The septum primum is a crucial structure that develops early in the formation of the heart, specifically in the division of the primordial atrium.
Development of the Septum Primum
During the development of the heart, the common atrium begins to be divided into the future left and right atria. The septum primum is the first wall to form in this process.
- Origin: The septum primum originally develops as a ridge of muscular tissue.
- Growth: It grows downward from the roof of the primordial atrium.
- Target: This ridge of muscular tissue grows toward the endocardial cushion tissue of the developing AV valves (atrioventricular valves), which are located at the base of the atrium.
As the septum primum grows towards the endocardial cushions, it leaves a temporary opening near the cushions called the ostium primum.
Function and Closure
The primary function of the septum primum is to begin the separation of the atrial chambers.
- Fusion: The septum primum eventually fuses with the cushion.
- Closure: This fusion effectively closes the primordial hole, the ostium primum, which was located between the developing AV valves and the growing septum primum.
This closure of the ostium primum is a critical step in ensuring proper blood flow separation in the developing heart. However, even after the ostium primum closes, another opening, the ostium secundum, forms elsewhere in the septum primum, maintaining a shunt (the foramen ovale) necessary for fetal circulation.
Think of it like building a wall (septum primum) across a room (primordial atrium). Initially, the wall starts from the ceiling and grows downwards, leaving a gap at the bottom (ostium primum). This wall eventually reaches and connects with the floor structures (endocardial cushions), closing that bottom gap.
Key Points about Septum Primum
Here is a summary of its characteristics:
| Feature | Description |
|---|---|
| Composition | Ridge of muscular tissue |
| Origin | Grows from the roof of the primordial atrium |
| Direction | Grows towards the endocardial cushion tissue |
| Initial Gap | Creates the ostium primum during its growth phase |
| Final Action | Fuses with the endocardial cushions, closing the ostium primum |
| Purpose | Initiates the division of the atrial chamber |
Understanding the development and fate of the septum primum is essential for comprehending the complex process of cardiac embryology and the formation of the atrial septum.
