How does compact bone differ from spongy bone?

Compact bone and spongy bone are two types of bone tissue with different structures and functions. Here are the key differences between compact bone and spongy bone:

1. Density: Compact bone is denser and more solid than spongy bone. It has a tightly packed arrangement of osteons (cylindrical structures that contain Haversian canals and concentric lamellae) with minimal spaces between them. This dense structure provides strength and rigidity to the bone, making it resistant to bending and breaking.

2. Structure: Compact bone is organized into Haversian systems. Each Haversian system consists of a central Haversian canal surrounded by concentric layers of bone lamellae. The Haversian canals contain blood vessels and nerves that supply the bone tissue with oxygen and nutrients.

3. Location: Compact bone forms the outer layer of long bones (diaphysis) and the thin layer covering the spongy bone in flat bones. It provides structural support and protection for the bone marrow and other soft tissues.

4. Strength and Rigidity: Compact bone is stronger and more rigid than spongy bone due to its dense structure and tightly packed osteons. It can withstand significant mechanical forces and protect the internal organs from external impacts and injuries.

5. Function: Compact bone primarily provides structural support and protection. It helps maintain the shape and integrity of bones and enables them to bear weight and resist external forces.

Spongy bone, also known as cancellous bone, has a different structure and function compared to compact bone:

1. Density: Spongy bone is less dense and has a more porous structure. It contains numerous small, interconnected spaces and cavities called trabeculae. These spaces are lined with bone-forming cells (osteoblasts) and contain bone marrow.

2. Structure: Spongy bone lacks Haversian systems and is composed of a network of trabeculae. The trabeculae are arranged to form a lattice-like structure that provides strength and flexibility while reducing the overall weight of the bone.

3. Location: Spongy bone is found in the interior of long bones (metaphysis) and forms the majority of the structure of short, flat, and irregular bones. It is also located at the ends of long bones, where it provides cushioning and shock absorption.

4. Strength and Flexibility: Spongy bone is less strong and rigid than compact bone but provides flexibility and energy absorption. It can withstand compressive forces and helps distribute mechanical stresses throughout the bone.

5. Function: Spongy bone has several functions, including providing structural support, protecting bone marrow, facilitating hematopoiesis (blood cell production), and storing minerals such as calcium and phosphorus.

In summary, compact bone is dense, strong, and rigid, forming the outer layer of bones and providing structural support and protection. Spongy bone is less dense, more porous, and flexible, located within bones and involved in hematopoiesis and mineral storage. Both types of bone tissue contribute to the overall strength, function, and health of the skeletal system.