Im Dünnschnitt für die elektronenmikroskopische Untersuchung werden die wellenförmig verlaufenden Bindegewebsfasern in unterschiedlichen Ebenen bzw. Richtungen getroffen. Die Kollagenfibrillen sind hier teils längs, quer und schräg angeschnitten, zum Teil ist die periodische Querstreifung zu erkennen. Zwischen den Kollagenfibrillen sind zahlreiche kleine elektronendichte Partikel, die den Proteoglykanen entsprechen, zu erkennen.

Legende:

	Collagen fibrils (sliced longitudinal)
	Collagen fibrils (sliced obliquely)
	Proteoglycans

Schematic structure of a microfibril

Microfibrils are microfibrillar subunits of the visible collagen fibrils seen in the specimen. Their periodically arranged light and dark transverse striations are determined by the storage of electron-microscopic stains in staggered gaps. These are created by a characteristic overlapping arrangement of tropocollagen molecules (the neighboring rows have a periodicity of 67 nm).

Transmission electron microscope (TEM)

The sections for examination under the transmission electron microscope are about 0.1µm thick. They are referred to as ultra-thin sections.

To obtain such ultra-thin sections, the tissues are embedded in plastic polymers like epon (instead of paraffin, which is used for examination under the light microscope) after fixation and dehydration. Ultra-thin sections are not stained with dyes, but contrasted with heavy-metal salts. The heavy-metal salts lead to a different electron scatter and thereby create a differentiated blackening of the photographic negative. A common method of creating contrast results with 5% uranyl acetate and lead citrate.

Es gibt verschiedene molekulare Formen des Kollagens, sog. Kollagentypen. Diese unterscheiden sich in ihrer chemischen Zusammensetzung, ihrer Morphologie und ihrer Pathologie. Die wichtigsten sind:

Typ I-Kollagen:
breite Kollagenfasern in Sehnen, Knochen, Lederhaut u.a.
Typ II-Kollagen:
mittlerer Faserdurchmesser, Gelenkknorpel u.a.
Typ III-Kollagen:
dünnere Fibrillen, Retikulinfasern u.a.
Typ IV- und V-Kollagen:

HistoNet2000 - Help

1. Organization of the screen surface

Right side: histologic specimen
Left side: information about the specimen (above) and general program functions (below)

2.Histologic specimen

Pull the mouse across the histologic specimen for training purposes. A small square with exclamation marks (dynamic labels) will appear where there is an important structure. You should then decide what structure this could be. To check your result, simply click the appropriate square, and the correct label will appear. The option “marked” allows you to see all labels for all structures simultaneously. These can be removed by clicking “unmarked”. This reactivates the dynamic labels.

3. Complementary information

Info: general information about the specimen, as well as a list of the dynamic labels
Drawing: schematic drawing of the specimen
Staining: information about the staining method for this specimen
Knowledge: short texts with basic histologic information, presently deactivated

4. General Program Functions

Home: returns you to the “start” page
Tutor: how to contact the HistoNet Team
Help: Instructions for Use appear
Exit: closes down the HistoNet program
Boxes: goes back to the other specimen of a topic
VM: provides virtual microscopy

We hope you will enjoy working with HistoNet2000 and learn a lot from it!

Specimen Nr. 02A

Specimen:

Staining:

Magnification:

Important structures :

Legende:

Transmission electron microscope (TEM)

HistoNet2000 - Help