Medullary

Medullary is an anatomical term used to describe the inner part of an organ or its marrow. The word derives from Latin medulla, meaning marrow, pith, or innermost part.

In human anatomy the term commonly denotes several regions: The medulla oblongata is the lower portion of the brainstem that contains autonomic centers regulating heart rate and respiration and serves as a relay between the brain and spinal cord. The renal medulla is the inner portion of the kidney, surrounding the renal pyramids and collecting ducts, and works with the cortex in urine formation and concentration. The medullary cavity is the central hollow space within long bones, lined by the endosteum and filled with bone marrow; red marrow produces blood cells in early life, while yellow marrow, rich in fat, predominates in adulthood. Medullary bone is a specialized tissue found in female birds that forms rapidly to provide a calcium reservoir for eggshell production.

In broader usage, medullary describes inner areas of other organs with a distinct inner region, including certain glands or lymphoid tissue.