Connective tissue

The collective term tissue refers to different tissue types. They have in common above all, that they are rich in intermediate cell mass ( intercellular ) and covering surfaces compared to tissues ( epithelia ) consist of relatively few cells. Connective tissue in the body has a variety of tasks that go far beyond a mere " binding " function: How to Hold connective tissue organ forms upright, is water storage and protective cover and plays an important role as a place of defense responses against pathogens.

The various tissues that are grouped under the term connective tissue, appear very different both with the naked eye (macroscopic ), and under the microscope ( histology ). In the literature there is no consensus as to which tissues are precisely allocated to the connective tissue. Consensus is generally about representing that in the strict sense loose, tight, reticular, gelatinous connective tissue and squamous types of connective tissue; Cartilage and bone tissue in the bit count as a support a broader sense also for connective tissue. Most also the adipose tissue is considered as a special form of connective tissue, sometimes the blood and the different types of muscle tissue.

All these Bindegewebstypen develop from the mesenchyme, which is called together with the gelatinous connective tissue as " embryonic connective tissue ."

• 3.1 Loose connective tissue 3.1.1 adipose tissue

• 3.6.1 cartilage
• 3.6.2 bone tissue

• 4.1 Acquired diseases
• 4.2 Hereditary Diseases

Development

In the embryonic development of the human develop from the mesoderm 34 to 35 somites. From the ventral and medial part of the sclerotome, which evolve to develop mesenchyme. Part in the formation of the mesenchyme but also has the neuroectoderm. The mesenchyme consists of multipotent stem cells whose numerous extensions of one another with Nexus (also gap junctions ) are a form of cell -cell contacts are connected. The cells are distribution joyful and amoeboid movement. From the mesenchyme each type of connective tissue develop in the course of further embryonic development.

Common features

The connective tissue consists of fixed ( local ) and mobile cells, as well as a rich intercellular substance, and extracellular matrix, which consists of a basic substance that can be incorporated into the collagenous, reticular and elastic fibers. This consisting of fibrillar proteins fibers - the main part are the collagens - form a dense meshwork, which is filled by highly swelling proteoglycans. The function of the former is to resist tensile forces, while the latter act compression damping. The interaction of the fiber mesh and Proteoglykanpuffer maintains the shape of organs. The intercellular substance, which is also used for storage of extracellular growth factors secreted by the fibroblasts, which are the precursor of the movable more stabilizing fibrocytes.

Connective tissue fibers

→ See also: collagen

The tensile strength but hardly extensible collagen fibers are 1-10 microns, rarely to 20 microns thick and have a cross-striation in the electron microscope, which is due to the overlapping arrangement of the collagen molecules in the synthesis of collagen fibrils about. Important for the stabilization of the fibrils hydroxylation of proline residues, vitamin C -dependent. In vitamin C deficiency therefore leads to a disorder of collagen synthesis, which results in the clinical picture of scurvy. In the tissues, there are a variety of different types of collagen, the most important are the collagen types I- IV:

Branched networks of type III collagen are called reticular fibers. With a diameter of 20-40 nm, they are significantly thinner than collagen fibers. They occur particularly in reticular connective tissue, but also in other tissues, for example in the space of Disse of the liver.

Elastic fibers are composed of the glycoprotein fibrillin and elastin protein embedded in it. They can be - in any direction - expand to many times their original length, due to the convoluted arrangement of elastin after they return back to their original length. The extensibility, however, is limited by the same tissue occurring collagens, which are significantly less elastic. Elastic fibers can be visualized by light microscopy with special Elastica staining. Elastic fibers are found in almost every type of connective tissue, but especially in lung tissue elastic arteries and elastic bands ( ligamentum flava ).

Mobile cells

Between the fibers and the fixed cells also amoeboid moving, free cells occur. These are largely in the service of the immune system. The cells derived from the bone marrow and have migrated from the blood into the connective tissue. In part, it is also typical blood cells (eg, granulocytes). On free cells are in connective tissue

• Granulocytes
• Lymphocytes
• Macrophages
• Plasma cells and
• Mast cells before.

In inflammatory processes, especially the granulocytes migrate into the connective tissue and are increasingly a correspondingly be seen in the specimen in greater numbers.

Special Bindegewebstypen

Loose connective tissue

Loose connective tissue is found as "filling" of open spaces in the body and forms the stroma, which is the connective tissue part of many organs. In the loose connective tissue outweigh the ground substance. In these collagen fibers and thin bundles of elastic fibers are embedded. Functionally, it serves not only as a filler, but also as a water reservoir, the displacement layer and as a lounge for numerous free cells.

Adipose tissue

→ Main article: Adipose tissue

Unlike other fatty tissue hardly Bindegewebstypen the intercellular substance is present. The specialized cells called adipocytes and store in their cytoplasm large amounts of fat ( triacylglycerols ). A distinction univakuoläres (white ) adipose tissue and plurivakuoläres (brown ) adipose tissue, the proportion of white adipose tissue far outweighs and may have structural or memory function.

Tight connective tissue

The tight connective tissue is characterized by an abundance of collagen fibers - significantly more than in the loose connective tissue. In contrast, the amount is greatly reduced at ground substance, also there are much fewer cells. It can be divided into the tight grid-like and the tight parallelfasrige connective tissue in the direction of the collagen fibers.

In tight braid -like connective tissue, the collagen fiber bundles intersect frequently, thus tensile strength in different directions is achieved. This type accordingly forms such as organ capsules, the sclera of the eye and the skin and the dura mater.

The tight parallelfasrige connective tissue forms tendons and ligaments. The collagen fibers are arranged in parallel in the pulling direction. The fibrocytes of the tendon tissue are referred to as Tendinozyten or " vane ". They have flat and two-dimensional, three-dimensional wing-like spurs, between which and on which align the collagen fiber bundles along to.

Reticular connective tissue

The reticular connective tissue is found only in the secondary lymphoid organs ( lymph nodes, spleen, and mucosa - associated lymphoid tissue) and in the bone marrow. Task of this tissue is to provide free cells, especially cells of the immune system, a lounge available.

The fibroblasts of the reticular connective tissue are called fibroblastic reticular cells. They form a vast three-dimensional network of reticular fibers. But these are always surrounded by foothills of the reticular cells, and have no contact with the intercellular space. This is in contrast to other types of tissue, in which, although also occur reticular fibers, but which are output from the local fibrocytes into the intercellular space.

Galler term ( collagenous ) connective tissue

The gelatinous connective tissue is typical of the umbilical cord (also called Wharton 's jelly ), but also occurs in the pulp of young teeth. The cells are flat, branched fibrocytes which together form a wide-meshed network. The extracellular matrix contains fine collagenous and reticular fibers and hyaluronic acid. This can bind a large amount of water in itself, so that the gelatinous consistency comes about, which awarded this connective tissue type his name. The strong trapping of water ensures the main task of this tissue to protect the vessels of the umbilical cord before pinch-off, without the umbilical cord is limited in its flexibility.

Squamous connective tissue

The squamous connective tissue is found in the bark of the ovary. The fibrocytes are close together and are often arranged " fischzugartig ". In the sparse intercellular few reticular fibers are present. From fibrocytes of the connective tissue squamous occur during the maturation of oocytes in the ovary, the theca cells, which form the theca follicular.

In some cases, the lining of the uterus (endometrium ) is regarded as a form of squamous connective tissue.

Supporting tissue

Supporting tissue can in turn be divided into different types of tissue:

• Cartilage tissue (eg supporting skeleton of cartilaginous fishes, pinna, juvenile epiphyses, articular surfaces, menisci ).
• Bone tissue

Cartilage tissue

→ Main article: cartilage

Cartilage tissue is a specialized form of connective tissue: It is firm but pressure elastic, malleable and can be cut. Cartilage -forming cells called chondrocytes which form cartilage matrix. This contains mainly type II collagen, but also rarer types of collagen. Aggrecan and continue to provide, inter alia, hyaluronic acid bound thereto a water storage, which is responsible for the consistency of the cartilage. Again, the consistency of the function plays an important role: Cartilage has shaping tasks (eg in the external ear ), keeps the airway open ( cartilage rings of the trachea ), and will take the form of joint cartilage for reduced friction. In addition, most of the bones are first created as a cartilage model in the development and ossified later. Cartilage has no power by nerves and blood vessels on (exception: Fetal cartilage), but is nourished by diffusion from the perichondrium ( perichondrium ).

It differs in detail three or four different types of cartilage:

• Hyaline cartilage
• Fetal cartilage ( can be as hyaline cartilage with blood vessels look )
• Elastic cartilage
• Fibrocartilage

Bone tissue

→ Main article: bone

Bone tissue is composed of a calcified matrix ( intercellular substance ), which is formed by osteoblasts and osteoclasts degrade. Also suitable osteoprogenitor before ( precursor of osteoblasts) and osteocytes. Bone matrix consists of about 1/ 3 of organic substance (in particular, type I collagen ), 2 /3 of the matrix are made of hydroxyapatite, a crystalline calcium salt, which is responsible for the hardness of the bone tissue. It differs from the lamellar bone of the woven bone, in which the collagen fibers are arranged lamellar form around a central canals ( Haversian channels).

Diseases

Many immune reactions and healing process of injuries play, at least partially, in the connective tissue. In addition, there are a number of diseases, which relate specifically to the connective tissue.

Acquired diseases

As already mentioned, it comes with a pronounced vitamin C deficiency to the clinical picture of scurvy.

For degradation of collagen occurs in periods of hunger, who are immobilized or zero gravity, as well as in rheumatoid arthritis and prolonged, high-dose administration of cortisone.

When fibrosis and sclerosis, there is an increased collagen ( type I ) synthesis, which leads to functional limitations or loss of the affected tissue.

Benign and malignant tumors also occur in the connective tissue. Benign tumors are here, for example, the fibroma or lipoma, malignant tumors are summarized under the term sarcomas. Specifically, these are, for example, fibrosarcoma, liposarcoma or the rhabdomyosarcoma.

Hereditary diseases

In the so-called brittle bone disease ( osteogenesis imperfecta ) is a gene mutation before, which leads to impaired formation of a collagen subunit, or completely prevented this. The result is a greatly increased tendency to fracture of bone.

The group of diseases described with the Ehlers -Danlos syndrome are also hereditary diseases. By an enzyme defect collagen fibrils can not be assembled correctly, which results in an injury angle and increased elasticity of the skin as well as a hyperextension of joints.

Marfan syndrome is a more or less pronounced instability of all connective tissues of the body.