Chondrocyte

A chondrocyte ( composition of Greek χονδρός chondros, cartilage ' and κντος kytos, cell '), and cartilage cell, is a company resulting from chondroblasts and resident of the cartilage cell. Together with the intercellular ( extracellular matrix), the chondrocytes form the main components of the cartilage.

The cartilage cell is the only living part of the cartilage, but does proportionately only about 1% of the cartilage from.

Bone growth

The bone growth ( ossification ) can be divided into interstitial growth ( linear growth ) and appositional growth ( increase in thickness ) are different.

• Interstitial growth

The total cartilage arises (like all connective and supporting tissue) from mesenchyme. The mesenchymal cells differentiate into rapidly proliferating chondroblasts. This form cartilage matrix, which, while it is still soft, it allows that the newly formed chondroblasts can remove from each other and continue to share ( interstitial growth). With the completion of the interstitial cartilage growth and maturation of the matrix resulting from the last cell divisions cartilage cells remain together in so-called isogenic groups and become no longer capable of dividing chondrocytes.

• Appositional growth

On the surface of the cartilage is from the mesenchyme, the connective tissue cartilage skin, perichondrium, educated, differentiate from the innermost layer, cells into chondroblasts that form the matrix and thus provide for a appositional growth.

Construction

Specific properties

If a division and grouping takes place, from which the matrix is composed and has the properties of cartilage formed is dependent on the respective of cartilage or the site of occurrence.

The following are distinguished:

• Hyaline cartilage (such as rib cartilage, articular cartilage, tracheal cartilage, nasal cartilage, larynx: thyroid cartilage, cricoid cartilage )

Hyaline cartilage is the most common of cartilage. At the edge of the hyaline tissue, the chondrocytes have an elliptical shape with the long axis parallel to the cartilage surface - the cave is cartilage by collagen fibers (type II) delineated from the surroundings. Inside the cartilage they are plump with finger- like projections and occur in groups of up to 8/10 cells that arose from the division of a single ( isogenic groups). Several cartilage cavities are also summarized by collagen fibers into functional units, the Chondronen. These are pressure- elastic.

A Chondron is surrounded by a territorial matrix ( Knorpelhof, Zellhof ).

Running between the Chondronen fibrous bands attaching the cell structure on the perichondrium or the bone. Chondronectin promotes adhesion of chondrocytes to collagen.

• Elastic cartilage (such as ear cartilage, larynx: Cartilago epiglottica )

The elastic cartilage is rare and initially resembles the hyaline cartilage. Chondrocytes can occur here individually or in small groups, they are elastic and the cartilage cave is also by collagen fibers (type II) delineated from the surroundings. The chondrones here have one or two, maximum three large chondrocytes. A single chondrocyte is surrounded by pericellular matrix (cartilage capsule).

• Fibrocartilage (eg pubic symphysis, intervertebral disc, articular cartilage: TMJ )

The little elastic chondrocytes of fibrocartilage are organized in small groups, but are mainly individually in the matrix. They are elongated and are bordered by collagen fibers of both type I and type II, where type I predominates by amount. Proteoglycans occur here only in low concentration; a perichondrium is missing.

Non-specific properties

They are embedded in the extracellular matrix formed by them and are there in small caves, known as lacunae. In addition, they show only a low metabolic activity ( bradytrophic tissue).

They have as their high expression synthesis performance over a well-trained Golgi apparatus and abundant rough endoplasmic reticulum. The structure of the cell is maintained by the cytoplasm network-like pull-through Vimentinfilamente.

The supply of the chondrocytes by diffusion from the capillaries of the perichondrium, the cartilage ( which has no perichondrium as an exception ) by the synovial fluid. Cartilage has no lymphatic vessels and nerves.

Chondrocytes can be isolated and cultured. Appropriate cultures are fixed on support material used for cartilage regeneration.

Function

Chondrocytes are among the fixed connective tissue cells ( fibrocytes, reticular cells, osteocytes, ...) and meet the basic function of secretion and mechanical stability. Do not communicate with other cells and are primarily responsible for the formation of the extracellular matrix of cartilage.

Chondrocytes in the synthesis of protein, RNA and DNA, as well as cell proliferation and to stimulate the uptake of amino acids.

The activity of the chondrocytes is increased by thyroxine and testosterone inhibited by cortisone, hydrocortisone ( cortisol) and estradiol.

Diseases

The best known chondrocyte disease is osteoarthritis. This leads to non- inflammatory degenerative joint damage and it can be very severe pain occur. In this disease it comes to the degradation of the extracellular matrix proteins of cartilage by proteases; the exact causes are still largely unknown.

The most successful method of treatment is the transplantation of chondrocytes. With the help of arthroscopy, the doctor removes chondrocytes from the Edged the defect. The cells are then propagated in the laboratory ( about three to four weeks), and then reused. After a few weeks when the chondrocytes have already integrated, the patient can move again without limitations. The advantage of this method is that the risk of rejection is low, because the implanted cartilage cells are taken from the body's cells from the patient.

There are other methods for the treatment of cartilage defects, the so-called cell-free methods. In these only one membrane with hyaluronic acid is used in the defect instead of cells. Some clinical studies have shown that the hyaluronic acid will help to regenerate cartilage tissue by pulling the chondrocytes to the defect site. This method is more cost effective than the cell transplantation to patients.

Achondroplasia (also chondrodysplasia ) is a common mutation which affects the growth of the skeletal system. Consequence is a Dysproportionierter dwarfism with relatively long trunk and rhizomelic shortening ( shortening medium extremities regions) of verplumpten limbs, by a predominantly quantitative disturbance of endochondral bone growth. The disease is autosomal dominant, but occurs in about 80% of cases due to new mutations (especially in the aging of the father). As a result of mutation of the cartilage cell receptor for fibroblast growth factor ( FGFR -3) is not sufficiently expressed, resulting in a disturbance of the chondrocyte proliferation and differentiation in the growth plate, which in turn causes defects in endochondral ossification result.