Connective Tissue - Histo Lec

• connective tissue - to elaborate and maintain variety of extracellular matrix which originate from embryonic mesenchyme (from mesoderm)
• connective tissue is made up of:

  1. tissue cells
  2. protein fibers
  3. ground substances
• fibers + ground substance = extracellular matrix (ECM)
• Functions of Connective Tissue

  1. To support organs and soft tissues of the body
  2. serves as a binding substance for organs and tissues
  3. protection of the body
  4. fat storage and insulation
  5. hematopoietic function
  6. protection against bacterial infection
  7. repair of the body
• Types of Connective Tissue Cells

  1. Fixed Cells
  2. Wandering cells
• fixed cells - considered as the permanent resident of connective tissue
• examples of fixed cells are fibroblast and adipocyte
• wandering cells - transient immigrants or temporary resident from the blood stream
• wandering cells examples are leukocytes, mast cells and plasma cells
• fibroblast

  • principal cells of connective tissue or most common connective tissue cell
  • responsible for the synthesis of fibers and ground matrix
  • derived from mesenchymal cells
• young fibroblast - active cell
• fibrocyte - quiescent
• Young Fibroblast (it has more rough ER)

  cytoplasm - abundant and irregularly branched, basophilic (RER and Golgi Apparatus)

  nucleus - ovoid, large, and pale staining with fine chromatin and a prominent nucleolus
• fibrocyte (mature fibroblast, spindle shaped, stellate shaped ; less rough ER)

  cytoplasm - acidophilic

  nucleus - darker and elongated. no nucleolus
• mesenchymal cells

  • similar but smaller than fibroblast, flattened in stellate shape
  • also known as multipotential or pluripotential cell
• macrophages

  • has the ability to take particulate materials with their cytoplasm and degrade the ingested substance with hydrolytic enzymes by phagocytosis
  • it can proliferate locally, present in all organs, constituting a diffuse system called "Mononuclear Phagocytic System"
  • also known as histiocytes
• Mononuclear Phagocytic System

  Liver - kupffer cells

  kidney - mesanglial cells

  bones - osteoclasts

  spleen - spleening macrophage

  lungs - alveolar macrophage

  placenta - hoffbauer cells

  skin - langerhans cells

  brain - microglial cells
• bloodstream = monocytes

  fixed cell = macrophage
• Fat Cells

  • specialized for storage of neutral fats or heat production
  • found in singly or in group
  • "signet ring" appearance
  • NOTE: fat globules pushes nucleus to the sides producing a signet ring appearance
• Plasma Cells

  • few or rare in connective tissue in most areas of the body
  • numerous in sites subject to the penetration of bacteria and foreign proteins and in areas of chronic inflammation
  • synthesize of the antibodies found in the bloodstream
  • precursor are the B-lymphocytes (blood)
• Mast Cells

  • large ovoid cell, are actively involved in anaphylactic sensitivity reactions
  • cytoplasm - abundant intensely staining basophilic granules
  • nucleus - spherical and centrally located
• Contents of Mast Cell Granules

  
  

  heparin - anticoagulant

  histamine - promotes increased vascular permeability and smooth muscle contraction

  serine proteases - activates inflammation

  chemotactic factors - attract leukocytes
• Collagen Fibers

  • most abundant protein in body (30% of dry weight of body)
  • colorless strands in fresh collagen fibers but present in great numbers that cause the tissue to become white
  • acidophilic when viewed in light microscope (pink in eosin)
  • there are 28 collagen types in vertebrates
• Reticular Fibers

  • principally Type III collagen
  • found in stroma of many glandular organs, basal lamina of most epithelia, and they form the supporting tissue lymphoid and blood forming organs such as kidney, liver, spleen, and lymph nodes
  • stains black
• Elastic Fibers

  • imparts a yellowish color due to the presence of elastin protein
  • they can be stretched by a small force and return back the original dimension when force is removed (rubber-like quality)
  • seen in lungs and blood vessels
  • resistant to most proteases, but is hydrolyzed by pancreatic elastase
• Ground Substance

  • translucent matrix that exhibits no structural organization
  • visible with light microscope
  • surrounds the cells and the fibers of connetive tissue
  • they contain acid (mucopolysaccharide or glycosaminoglycans), hyaluronic acid, chondroitin sulfate, dermatan sulfate, keratan sulfate, and heparan sulfate
• Types of Collagenous Connective

  1. Loose
  2. Dense (subdivided into dense regular and irregular)
• Loose Connective Tissue

  • "areolar" tissue
  • widely distributed in the human body
  • composed of fibers which are relatively few, far apart, and runs in many directions
  • found in papillary of dermis, in the hypodermis of skin, pia mater of spinal cord, endoneurium, and endomysium of muscle and nerve
• Dense Connective Tissue - occurs in the form of bands, sheets, cord, or bundles
• Dense Irregular

  • bundles in arrangement but are randomly oriented or runs in few directions
  • found in the dermis of the skin, submucosa of esophagus, capsule of organs, periosteum, and perichondrium
• Dense Regular

  • occurs in cordlike structure and as bands
  • the collagenous fibers are usually in bundles that are oriented parallel to one direction
  • seen in tendons, ligaments, aponeurosis and fascia
• Elastic Tissue

  • abundance of elastic fiber in a tissue confers great elasticity
  • takes the form of fibers and fenestrated lamellae or sheets
  • found in the wall of organs, large artery, trachea, bronchi and vocal chords
• White/Yellow Adipose Tissue

  • comprises the bulk of the body
  • an adult fat or mature form of adipose tissue from which range its color from white to dark yellow
  • cell contains a single large fat droplet in the cytoplasm, unilocular as to morphology
• Brown Adipose Tissue

  • fetal fat or immature form, its color ranges from tan to reddish brown
  • cell contains multiple lipid droplets in the cytoplasm, hence it is multilocular as to morphology
  • found in interscapular and inguinal regions of newborn
• Mucous Connective Tissue

  • has abundance of ground matrix composed chiefly of hyaluronic acid
  • a jelly-like tissue containing collagen fibers and a few elastic or reticular fibers
  • example: wharton's jelly of umbilical cord
• Subtypes of Connective Tissue

  1. Collagenous
  2. Elastic
  3. Reticular
  4. Adipose
  5. Undifferentiated Mesenchymal Tissue
• Connective tissues all consist primarily of extracellular material rather than cells
• stroma - supports the organ's unique functional components or parenchyma
• adipocytes are very large cells specialized for storage of triglycerides and they predominate in a specialized form of connective tissue called adipose tissue
• macrophages are short-lived cells that differentiate in connective tissue from precursor cells called monocytes circulating in the blood