Bone marrow is a soft, spongy tissue found within the cavities of bones. This tissue plays a central role in various bodily functions, including the production of blood cells. Yellow marrow represents a specific type of bone marrow, distinguished by its predominantly fatty composition. It is typically located in the medullary cavity, which is the central hollow space within long bones.
Key Components of Yellow Marrow
Yellow marrow is primarily composed of adipocytes, specialized fat cells that store fat as triglycerides. Beyond adipocytes, yellow marrow also contains mesenchymal stem cells (MSCs). These multipotent stem cells possess the ability to differentiate into various cell types, including cartilage, bone, and fat cells. Additionally, yellow marrow contains a network of blood vessels that supply nutrients and remove waste products. While predominantly fatty, yellow marrow does contain a minimal presence of hematopoietic cells, which are precursors to blood cells.
Primary Functions
The main function of yellow marrow is to serve as an energy reserve for the body. Its high concentration of adipocytes stores lipids, which can be metabolized for energy during periods of low calorie intake or high energy demand. Yellow marrow also has a secondary, emergency role in blood cell formation. In situations of significant blood loss or other extreme conditions, yellow marrow can convert back to red marrow. This conversion allows it to contribute to the production of new blood cells, adapting to the body’s increased hematopoietic needs.
How It Differs from Red Marrow
Yellow marrow contrasts significantly with red marrow in composition and function. Red bone marrow is primarily made up of hematopoietic tissue, which is responsible for the active production of all types of blood cells, including red blood cells, white blood cells, and platelets. In contrast, yellow marrow is predominantly adipose tissue, with a much lower capacity for blood cell production.
Red marrow is abundant in infants and young children, and in adults, it is mainly found in flat bones such as the sternum, ribs, and pelvis, as well as the ends of long bones. Yellow marrow gradually replaces red marrow as individuals age and is primarily located in the shafts of long bones in adults. Red marrow is highly vascularized due to its active metabolic role, while yellow marrow has a poorer vascular supply.