1. Connective tissue fibers and their formation
Dr. Anna L. Kiss
Department of Human Morphology and Developmental Biology
Semmelweis University
Budapest
2013
Fibroblast, fibrocyte, mast cells, macrophages, adipocytes, ground substance, proteoglicans, adhesion molecules

2. Connective tissue components
Cells Extracellular matrix
fix
mobile
fibers
ground substance
proteoglycans
glycosaminoglycans
adhésion
glycoproteins
fibrocyte
reticular cell
adipocyte
melanocyte
mesoblast
macrophag
mast cell
plasma cell
granulocyte
(neutrophil,
eosinophil)
collagen
elastic
reticular
fibrillin
hyaluronic acid
chondroitin sulphate
heaparan sulphate
keratan sulphate
dermatan sulphate
fibronektin
laminin
tenascin
enactin
trombospondin

3. Connective tissue fibers
collagen fibers: inelastic, flexible, remarkably high tensile strength
elastic fibers: elastic, less tensile strength
reticular
fibrillin

4. Collagen fibers they often form thinner or thicker bundles
light microscopically: pink (eosinophil,HE) or blue bundles (anilin blue)
EM: cross striation: periodically arranged light and dark bands
bundles of fibrilles (d: 50-90nm)
the collagen fibers are composed of collagen molecules

5. Collagen fibers (HE staining)

6. fibrocytes

8. Collagen protein
collagen is a fibrous glycoprotein, which provides tensile strength of the ECM
is composed of tropocollagen:
- 290 nm long and 1.5 nm thick, α-helical polipeptide: procollagen
- 3 α-helical polipeptide chains assembled in a triple helix
special amino acid sequence: repeating glycine-x-y amino acids;
in most cases (30%) x and y: proline and hydroxyproline; + hydroxilysine and alanin
procollagen molecules are connected with each other by covalent bonds (between lysine)
overlapping arrangment of the procollagen subunits: a one-quarter (67 nm) overlap between adjacent molecules, 40 nm gap between the ends cross striation (only electron microscopically!!!)

9. procollagen is made of 3 polipeptides: triple helix
procollagen molecule
40nm gap
collagen fibrillum
procollagen molecules are connected with each other by covalent bond (between lysine)
overlapping arrangment of the procollagen subunits: a one-quarter (67 nm) overlap between adjacent molecules, 40 nm gap between the ends cross striation (only electron microscopically!!!)

10. RGD sequence and its significance
RGD sequence: arg-gly-asp: signal tripeptid
is present in most of the collagen molecules
binds to integrin-like receptors of the connective tissue cells cells are attached to collagen
they migrate on collagen
this connection can stimulate cell division or differentiation

11. Collagen synthesis
1.) synthesis of the α-chain in rER (typical export protein synthesis)
2.) protein enters the ER lumen: a.) signal peptide is cut off,
b.) hydroxyproline and hydroxylysine formation; requeires ascorbic acid (vitaminC) as cofactor
3.) transport to the Golgi;
4.) glycosylation of some lysines (different collagen types have variable amout of carbohydrate); triple helix formation procollagen
5.) vesicular transport from the Golgi to the plasma membrane; exocytosis
6.) enzymatic (procollagen peptidase) removal of most of the non-helical region: tropocollagen is formed
7.) polimerization of tropocollagen: fibrillum
(in the invagination of the cell membrane)

12. Vitamin C deficiency: Scurvy
During the boisynthesis of collagen: hydroxyproline and hydroxylysine formation; requeires ascorbic acid (vitaminC) as cofactor
- wound fail to heal
- bone formation is impaired

13. Fibroblast EM picture

14. Fibroblast: collagen secretion

15. Types of collagen
Collagen family: about 25 α-helical collagen molecules
they can be combined in triplets in different way
about 15 types of collagen, sighned by Roman number
Type I: bone, tendon, skin
Type II: hyalin and elastic cartilage (thinner than Type I)
Type III: reticular fibers, basement membrane (firstly synthesized during wound healing), wall of blood vessels
Type IV: basal lamina
Type V: amnion and chorion

16. Types of collagen
Type VII: hemidesmosomes, anchoring the basal lamina to the connective tissue
Type IX: is bound to TypeII collagen in cartilage
Type XII: is bound to TypeI collagen

17. Reticular fibers extremely thin fibers: d:0.5-2µm
form an extensive network in certain organs
large amount of glycoproteins are associated to the fibers
composed of mainly collagen TypeIII

20. centriole
Golgi
nucleus
rER
reticular fibers
(TypeIII collagen) ensheathed
by processes of fibroblasts

21. Elastic fibers
elastic fibers are common in tissues which require the ability to deform repetitively and reversibly
elastic fibers have an amorphous core consisting of elastin surrounded by fibrillin
elastin is synthesized as a soluble monomer,
monomers are cross-linked – lysyl oxidase: tropoelastin – exocytosis
turnover is extremely slow,
synthesized mainly during development, any damaged elastin is either not replaced, or replaced by nonfunctional fibers

22. Elastic fibers
elastin

23. collagen fibrilles
elastin
fibrillin

27. Fibrillin extremely thin (d: 8-10nm) filaments only by EM
fibrillin: is a glycoprotein
Marfan syndrome: autosomal dominant genetic disorder; defect in fibrillin formartion
symptomes: skeletal, cardiovascular and ocular:
extremely long and thin limbs, hollow chest, scoliosis and elongated fingers.
prolapse of the mitral valve, dilated aorta,
demaged Descemet membrane and zonule fibers of the lens

28. Types of connective tissue

29. Mesenchymal tissue

30. Types of connective tissue
loose connective tissue
few fibers, irregular structure
the most frequent type,
fills in spaces, connects organs with each other

31. dense regular connective tissue
many collagen fibers in regularly arranged bundles
dense irregular connective tissue
many collagen fibers, in irregularly arranged bundles

32. white and brown adipose tissue
adipocytes, a few reticular fibers
„Fat pad”
white and brown adipose tissue

33. Brown adipose tissue

34. Irodalom Röhlich Pál: Szövettan. Budapest, 1999
A szövettani képek a Humánmorfológiai és Fejlődésbiológiai Intézet gyűjteményéből származnak.
Carola R, Harley JP, Noback CR: Human Anatomy & Physiology, McGraw-Hill Inc., USA, 1990