Interatrial septum - wikipedia Interatrial septum Interatrial septum Interior of right side of heart. ( labeled at left of image, as ' atrial septum ' ) Interior of dorsal half of heart of human embryo of about thirty - five days. Identifiers MeSH D054087 TA A12. 1.00. 019 FMA 7108 Anatomical terminology ( edit on Wikidata ) The interatrial septum is the wall of tissue that separates the right and left atria of the heart. Contents 1 Structure 2 Development 2.1 At birth 3 Clinical significance 4 References 5 External links Structure The intratrial septum is a septum that lies between the left atrium and right atrium of the human heart. Development See also : Heart development The interatrial septum forms during the first and second months of fetal development. Formation of the septum occurs in several stages. The first is the development of the septum primum, a crescent - shaped piece of tissue forming the initial divider between the right and left atria. Because of its crescent shape, the septum primum does not fully occlude the space between left and right atria ; the opening that remains is called the ostium primum. During fetal development, this opening allows blood to be shunted from the right atrium to the left. As the septum primum grows, the ostium primum progressively narrows. Before the ostium primum is completely occluded, a second opening called the ostium secundum begins to form in the septum primum. The ostium secundum allows continued shunting of blood from the right atrium to the left. To the right of the septum primum, the septum secundum begins to form. This thick, muscular structure initially takes on the same crescent shape as the septum primum, except that it originates anteriorly, whereas the septum primum originates posteriorly. As the septum secundum grows, it leaves a small opening called the foramen ovale. The foramen ovale is continuous with the ostium secundum, again providing for continued shunting of blood. The ostium secundum progressively enlarges and the size of the septum primum diminishes. Eventually, the septum primum is nothing more than a small flap that covers the foramen ovale on its left side. This flap of tissue is called the valve of the foramen ovale. It opens and closes in response to pressure gradients between the left and right atria. When the pressure is greater in the right atrium, the valve opens ; when the pressure is greater in the left atrium, the valve closes. Because the lungs are nonfunctional in fetal life, pressure in the pulmonary circulation is greater than that of the systemic circulation. Consequently, the right atrium is generally under higher pressures than the left atrium, and the valve of the foramen ovale is normally open. At birth At birth, there is a reversal in the pressure gradient between the atria, resulting in functional closure of the valve of the foramen ovale. Permanent anatomical closure of the foramen ovale occurs with time in normal infants. Inappropriate closure of the foramen ovale results in patent foramen ovale. Clinical significance Main article : Atrial septal defect An Atrial septal defect is a relatively common heart malformation that occurs when the interatrial septum fails to develop properly. Persistence of the ostium secundum is the most common atrial septal defect. Additionally, in a subset of the population, the foramen ovale is not overtly patent but the two septa have not fused. In normal physiologic circumstances, the septum primum acts as a one - way valve preventing blood flow as described above ; but, if pathologic conditions cause right atrial pressure to exceed left atrial pressure, blood may flow through the foramen ovale from right to left. Failure of the septum primum to fuse with the endocardial cushion can lead to an ostium primum atrial septal defect. This is the second most common type of atrial septal defect and is commonly seen in Down 's syndrome. Typically this defect will cause a shunt to occur from the left atrium to the right atrium. Children born with this defect may be asymptomatic, however, over time pulmonary hypertension and the resulting hypertrophy of the right side of the heart will lead to a reversal of this shunt. This reversal is called Eisenmenger 's syndrome. References Gray 's Anatomy : The Anatomical Basis of Clinical Practice, 39th ed. ( 2005 ). ISBN 0 - 443 - 07168 - 3 `` Septum, interatrial. '' Stedman 's Medical Dictionary, 27th ed. ( 2000 ). ISBN 0 - 683 - 40007 - X ^ Jump up to : Diagram of Ostium Secundum Atrial Septal Defect at Mayo Clinic Jump up ^ `` ostium primum atrial septal defect ''. GPnotebook. External links Diagram Animation, from Indiana University Development of the circulatory system Heart Tubular heart Truncus arteriosus Bulbus cordis Primitive ventricle Primitive atrium Sinus venosus Chamber formation Atrioventricular Primary interventricular foramen Endocardial cushions Septum intermedium Atrioventricular canal Atrial Septum primum Foramen secundum Primary interatrial foramen Septum secundum Foramen ovale Other Aorticopulmonary septum Protein signalling in heart development Vessels Arteries Dorsal aorta Aortic arches Aortic sac Veins Anterior cardinal vein Posterior cardinal vein Common cardinal veins Lymph vessels Lymph sacs Other Vascular remodelling in the embryo Extraembryonic hemangiogenesis Blood islands Chorion Connecting stalk Yolk sac Placenta Fetal circulation umbilical cord : Umbilical vein → Ductus venosus → Inferior vena cava → Heart → Pulmonary artery → Ductus arteriosus → Aorta → Umbilical artery yolk sac : Vitelline veins Vitelline arteries Retrieved from `` https://en.wikipedia.org/w/index.php?title=Interatrial_septum&oldid=825333622 '' Categories : Embryology of cardiovascular system Talk Contents About Wikipedia Italiano Nederlands Polski Português Edit links This page was last edited on 12 February 2018, at 20 : 24 ( UTC ). 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Question: the flaplike opening in the interatrial septum of the fetus
Answer: the valve of the foramen ovale