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Connective Tissue (Matrix and cells) - Coggle Diagram

- - - - Macrophages ("big-eaters") - These cells are monocytes, which migrate out of the blood and into the fibrous CTs. They can be either fixed (such as in the liver) or they can migrate into CTs on demand. These cells are phagocytic ("eater cells"). Macrophages primarily function in the removal of bacteria and cell debris (such as in wound healing), but also function in the immune response by presenting concentrated antigens to lymphocytes.
      - Mast Cells - Large cells positioned near blood vessels, primarily in the skin and mucous membranes. These cells contain granules that mediate inflammation and increase sensitization of local pain receptors (nociceptors) in the CT.
      - Reticular cells - Most histologists consider reticular cells to be fibroblasts since they secrete type III collagen
      - Fibroblasts - responsible for secreting the majority of stromal and ground substance elements of CTs.
      - Pericyte –Found along the walls of capillaries, Helps to control the blood flow to the Central Nervous System (CNS). May also help in controlling blood flow during ischemia.
      - Mesenchymal cells - Just a reminder, the stem cells for fibroblasts are present in CTs as a source of renewal and replacement.
      - Adipocytes (fat or adipose cells) - Though adipocytes are generally classified as connective tissue, there are some characteristics of adipose tissue that do not fit our description of fibrous CTs. For instance, adipocytes store large amounts of lipid, but do not secrete extracellular fibers. Interestingly, EACH adipocyte is surrounded by its own basement membrane which actually separates it from the surrounding fibrous CT. However, adipocytes are thought to differentiate from mesenchymal cells so they can be properly classified as connective tissue.
    - - White Blood Cells - White blood cells can migrate out of the blood into connective tissues.
      - Pigment Cells - Pigmented cells are either melanocytes or melanophages. Both of these cells contain the pigment melanin. The difference is that melanocytes PRODUCE melanin (they contain the enzyme tyrosinase), and melanophages are passive carriers of melanin (they lack the enzyme necessary to form melanin). You cannot tell these two cells apart with regular histological techniques.
  - - - collagen
        
        unbranched, and stains acidophilic with H&E stain, a structural glycoprotein
        
        See formation of collagen in lecture
        
        Type III: small, banded; reticular CT (CT of organs), smooth muscle, endoneurium, blood vessels, lung, lymphoid tissues, bone marrow, and fetal skin. Can only be viewed with special staining (heavy metals).
        
        Reticular CT is a type of collagen. It appears different because of the Type III collagen, which is a very thin fibril that forms a loose mesh of support, especially prevalent in lymphoid organs and bone marrow. Reticular fibers are so fine that normal H&E staining does not allow viewing with the light microscope, a heavy metal stain (silver) is usually needed.
        
        Type II: small, banded; cartilage (hyaline and elastic), intervertebral disks, and vitreous of eye; difficult to view individual fibers; appears as a fairly amorphous matrix.
        
        Type IV: sheet-like layers; basement membranes, kidney glomeruli, and lens capsule. Usually, not able to observe with the light microscope.
        
        Type I: most abundant type of collagen; large, banded; found in skin, bone, tendons, ligaments, dentine, sclera, fascia, and organ capsules. Easily viewed with H&E stain and the light microscope.
      - elastin
        
        Elastic fibers are secreted by fibroblasts and are found scattered among the collagen in most locations where fibrous CT is found.
        
        elastic CT: when the predominant fiber is elastin
        
        composed of microfibrils (fibrillar glycoprotein) and the globular protein elastin
    - - GAGs (glycosaminoglycans): High molecular weight polymers with repeating disaccharide units. The ability of GAGs to bind large amounts of water gives them the property of resisting compression.
        
        Hyaluronic acid - linker protein that binds proteoglycans; important in maintaining the compressive properties of cartilage and synovial fluid.
        
        Chondroitin sulfates - bind large amount of water and sodium ions in cartilage, bone, skin, and fibrous CTs.
        
        Dermatan sulfate - bind large amounts of water and sodium in the skin, blood vessels and heart.
        
        Heparin sulfate - heparin binds large amounts of water and sodium in basement membranes, the lung, liver, and skin.
        
        Keratan sulfate - binds large amounts of water and sodium in cartilage, the cornea and intervertebral disks.
      - Proteoglycans - GAGs are usually complexed to form large proteins called proteoglycans.
      - Water - also called interstitial, extracellular or intercellular fluid
      - Proteoglycan aggregates - In cartilage, proteoglycans are bound to long strands of hyaluronic acid, forming a huge complex of water-binding molecules. These complexes are called proteoglycan aggregates.