Connective Tissue

Connective Tissue

1. Embryonic Development 3 germ layers

   • Endoderm
   • Mesoderm
     • Developes into mesenchyme
     • Mesenchyme
       • Embryoic Connective tissue
       • Mobile mesenchymal cells
         • Mesenchymal cells have gap junctions, allow communication between the cells
       • Secrete fibers and ground substance
       • Fusiform (spindle shapes) and/or stellate cells
   • Ectoderm

2. wharton's Jelly

   • undifferentiated muscous connective tissue
   • Found in the umbillical cord
   • Reticular fibers

3. Connective tissue proper

   • Dense connective tissue
     • Dense Regular
       • Oriented along the stess axis
       • tendons and ligaments aponeuroses
         • Tendons
           • Outter covering= epitenon
           • Bindles of fibers= tendon fassicles bound by endotendenium
           • Tendinocytes
             • Type of fibroblast
               • Migrate to sited of stress and provide collagen bundles
             • Secrete Elastin
               • recoil and flexibility
             • Secrete Type I and Type III collagen
             • Tenoblast becoes tenocyte
             • Lots of rough ER
           • Orientation of the collogen fibers provide mechanical properties
             • needed to reduce stress on the underlying muscle tissue
           • Tendons=more organized
             • Handle more stress than ligaments
         • Ligaments
           • become sandwhiched as development occures
           • More elastic
           • Rounded nuclei
           • Less collagn than tendons
             • more glycosaminoglycans
         • aponeuroses
           • Broad, flat tendons
           • Muscle to Muscle
           • Orthogonal Array
             • Strong yet flexable
             • fibers are oriented 90 degrees to eachother
             • transparent
             • Cornea
     • Dense iregular
       • fibers are oriented in many directions
       • Povides strength
       • mucosa of hollow organs
       • reticular layer of the dermis
     • Depends on amont of protein (collogen)
     • More fibers, less cells, less ground substance
   • Loose connective tissue
     • AKA Areolar
     • Most widespread
     • More cells, fewer fibers
       • Greater variety of cells
     • Geater flexibility
     • Found under all epithelia tissue (including glands) and small blood vessels
   • Specialized connective tissue
     • Reticular
     • Elastic
     • Blood
     • Bone
     • adipose
     • Hemopoetic
     • Lymphatic

4. Three types of fibers

   • Collagen
     • Made of collagen fibrils
       • vary in size
       • Stain with acidic dye
       • Alpha chains form mature collagen
       • Lyseine and hydroxylisine cross-link
     • Is a secreted protein: pre-pro collagen on rough ER
       • pre-pro collagen>>Pro collagen>>secreted and cleaved to tropocollagen>> tropocollogen
         • aggregates to form collagen fibrils>> collagen fibrils assemble into collagenn fibers
     • Over 20 distinct types
       • fibrilar: Form long fibrils
         • Type I-III, V and XI
       • Type IV, VIII and X form sheets and meshworks
         • TypeVIII and X= Hexagonal forming
       • Type VI, VII , IX, XII, XIV, XVIII = Linking and anchoring roles
       • **Basement membrane forming types= IV, VI and VII
       • ***Transmembrane collagen proteins
         • Type XXV = Brain specific
         • Type XXIII= metastatic cancer
         • Type XIII= Focal adhesion
         • Type XVII=hemidesmosomes
       • ***FACITS
         • Types IX, XII, XIV, XVI, XIV, XX, XXI, XXII
         • Fibril accociated, interupted triple helices
     • Tissues subject to high tensile stress
       • tend to have thick collagen fibers
     • Translation of mRNA occures in cytoplasm
     • constantly degraded and synthesized
       • Remodeling of the ECM is done by proteases called MMPs
         • MMPs= Matrix Metalloproteases
           • Requires Zn+ -- cofactor
           • MMP 1, 8 and 13= Collagenases
             • Degrade collegen type II, II and X
           • MMP 2 and 9 = gelatinases
             • degrade denatured collagen laminin, fibronectin and elastin
           • MMP 3 and 10= stromolycins
             • degrades denatured collagen, proteoglycan and fibronectin
           • Tissue inhibitor metalloprotease TIMPS
             • Inhibit MMPs
       • fibroblasrs and macrophaes can phagocytize collagen
     • Collagenopathies
       • diseases caused by mutations in collagen types
       • Type XVI collagenopathies
       • Type I Collagenopathy
         • Osteogensis Imperfecta
         • brittle bones, abnormal teeth, thin skin, weak tendons
           • blue sclera, hearing loss, prone to fractures
       • Type II Collagenopathy
         • kniest dysplasia, achondrogenesis
         • short stature, blindness, restricted joint motility and joint abnormailities
       • Type III Collagenopathy
         • Hypermobility ethlers-danlos syndrome
           • hyper mobile joins, dislocations, deformed finger joints
             • early onset osteoarhritis
         • Vascular ethlers-danlos syndrome
           • thin, translucent skin, bruising, high mortality and morbidity
       • Type IV Collagenopathy
         • Alport's Syndrome
         • hematuria -> changes in glomerular basement membrane
           • progressive hearing loss and ocular changes
       • Type X Collagenopathy
         • schmid metaphyseal chondrodysplasia
         • skeletal deformaties, chondrodysplasia and metaphesis of long bone
           • modification of verabral bodies
   • Reticular
     • type III collagen secreted by reticular cells
     • reticular fibers cross link to form reticulum
     • found on the surace of muscle cells, adipose and shwann cells
       • form the reticular lamina of the basement membrane of epithelium
     • heavily glycosilated
       • PAS or Silver stain
   • Elastic
     • Abundand in skin, lungs, arteries and bladder-- "concentric lamina"
     • produced by smooth muscle and fibroblasts
     • rich in proline and glycine but not hydroxyproline or hydroxylysine
       • important for not formin thick filaments
     • Glycoprotein (fribrillin I)>>Polymerizes (56nm)>>Emilin-1, MAGP-1 and tropoelastin fuse to form fiber