Primary interatrial foramen
Primary interatrial foramen Interior of dorsal half of heart from a human embryo of about thirty days. (Ostium primum visible below septum primum, but not labeled.) Latin foramen primum Gray's subject #135 512 Code TE E184.108.40.206.2.1.1
In the developing heart, the atria initially communicate with each other by an opening between the free edge of the septum primum and the AV cushions, known as the primary interatrial foramen or 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 as the ostium primum closes, the communication between the atria is preserved with the formation of an opening in the upper part of the septum primum; this opening is known as the ostium secundum as it is chronologically the second opening that occurs in the septum prium.
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. The part of the septum primum that remains to the left of the septum secundum acts as a one way flow valve due to the greater pressures in the right atrium compared to the left atrium. At birth the neonate begins breathing and the associated decrease in pulmonary vascular resistance leads to a reversal of the pressure differential between the atria. The left atrium now has a greater pressure compared to the right, effectively closing the one way flow valve formed by the two septae. The 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. Additionally, in a subset of the population, the foramen ovale is not overtly patent, however the two septae have not fused. In normal physiologic circumstances the septum primum acts as a one way valve preventing blood flow as described above, however 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 atrio-ventricular 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 syndrome.
- Embryology at Temple Heart98/heart97a/sld036
- Overview and diagram at um.edu.mt
- MedEd at Loyola GrossAnatomy/thorax0/Heart_Development/Atria.html
Prenatal development/Mammalian development of circulatory system (GA 5, TE E5.11) Heart developmentTubular heartSepta/ostiaOtherAtrioventricular canal · Primary interventricular foramen Vasculogenesis,
Blood island of umbilical vesicleDevelopment of arteriesDevelopment of veinsAnterior cardinal vein · Posterior cardinal vein · Common cardinal veinsDevelopment of lymph vesselsLymph sacsDevelopment of circulatory system about teeth near childrenanuli: Anulus sanguineus perienameleus · lacunae: Lacuna sanguinea supraenamelea (Ductus sanguineus mesialis · Ductus sanguineus distalis · Ductus sanguineus lingualis · Ductus sanguineus palatinus · Ductus sanguineus buccalis · Ductus sanguineus labialis), Lacuna sanguinea apicalis, Lacuna sanguinea periodontalis, Lacuna sanguinea parodontalis, Lacuna sanguinea gingivalis
Wikimedia Foundation. 2010.
Look at other dictionaries:
Foramen secundum — Latin foramen secundum Days 33 Code TE E220.127.116.11.2.1.2 The ostium secundum (or foramen secundum) is a foramen in the septum primum. It should not be confused with the foramen ovale, which is a foramen in the septum secundum … Wikipedia
Foramen ovale (heart) — Not to be confused with ostium secundum. Foramen ovale (heart) Sketch showing foramen ovale in a fetal heart. Red arrow shows blood from the inferior caval vein. HF: right atrium, VF: left atrium. HH og VH: right and left ventricle. The heart… … Wikipedia
Foramen — A natural opening. Although a foramen is usually through bone, it can be an opening through other types of tissue, as with the foramen ovale. * * * An aperture or perforation through a bone or a membranous structure. SYN: trema (1). [L. an… … Medical dictionary
Circulatory system — This article is about the organ system. For the band, see Circulatory System. For transport in plants, see Vascular tissue. Circulatory system … Wikipedia
Embryology — 1 morula, 2 blastula 1 blastula, 2 gastrula with blastopor … Wikipedia
Placenta — For the ancient Roman bread, see placenta (food). For the placenta of fruit, see placentation. Placenta Placenta Precursor … Wikipedia
Ductus arteriosus — Artery: Ductus arteriosus Plan of the fetal circulation. ( Ductus arteriosus visible at upper right.) … Wikipedia
Ductus venosus — Vein: Ductus venosus Fetal circulation. The ductus venosus (red) connects the umbilical vein to the inferior vena cava … Wikipedia
Chorion — For the chorion in invertebrate eggs, see Chorion (egg). Chorion Diagram showing earliest observed stage of human embryo … Wikipedia
Umbilical artery — Artery: Umbilical artery Fetal circulation; the umbilical vein is the large, red vessel at the far left. The umbilical arteries are purple and wrap around the umbilical vein … Wikipedia