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Connective tissue What is connective tissue? As the name suggests, it connects the various tissues of the body and gives them support. 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 mesenchymeembryonal CT 4) have functions of connection, supporting, protecting, nutrition, defence and repairing mesenchyme ---mesenchymal cell: /structure: stellate/star 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 Major constituents cells extracellular Fiber matrix Ground substance 1) cells: seven types of cells are present in LCT Fibroblasts Fixed cells Adipose cells Mast cells cells Macrophages of Undifferentiated mesenchymal cell CT Plasma cell Transient cells Blood cell Macrophage 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 EM: RER Golgi 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(TNFα、 IFN (interferon) or interleukin) 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/BLC ③plasma cell ---structure: LM: round or ovoid Round eccentrically-located nucleus more spot-liked heterochromatin Basophilic cytoplasm with 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: Mast cells degranulation results in the release of histamine and other vasoactive mediators which induce the immediate hypersensitivity response (characteristic of urticaria(whealitch), allergic rhinitis (sneeze) and asthma (cough)) and anaphylactic shock. ⑤adipose cell(fat 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 This is a higher magnification of fat cell with a large lipid droplets and cytoplasm pushed to the periphery membrane, nucleus is flattened against the membrane also. ⑥undifferentiated mesenchymal cell ---structure:similar to fibrocyto ---function:multidifferentiating potential ⑦leukocytes: neutrophil,acidophil and lymphocyte 2) fibers ①collagenous fiber(white fiber) LM: Main fiber 1-20 um in diameter Belt-liked wave and branch to form a network Eosinophilic EM: parallel-arranged fibrils Fibril: 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 Physical properties: As their name implies elastic fibers can be stretched (like a rubber band ) and return to their original length when tension is released. 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 (polysaccharide) 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 edema 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