2024 NUIG Lecture 7 embryology and septal formation v2.pptx

ecture 7 eart Embryology & Clinical Case uffy 2024 Pre- versus post-natal circulation Foetal circulation 2 right to left shunts Atrial septum Ductus arteriosus Allow blood to bypass foetal lungs Intra-atrial Septum Formation Septation Right atrial Entrance of sinus venosus has shifted over to right...

ecture 7 eart Embryology & Clinical Case uffy 2024 Pre- versus post-natal circulation Foetal circulation 2 right to left shunts Atrial septum Ductus arteriosus Allow blood to bypass foetal lungs Intra-atrial Septum Formation Septation Right atrial Entrance of sinus venosus has shifted over to right Atrium enlarges in size Some of the new wall is formed from the sinus venosus (smooth wall of right atrium) Right venous valve Crista terminalis Valve of IVC Valve of coronary sinus Development of the Atrial septum Septum primum Sickel shaped Grows from roof of atrium into lumen Ostium primum Opening at lower free edge of septum primum Cell death / perforations in upper septum Before ostium primum closes Form ostium secundum Septum primum Fuses with endocardial cushions Ostium Secundum Septum secundum Grows from roof of atria Never becomes a complete septum Lower free edge - Foramen Ovale Closure of the Atrial Septum Pre-natal Lungs deflated High pulmonary peripheral vascular resistance (PVR) & arterial pressures Blood flows from right to left Post-natal Lungs inflate Pulmonary PVR reduces Pulmonary arterial (& right heart) pressures drop Pressures now LA > RA Closure Physiological, then anatomical Atrial Septal Defects Left-to-right shunting of blood Exercise intolerance in older children/adults Acyanotic heart disease May be asymptomatic Auscultation: -Ejection systolic murmur Ostium Primum defect Septum primum fails to close ostium primum Just above AV valves Risk of associated valve defects Ostium secundum defects Most common defect 70% of ASDs Occur in region of fossa ovalis Septum primum & secondum fail to fuse Two main causes Excessive resorption of septum primum Underdevelopment or absence of septum secundum Closure of Ductus Arteriosus Pre-natal Blood flows from right to left Post-natal Bradykinin released Smooth muscle contracts Physiological, then anatomical closure -Ligamentum arteriosum Closure of ductus arteriosus Patent ductus arteriosus (PDA) Postnatal blood flow left to right Pulmonary hypertension “machine-like” murmur (systole & diastole) Interventricular Septum Muscular part Majority of septum Formed by medial walls of expanding ventricles Membranous part Superiorly an interventicular foramen exists Tissue from inferior endocardial cushion closes this foramen Ventricular septal defect 2 main forms Muscular vs. membranous Spontaneous closure may occur