What is the structure and function of septa?

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Septa are the walls that partition the heart into its separate chambers. There are two main septa: the interatrial septum between the atria and the interventricular septum between the ventricles. The interventricular septum is mainly muscular, with a small membranous portion near the base of the heart; the interatrial septum is primarily muscular as well. These walls are made of myocardium covered by endocardium, and the interventricular septum houses part of the heart’s conduction system to help coordinate ventricular contraction.

The primary function is to keep oxygen-rich blood in the left side of the heart from mixing with oxygen-poor blood on the right, which preserves the separation between the pulmonary and systemic circulations. The septa also provide structural support for the heart and, in the case of the interventricular septum, contain pathways important for impulse conduction to ensure synchronized beating. In fetal life, the interatrial septum includes a foramen ovale that allows shunting of blood between atria; after birth it closes to form the fossa ovalis.

This description contrasts with structures that are valves (which prevent backflow), nerves (which regulate heart rate), or the outer fibrous rings around valves (annuli fibrosi), none of which are septa.