Ostium primum

Infobox Embryology
Name = Ostium primum
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Caption = Interior of dorsal half of heart from a human embryo of about thirty days. (Ostium primum visible below septum primum, but not labeled.)


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In the developing heart, for a time the atria communicate with each other by an opening between the free edge of the septum primum and the AV cushions, known as the ostium primum (interatrial foramen primum), below the free margin of the septum.

Closing of ostium primum

This opening is closed by the union of the septum primum with the septum intermedium, and the communication between the atria is reestablished through an opening which is developed in the upper part of the septum primum; this opening is (confusingly) known as the foramen secundum.

A second entity, the septum secundum, develops to the right of the septum primum and the opening between the upper and lower limbs of the septum secundum is known as the foramen ovale of the heart and persists until birth.

These two septae fuse later in life, to complete the formation of the atrial septum. Persistence of the ostium secundum is the most common atrial septal defect. [ [http://www.mayoclinic.org/atrial-septal-defect/types.html Diagram of Ostium Secundum Atrial Septal Defect at Mayo Clinic] ]

Clinical significance

Failure to fuse can lead to an ostium primum atrial septal defect. [GPnotebook|-402259967 ] This is the second most common type of atrial septal defect. [ [http://www.mayoclinic.org/atrial-septal-defect/types.html Diagram of Ostium Secundum Atrial Septal Defect at Mayo Clinic] ]

References

External links

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* [http://staff.um.edu.mt/acus1/Heart-b.htm Overview and diagram at um.edu.mt]
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