Chapter 3 Connective tissue

1.       General features: 1)   small number of cells and large amount of extracellular ground substance 2)  extracellular is composed of fibers and amorphous ground substance-matrix 3)   all of them originate from mesenchyme-embryonal CT 4) have functions of connection, supporting, protecting, nutrition, defence and repairing

mesenchyme ---mesenchymal cell: /structure: stellate in shaped with processes a large nucleus,with clear nucleoles slight basophilic cytoplasm /function: a.    undifferentiated cell b. multiple developmental potential→CT cell, SM and endothelial cell ---matrix

2.       Classification ---CT in narrow sense means connetive proper which include loose CT, dense CT, adipose T and reticular tissue ---CT in wide sense includes cartilage, bone and blood

3. Loose connective tissue(areolar tissue) features: have more types of cells and less fibers functions: connection,supporting,defence and repairing consists of cells, fiber and ground substance

cells: seven types of cells are present in LCT

① fibroblast ---structure: LM: large,flattened cell with processes- stellate in shaped Large ovoid pale nucleus-contain more fine chromatin, with clear one-two nucleoli Weakly basophilic cytoplasm-homogeneous

EM: rich in RER,Golgi appatatus and free ribosome ---function: synthesize fibers and ground substance

Synthesis of collagenous fiber Three steps: a.synthesis of procollagen(RER) → process(Golgi) → out of cell b.procollagen→ tropocollagen → fibril c.fibril → collagenous fiber

*fibrocyte: still state or inactive fibroblast ---structure: spindle-shaped, small N:small,dark stained Acidophilic cytoplasma EM: less organelles ---function: become into fibroblast for repairing

②macrophage ---structure: LM: round or ovoid-irregular in shape when it have short blunt processes_pseudopodium Small and dark nucleus Acidophilic cytoplasm

EM: rich in a. lysosome b. Phagosome← phagocytosis and pinosome ←pinocytosis c.  Remnant d.  Microfilament and microtubule

---function: a.    Chemotaxis: chemotactic factor b. phagocytosis: Special phagocytosis: recognize Bacterium, virus and foreign cell non special: carbon particles, dust and dead cells *Phagosome(pinosome) + primary lysosome →secondary lysosome →remnants

c.  secretion: lysozyme, complement and interleukin-I (IL-1)and interferon(INF) b.     antigen presenting function: *capture antigen→processes→+ MHC II molecule (major histocompatibility complex molecules) →antigen-MHC II complexes→TLC

③plasma cell ---structure: LM: round or ovoid Round eccentrically-located nucleus with more spot-liked heterochromatin Basophilic cytoplasm

EM: rich in parallelly arranged RER, free ribosome and Golgi complex ---function: synthesize and secrete immunoglobulin, Ig-antibody

④mast cell ---structure: LM: round and large cell Small dark-stained nucleus Basophilic secreting granules

Basophilic secreting granules: heparin:an anticoagulant Histamine: cause cap. permeability↑, cap. leakage to form oedema and contraction of SM Eosinophil chemotactic factor Cytoplasm contain: leukotriene- slow reaction substance ---function: cause allergic reaction

⑤fat cell ---structure: large, round or polygonal flattened ovoid nucleus located on one side of cell thin layer of cytoplasm a large lipid droplet ---function: synthesize and store fat

⑥undifferentiated mesenchymal cell ---structure:similar to fibrocyto ---function:multidifferentiating potential ⑦leukocytes: neutrophil,acidophil and lymphocyte

2) fibers

①collagenous fiber(white fiber) LM: 1-20 um in diameter Belt-liked wave and branch to form a network Eosinophilic

EM: parallel-arranged fibrils 20-200nm in diameter Have periodic cross striation at 64nm interval *formation: Extracellular polymerize collagen(type I and III) →collagenous fibril → collagenous fiber

② elastic fiber (yellow fiber) LM: thinner and less, 0.2-1.0 um Slight red(HE), purple(aldehyde fuchsin) or brown(orcein) Branch and form a network EM: core: elastin-low electron density Peripheral: microfibril 10-12 nm, electron dense ↑ fibrillin

③reticular fiber LM: thin and less,0.2-1.0 um in diameter Branch to form network Argyrophilic fiber(silver impregnation method) EM: type III collagen 64nm cross striation ---distribution: reticular tissue connecting portion, e.g.reticular lamina

3) ground substance ---amorphous colloidal substance ---consists of proteoglycan, glycoprotein and tissue fluid

①proteoglycan-large molecular complex ---glycosaminoglycans: chondroitin sulfate keratin sulfate dermatan sulfate heparin sulfate hyaluronic acid: 2.5um long --protein *molecular sieve

② glycoprotein: proteins ---fibronectin cells←fibronectin→collagen ↓ proteoglycan ---laminin ---chondronectin ---function: Connection affect the differentiation and movement of cells

③ tissue fluid tissue artery → Tissue fluid → vein →blood steam cells dehydration oedema

4.    Dense connective tissue ---more fiber ---connection and supporting

1) regular DCT: parallelly-arranged collagenous fibers tendon cells: /special fibroblast /wing-liked processes ---distribution: tendons, ligament and cornea

2) irregular DCT: Fiber arranged in bundles,runing in different direction Fibroblast less ground substance ---distribution: dermis, sclera and capsule of some organs

3) elastic T: elastic fiber in bundles or in membrane ligament and large artery

5. adipose tissue ---LCT+fat cells ---white fat T: single fat cell distribution in subcutaneous tissue, mesenterium ---brown fat T: fat cell contain many small lipid droplets, rich in large mitochondria centrally-located nucleus rich in cap. distribution: neonate

6. reticular tissue ---reticular cells: stellate with processes-form network round, ovoid and pale nucleus with 1-2 nucleoli EM: rich in RER ---reticular fiber: connect to form network ---distribution: hemopoietic tissue and lymphatic tissue