The periosteum is a

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...

that covers the outer surface of all

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

s, except at the articular surfaces (i.e. the parts within a joint space) of long bones. (At the joints of long bones the bone's outer surface is lined with "articular cartilage", a type of hyaline cartilage.)

Endosteum The endosteum (: endostea) is a thin vascular membrane of connective tissue that lines the inner surface of the bony tissue that forms the medullary cavity of long bones. This endosteal surface is usually resorbed during long periods of malnutr ...

lines the inner surface of the medullary cavity of all

long bone The long bones are those that are longer than they are wide. They are one of five types of bones: long, short, flat, irregular and sesamoid. Long bones, especially the femur and tibia, are subjected to most of the load during daily activities ...

Structure

The periosteum consists of an outer fibrous layer, and an inner ''cambium layer'' (or osteogenic layer). The fibrous layer is of dense irregular connective tissue, containing fibroblasts, while the cambium layer is highly cellular containing

progenitor cells A progenitor cell is a Cell (biology), biological cell that can Cellular differentiation, differentiate into a specific cell type. Stem cell, Stem cells and progenitor cells have this ability in common. However, stem cells are less specified than ...

that develop into

osteoblast Osteoblasts (from the Greek combining forms for " bone", ὀστέο-, ''osteo-'' and βλαστάνω, ''blastanō'' "germinate") are cells with a single nucleus that synthesize bone. However, in the process of bone formation, osteoblasts fu ...

s. These osteoblasts are responsible for increasing the width of a

(the length of a long bone is controlled by the

epiphyseal plate The epiphyseal plate, epiphysial plate, physis, or growth plate is a hyaline cartilage plate in the metaphysis at each end of a long bone. It is the part of a long bone where new bone growth takes place; that is, the whole bone is alive, with ma ...

) and the overall size of the other bone types. After a

bone fracture A bone fracture (abbreviated FRX or Fx, Fx, or #) is a medical condition in which there is a partial or complete break in the continuity of any bone in the body. In more severe cases, the bone may be broken into several fragments, known as a ''c ...

, the progenitor cells develop into osteoblasts and chondroblasts, which are essential to the healing process. The outer fibrous layer and the inner cambium layer are differentiated under electron micrography. As opposed to osseous tissue, the periosteum has

nociceptor A nociceptor (; ) is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sensation of pain to direct attention to the body part, ...

sensory neuron Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded receptor potentials. This process is called sensory transduc ...

s that make it very sensitive to manipulation. It also provides nourishment by providing the blood supply to the body from the marrow. The periosteum is attached to the bone by strong collagen fibres called " Sharpey's fibres", which extend to the outer circumferential and interstitial

lamellae Lamella (: lamellae) means a small plate or flake in Latin, and in English may refer to: Biology * Lamella (mycology), a papery rib beneath a mushroom cap * Lamella (botany) * Lamella (surface anatomy), a plate-like structure in an animal * Lame ...

. It also provides an attachment for muscles and tendons. The periosteum that covers the outer surface of the bones of the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

is known as the ''pericranium'', except when in reference to the layers of the scalp.

Etymology

The word periosteum is derived from the Greek ''peri-'', meaning "surrounding", and ''-osteon'', meaning "bone". The ''peri'' refers to the fact that the periosteum is the outermost layer of long bones, surrounding other inner layers.

Structure

Etymology

Additional images

See also

References

Further reading

External links