HISTOOOO (PPT: Connective tissue)

• Connective Tissue


  Formed by three classes of components: cells, fibers, ground substance
• Extracellular Matrix (ECM)


  • Major constituent of connective tissue
  • Composed of protein fibers and ground substance
• Ground Substance


  Highly hydrophilic, viscous complex of anionic macromolecules (glycosaminoglycans and proteoglycans) and multiadhesive glycoproteins (laminin, fibronectin, and others)
• Functions of Connective Tissue


  • Storage (lipids, water, electrolytes)
  • Transport (nutrients, metabolic wastes)
  • Defense (phagocytic, antibody producing cells)
  • Repair (great capacity for regeneration)
• Fixed Cells in Connective Tissue

  • Fibroblasts
  • Fat cells
  • Undifferentiated mesenchymal cells
  • Reticular cells
• Wandering/Mobile Cells in Connective Tissue

  • Neutrophils
  • Monocytes
  • Lymphocytes
  • Mast cells
  • Plasma cells
  • Macrophages
• Mesenchyme


  Embryonic tissue where all types of connective tissues originate, formed by elongated undifferentiated cells with oval nuclei, prominent nucleoli and fine chromatin

  
• Fibroblasts


  • Originate locally from undifferentiated mesenchymal cells
  • Synthesize collagen, elastin, glycosaminoglycans, proteoglycans and multiadhesive glycoproteins
  • Most common cells in connective tissue

  
• Fibroblasts (active)


  Large cells with large, euchromatic nuclei and basophilic cytoplasm

  
• Fibroblasts (quiescent/fibrocytes)


  Smaller cells with less prominent, heterochromatic nuclei
• Adipocytes


  Also known as fat cells, connective tissue cells specialized for storage of neutral fats or production of heat
• Functions of Adipose Tissue

  • Storage of neutral fats or production of heat
  • Key regulators of body's energy metabolism
  • Shock absorbers
  • Insulators
  • Protecting organs
  • Aesthetic purposes
• Types of Adipose Tissue

  • White adipose tissue
  • Brown adipose tissue
• White Adipose Tissue


  More common, composed of cells containing one large central droplet of whitish-yellow fat
• Brown Adipose Tissue


  Contains cells with multiple lipid droplets interspersed among abundant mitochondria, giving them a darker appearance
• Mast Cells, Macrophages, Plasma Cells


  • Originate from hematopoietic stem cells in bone marrow
  • Transient cells of most connective tissues
  • Usually die by apoptosis
• Macrophages


  • Characterized by an irregular surface with pleats, protrusions, and indentations
  • Have well-developed Golgi apparatus, many lysosomes, and rough ER
• Activated Macrophages


  Stimulated macrophages that change their morphological characteristics and metabolism, acquire enhanced phagocytosis and intracellular digestion, and exhibit increased metabolic and lysosomal enzyme activity
• Types of Macrophages


  • Kupffer cells (liver)
  • Microglial cells (central nervous system)
  • Langerhans cells (skin)
  • Osteoclasts (bone tissue)
  • Multinuclear giant cells (connective tissue)

  
• Mast Cells


  Large, oval or round connective tissue cells, 20–30 μm in diameter, with cytoplasm filled with basophilic secretory granules
• Metachromasia


  Displayed by mast cells due to high content of acidic radicals in their sulfated glycosaminoglycans, which can change the color of some basic dyes
• Important Molecules Released from Mast Cell Granules

  • Heparin
  • Histamine
  • Serine proteases
  • Eosinophil and neutrophil chemotactic factors
  • Leukotrienes C4, D4, and E4 (SRS-A)
• Types of Mast Cells

  • Perivascular mast cells (near small blood vessels in skin and mesenteries)
  • Mucosal mast cells (mucosa lining digestive and respiratory tracts)
• Plasma Cells


  Large, ovoid cells with basophilic cytoplasm due to richness in rough ER, and eccentrically placed spherical nucleus with alternating areas of heterochromatin and euchromatin

  
• Diapedesis


  Migration of leukocytes from the blood vessels to the connective tissue, which increases greatly during inflammation
• Inflammation


  Vascular and cellular defensive reaction against foreign substances, characterized by redness, swelling, heat, and pain
• Chemical Mediators of Inflammation


  Substances of various origin that induce some of the events characteristic of inflammation
• Leukocytes do not return to the blood after arriving in connective tissue except for the lymphocytes
• Chemotaxis


  Responsible for the migration of large quantities of specific cell types to regions of inflammation
• Three Main Types of Connective Fibers

  • Collagen
  • Reticular
  • Elastic fibers
• Collagen


  • Various types present in skin, bone, cartilage, smooth muscle, and basal lamina
  • Molecules of long fibril-forming collagens aggregate to form fibrils visible under microscope
• Collagen Types that Form Fibrils

  • Type I
  • Type II
  • Type III
  • Type V
  • Type XI
• Fibril-Associated Collagens


  • Type IX
  • Type XII
  • Type XIV
• Anchoring Collagen (Type VII)


  Present in the anchoring fibrils that bind the basal lamina to reticular fibers in the underlying connective tissue
• Collagen Type IV


  Assembles as a lattice-like network in the basal lamina
• Osteogenesis imperfecta results from mutations in the alpha1 (I) or alpha2 (I) collagen genes, most often due to deletions
• Progressive systemic sclerosis presents an excessive accumulation of collagen (fibrosis) on almost all organs, causing hardening and functional impairment
• Keloids are local swellings caused by abnormal amounts of collagen that form in scars of the skin, occurring most often in individuals of black African descent
• Scurvy, caused by Vitamin C deficiency, leads to degeneration of connective tissue due to fibroblasts synthesizing defective collagen
• Disorders Resulting from Defects in Collagen Synthesis

  • Ehlers-Danlos type IV (faulty transcription or translation of collagen type III)
  • Ehlers-Danlos type VI (faulty lysine hydroxylation)
  • Ehlers-Danlos type VII (decrease in procollagen peptidase activity)