Connective Tissue Li-zhongjie

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 ）.

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

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

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

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

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

CT in narrow sense means connective tissue proper, include: loose CT adipose tissuereticular tissuedense CT

2.1 Loose connective tissue 1) consists of 7 types of cells, 3 types of fiber and ground substance 2 ） The most widely distributed in the body 3) functions: connection, supporting, defence and repairing

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

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

② macrophage （ The mononuclear phagocyte system ） ---structure: LM: round or ovoid-irregular in shape Small and dark nucleus Acidophilic cytoplasm

EM: rich in lysosome Phagosome: phagocytosis pinosome : pinocytosis Residual bodies Microfilament and microtubule

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

(2)non special phagocytosis: carbon particles, dust and dead cells

c. Bioactive product secretion: lysozyme, complement, interleukin-1 (IL-1), interferon (INF) and growth factor. d. antigen presenting function * capture antigen → processes → + MHC II molecule (major histocompatibility complex molecules) → antigen-MHC II complexes → T lymphocytes

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 The mononuclear phagocyte system

③ plasma 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 ）

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

Basophilic secreting granules: heparin: an anticoagulant Histamine: increase vascular permeability, capillary leakage to form edema, promotes the contraction of the smooth muscles Eosinophil chemotactic factor Other bioactive chemicals

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

⑤ 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

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

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

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 summary

Question 1. What kind of cells present in loose connective tissue? And what are the structure AND functions of those cells?

2.1.2 fibers Collagenous fiber Elastic fiber Reticular fiber

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

EM: parallel-arranged fibrils Fibril: nm in diameter Have periodic cross striation at 64nm interval

collagen (type I and III) collagenous fibril collagenous fiber * formation of collagenous fibers:

② elastic fiber (yellow fiber) LM: thinner and less, um Slight red (HE) branch and form a network EM: core: an amorphous substance--elastin-low electron density Peripheral: microfibril nm, electron dense Function rubber-like properties

③ reticular fiber LM: thin and less, um in diameter Branch to form network black (silver impregnation method) ---distribution: reticular tissue connecting portion, e.g.reticular lamina

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

① Proteoglycan: mostly of Proteoglycans and Hyaluronic acid.

Molecular sieve: The entangled macro-molecular proteoglycan aggregate forms a bottle brush-like structure To exclude or entrap molecules of different sizes Serves as a physical barrier to prevent the spread of bacteria and other microorganisms.

② Glycoprotein Fibronectin Laminin chondronectin

③ tissue fluid Arterial end→ Tissue fluid → venous end →blood steam oxygen, nutrients waste material, carbon dioxide cells Acts as the midium for exchange of metabolites between circulating and tissue cells

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 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 ---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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