Septum - Definition

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A septum is an anatomical term signifying a membrane that separates two cavities inside an organ. The interventricular septum is therefore the membrane that separates the right ventricle from the left, and the interatrial septum separates the two atriums of the heart. Other types include the septum lucidum, or pellucidum, which separates the ventricles of each brain hemisphere, and the nasal septum separating the two nostrils. When an abnormal orifice is found in certain septums, the two cavities are in contact. This can particularly be the case in certain cardiac malformations, such as ventricular septal defect (VSD) affecting the septum between the ventricles, and atrial septal defect (ASD) for the atrial septum.