Connective Tissue LiDongMei may75119@163.com

1. Introduction Connective tissue is versatile，the types including Connective Tissue proper and the specialized Cartilage ，Bone and Blood. Connective tissue comprises a diverse group of cells embedded in a tissue-specific extracellular matrix（ECM）.

1.1 Classification Connective Tissue proper Cartilage ※ Bone ※ Blood ※ Loose connective tissue ※ Dense connective tissue Adipose tissue Reticular tissue Cartilage ※ Bone ※ Blood ※

1.2 Component Cell Connective tissue amorphous Ground substance Extracellular matrix（ECM） Fiber

1.3 Characteristics Have small number of cells but have much extracellular matrix. all of them originate from mesenchyme-embryonic CT have functions of connection, supporting, protecting, nutrition, defence and repairing

mesenchymal cell structure: 1)stellate in shaped with processes 2)a large nucleus,with clear nucleoles 3)slight basophilic cytoplasm function: 1) undifferentiated cell 2) multiple developmental potential

1.4 Functions have functions of connection, supporting, protecting, nutrition, defence and repairing

2. Connective tissue proper Loose(areolar) connective tissue※ Dense connective tissue Adipose tissue Reticular tissue

2.1 Loose connective tissue 1) functions: connection, supporting, defence and repairing 2）consists of 7 types of cells, 3 types of fiber and ground substance

2.1.1 Cells in loose connective tissue there are 7 types of cells present in LCT ※ Fibroblast※ Macrophage※ Plasma cell Mast cell Fat cell undifferentiated mesenchymal cell Leukocytes

① fibroblast ---structure: LM: large,flattened cell in shaped Large ovoid pale nucleus with clear one-two nucleoli Weakly basophilic

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

Synthesis of collagenous fiber in three steps: a. synthesis of procollagen (RER) → process (Golgi) → procollagen → 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 （The mononuclear ---structure: LM: phagocyte system） ---structure: LM: round or ovoid-irregular in shape Small and dark nucleus Acidophilic cytoplasm

EM: rich in a.  lysosome b. Phagosome c.  Remnant

Function: a. Phagocytosis: Special phagocytosis: recognize Bacterium, virus and foreign cell Non special: carbon particles, dust and dead cells

B. secretion: cytokines, growth factors and complement protein. C. antigen presenting function: *capture antigen→processes→+ MHC II molecule (major histocompatibility complex molecules) →antigen-MHC II complexes→T lymphocytes

The mononuclear phagocyte system Monocyte in blood is the precursor of macrophages Liver: Kupffer cells Central nervous system: microglial cells Skin: Langhans cells Lymph node: dendritic cells Bone: osteoclast

Langhans cell

③plasma cell ---derive from B lymphocyte ---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 antibody（immunoglobulin）

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

EM function: Membrane bound granules A few Mitochondria A little RER cause allergic reaction

⑤fat cells (adipose cells) ---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 fibrocyte ---function: multidifferentiating potential

⑦leukocytes: Granulocyte: neutrophil, eosinophil and basophil Agranulocyte: lymphocyte (B, T) monocyte Myofibroblasts, Pigment cells

summary A. Classification of CT B. 7 types of cell in LCT 1. fibroblast 2. macrophage 3. plasma 4. mast cell 5. fat cell 6. undifferentiated mesenchymal cells 7. leukocyte

Questions: 1. What kind of cells present in loose connective tissue? And what are the functions of those cells? 2. What is (are) the structure cell(s) of connective?

2.1.2 fibers Collagenous fiber Elastic fiber Reticular fiber

Collagenous fiber(white fiber) LM: 1-20 um in diameter Belt-liked wave and branch to form a network Acidophilic are inelastic and have great tensile strength

EM: parallel-arranged fibrils 20-200nm in diameter formation: Extracellular polymerize collagen molecule (type I and III) →collagenous fibril → collagenous fiber

elastic fiber (yellow fiber) LM: EM： thinner and less Slight red(HE), purple or blue(special stained) Branch and form a network EM： core: elastin Peripheral: microfibril

reticular fiber LM: thin and less,0.2-1.0 um in diameter Branch to form network black (silver impregnation method) ---distribution: reticular tissue connecting portion, e.g.reticular lamina

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

Function of the ground substance Connection affect the differentiation and movement of cells a barrier to the penetration of foreign particles

Summary Loose connective Tissue 3 fibers and 7 kinds of cells

2.2   Dense connective tissue ---Abundant fibers and few cells ---connection and supporting Dense regular CT; Dense irregular CT;Elastic CT

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

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

2.2.3 Elastic Tissue: elastic fiber in bundles or in membrane ligament and large artery

2.3 adipose tissue ---LCT+fat cells ---white fat T: single fat cell ---brown fat T: fat cell contain many small lipid droplets, rich in large mitochondria centrally-located nucleus

2.4 reticular tissue components: Reticular cells reticular fibers ground substance distribution: hemopoietic tissue lymphatic tissue