title: In situ morphology of the foramen ovale in the fetal and neonatal rat.
abstract: In situ cross-sectional morphology of the foramen ovale was studied after rapid whole-body freezing of the fetal and neonatal rat. In the fetus, the foramen ovale was open widely toward the left atrium with a thin, short primum septum. The opening area of the foramen ovale was 40% of the cross-section of the thoracic inferior vena cava, and the ratio of the long diameter to the short diameter was 2 to 1. After birth, the primum septum became longer, thicker, and straighter, with less leftward bowing. The opening of the foramen ovale diminished in the first 2 d and closed completely 3 d after birth. Postnatal thickening of the primum septum was very remarkable, increasing by 400% in the first 2d, while only minimal change was noticed in the right and the left atrial walls. The length of the primum septum was short and was only 90% of the diameter of the fossa ovalis in the fetus. It increased and reached 97% and 111% of the diameter of the fossa ovalis 1 and 2 d after birth, respectively. The septum secundum also grew rapidly after birth, and its length and width increased by 40% and 29% after 1 and 2 d, respectively. These observations indicate a sudden, explosive growth of the atrial septum in the early neonatal period in the rat.
authors.affiliation: Department of Pediatric Cardiology, Tokyo Women's Medical College, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Momma
authors.forename: T
authors.initials: T
authors.lastname: Ito
authors.forename: M
authors.initials: M
authors.lastname: Ando
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D005318:Fetal Heart / Q000033:anatomy & histology*; D006346:Heart Septum / Q000033:anatomy & histology* / Q000254:growth & development; D051381:Rats; D017208:Rats, Wistar