What is the thin outer layer of connective tissue covering bones?

What is the thin outer layer of connective tissue covering bones?

• A. Periosteum
• B. Endosteum
• C. Osteoid
• D. Epiphysis

Answer: (A)

The thin outer layer that covers bones is the periosteum. This dense connective tissue wraps the bone surface except at joints where articular cartilage sits. It has two parts: a tough outer fibrous layer that anchors tendons and ligaments, and an inner cambial (osteogenic) layer rich in cells that can become bone-forming osteoblasts. This inner layer is key for growth in thickness (appositional growth) and for bone repair after injury. The periosteum also contains tiny blood vessels that penetrate into the bone through channels, helping nourish bone tissue. In contrast, endosteum lines the inner surfaces of bone, including the medullary cavity; osteoid is the unmineralized bone matrix produced by osteoblasts before it hardens, and epiphysis refers to the end portion of a long bone, not a covering layer.

The thin outer layer that covers bones is the periosteum. This dense connective tissue wraps the bone surface except at joints where articular cartilage sits. It has two parts: a tough outer fibrous layer that anchors tendons and ligaments, and an inner cambial (osteogenic) layer rich in cells that can become bone-forming osteoblasts. This inner layer is key for growth in thickness (appositional growth) and for bone repair after injury. The periosteum also contains tiny blood vessels that penetrate into the bone through channels, helping nourish bone tissue. In contrast, endosteum lines the inner surfaces of bone, including the medullary cavity; osteoid is the unmineralized bone matrix produced by osteoblasts before it hardens, and epiphysis refers to the end portion of a long bone, not a covering layer.