Red vs Yellow Bone Marrow
Bone marrow lies in the spaces between trabeculae of bones and generally consists of several elements, including blood vessels, nerves, mononuclear phagocytes, stem cells, blood cells at different stages of maturation, and fat. They are made up of three main components, namely water, protein and fat. Bone marrow is the fourth biggest organ system of the human body when compared to its body weight. The main role of bone marrow is to provide red blood cells, white blood cells, and platelets, based on the body’s requirements. Apart from that, it also acts as rich fat reserves in the body. In adult humans, active bone marrow is present in the pelvic bones, vertebrae, cranium and mandible, sternum and ribs, and proximal ends of the humerus and femur. According to the composition, there are two types of bone marrow; yellow bone marrow and red bone marrow.
Red Bone Marrow
Red marrow is composed of a delicate, highly vascular, fibrous tissue containing stem cells. These stem cells produce the cellular components including red blood cells, white blood cells, and platelets to meet the requirements for oxygenation, coagulation and immunity in organisms. Red bone marrow also contributes to the destruction of old red blood cells in the body. At birth, only red marrow is present in the body. However, with birth, conversion of the red marrow to yellow marrow begins immediately and it progresses from the peripheral to the central parts of the skeleton. In higher vertebrates such as mammals, blood formation in adults takes place mainly in the red bone marrow. But in lower vertebrates, a number of other organs such as liver and spleen may also produce blood cells.
Yellow Bone Marrow
Yellow bone marrow contains more fat (80%) and is haematopoietically inactive. It is found in the medullary cavity and the hollow interior of the middle portion of long bones. Yellow bone marrow mainly serves as storage sites of fat and may be converted to red bone marrow under certain condition like, severe blood loss or fever. Normally these fat cells are the last resorts for body’s energy requirements and can be used in an event of extreme hunger. But its main function is the conversion into red marrow upon any requirement by the body. This yellow marrow has the ability to convert itself within 1 to 2 hours to take over the role of red marrow.
What is the difference between Red and Yellow Bone Marrow?
• Red bone marrow contains 40% water, 40% fat, and 20% proteins and is highly vascularized. In contrast, yellow bone marrow contains 15% water, 80% fat, and 5% protein and is poorly vascularized.
• In adults, peripheral skeleton contains yellow bone marrow, whereas red bone marrow is confined to the spine, the ribs, proximal femur and humerus, and the skull.
• Red bone marrow is composed of leucocytes and platelet precursors and is haematopoietically active, whereas yellow bone marrow is haematopoietically inactive.
• The amount of red marrow continues to decrease while the amount of yellow marrow continues to increase throughout the life time.
• Unlike yellow bone marrow, only red bone marrow has the ability of producing cellular components like red blood cells, white blood cells and platelets.