Connective tissue
Not only a tissue glue…
 General composition of connective tissue (CT)
Cells and extracellular matrix
Matrix – fibrous and amorphous
Fibrous component
- collagen
- reticular
- elastic
Amorphous component (amorphous ground substance)
- Complex matrix consisting of glycosaminoglycans, glycoproteins and proteoglycans,
depending on tissue type (connective  ligament  cartilage  bone)
Cells
Connective tissue – permanent and transient cell populations (fibroblasts/myofibroblasts,
immune cells, adipocytes, adult stem cells)
Cartilage – chondroblasts/chondrocytes
Bone – osteoblasts/osteocytes/osteoclasts
 Embryonic origin of CT
• Mesenchyme = loose tissue between germ layers
• Complex network of star- or spindle-shaped cells
• Jelly-like amorphous ground substance
http://www.mun.ca/biology/desmid/brian/BIOL3530/DB_Ch02/DBNModel.html
DAY 12 of embryonic development
 Basic derivatives of CT
Connective BoneCartilage
Mesenchyme
 Classification of CT
Embryonic CT
- Mesenchyme
- Jelly-like CT (Wharton jelly, dental pulp, strom of iris)
Adult CT
- Areolar (loose, interstitial) CT
- Dense collagen irregular CT
- Dense collagen regular CT
- Fat (adipose tissue)
- Cartilage
- Bone
- Blood and hematopoietic tissue
- Lymphatic tissue
CT
Specialized CT
Trophic CT (body liquids)
 Cells of connective tissue
Cells
- Fibroblasts/fibrocytes/myofibroblasts
- Heparinocytes
- Macrophages of CT = histiocytes
- Plasma cells
- Lymphocytes
- Adipocytes
- Adult stem cells
Extracellular matrix
- Fibrous compound
- Amorphous ground substance
 Cells of connective tissue
Mesenchymal (adult) stem cells
Koch et al. BMC Biotechnology 2007 7:26 doi:10.1186/1472-6750-7-26
 Extracellular matrix – fibrous component
Collagen fibers
- family of fibrous proteins encoded by >35 genes (2013)
- polymer – subunit = tropocollagen; triple helix
- different structural and mechanical properties (strength, elasticity, pliability…)
- most abundant protein in human body ( 30% dry weight)
Type Localization Structure Main function
I
Bone, tendons, meniscus, dentin, dermis,
capsules of organs, loose CT 90% of type I
Fibrils (75nm) – fibers
(1-20m)
Resilience in pull
II
Hyaline and elastic cartilage Fibrils (20nm) Resilience in pressure
III
Skin, veins, smooth muscles, uterus, liver,
spleen, kidney, lung
Like I, high content of
proteoglycans and
glycoprotiens, reticular
network
Shape formation
IV
Basal lamina of epithelium and endtohelium,
basal membranes
No fibrils or fibers Mechanical support
V
Lamina of muscle cells and adipocytes, fetal
membranes
Like IV
VI
Interstitial tissue, chondrocytes – adhesion Connecting dermis and
epidermis
VII Basal membrane of epithelium
VIII Some endothelia (Cornea)
X
Growth plate, mineralized cartilage Growth of bones,
mineralization
 Collagen
 Collagen
 Collagen in LM
AZAN
HES
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Julian Voss-Andreae
"Unraveling
Collagen",
2005
Orange Memorial Park
Sculpture Garden, City of
South San Francisco, CA
 Elastic fibers
• less abundant than collagen
• polymer – tropoelastin
• minimal tensile resistance, loss of elasticity if overstretched
• reduction of hysteresis = allow return back to original state after mechanic change
 Reticular fibers
• collagen 3D meshwork
• bone marrow, spleen, lymphatic nodules
• microenvironment for e.g. hematopoietic stem cells and progenitors
Amorphous extracellular matrix
Colorless, transparent, homogenous substance consisting of glycosaminglycans,
proteoglycans and structural glycoproteins
 Extracellular matrix – ground matrix
 Glycosaminoglycans
linear polysaccharides composed of two disaccharide subunits
– uronic acid and hexosamine
glucosamin or galactosamin
glucuronic or iduronic acid
polysaccharides rich in hexosamines = acid mukopolysaccharides
Glycosaminoglycan Localization
Hyaluronic acid Umbilical cord, synovial fluid, fluid of corpus vitreum,
cartilage
Chondroitinsulphate Cartilage, bone, cornea, skin, notochord, aorta
Dermatansulphate Skin, ligaments, adventitia of aorta
Heparansulphate Aorta, lungs, liver, basal membranes
Keratansulphate Iris, cartilage, nucleus pulposus, anulus fibrosus
 Glycosaminoglycans
They bind to protein structures (except for hyaluronic acid)
 Proteoglycans
— protein + dominant linear saccharide
component
— proteoglycan aggregates
— water-binding, volume dependent of
hydratation
— aggrecan (cartilage)
— syndecan
— fibroglycan
• dominant protein + branched saccharide component
• interaction between cells and ECM
― fibronectin – connects collagen fibers and
glykosaminoglycans, cell adhesion and
migration
― laminin – basal lamina – epithelial integrity
― chondronectin – cartilage – adhesion of
chondrocytes to collagen
(J. Nutr. 136:2123-2126, 2006)
 Structural glycoproteins
 Composition of amorphous ground matrix
 Classification of specialized connective tissue
http://www.exploringnature.org/db/detail.php?dbID=21&detID=691
 Adipose tissue
• Adipocytes, fibroblasts, reticular, collagen and elastic fibers, capillarie
• White and brown adipose tissue
 Brown adipose tissue
• fetus and child to 1st year of life
• fast source of energy
• typical localization – between
shoulder blades, axilla, mediastinum,
around kidneys, pancreas, small
intestine
• small cells with numerous fat
droplets
 White adipose tissue
• adipocytes are actively form until 2nd year of life
• no innervations, but rich vascularisation
• adipocytes with only one lipid droplet
• leptin (adipokinins)
 Instructions
1. Turn on the light source
2. Start with the lowest magnification (usually red, 5x)
3. Insert the slide with cover glass facing up
4. Focus on the sample using the rough focusing screw (big knob)
5. Then the adjust focusing using microscrew (small knob on the big one)
6. If the sample is not focused properly, use the optical correction
7. Make a general scheme of the tissue
8. Use higher magnification to observe details (10, 20x)
9. NEVER USE THE HIGHEST LENS (BLACK) = IMMERSION USE ONLY
10.When you finish, remove the slide, put the red lens to the position, switch off the
light, cover the microscope
11. Enjoy the trip to the world of microscopic structures