In the developing heart of a human embryo, the cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum, which grows downward into the cavity. The increasingly smaller gap below it (before it fuses with the endocardial cushion) is known as the ostium primum (i.e. "the first opening"). The septum primum eventually fuses with the endocardial cushion, closing the ostium primum off completely. Meanwhile, perforations appear in the superior part of the septum primum, forming the ostium secundum (i.e. "the second opening"). This will eventually form part of the fossa ovalis.
Other articles related to "septum primum, septum, 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 ... 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 ... 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 ...
... atria are separated from one another by the septum primum except for a small opening in the septum, the ostium primum ... As the septum primum grows, the ostium primum narrows and eventually closes ... from the inferior vena cava wears down a portion of the septum primum, forming the ostium secundum ...
Famous quotes containing the word primum:
“Every man is a creative cause of what happens, a primum mobile with an original movement.”
—Friedrich Nietzsche (18441900)