medullas

Medullas, the plural form of medulla, refer to the inner or central part of various organs or structures in animals, including humans. The term comes from the Latin medulla meaning “marrow” or “inner part.” In formal scientific writing, the plural is often medullae, though medullas is also used in everyday language.

In anatomy, several well-known medullas illustrate the concept. The medulla oblongata is the lowest part of the brainstem and contains centers that regulate autonomic functions such as respiration and heart rate. The adrenal medulla is the inner portion of the adrenal gland and secretes catecholamines like epinephrine and norepinephrine in response to stress. The renal medulla is the inner region of the kidney, housing structures involved in urine concentration, including the loops of Henle and collecting ducts. In bone, the medullary cavity runs through the diaphysis of long bones and contains bone marrow, where hematopoiesis occurs in youth and fatty marrow becomes more prominent with age. In hair, the medulla is the central core of the hair shaft, consisting of loosely arranged cells and air spaces; not all hair types have a distinct medulla.

Medullas are named for their common role as inner, supportive, or regulatory regions, though their specific functions vary widely by organ. The term’s usage can alternate between indisputable anatomical description and more descriptive naming, with medullae preferred in some scholarly contexts.