indicated by a median muscular ridge, the indicated by a median muscular ridge, the primordial interventricular septumprimordial interventricular septum

Is a thick crescentic fold has a concave Is a thick crescentic fold has a concave free edgefree edge

Initially most of its height results from Initially most of its height results from dilation of the ventricles on each side of dilation of the ventricles on each side of the IV septumthe IV septum

Partitioning of Primordial VentriclePartitioning of Primordial Ventricle

Medial walls of the enlarging ventricles approach Medial walls of the enlarging ventricles approach each other and fuse to form the primordium of each other and fuse to form the primordium of the muscular part of the IV septumthe muscular part of the IV septum

Active proliferation of myoblasts in the septum Active proliferation of myoblasts in the septum increase its sizeincrease its size

Until the 7Until the 7thth week there is a crescent shaped week there is a crescent shaped interventricular foramen between the free edge interventricular foramen between the free edge of IV septum and the fused endocardial cushionof IV septum and the fused endocardial cushion

Interventricular ForamenInterventricular Foramen

The IV foramen permits communication The IV foramen permits communication between the right and the left ventriclesbetween the right and the left ventricles

It usually closes by the end of the 7It usually closes by the end of the 7thth week week as the bulbar ridges fuse with the as the bulbar ridges fuse with the endocardial cushionendocardial cushion

Closure of IV ForamenClosure of IV Foramen

Formation of the membranous part of the Formation of the membranous part of the IV septum result from the fusion of tissues IV septum result from the fusion of tissues from 3 sources:from 3 sources:

The right bulbar ridgeThe right bulbar ridge The left bulbar ridgeThe left bulbar ridge The endocardial cushionThe endocardial cushion

Interventricular SeptumInterventricular Septum

The membranous part of the IV septum is The membranous part of the IV septum is derived from an extension of tissue from derived from an extension of tissue from the right side of the endocardial cushion to the right side of the endocardial cushion to the muscular part of the IV septumthe muscular part of the IV septum

This tissue merges with the This tissue merges with the aorticopulmonary septum and thick aorticopulmonary septum and thick muscular part of the IV septummuscular part of the IV septum

Interventricular SeptumInterventricular Septum

After closure of the IV foramen and After closure of the IV foramen and formation of the membranous part of the formation of the membranous part of the IV septum, the pulmonary trunk is in IV septum, the pulmonary trunk is in communication with the right ventricle and communication with the right ventricle and the aorta with the left ventriclethe aorta with the left ventricle

Trabeculae CarnaeTrabeculae Carnae

Cavitation of the ventricular walls forms a Cavitation of the ventricular walls forms a sponge-work of muscular bundles called sponge-work of muscular bundles called trabeculae carnaetrabeculae carnae

Some of these bundles become the Some of these bundles become the papillary muscles and tendinous cordspapillary muscles and tendinous cords

The tendinous cords run from the papillary The tendinous cords run from the papillary muscles to the atrioventricular valvesmuscles to the atrioventricular valves

Tetralogy of FallotTetralogy of Fallot

Classic group of four cardiac defects:Classic group of four cardiac defects:

Pulmonary stenosisPulmonary stenosis Ventricular septal defectVentricular septal defect Dextroposition of aortaDextroposition of aorta Right ventricular hypertrophyRight ventricular hypertrophy