The membranous part of the interventricular septum is between –
**Core Concept**
The membranous part of the interventricular septum is a thin, fibrous structure that separates the left and right ventricles of the heart. It is composed of a thickened endocardium and a thin layer of fibrous connective tissue.
**Why the Correct Answer is Right**
The membranous septum is located between the right ventricle and the apex of the heart. This area is particularly susceptible to defects, such as atrioventricular septal defects (AVSDs) and ventricular septal defects (VSDs). The membranous septum is also the site where the atrioventricular (AV) bundle, a bundle of specialized cardiac conduction fibers, penetrates the septum to reach the ventricles.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the membranous septum is not located between the left and right atria, which is the definition of the atrial septum.
**Option B:** This option is incorrect because the muscular part of the interventricular septum is the thicker, more muscular portion of the septum, whereas the membranous septum is thin and fibrous.
**Option C:** This option is incorrect because the apical region of the heart refers to the lower portion of the ventricles, not the location of the membranous septum.
**Clinical Pearl / High-Yield Fact**
The membranous septum is a critical area for cardiac conduction, and defects in this region can lead to congenital heart defects and arrhythmias. The AV bundle's penetration through the membranous septum is a key point of consideration in cardiac anatomy and electrophysiology.
**Correct Answer: D. The apex of the heart.