The septum secundum is a

muscular Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...

flap that is important in

heart development Heart development, also known as cardiogenesis, refers to the prenatal development of the heart. This begins with the formation of two endocardial tubes which merge to form the tubular heart, also called the primitive heart tube. The heart is t ...

. It is semilunar in shape, and grows downward from the upper wall of the

atrium Atrium may refer to: Anatomy * Atrium (heart), an anatomical structure of the heart * Atrium, the genital structure next to the genital aperture in the reproductive system of gastropods * Atrium of the ventricular system of the brain * Pulmona ...

immediately to the right of the

septum primum During heart development of a human embryo, the single primitive atrium becomes divided into right and left by a , the septum primum. The septum primum () grows downward into the single atrium. Development The gap below it is known as the ostium ...

and

ostium secundum The foramen secundum, or ostium secundum is a in the septum primum, a precursor to the interatrial septum of the human heart. It is not the same as the foramen ovale, which is an opening in the septum secundum. Development The foramen secund ...

. It is important in the closure of the foramen ovale after

birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the f ...

Structure

Development

At the end of the fifth week of development, the septum secundum grows from the upper wall of the

primitive atrium The primitive atrium is a stage in the embryonic development of the human heart. It grows rapidly and partially encircles the bulbus cordis; the groove against which the bulbus cordis lies is the first indication of a division into right and left ...

. It grows to the right of the

, which has already started growing. It grows down towards the

septum intermedium Endocardial cushions project into the atrial canal The proper development of the atrioventricular canal into its prospective components (The heart septum and associated Heart valve, valves) to create a clear division between the four compartments ...

formed from the

endocardial cushions Endocardial cushions, or atrioventricular cushions, refer to a subset of cells in the development of the heart that play a vital role in the proper formation of the heart septa. They develop on the atrioventricular canal and conotruncal region of ...

. Before

, it does not fuse with the septum intermedium, leaving a gap to form the foramen ovale. Shortly after birth, it fuses with the

to form the

interatrial septum The interatrial septum is the wall of tissue that separates the right and left atria of the heart. Structure The interatrial septum is a that lies between the left atrium and right atrium of the human heart. The interatrial septum lies at angl ...

, and the foramen ovale is closed. The fossa ovalis denotes the free margin of the septum secundum after birth.

Clinical significance

Sometimes, the fusion of the septum secundum to the

is incomplete, and the upper part of the foramen remains patent. This creates an

atrial septal defect Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this d ...

(ASD).

References

External links

* *
Overview at edu.mt
* Embryology of cardiovascular system {{Portal bar, Anatomy