Cartilage

Cartilage tissue is a solid both compressive and bending elastic support avascular tissue, which also forms in the development of the system of the bony skeleton. It can be cut, and is like the other binding and Stützgewebsarten of cells and the surrounding intercellular substance, which consists of shaped and unshaped components.

Construction

As cartilage cells occur chondroblasts, chondrocytes, and chondroclasts. As chondroblasts ( " Knorpelbildner " ) are referred to the progenitors of chondrocytes. They are derived from mesenchymal stem cells and provide the active form of the cartilage cell, since they are able to synthesize all components of the cartilage matrix. Once you have set this synthetic function, they differentiate into chondrocytes, the actual cartilage cells. The chondrocytes are smaller than chondroblasts, spherically shaped, have a rounded nucleus and contain a lot of water, fat, and glycogen. Their number, location, and density is specific to each of cartilage. Chondrocytes can still share in the immature state, which can lead to the characteristic appearance of " isogenic groups ". They arise when the dividing cells are already surrounded by cartilage matrix and not as soft can apart. The isogenic groups chondrocyte complexes in which each complex is evolved from a single chondrocytes. The individual complexes appear to be surrounded by a cartilaginous capsule and cartilage in a cavity ( lacuna ) to lie, however, occurs only when the fixation and reflects the originally occupied by the chondrocytes place. This is followed by a Knorpelhof follows, the clear dyeable is by its basophilic property ( = territory ). The isogenic groups are usually arranged in a columnar manner. The isogenic group and their territory is perceived as " Chondron " together. Once the chondrocytes are differentiated, they lose their ability to divide. As chondroclasts is called again phagocytes, who specializes in cartilage. They are much larger and formed by the merger of several monocytes and thus usually multinucleated giant cells. You play the main role in the degradation of early cartilage-bone model ( endochondral ossification ) for later bone or, in this context, in the healing of fractures.

The intercellular substance consists of formed and unformed components. The molded components you count the fiber content of collagenous and elastic fibers, which is different in each case for the three types of cartilage. Main components of the intercellular substance are unformed water (approx. 70%), proteoglycans (mainly aggrecan ) and hyaluronic acid. Proteoglycans are polyanionic and therefore attract sodium cations, which in turn cause the inflow of water.

Cartilage is devoid of blood vessels and nerves in the adult. The nutrition of the cells must therefore take place by diffusion. This is done either through a connective tissue, a protective shell ( perichondrium ) which the cartilage ( except for articular cartilage and fibrocartilage ) covering a cartilage skin, or in the articular cartilage of the synovial fluid of the joint space.

Subdivision

The intercellular substance determined by the nature of their composition and fiber content of the subdivision of the cartilage in

• Hyaline,
• Elastic and
• Fibrocartilage.

Hyaline cartilage

Hyaline cartilage has a high compressive elasticity, so you can find him wherever mainly compressive loads occur (such as in most joint surfaces ). The chondrocytes are here singly or few together. They differ from the transparent intercellular ( interstitial substance, extracellular matrix ), in which they (mainly type II and type IX and XI) are even with the collagen fibers. Since the fibers have the same refractive index as the intercellular substance of hyaline cartilage in a microscope usually appears as a uniform mass. The collagen fibers are here so hidden ( masked). If the aging process but decreases the intercellular substance, some of the fibers are visible again. They are called asbestos fibers. The demarcation of fibrocartilage must then be about the shape and arrangement of the chondrocytes.

In hyaline cartilage, there are early calcification. His vessel Poverty increases, along with the often high mechanical stress, degenerative processes. In articular cartilage lacks the surrounding perichondrium and thus also the mesenchymal cells that can differentiate into chondroblasts, leaving little regeneration can take place. ( The nutrition of the cartilage via the synovial fluid )

Hyaline cartilage is a joint, ribs, nose cartilage, is present in the cartilage rings of the trachea, in the epiphyses and in the cartilaginous skeleton preformed. In the hematoxylin- eosin staining of hyaline cartilage has a milky- bluish color.

Elastic cartilage

Elastic cartilage is the largest cartilage cell. He is basically constructed as hyaline cartilage, but it is traversed in the extracellular matrix with addition of abundant elastic fibers that provide its characteristic yellowish color and consist of fibrillin, which is associated with amorphous elastin. Through the interaction of these components of the elastic cartilage is very pressure and bending elastic. Furthermore, it has no tendency to calcification.

Elastic cartilage is found in the auricle, the external auditory canal, the Eustachian tube, the epiglottis, the cartilage corniculata and small bronchi.

Fibrocartilage

Fibrocartilage is also known as fibrocartilage and has fewer cells than the first-mentioned two types, but many collagen, including Type I In the case it is not perichondrium occurs.

Fibrocartilage comes anywhere before where shear forces, such as in the fibrous ring ( annulus fibrosus ) of the intervertebral discs ( intervertebral discs ), the pubic symphysis and other symphysis, the articular lips ( acetabular labrum, glenoid labrum ) and the menisci.

Formation of cartilage tissue and its growth

In the formation of cartilage, which is also called chondrogenesis process, first zoom from the mesenchyme located close together chondroblasts. This eventually take their function and but there is a matrix from which is rich in Chondromukoprotein. At the same time tropocollagen is produced and deposited in the extracellular space as collagen. By producing these substances, the chondroblasts move ever further apart. At the same time they differentiate into chondrocytes, which may either be individually or in the matrix multiply by division and then occur as isogenic groups. The growth of the cartilage happens thus primarily by the increase in size of the intercellular substance, which is also called interstitial growth and occurs only in the context of cartilage formation. For the further growth and to a limited extent also in the regeneration of cartilage tissue, the addition growth ( appositional growth) is primarily responsible. Here it come from the formation of cartilage tissue from the surface, ie, by the perichondrium. In its inner layer sit chondroblasts, which can synthesize the matrix and divide mitotically yet.

Diseases and injuries of the cartilage

In cartilage nutrition disorders there is a decay of the inter- chondrocyte matrix. One speaks of a unmasking of cartilage. The surface is rough, this limits the function of the affected joint, osteoarthritis develops. Very often, the cartilage disease of the kneecap ( Chondromalacia patellae ), the relatively early, even in children, can lead to difficulties. In the chest, it may, on the border between bony and cartilaginous rib, come to bizarre calcifications, it is called chondrocalcinosis.

Polychondritis (from " poly ": Greek = a lot, " chondr ": Greek chondros = cartilage and " -itis " suffix for inflammatory diseases, in English usage relapsing polychondritis ): The relapsing polychondritis is an extremely rare disorder characterized by mostly relapsing -like, but sometimes permanently persistent inflammation of the cartilage. May be involved all the structures or organs that are composed of cartilage or in which cartilaginous components are present.

The chondrosis is an expression of degenerative changes of the cartilage. In intervertebral discs, this results in a narrowing of the intervertebral spacing of one or more vertebral segments in comparison to the rest, without Deckplattensklerosierung of the vertebral bodies. The height of the intervertebral spaces decreases. In block vertebrae, the intervertebral space is canceled. The cause congenital or acquired disorders come ( degenerative, inflammatory, surgical) in question. Chondrosen with involvement of the underlying bone is called osteochondrosis. This will solve cartilage from the cartilage Association, this is called osteochondritis dissecans.

Cartilage structures can also be damaged. Such damage can be caused by a variety of causes, from an unfortunate fall or a sports injury ( traumatic), previous knee injury ( post- traumatic) or wear arise with time. The immobilization ( immobilization) for long periods can also result in cartilage damage.

Damage to the cartilage caused by overloading, such as jogging, is often discussed, but can not be detected so far. Rather Scientific studies show a good adaptation (adaptability ) of the human cartilage in chronic exposure, unless a Vorschaden is still available. For long- distance runners, a recovery of the cartilage structure shows a few minutes after completion of the physical activity.

In recent decades, surgical procedures for cartilage repair have been established. The aim of joint cartilage repair treatment to restore the surface of the hyaline articular cartilage.