Medullae

Medullae is the plural form of medulla, a term used in anatomy to denote the inner part or core of an organ, as opposed to its outer layer or cortex. The word comes from Latin medulla, meaning marrow or innermost part. In physiology and anatomy, medullae are identified in several organs where the inner region has distinct structure and function.

Medulla oblongata is a well-known example in the brainstem. It lies above the spinal cord and contains nuclei that regulate essential autonomic functions, including breathing, heart rate, and blood pressure, as well as reflex centers for coughing, swallowing, and vomiting. The medulla is continuous with the spinal cord and forms part of the myelencephalon in embryology.

Renal medulla refers to the inner portion of the kidney, surrounding the renal papillae and renal pelvis. It contains the renal pyramids, where urine concentration and water reabsorption are aided by a hyperosmotic medullary interstitium and the vasa recta.

Adrenal medulla is the inner region of the adrenal gland, composed of chromaffin cells that secrete catecholamines (epinephrine and norepinephrine) in response to sympathetic stimulation. This part of the gland functions as a neuroendocrine organ, linking the nervous system to hormonal release during stress.

In bones, the term is encountered in reference to the medullary cavity, the central marrow-containing space within the diaphyses of long bones. It houses red and/or yellow bone marrow, involved in hematopoiesis and fat storage.

Across contexts, medullae denote inner, often functionally specialized regions that differ from outer cortical or surrounding tissue.