Histo.3

• Objectives


  • List the classification of connective tissue and its major histological features
  • Provide examples where they are found in the body
  • Cells of the connective tissue(types,functions,site of location in connective tissue and differentiation among them histologically
• Connective tissue


  Provides support, binds together, and protects tissues and organs of the body
• Components of connective tissue


  • Cells
  • Protein fibers
  • Ground substance
• Extracellular matrix


  The major component of most connective tissue, made up of fibers and ground substance
• Cells of connective tissue


  • Fibroblasts (fibrocytes)
  • Adipocytes (fat cells)
  • Macrophages
  • Mast cells
  • Plasma cells
  • Other leukocytes
• Fibroblasts


  The major cells of connective tissue proper, elongated and irregularly shaped with oval nuclei that synthesize and secrete most components of the ECM
• Adipocytes


  Very large cells specialized for storage of triglycerides, predominate in adipose tissue
• Macrophages


  Short-lived cells that differentiate in connective tissue from precursor cells called monocytes, function in ECM turnover, phagocytosis, and antigen presentation
• Mast cells


  Originate from blood cell precursors, filled with granules for the release of various vasoactive agents and other substances during inflammatory and allergic reactions
• Plasma cells


  Short-lived cells that differentiate from B lymphocytes, specialized for the abundant secretion of specific antibodies (immunoglobulins)
• Connective tissue fibers


  • Collagen fibers
  • Elastic fibers
  • Reticular fibers
• Collagen fibers


  Tough, thick, fibrous proteins that do not branch, most abundant fibers found in almost all connective tissue
• Types of collagen fibers


  • Type I
  • Type II
  • Type III
  • Type IV
• Type I collagen fibers


  Found in the dermis of skin, tendons, ligaments, and bone, very strong and offer great resistance to tensile stresses
• Type II collagen fibers


  Present in hyaline cartilage and elastic cartilage, provide resistance to pressure
• Type III collagen fibers


  Thin, branching reticular fibers that form the delicate supporting meshwork in organs like lymph nodes, spleen, and bone marrow
• Type IV collagen fibers


  Present in the basal lamina of the basement membrane, to which the basal regions of the cells attach
• Reticular fibers


  Thin, form a delicate netlike framework in the liver, lymph nodes, spleen, hemopoietic organs, and other locations where blood and lymph are filtered, also support capillaries, nerves, and muscle cells
• Elastic fibers


  Thin, small, branching fibers that allow stretch, composed of microfibrils and the protein elastin, return to original size without deformation
• Locations of elastic fibers


  • Lungs
  • Bladder
  • Skin
  • Walls of aorta and pulmonary trunk
• Types of connective tissue

  • Connective Tissue Proper (loose, dense irregular, dense regular)
  • Embryonic Connective Tissues (mesenchyme, mucoid)
  • Specialized Connective Tissues (reticular, adipose, cartilage, bone, blood)
• Loose (areolar) connective tissue

  More prevalent in body, exhibits loose, irregular arrangement of cells and fibers, abundant ground substance, many cells and little collagen, allows tissue to move freely, supports microvasculature, nerves, and immune defense cells
• Dense irregular connective tissue

  Little ground substance, few cells (mostly fibroblasts), much densely packed collagen fibers with random orientation, provides strong tissue support, protects organs, resists tearing
• Dense regular connective tissue

  Almost completely filled with parallel bundles of collagen, few fibroblasts aligned with collagen and minimal ground substance, provides strong connections within musculoskeletal system, strong resistance to force
• Mesenchyme


  Sparse, undifferentiated cells, uniformly distributed in matrix with sparse collagen fibers, contains stem/progenitor cells for all adult connective tissue cells
• Mucoid (mucous) connective tissue

  Gelatinous, with sparse collagen fibers and scattered fibroblasts, supports and cushions, found most abundantly around blood vessels in the umbilical cord
• Reticular connective tissue


  Delicate network of reticulin/collagen III with attached fibroblasts (reticular cells), supports blood-forming cells, many secretory cells, and lymphocytes in most lymphoid organs
• Types of adipose tissue


  • White adipose tissue (specialized for fat storage)
  • Brown adipose tissue (contains cells with multiple lipid droplets and abundant mitochondria, releases heat to warm blood)
• Dense regular connective tissue


  Composed of type I collagen fibers oriented in the same direction, provides tensile strength in one direction
• Dense irregular connective tissue


  Contains type I collagen fibers woven in multiple directions, provides tensile strength in multiple directions
• Embryonic connective tissue


  Formed during embryo development, mesenchyme develops into various connective tissues, mucoid connective tissue is a gelatinous substance found in the umbilical cord
• Connective tissue cells


  • Fixed cells (fibroblasts, adipocytes, macrophages, mast cells)
  • Transient cells (leukocytes that migrate from bloodstream)