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Atrial septation in the chick and rat: a review
Insights
The chick and rat heart septa primum develop rapidly, forming foramina secundum to maintain blood flow. These openings close as the septum matures, ensuring a fully partitioned heart post-hatching and gestation.
Area of Science:
- Developmental Biology
- Cardiovascular Embryology
- Comparative Anatomy
Background:
- The interatrial septum is crucial for fetal circulation, allowing oxygenated blood to bypass the lungs.
- Understanding septum primum development provides insights into congenital heart defects.
Purpose of the Study:
- To compare the developmental timeline and morphological characteristics of the septum primum in chick and rat embryos.
- To elucidate the formation and closure mechanisms of foramina primum and secundum.
Main Methods:
- Comparative embryological analysis of chick and rat hearts.
- Histological examination of developing septa.
- Scanning electron microscopy (SEM) for detailed surface morphology.
Main Results:
- Septum primum forms early in chicks (days 3-4) and later in rats (day 12).
- Foramen secundum formation involves multiple perforations coalescing into a single aperture in rats, and multiple foramina in chicks.
- Specialized cells observed during chick foramen formation disappear as development progresses.
Conclusions:
- Both species utilize a septum primum with a transient interatrial communication (foramen secundum) during development.
- Species-specific differences exist in the timing and detailed mechanisms of foramen secundum formation and septum maturation.
Abstract:
Septum primum of the chick and rat heart develops as a solid, crescentic fold on the inner atrial wall. In the chick this septum forms during days 3 and 4 of incubation. The same septum begins development during day 12 in the rat. In both species the septum grows rapidly toward the two endocardial cushions, decreasing the size of foramen primum in the process. A second foramen, foramen secundum, develops in the septum primum to maintain an interatrial shunt. Multiple foramina form in the middle and dorsal portions of the chick septum primum. These foramina continue to form until the middle of the second week of incubation. Prominent rounded cells are abundant on the chick septum in the region of foramina formation. These cells are no longer demonstrable when new foramina cease to be formed. At the time of hatching the cords of tissue separating foramina have thickened and fewer foramina exist. By day 2 after hatching the septum is an imperforate partition. The septum is seen to protrude into the left atrium, even after hatching. Foramen secundum forms very rapidly in the rat. Scanning electron microscopy indicates that it develops initially as multiple perforations which quickly coalesce into one aperture in the middle and ventral portions. The rat has a septum secundum which develops just to the right of septum primum. The valves of the sinus venosus project into the right atrium of the rat heart. Nodules are prominent features of the right valve early during the third week of gestation.
