Development of Interatrial septum DR SUVARNA GULANIKAR ASSIT

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Development of Interatrial septum DR. SUVARNA GULANIKAR ASSIT. PROF DEPT OF ANATOMY

Development of Interatrial septum DR. SUVARNA GULANIKAR ASSIT. PROF DEPT OF ANATOMY

Development of Interatrial septum • At the end of lecture student should able to

Development of Interatrial septum • At the end of lecture student should able to 1. Describe development of sinus venosus 2. Describe steps of development of interatrial septum 3. Enumerate changes after birth in IAS. 4. Discuss formation of right and left atria 5. Describe ASD and its types

Development of sinus venosus • • Between 5 th to 10 th week Sinus

Development of sinus venosus • • Between 5 th to 10 th week Sinus venosus represents venous end of developing heart After cardiac looping it lie dorso caudal to primitive atrium. It grows in transverse direction & become fusiform in shape.

Development of sinus venosus • Parts of sinus venosus: 1. Body 2. Right and

Development of sinus venosus • Parts of sinus venosus: 1. Body 2. Right and Left horns • Tributaries of each horn 1. vitelline vein (from the yolk sac), 2. umbilical vein (from the placenta) 3. common cardinal vein / Duct of cuvier 4. Each common cardinal vein receives i. Ant. Cardinal vein- from cephalic part of body wall ii. Post. Cardinal vein- from caudal part of body wall

 • Regression of left horn and its tributaries: ü due to deepening of

• Regression of left horn and its tributaries: ü due to deepening of left groove of sinu atrial junction, left part of the sinus venosus becomes completely separated from the atrial chamber. ü with obliteration of left vitelline & common cardinal veins left horn regresses in size and now appears as another tributary of the right half of the sinus venosus. & finally form coronary sinus. ü now most of the blood drains to right horn of sinus venosus. ü So right horn enlarge in size & form only communication to atrial chamber

 • FATE OF SINUATRIAL ORIFICE: ü The sinus venosus communicate with primitive atria

• FATE OF SINUATRIAL ORIFICE: ü The sinus venosus communicate with primitive atria by a wide opening, known as sinoatrial orifice. Ø Change in size and orientation of SA orifice– ü Initially S. A. orifice is large & wide , occupy median position ü Later due to formation of sinoatrial fold it reduce in size & shifted to right side of dorsal wall of primitive atrium ü Now become narrow slit like opening , which has 2 valvesright & left venous valves. ü These valves fuse cranially & form SEPTUM SPURIUM ü and meet caudally to form SINUS SEPTUM

Development of Interatrial Septum 1. Development of Atrioventricular [A-V] cushions / septum intermedium 2.

Development of Interatrial Septum 1. Development of Atrioventricular [A-V] cushions / septum intermedium 2. Formation of septum primum 3. Formation of foramen primum & foramen secondum 4. Formation of septum secondum 5. Formation of foramen ovale 6. Changes after birth 7. Congenital anomalies

q. AV cushion / septum intermedium: [ 5 th wk of IUL. ] ü

q. AV cushion / septum intermedium: [ 5 th wk of IUL. ] ü Atrioventricular Canal is the communication between common atrial chamber and ventricle. ü It is circular in shape initially & later becomes transverse. ü now, Two thickenings, appear on the dorsal and ventral walls of AV canal by proliferation of subendocardial mesenchymal cells & form ventral & dorsal endocardial cushions. ü They grow toward each other and fuse. The fused cushions form the septum intermedium. it divides AV canal into right & left AV orifice.

q Appearance of septum primum: [6 th wk] ü Due to pressure of bulbus

q Appearance of septum primum: [6 th wk] ü Due to pressure of bulbus cordis , roof of primitive atrium get notched & initiates development of septum primum ü now a thin sickle-shaped fold develop from the roof and dorsal wall of primitive atrium. This fold is called septum primum. ü It is located in midline & to left of septum spurium. ü Its lower free margin is concave & grows downward toward septum intermedium.

q Appearance of FORAMEN [OSTIUM]PRIMUM: ü Now the Gap appear between septum primum and

q Appearance of FORAMEN [OSTIUM]PRIMUM: ü Now the Gap appear between septum primum and septum intermedium known as foramen primum. q Appearance of FORAMEN [OSTIUM ]SECONDUM: ü Before the foramen primum closed, breaking down of the upper part of the septum primum occurs [APOPTOSIS]. ü So new gap appear known as foramen secundum. ü The septum primum now has a free upper edge

q Appearance of septum secundum: [7 th wk] ü Now septum secundum grows down

q Appearance of septum secundum: [7 th wk] ü Now septum secundum grows down from the roof of the atrial chamber, to right of the septum primum. ü As it grows, overlaps the free upper edge of the septum primum, Ø septum primum - thin, mobile & act as a Flap valve. Ø Septum secondum- thick , immobile ü Its lower free margin is sickle shaped & thick & firm known as Crista Dividens.

q Appearance of foramen ovale: ü Now blood flow through the slit like interval

q Appearance of foramen ovale: ü Now blood flow through the slit like interval between septum primum & secondum. ü It is an oblique valvular passage that allows blood to flow from right to left, but not from left to right known as foramen ovale ü This is patent throughout fetal life. ü Function - allows blood to bypass pulmonary circulation and shunts most of the blood from right atrium to left atrium instead of right ventricle.

q CHANGES AFTER BIRTH Ø Before birth – blood moves from RA to LA.

q CHANGES AFTER BIRTH Ø Before birth – blood moves from RA to LA. So thin flap of septum primum moves away for smooth blood flow. Ø After birth – ü Pulmonary circulation established-- pressure of LA increased. ü Now blood flow from LA to RA. ü So thin septum primum comes in apposition with septum secundum & ü foramen ovale closes functionally later structurally

 • functional closure of the foramen ovale – • immediately after birth •

• functional closure of the foramen ovale – • immediately after birth • is facilitated by 2 factors 1. decrease in right atrial pressure from occlusion of placental circulation 2. increase in left atrial pressure due to increased pulmonary venous return. • Structural closure – [complete fusion of septum primum & secondum] • 72 hours to 2 weeks. ü annulus /limbus fossa ovalis represents lower free edge of septum secundum ü fossa ovalis represents the septum primum.

Congenital anomalies • ASD [atrial septal defect]- Types 1. Osteum secondum defect 2. Osteum

Congenital anomalies • ASD [atrial septal defect]- Types 1. Osteum secondum defect 2. Osteum primum defect 3. Sinus venosus defect 4. Common atrium • probe patency of foramen ovale; • Premature closure of foramen ovale

Congenital anomalies q. Atrial septal defects (ASD) • Definition ü ASDs are congenital anomalies

Congenital anomalies q. Atrial septal defects (ASD) • Definition ü ASDs are congenital anomalies that involve defective formation of interatrial septum result in abnormal communication between right & left atria. • Incidence ü 6. 4 in 10, 000 births. • More common in females (2: 1) than in males. • Cause: Mutation of NKX 2. 5. • : mutation of TBX 5

ASD - TYPES q Ostium secundum defects – One of the commonest congenital heart

ASD - TYPES q Ostium secundum defects – One of the commonest congenital heart diseases. [70 – 80 % of all ASD] • Failure of septum secundum to cover septum primum results in ostium secundum defect. • Cause - short septum secundum or more absorption of septum primum [Excessive apoptosis]. • Effect- formation of large foramen ovale that does not close after birth, result in formation of Lt to Rt shunt.

Ostium secundum defects

Ostium secundum defects

ASD - TYPES q Osteum primum defect [15 -20%] • Failure of septum primum

ASD - TYPES q Osteum primum defect [15 -20%] • Failure of septum primum to close foramen primum result in septum primum defect. q. Endocardial cushion defect • Failure of fusion of AV cushions, leads to persistent AV canal. • septum primum not fused with AV cushions results in persistent foramen primum.

Osteum primum defect

Osteum primum defect

q. Sinus venosus ASD [5%] • Incomplete absorption of sinus venosus in right atrium

q. Sinus venosus ASD [5%] • Incomplete absorption of sinus venosus in right atrium results in defective atrial septum near the opening of SVC. q. Common atrium/Cortrioculare biventricularae • rare condition with a failure of development of the interatrial septum.

cor triloculare biventriculare SINUS VENOSUS ASD

cor triloculare biventriculare SINUS VENOSUS ASD

q probe patency of foramen ovale; • In 20% of cases, ü fusion of

q probe patency of foramen ovale; • In 20% of cases, ü fusion of the septum primum and septum secundum is incomplete, and a narrow oblique cleft remains between the two called as probe patency of foramen ovale; • it does not allow intracardiac shunting of blood. • Probe patency test –POSITIVE- [small probe can be passed through the foramen ovale. ] q Premature closure of foramen ovale [before birth] ü Massive hypertrophy of RA &RV ü Underdeveloped left side of heart ü Death shortly after death

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