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Overview of Connective Tissue Characteristics and Classification

Connective tissue (CT) is defined by a limited number of cells and abundant extracellular ground substance, lacking polarity. All connective tissues originate from embryonic mesenchyme and serve vital functions such as connection, support, protection, nutrition, defense, and repair. There are two classifications: CT proper (loose and dense connective tissues) and specialized forms (cartilage, bone, and blood). Key cell types include fibroblasts, macrophages, and adipocytes, each with distinct structures and functions. These components make CT essential for tissue integrity and physiological functions.

cedric-adams
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Overview of Connective Tissue Characteristics and Classification

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  1. Chapter 3 Connective tissue

  2. 1.       General features: 1)   small number of cells and large amount of extracellular ground substance 2)  no polarity 3)   all of them originate from mesenchyme -embryonic CT 4) have functions of connection, supporting, protecting, nutrition, defence and repairing

  3. 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

  4. 2.Classification (1) CT in narrow sense means connetive tissue proper which include: loose CT dense CT adipose T reticular tissue

  5. (2) CT in wide sense includes : cartilage bone blood

  6. 3.Loose connective tissue (areolar tissue) • consists of cells, fiber and ground substance features: have more types of cells and less fibers

  7. functions: connection, supporting, defence and repairing

  8. Cells:

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

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

  11. 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

  12. fibroblast fibroblast fibrocyte fibrocyte

  13. ②macrophage ---structure: LM: • Round, ovoid or irregular in shape • have short blunt processes: pseudopodium • Small and dark nucleus • Acidophilic cytoplasm

  14. EM: rich in • a.Lysosome（溶酶体） • b.Phagosome: phagocytosis（吞饮作用） • pinosome（吞饮体）: pinocytosis(胞饮作用) • c.Remnant • d.Microfilament and microtubule

  15. ---function: a.    Chemotaxis: chemotactic factor b. phagocytosis: (1)Special phagocytosis: recognize bacterium, virus and foreign cell phagocytosis

  16. (2)non specialphagocytosis: carbon particles, dust and dead cells

  17. c.secretion: lysozyme（溶菌酶）, complement and interleukin-I (IL-1)and interferon(INF) d.antigen presenting function

  18. ③plasma cell ---structure: LM: • round or ovoid • Nucleus with more spot-liked heterochromatin which located eccentrically • Basophilic cytoplasm

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

  20. ④mast cell ---structure: LM: • Round and large cell • Small dark-stained nucleus • Basophilic secreting granules

  21. Basophilic secreting granules: • heparin: an anticoagulant • Histamine: cause cap. permeability↑, cap. leakage to form edema and contraction of SM • Eosinophil chemotactic factor (chemotactic factor: macrophage, leukocytes)

  22. Cytoplasm contain: slow reaction substance ---function: to cause allergic reaction

  23. 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

  24. ⑥undifferentiated mesenchymal cell ---structure: similar to fibrocyte ---function: multidifferentiating potential

  25. ⑦leukocytes: neutrophil, acidophil and lymphocyte, ect. lymphocyte neutrophil acidophil

  26. 2) fibers

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

  28. EM: parallel-arranged fibrils Fibril: • 20-200nm in diameter • Have periodic cross striation at 64nm interval

  29. ② elastic fiber (yellow fiber) LM: • thinner and less, 0.2-1.0 um • Slight red (HE) branch and form a network EM: • core: elastin-low electron density • Peripheral: microfibril 10-12 nm, electron dense ↑ fibrillin（微纤维蛋白）

  30. ③reticular fiber LM: • thin and less,0.2-1.0 um in diameter • Branch to form network • Argyrophilic fiber (silver impregnation method)

  31. EM: type III collagen 64nm cross striation ---distribution: reticular tissue connecting portion, e.g. reticular lamina

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

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

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

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

  36. 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

  37. white fat T brown fat T

  38. 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

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