Connective Tissue

1. Normal connective tissue: loose CT, submucosa, papillary dermis of the skin; dense CT
2. Dense connective tissue: dense regular CT, tendon, bone, cornea; dense irregular CT: dermis, organ capsules
3. Specialized connective tissues: bone, cartilage, bone marrow, adipose tissue

• Permanent resident cells: fibroblast -> fibrocyte, myofibroblast (smooth muscle + fibroblast), osteoblast, adipocyte
• Permanent guest cells: macrophages (from monocyte), mast cells (histamine)
• Transient cells: basophils, eosinophils, lyphoncytes, monocytes, neutrophils, plasma cells

1. Extracellular matrix: collagen, elastin, fibrillin, fibronectin; proteoglycans, glycoproteins
2. Collagen: Gly-X-Y triple helix
3. Collagen synthesis: RER (prepro-alpha chain) -> Golgi (hydroxylation, Vc, glycosylation) -> triple helix -> procollagen secreted -> propeptides cleaved -> tropocollagen -> fibrils, lysyl oxidase, Cu+. Scurvy: Vc deficiency -> hydroxylation deficiency. Ehlers-Danlos Syndrome: collagen, lysine hydroxylase gene mutations, procollagen can't turn into tropocollagen.

• Type I collagen: most, tendon, ligaments, bone, skin, cornea. Osteogenesis Imperfecta: collagen gene mutation; "blue sclera"
• Type II collagen: cartilage, intervertebral discs, vitreous body of the eye
• Type III collagen: reticular fibers, blood vessels, PAS, silver stain
• Type IV collagen: basal lamina

1. Elastic fibers: elastin, fibrillin, artery wall, alveolar wall, skin. Marfan syndrome, fibrillin gene mutation on chromosome 15.
2. Reticular fibers: type III collagen, lymphatic tissues, bone marrow, liver stroma

• Fibronectin: binds to collagen, etc; cell interactions
• Proteoglycans: glycoaminoglycans attach to a protein core, sulfated residues, "-" charge, attach to hyaluronan by linker protein
• Glycoproteins: laminin (basement membrane), binds to integrins via entactin (link laminin to type IV collagen)