| Periosteum | |
|---|---|
 The periosteum covers the outside of bones. | |
 | |
| Details | |
| Location | Outer surface of all bones |
| Identifiers | |
| Latin | periosteum |
| MeSH | D010521 |
| TA98 | A02.0.00.007 |
| TA2 | 384 |
| TH | H2.00.03.7.00018 |
| FMA | 24041 |
| Anatomical terminology | |
The periosteum is a membrane that covers the outer surface of all bones, [1] except at the articular surfaces (i.e. the parts within a joint space) of long bones. [nb 1] Endosteum lines the inner surface of the medullary cavity of all long bones. [2]
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 that develop into osteoblasts. [3] These osteoblasts are responsible for increasing the width of a long bone [nb 2] and the overall size of the other bone types. After a bone fracture, 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. [4]
As opposed to osseous tissue, the periosteum has nociceptors, sensory neurons that make it very sensitive to manipulation. It also provides nourishment by providing the blood supply to the body from the marrow. [5] The periosteum is attached to the bone by strong collagen fibres called "Sharpey's fibres", which extend to the outer circumferential and interstitial lamellae. It also provides an attachment for muscles and tendons.
The periosteum that covers the outer surface of the bones of the skull is known as the pericranium, except when in reference to the layers of the scalp.
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. [6]
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, and enable mobility. Bones come in a variety of shapes and sizes and have complex internal and external structures. They are lightweight yet strong and hard and serve multiple functions.
Cartilage is a resilient and smooth type of connective tissue. It is a semi-transparent and non-porous type of tissue. It is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and the bronchial tubes, and the intervertebral discs. In other taxa, such as chondrichthyans, but also in cyclostomes, it may constitute a much greater proportion of the skeleton. It is not as hard and rigid as bone, but it is much stiffer and much less flexible than muscle. The matrix of cartilage is made up of glycosaminoglycans, proteoglycans, collagen fibers and, sometimes, elastin. It usually grows quicker than bone.
Bone healing, or fracture healing, is a proliferative physiological process in which the body facilitates the repair of a bone fracture.
The synovial membrane is a specialized connective tissue that lines the inner surface of capsules of synovial joints and tendon sheath. It makes direct contact with the fibrous membrane on the outside surface and with the synovial fluid lubricant on the inside surface. In contact with the synovial fluid at the tissue surface are many rounded macrophage-like synovial cells and also type B cells, which are also known as fibroblast-like synoviocytes (FLS). Type A cells maintain the synovial fluid by removing wear-and-tear debris. As for the FLS, they produce hyaluronan, as well as other extracellular components in the synovial fluid.
The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as mice, cats, birds and dogs, but not in whales, or most reptiles.
Osteoblasts are cells with a single nucleus that synthesize bone. However, in the process of bone formation, osteoblasts function in groups of connected cells. Individual cells cannot make bone. A group of organized osteoblasts together with the bone made by a unit of cells is usually called the osteon.
A synovial joint, also known as diarthrosis, joins bones or cartilage with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer boundary of a synovial cavity, and surrounds the bones' articulating surfaces. This joint unites long bones and permits free bone movement and greater mobility. The synovial cavity/joint is filled with synovial fluid. The joint capsule is made up of an outer layer of fibrous membrane, which keeps the bones together structurally, and an inner layer, the synovial membrane, which seals in the synovial fluid.
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 and they are crucial for skeletal mobility. They grow primarily by elongation of the diaphysis, with an epiphysis at each end of the growing bone. The ends of epiphyses are covered with hyaline cartilage. The longitudinal growth of long bones is a result of endochondral ossification at the epiphyseal plate. Bone growth in length is stimulated by the production of growth hormone (GH), a secretion of the anterior lobe of the pituitary gland.
Hyaline cartilage is the glass-like (hyaline) and translucent cartilage found on many joint surfaces. It is also most commonly found in the ribs, nose, larynx, and trachea. Hyaline cartilage is pearl-gray in color, with a firm consistency and has a considerable amount of collagen. It contains no nerves or blood vessels, and its structure is relatively simple.
The perichondrium is a layer of dense irregular connective tissue that surrounds the cartilage of developing bone. It consists of two separate layers: an outer fibrous layer and inner chondrogenic layer. The fibrous layer contains fibroblasts, which produce collagenous fibres. The chondrogenic layer remains undifferentiated and can form chondroblasts. Perichondrium can be found around the perimeter of elastic cartilage and hyaline cartilage.
Chondrocytes are the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans. Although the word chondroblast is commonly used to describe an immature chondrocyte, the term is imprecise, since the progenitor of chondrocytes can differentiate into various cell types, including osteoblasts.
Endochondral ossification is one of the two essential pathways by which bone tissue is produced during fetal development of the mammalian skeletal system, the other pathway being intramembranous ossification. Both endochondral and intramembranous processes initiate from a precursor mesenchymal tissue, but their transformations into bone are different. In intramembranous ossification, mesenchymal tissue is directly converted into bone. On the other hand, endochondral ossification starts with mesenchymal tissue turning into an intermediate cartilage stage, which is eventually substituted by bone.
Intramembranous ossification is one of the two essential processes during fetal development of the gnathostome skeletal system by which rudimentary bone tissue is created. Intramembranous ossification is also an essential process during the natural healing of bone fractures and the rudimentary formation of bones of the head.
Ossification in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in the formation of normal, healthy bone tissue: Intramembranous ossification is the direct laying down of bone into the primitive connective tissue (mesenchyme), while endochondral ossification involves cartilage as a precursor.
Chondroblasts, or perichondrial cells, is the name given to mesenchymal progenitor cells in situ which, from endochondral ossification, will form chondrocytes in the growing cartilage matrix. Another name for them is subchondral cortico-spongious progenitors. They have euchromatic nuclei and stain by basic dyes.
In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint. Each joint capsule has two parts: an outer fibrous layer or membrane, and an inner synovial layer or membrane.
Short bones are designated as those bones that are more or less equal in length, width, and thickness. They include the tarsals in the ankle and the carpals in the wrist. They are one of five types of bones: short, long, flat, irregular and sesamoid. Most short bones are named according to their shape as they exhibit a variety of complex morphological features
Sharpey's fibres are a matrix of connective tissue consisting of bundles of strong predominantly type I collagen fibres connecting periosteum to bone. They are part of the outer fibrous layer of periosteum, entering into the outer circumferential and interstitial lamellae of bone tissue.
The endosteum 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.
Osteochondroprogenitor cells are progenitor cells that arise from mesenchymal stem cells (MSC) in the bone marrow. They have the ability to differentiate into osteoblasts or chondrocytes depending on the signalling molecules they are exposed to, giving rise to either bone or cartilage respectively. Osteochondroprogenitor cells are important for bone formation and maintenance.
