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
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