connective

General features, components and functions of connective tissue 

  • Features: 

    • Connects tissues together 

    • No free surface, connect tissue underneath epithelium 

    • Has nerve supply (except cartilage) 

    • Highly vascular (except cartilage and tendon) 

    • Develops from embryonic connective tissue: mesenchyme (comes from mesoderm) 

      • Mesenchyme cells are undifferentiated cells that produce intercellular material 

  • Components:  

    • Specialised cells 

    • Extracellular matrix: greatest volume of CT 

      • Protein fibers 

        • Collagen 

        • Elastic  

        • Reticular 

      • Ground substance (filling) 

  • Functions: 

    • Supports, surrounds, connects other tissues 

    • Forms structural framework of body 

    • Defends from invasion by microorganisms  

    • Stores energy reserves 

    • Protects delicate organs 

    • Transports fluids and dissolved material from one region to another 

  • Types: 

    • Fixed: home based 

      • Resident population of cells 

      • Stable, long-lived 

    • Transient: wander around (perform something then die) 

      • Free or wandering cells 

      • Originate mainly in bone marrow 

      • Most are short-lived 

 

-blast, -cyte, -clast terminology 

  • -blast cells: produce matrix 

  • -cyte cells: maintain matrix 

  • -clast cells: break down matrix 

 

Major cell types in CT and what do they do 

  • Fixed/resident cells 

    • Fibroblasts/fibrocytes 

      • Myofibroblasts: healing 

        • Have properties of both fibroblasts and smooth muscle cells 

        • Hard to distinguish from fibroblasts unless by electron microscope 

        • Contains large bundle of myofilaments 

        • Usually seen as an isolated cell 

    • Mesenchymal stem cells 

    • Macrophages: WBC/vacuum cleaners 

      • Derives from monocytes originating in bone marrow 

      • Either fixed or wandering 

        • Fixed: long cytoplasmic processes 

        • Wandering: ovoid shape 

      • Irregular shape, uneven cell surface, large 

      • Active in phagocytosis (picks up stains) 

      • Abundant golgi, mitochondria, ER, secretory vesicles 

      • Large lysosomes (dissolve things within cell) 

      • May fuse with other macrophages to form multinucleated, foreign-body giant cell 

      • Antigen presenting cell 

        • Digests foreign antigen and presents part of antigen to immune cell for memory 

    • Mast cells: stimulate and induce inflammatory response 

      • Large ovoid cell with small nucleus 

      • Filled with large basophilic granules in cytoplasm 

      • Stores chemicals which mediate inflammatory process 

        • Heparin: blood thinner 

        • Histamine: invokes & intensifies inflammatory response 

        • Leukotrienes: attract wandering cells 

      • Promote allergic reactions AKA hypersensitivity reactions 

      • Arise in bone marrow 

    • Adipose cells 

      • Clustered together in fat 

 

  • Cardinal sings of inflammation: 

    • Redness 

    • Heat 

    • Swelling 

    • Pain 

    • Loss of function 

 

  • Transient/wandering cells 

    • Part of the immune system 

      • Leukocytes 

        • Including: lymphocytes, neutrophils, eosinophils, basophils, monocytes 

        • WBC frequently migrating through capillary walls into connective tissue 

        • Functions: inflammation, invasion by foreign elements and immune response 

      • Plasma 

        • Antibody-producing cells derived from B lymphocytes 

        • Short life span 

        • Large, ovoid, basophilic cytoplasm 

        • Found in lamina propria of GI tract and Resp tract, and salivary glands 

  • Diapedesis vs Chemotaxis 

    • Diapedesis: mechanism of WBCs leaving the bloodstream towards site of injury 

    • Chemotaxis: chemicals released by mast cells that trickle down to the vessel and form a pathway to where wandering cells must go to find the place of injury 

 

Describe extracellular matrix 

  • Greatest concentration of connective tissue 

  • Most important component is ground substance which surrounds CT  

    • Constituents: GAGs, proteoglycans, and multiadhesive glycoproteins 

What are the three types of connective tissue fibers and any unique 

characteristics they may have 

  1. Collagen: flexible, high tensile strength 

    1. Collagen synthesis: 

      1. Made by fibroblasts 

      2. Triple helix composed of 2 A1 & 1 A2 peptide chains 

      3. Needed in formation of bone 

        1. When assembly of collagen is compromised, birth defects can occur 

          1. Osteogenesis imperfecta: imperfect formation of bone 

    2. Type I: most abundant type, multidirectional to increase its strength 

    3. Type IV: made by epithelial cells, basal lamina 

    4. Type VII: anchoring fibrils, U-shaped to sink into tissue and anchor 

  2. Reticular fibers (Type III collagen): thin, arranged in network or mesh 

    1. Keloid: adding up of collage during wound healing 

  3. Elastic fibers: thin and straight fibers arranged in network 

    1. Fibrillin: forms framework for elastofibril to attach 

      1. Marfan syndrome: genetic mutation causing long limbs -> lose elasticity -> heart contracts and aorta expands but no elastic tissue to bring them back to their normal size causing a decrease in life expectancy 

 

Ground substance components and examples of them we gave in class 

  • Surrounds cells and fibers of CT, amorphous (no clear shape) and unstructured 

  • Components: 

    • GAGs: most common 

    • Proteoglycans 

    • Mult adhesive glycoproteins 

GAGs 

  • Major building blocks of connective tissue 

  • GAG + protein: glycoprotein 

Glycoproteins/proteoglycans: 

  • Proteoglycan: proteins that help bind the epithelial cell with underlying connective tissue 

    • Aggrecan in cartilage 

    • Syndecan in epithelial cells 

    • Integrins: binds cells and extracellular matrix 

  • Glycoproteins: support, bind and buffer extracellular matrix 

Multi adhesive glycoproteins 

  • Bind cells through integrin receptors to form intensive matrix network 

    • Fibronectin: binds to integrins  

Describe the different types of connective tissues and examples of tissues with 

them. Be able to compare and contrast them. 

  •  Connective tissue proper 

    • Loose (areolar)  

      • Numerous fibroblasts and macrophages, all other cell types present 

      • Delicate consistency, flexible, very vascular, not resistant to stress 

    • Dense 

      • Irregular  

        • Cells are mainly fibroblasts (to be stronger) 

        • Most of tissue consists of collagen 

          • Typically type I strong fibers running in different directions  

        • Types: 

          • Dermis 

          • Sheathes & capsules (joints) 

      • Regular 

        • Cells are mainly fibroblasts 

        • Collagen fibers all oriented in the same direction 

        • Types: 

          • Tendon/aponeuronsis 

          • Ligaments 

          • Elastic tissues 

  • Connective tissue w special properties 

    • Embryonic:  

      • mesenchyme embryonic tissue gives rise to connective tissue 

      • Mucous CT: 

        • Found primarily in umbilical cord 

        • Wharton's jelly, also found in pulp of young teeth 

    • Reticular: form a net 

      • Forms delicate stroma (dupportive framework) of lymphoid and soft organs by reticular cells which are specialised fibroblasts 

      • In hemopoeitic portion of the bone marrow (cells that give rise to bone) 

      • Around blood vessels 

      • Binds smooth muscle cells together 

    • Adipose 

    • Fluid (hematopoietic)  

  • Supporting connective tissue: cartilage