Bone Structure

Long bones like the femur contain cortical bone and cancellous bone. Cortical, or compact bone, forms a dense protective outer shell along the shaft, while cancellous, or spongy bone, occupies the rounded ends. Each type has distinct structural features and functions within the skeletal system.

The periosteum is a membrane covering cortical bone that contains connective tissue, capillaries, and nerves. It provides structural support and supplies nutrients and oxygen to the bone tissue. The periosteum also plays a role in bone growth and repair processes.

Osteons are structural units arranged in concentric rings called lamellae. Each osteon contains osteoblasts, cells critical for bone formation and growth, which mature into osteocytes in hollow spaces called lacunae. A Haversian canal runs through the center, carrying blood vessels, lymphatic vessels, and nerve fibers.

The medullary canal is a cavity within the shaft of long bones that stores yellow bone marrow, composed primarily of fat cells. This space is lined by the endosteum, a thin membrane where bone growth, remodeling, and repair occur. The medullary canal provides structural support while minimizing bone weight.

Trabeculae are grouped arrangements forming a honeycomb-like network in cancellous bone. They align along stress points to maximize strength with minimal mass. Between trabecular pores lies red bone marrow containing hematopoietic stem cells that produce red and white blood cells and platelets for circulation.

Red bone marrow occupies the spaces between trabeculae in cancellous bone at the bone ends and contains hematopoietic stem cells that produce blood cells and platelets. Yellow bone marrow fills the medullary canal in the shaft and consists primarily of fat cells. Both types serve distinct metabolic and storage functions.

Osteoblasts are cells critical for bone formation and growth, located within osteons in compact bone. As bone matures, osteoblasts differentiate into osteocytes, which reside in lacunae and maintain bone tissue. Together, these cells sustain bone integrity and support ongoing remodeling processes.