What is the term for the inner, or central portion of an organ?

The term for the inner or central portion of an organ is "medulla." This terminology is often used in various anatomical contexts to refer specifically to the innermost part of certain organs, such as the adrenal medulla, found within the adrenal glands, or the renal medulla in the kidneys. The medulla serves essential functions, often related to the organ's primary role, and encompasses the central region that is distinct from the outer layers. This distinction is critical in understanding the structure and function of organs in the body, where the medulla may contain specific cells, tissues, or fluids that perform vital roles.

The other options reference related but different concepts. The medulla oblongata is a part of the brainstem responsible for autonomic functions such as breathing and heart rate, but it is not a general term for the inner part of an organ. The medullary canal is a hollow space within long bones where bone marrow is stored but does not represent a central portion of an organ in a broader sense. Meninges are protective membranes that cover the brain and spinal cord, which also do not pertain to the internal structure of other organs. Understanding these definitions helps clarify why "medulla" is the correct answer in this context.