What fills the end of the medullary cavity?

• A. Ligaments
• B. Bone marrow
• C. Cartilage
• D. Synovial fluid

Answer: (B)

The end of the medullary cavity is filled with bone marrow, which serves crucial functions in the body. Bone marrow is a type of connective tissue responsible for the production of blood cells, including red blood cells, white blood cells, and platelets. This soft tissue plays an essential role in hematopoiesis, the process of creating new blood cells.

In adults, the medullary cavity within long bones often contains yellow bone marrow, which is rich in fat cells but can convert to red marrow if the body needs to increase blood cell production, such as during times of significant blood loss or increased demand for red blood cells. In children, the medullary cavities predominantly contain red bone marrow.

The other options do not accurately describe what fills the end of the medullary cavity. Ligaments are fibrous tissues that connect bones to other bones, cartilage is a smooth tissue that covers the ends of bones at joints, and synovial fluid is a viscous liquid found within joint cavities that lubricates and reduces friction between articular cartilage surfaces. None of these substances fulfill the role or occupy the medullary cavity as bone marrow does.