List of abbreviations

Vocabulary of micros- copic anatomy specialist terms explained in English + German

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!

dieser Seite Editor: Dr. med. H. Jastrow

Conditions of use

collagen fibrils type1 tendon (rat)	collagen fibrils with 67 nm striping (rat)	collagen fibrils ovary stroma (rat)	collagen fibrils type 1 and 3 (rat)	type 1 + 3 collagen fibrils of sub- cutaneous connective tissue (rat)	human collagen fibres formed of type 1 + 3 collagen fibrils

collagen fibrils type 1 + elastic fibres (monkey)	bundle of type 1 collagen fibrils of monkey cornea	collagen fibres, mast cell Ligamentum ovarii (rat)	human collagen fibrils type 1

human collagen fibrils type 1, cross-section	detail thereof	human collagen fibrils	collagen and elastic fibres from liver stroma (rat)	collagen fibres next to a large elastic fibre in human subcutis

Collagen fibres (Terminologia histologica: Fibrae collageni) are stable fibres of the extracellular connective tissue consisting of collagen fibrils (Terminologia histologica: Fibrilla collageni). They may associate to each other forming larger collagen fascicles (Terminologia histologica: Fasciculi collageni). Collagen fibres are hardly fractioning light when regarded with a light microscope, however, with a polarisation microscope a compound fraction is apparent. The unbranched fibres are very resistant to traction and about 5% stretchable. They are soluble in cooking water whereby they become glue. Their Latin name derives from this fact (Kolla = glue). They swell up when acids are added, are soluble in leach and are rapidly digested by pepsin. Applying light microscopic staining procedures the have the following colours. red (haematoxylin-eosin, see image 1; "van Gieson"); blue (Azan), see image 2; green ("Masson-Goldner"), see image 3; yellow to gray-green (iron-haematoxylin). In the electron microscope longitudinally cut collagen fibrils are some micrometers long and show characteristic bands (see below). In cross-sections the fibrils have round profiles with diameters of 50 to maximal 200 nm.
The table shows 14 different types of collagen (for further ones cf. special literature):

type	chains	composition of triple helix	triple helix length, structural details	occurrence, specialities
collagens with long fibrils with 67 nm periodicity of bands fibrils may consist of different types of collagens, e.g. type I + III + V or type II + XI
I	a1(I); a2(I)	[a1(I)]2[a2(I)]	300 nm; diameter of fibrils 50 to maximal 200 nm chains 1.050 amino acids long	subcutis, tendon, bones, dentin, Bowman's membrane, sclera & cornea of the eye in nearly all kinds of connective tissues but not in cartilage
If	a1(I); a2(I)	[a1(I)]3	300 nm	foetal form
II	a1(II)	[a1(II)]3	300 nm; diameter of only ~30 nm; covered by a viscous matrix of proteoglycans	hyaline- and fibrous cartilage, vitreal body of the eye, chorda dorsalis, tectorial membrane of the inner ear
III	a1(III)	[a1(III)]3	300 nm; diameter of ~40 nm; usually together with type I	in type I fibrils, form reticular fibres, loose connective tissue, corneal stroma, subcutis, muscles, walls of blood vessels
V	a1(V); a2(V); a3(V)	[a1(V)]3, [a1(V)]2[a2(V)] und [a1(V)][a2(V)][a3(V)]	390 nm; N-terminal globular domain usually together with type I	in type I fibrils, foetal tissues and membranes; interstitial tissue, bones, Bowman's membrane, tectorial membrane, around smooth muscle cells, corium, placenta
XI	a1(XI); a2(XI); a3(XI)	[a1(XI)][a2(XI)][a3(XI)]	300 nm; often together with type II, thin fibres	in type I fibrils, hyaline cartilage, tectorial membrane
fibril associated collagens with a triple helix which is disrupted by globular domains
IX	a1(IX); a2(IX); a3(IX)	[a1(IX)][a2(IX)][a3(IX)]	200 nm; N-terminal globular domain; covalently bound to the surface of type II fibrils	cartilage, vitreous body, tectorial membrane, binds glycosaminoglycans
XII	a1(XII)	[a1(XII)]3	large N-terminal globular domain; cross-like molecule, bound to the surface of collagen type I	embryonal tendons, subcutis, corneal stroma
XIV	a1(XIV)	[a1(XIV)]3	large N-terminal globular domain; cross-like molecule	fetal subcutis, tendons
fibril associated collagens which form string of beat-like filaments
VI	a1(VI); a2(VI); a3(VI)	[a1(VI)][a2(VI)][a3(VI)]	150 nm; N- and C-terminal globular domain; bands with periodicity of 150 nm, collagen type I associated	in most interstitial tissues, at the connection of muscles to tendons, pericellular matrix of cartilage, in the walls of blood vessels, in the endomysium
collagens that show leaf-like association
IV	a1 to 5(IV)	[a1(IV)]2[a2(V)] and other forms	60 nm long triple helix region and 40 nm long globular domains; formation of tetramers	all basement membranes, formation of a two-dimensional interconnected network, is secreted by cells of endothelium, epithelium, glia cells and fat cells
VIII	a1(VIII); a2(VIII)	?	regular triangular gutter	subendothelial tissue, Descemet's membrane of the cornea of the eye
X	a1(X)	[a1(X)]3	150 nm; C-terminal globular domain	secreted by hypertrophic chondrocytes thus present in the epiphyseal plate during growth of bones
collagens which are anchoring fibrils
VII	a1(VII)	[a1(VII)]3	450 nm; dimer; globular domain on both ends	forms the short anchoring fibrils which connect the basal lamina of epithelia to the deeper loose connective tissue whenever a basement membrane is present
collagens of which only the DNA was shown
XIII	a1(XIII)	?	?	only the c-DNA of this protein was shown in endothelial cells

The most common types of collagen are I, II and III. When longitudinally cut the collagen types I, II, III, V and XI show a characteristic periodicity of 67 nm, which is due to a regular shift of the single molecules in the fibril. Biochemically the proteins of which the collagens consist have a-chains with Gly-Pro-X as most common sequence of amino acids, whereby X can be any amino acid.
The synthesis of collagens takes place on the ribosomes of the rough endoplasmic reticulum in resident connective tissue cells, mostly fibroblasts or fibrocytes. Signalling peptides are linked on the primarily single chains, then single proline and lysine rests are hydroxylated and oligosaccharids are coupled to them. Further, galactose is bound to hydroxylysine. The chains aggregate to a first triplehelix and make disulfide bridges. The triple helical procollagen is formed from the C to the N terminus and then is transported to the Golgi apparatus where glucose is linked to the O-coupled oligosaccharids. Then the complex is transported via Golgi vesicles to the cell membrane for exocytosis. After release into the extracellular space N- and C-terminal propeptides are uncoupled resulting in the tropocollagen molecule which is the unit component of the fibrils. The latter is 1.2 nm thick and has a length of 300 nm. The single tropocollagen molecules aggregate in a way that they are shifted by one quarter of their length from lateral to make covalent binding to each other. Thus less than 18 nm thick filaments are formed which are not yet striated. The latter grow slowly by further aggregation of tropocollagen to form the final striated collagen fibrils. Collagen fibres then are formed by aggregation of a considerable number of such fibrils which then are interlinked by aggregation of proteoglycans. Collagen fibres are of different sizes depending on the kind of tissue and local biomechanical requirements and have a characteristic texture and a main direction of course.

--> other fibres in connective tissue: elastic, reticular
--> ground substance, mobile and immobile connective tissue cells, connective tissue
--> Electron microscopic atlas Overview
--> Homepage of the workshop