The periosteum is a tough, fibrous membrane that surrounds the outer surface of all bones except at the joints where articular cartilage is present. It has two distinct layers:

1. Outer Fibrous Layer:

* Composed of dense irregular connective tissue.

* Contains collagen fibers that are interwoven and run in different directions, providing strength and tensile strength.

* Contains blood vessels and nerves that supply the bone.

* Sharpey's fibers extend from this layer into the bone matrix, anchoring the periosteum to the bone.

2. Inner Cellular Layer (Cambium Layer):

* Thinner than the outer layer.

* Contains osteoprogenitor cells, which are undifferentiated cells that can develop into osteoblasts.

* Responsible for bone growth in thickness and bone repair.

* Contains blood vessels that nourish the bone.

Functions of the Periosteum:

* Protects the bone from injury.

* Provides attachment for tendons and ligaments.

* Nourishes the bone through its blood vessels.

* Contributes to bone growth and repair.

Note: The periosteum plays a crucial role in bone development, growth, and repair. It is essential for maintaining bone health and integrity.