Septum primum

Septum primum is a structure in the embryonic heart that plays a crucial role in the formation of the heart's four chambers. It is a thin, crescent-shaped piece of tissue that grows towards the endocardial cushions, eventually forming the atrial septum and separating the left and right atria.

Development

The septum primum originates from the dorsal wall of the primitive atrium during the fourth week of human embryogenesis. As it grows, it leaves a small opening at the bottom known as the Ostium primum. This opening allows blood to flow between the two atria.

As the septum primum nears the endocardial cushions, the ostium primum begins to close. Simultaneously, perforations appear in the upper part of the septum primum, forming the Ostium secundum. This second opening ensures that blood can continue to flow between the atria even after the ostium primum is fully closed.

Role in Heart Formation

The septum primum is integral to the formation of the heart's four chambers. It separates the primitive atrium into the left and right atria, a crucial step in the development of a fully functional human heart.

The septum primum also plays a role in the formation of the foramen ovale, a small hole in the fetal heart that allows blood to bypass the lungs. After birth, the foramen ovale closes, marking the transition from fetal to adult circulation.

Clinical Significance

Abnormalities in the development of the septum primum can lead to congenital heart defects such as atrial septal defects (ASD). These defects can cause problems with blood flow and oxygenation, leading to symptoms such as shortness of breath and fatigue.