connective tissue

• Specialized Connective Tissues

  • Reticular Tissue
  • Adipose Tissue
  • Cartilage
  • Bone
• Connective Tissue Cells

  • Resident Cells (Fixed)
  • Visiting Cells (Wandering)
• Types of Embryonic Connective Tissues

  • Mesenchyme
  • Mucoid (Mucous) Connective Tissue
• General function of connective tissue

  1. Enclosing and separating

  2. Connecting tissues to one another

  3. Supporting and moving

  4. Storing

  5. Cushioning and insulating

  6. Transporting

  7. Protecting and Defense
• Types of Connective Tissue Proper

  • Loose Collagenous (Loose Connective Tissue; aka Areolar Connective Tissue)
  • Dense Collagenous (Dense Connective Tissue)
• Mast Cells


  Function in local inflammatory response, tissue repair, innate immunity, and allergic responses
• White Adipose Cells


  Store fat as a single large droplet, function in insulation and organ protection
• Fixed Cells in Connective Tissue

  1. Mesenchymal Cell

  2. Fibroblasts (active)/Fibrocytes (inactive)

  3. Reticular Cells

  4. Adipose Cells

  5. Mast Cells (Mastocytes; Histaminocytes)
• Extracellular Matrix components


  • Connective Tissue Fibers
  • Ground Substance
• Embryonic Mesenchyme


  • Develops mainly from the middle layer of the embryo (mesoderm), consists largely of viscous ground substance with few collagen fibers
• Brown Adipose Cells


  Store fat as multiple lipid droplets, generate body heat, found in hibernating animals and newborns
• Types of connective tissue

  • Connective Tissue Proper aka Collagenous Connective Tissue
  • Embryonic Connective Tissues
  • Specialized Connective Tissues
• Types of Leukocytes (WBCs)

  • Neutrophils
  • Eosinophils
  • Basophils
  • Monocytes
  • Lymphocytes
• Plasma Cells are antibody-producing cells with a lifespan of 10-20 days, differentiating from B-lymphocytes, and are numerous in connective tissues accessible to foreign proteins and bacteria
• Mast cell degranulation


  Release of molecules triggering allergic response
• Mast cells


  • Oval to irregular shape, filled with basophilic granules that almost obscure the nucleus
  • Contain secretory granules including Heparin, Histamine, Serine proteases, Eosinophil/Neutrophil chemotactic factors, Cytokines, and Phospholipid precursors
  • Located near small blood vessels in skin and mesentery (perivascular mast cells) and in the tissue lining the digestive tract (mucosal mast cell)
  • Function as "sentinels" detecting invasion by pathogens
• Contents of mast cell secretory granules

  • Heparin (anticoagulant)
  • Histamine (promotes smooth muscle contraction, increases vascular permeability)
  • Serine proteases (activator of inflammatory mediators)
  • Eosinophil/Neutrophil chemotactic factors (attracts these leukocytes)
  • Cytokines (polypeptides that direct activities of leukocytes)
  • Phospholipid precursors (converted to inflammatory mediators)
• Macrophages are precursor cells of monocytes, with resident and wandering types, where wandering macrophages are part of the inflammatory response and resident macrophages are less active in inflammation
• Macrophages


  • 10-30 μm in size, eccentrically located kidney or oval-shaped nucleus, located in connective tissue of most organs, function in phagocytic action, immune response, and turnover of protein fibers in the connective tissue
• Collagen Fibers


  • Present in all connective tissue, provide tensile strength, made up of Type I Collagen, most abundant protein in the body, formed in fibroblasts, precursor protein is procollagen, stabilized by hydrogen bonds, various types including Fibrillar collagen, Network or sheet forming collagen, and Linking/anchoring collagen
• Types of Connective Tissue Fibers

  • Collagen Fibers
  • Reticular Fibers
  • Elastic Fibers
• Mutations in collagen Type VII are associated with certain conditions
• Functions of Reticular Fibers


  • Surround individual smooth muscles, adipocytes, nerve tissues, small blood vessels
  • Stroma of spleen, liver, lymph nodes, and endocrine glands
  • Reticular lamina
• Locations of Elastic Fibers


  • Stroma of lungs, large blood vessels, elastic ligaments, vocal cords, ligamentum flavum, ear auricles, bladder
• Edema is the excessive accumulation of interstitial fluid
• Types of Collagen

  • Fibrillar collagen
  • Network or sheet forming collagen
  • Linking/anchoring collagen
• Glycosaminoglycans (GAGs) attract water molecules into the matrix due to their negative charge
• Keloid is caused by an abnormal amount of Type I collagen in scar tissue
• Major Glycosaminoglycans (GAGs)

  • Hyaluronic acid
  • Keratan sulfate
  • Chondroitin sulfate
  • Dermatan sulfate
  • Heparan sulfate
• Wound healing stages

  Type III collagen predominates in the early stage and is later replaced by Type I collagen
• Vitamin C is important in the cross-linking of collagen
• Epidermolysis bullosa causes skin to easily break and blisters to occur even with minor trauma
• Vitamin C deficiency leads to scurvy
• Connective tissue in large arteries made up of elastic fibers


  Can lead to aneurysms
• Marfan syndrome is associated with mutations in fibrillin and presents with specific characteristics
• Elastin


  Connective tissue protein with rubber-like properties for extensibility and elastic recoil
• Ground Substance


  Transparent, amorphous, homogenous, gel-like material that fills the space between cells and fibers of the connective tissue
• Fibronectin


  • Synthesized by fibroblasts
  • Has binding sites for collagen and GAGs, integrins
  • Function: cell adhesion, cell migration
  • Medical significance: serves as a common target for bacterial adhesins in the gastrointestinal tract
• Multiadhesive Glycoproteins


  • Large molecules with branched oligosaccharide chains
  • Have multiple binding sites for cell surface integrins and other matrix macromolecules
  • Function: cell adhesion and migration
• Sulfated GAGs


  • Sulfate and carboxyl groups render the GAGs acidic