histology connective tissue

• Connective tissues


  • Serves a variety of functions
  • To support organs and soft tissues of the body, most conspicuous function
  • Serves as a binding substance for organs and tissues
  • Protection of the body
  • Fat storage and insulator
  • Hematopoietic function
  • Protection against bacterial infection
  • Repair of the body
• Mesenchyme


  Embryonic tissue characterized by branched cells embedded in an abundant amorphous intercellular substance, derived from the mesoderm and spreads throughout the fibers, surrounding and penetrating the developing organs
• Connective Tissue Cells


  • Fixed cells (fibroblasts, mesenchymal cells, reticular, fat cells)
  • Wandering cells (WBC, mast cells, plasma cells)
• Fibroblasts


  • Principal cells of connective tissue responsible for the synthesis of fibers and ground matrix
  • Young fibroblast has abundant and irregularly branched cytoplasm, ovoid large pale staining nucleus with fine chromatin and prominent nucleolus, basophilic cytoplasm
  • Mature fibrocyte is spindle-shaped with processes, darker elongated nucleus, acidophilic cytoplasm
• Mesenchymal Cells


  • Similar but smaller than fibroblasts, flattened or stellate shaped, multipotential cells able to transform into other cell types
• Macrophages/Histocytes


  • Monocular cells with ability to phagocytose and degrade particulate materials, derived from bone marrow precursor cells that become monocytes and migrate to connective tissue
• Fat Cells


  • Connective tissue cells specialized for storage of neutral fats or heat production, accumulate lipid globules displacing the nucleus to one side
• Plasma Cells


  • Ovoid cells with eccentric nucleus and intensely basophilic cytoplasm, dark staining "cartwheel" or "spokewheel" chromatin pattern, responsible for antibody synthesis
• Mast Cells


  • Large ovoid cells with abundant intensely staining basophilic cytoplasmic granules, contain heparin, histamines, and serotonin, involved in anaphylactic reactions
• Connective Tissue Fibers


  • Collagen Fibers
  • Elastic Fibers
  • Reticular Fibers
• Collagen Fibers


  Most numerous fibers in connective tissue, colorless strands that appear white in bulk, 0.5-2um diameter and indefinite length, wavy course when not under tension, birefringent, elastic and strong, stain pink with eosin
• Types of Collagen


  • Type I - most abundant, widespread
  • Type II - in cartilage
  • Type III - associated with Type I, in reticular fibers
  • Type IV - in basal lamina and basement membrane
  • Type V - in fetal membranes and other tissues
  • Type VII - anchoring fibrils of basal lamina
• Collagen Type I and III are the most common types
• Elastic Fibers


  Impart a yellowish color, slender 0.2-1.0um diameter fibers that can be stretched and return to original dimensions, resistant to boiling and hydrolysis
• Reticular Fibers

  Very slender 0.5-2um diameter fibrils that form delicate networks, stain with silver, collagenous component is mainly Type III collagen, found in stroma of glandular organs, basal lamina, and supporting tissue of lymphoid and blood forming organs
• Ground Matrix


  Translucent matrix surrounding cells and fibers, contains acid mucopolysaccharides or glycosaminoglycans like hyaluronic acid, chondroitin sulfate, dermatan sulfate, keratin sulfate, and heparin sulfate
• Subtypes of Connective Tissue


  • Fibrous connective tissue (collagenous, elastic, reticular)
  • Adipose tissue
  • Undifferentiated mesenchymal tissue
  • Mucous connective tissue
  • Bone or Osseous (compact, spongy)
  • Cartilage (hyaline, elastic, fibrous)
  • Myeloid tissue or bone marrow
  • Blood and Lymph
  • Lymphatic tissue (loose, dense, nodular)
• Loose Connective Tissue


  • Widely distributed, forms superficial fascia and stroma of organs, surrounds blood vessels and nerves, contains potential spaces ("areolar tissue"), collagen fibers are relatively few and randomly oriented
• Dense Irregular Connective Tissue


  • Collagenous fibers arranged in randomly oriented bundles, found in dermis, submucosa, organ capsules, periosteum, perichondrium
• Dense Regular Connective Tissue


  • Collagenous fibers in parallel bundles or bands, high tensile strength, found in tendons, ligaments, aponeuroses
• Fibrous Connective Tissue


  • Dense regular
  • Dense irregular
• Elastic Tissue


  • Elastic fiber predominates
  • Confers great elasticity
  • Takes the form of fibers and fenestrated lamellae or sheets
  • Found in wall of hollow organs, large artery, internal elastic membrane of medium sized artery, trachea, bronchi, vocal cords, yellow ligaments of vertebral column, suspensory ligament of penis
• Reticular Tissue

  • Reticular fiber predominates
  • Forms supporting framework of bone marrow, lymphoid and hematopoietic organs
  • Characterized by presence of mesenchymally derived cellular reticulum and fine extracellular fibrils
  • Fibrils are called reticular fibers, cells are reticular cells
  • Fibrils have special staining affinity to silver salts (argyrophilic fibers)
  • Found in close association with basal lamina of most epithelia
• Adipose Tissue


  • Adipose cells predominate
  • Adipose cells are large, oval or spherical with single large fat droplet displacing cytoplasm to periphery
  • Nucleus is flattened and surrounded by small amount of cytoplasm (signet ring appearance)
  • Functions: storage of fat, insulation against heat loss, mechanical support
• Types of Adipose Tissue


  • Yellow or White adipose tissue
  • Brown adipose tissue
• White Adipose Tissue


  • Common or yellow or white adipose tissue
  • Comprises bulk of body
  • Adult or mature form
  • Color ranges from white to dark yellow
  • Adipose cell contains single large fat droplet (unilocular)
• Brown Adipose Tissue


  • Fetal fat or immature form
  • Color ranges from tan to reddish brown
  • Cell contains multiple lipid droplets in cytoplasm (multilocular)
  • Found in interscapular and inguinal regions of newborns
• Undifferentiated Mesenchymal Tissue


  • Mesenchymal cells predominate
  • Mesenchymal cells are multipotential (pluripotential)
  • Can be found in some parts of uterus, fallopian tube, along blood vessels
• Mucous Connective Tissue


  • Abundance of ground matrix composed chiefly of hyaluronic acid
  • Jelly-like tissue containing collagen, elastic or reticular fibers
  • Composed of large stellate fibroblast cells with processes contacting neighbors
  • Few macrophages and lymphoid wandering cells present
  • Intercellular substance is abundant, soft, jelly-like and homogenous
  • Examples: Wharton's jelly of umbilical cord, pulp of young teeth
• Bone


  • Specialized dense connective tissue
  • Intercellular substance or matrix is infiltered with calcium salts
  • Consists of cells, fibers, and ground matrix
  • Extracellular components are calcified, making it hard and unyielding
  • Functions: support of fleshy structures, protection of vital organs, attachment of muscles/tendons/ligaments, shape contribution, lever for movement
• Bone Cells


  • Osteoprogenitor cells
  • Osteoblasts
  • Osteocytes
  • Osteoclasts
• Osteoprogenitor Cells


  • Relatively undifferentiated cells with capacity for mitosis
  • Active during normal bone growth, undergo division to transform into osteoblasts or units giving rise to osteoclasts
• Osteoblasts


  • Bone forming cells
  • Responsible for synthesis of organic components of bone matrix
  • Exclusively located at bone tissue surface when engaged in matrix synthesis
  • Have cuboidal shape and basophilic cytoplasm
• Osteocytes


  • Mature cells found encapsulated in laminae of mineralized bone matrix
  • Lodged in lacunae of cavities
  • Have filopodial processes from adjacent cells connected by gap junctions within canaliculi radiating from lacunae
• Osteoclasts


  • Multinucleated giant cells involved in resorption and remodeling of bone tissue
  • Large, extensively branched motile cells found living within enzymatically etched depressions in matrix called Howship's lacunae
• Components of Bone


  • Organ component
  • Collagen
  • Ground Substance
• Collagen in Bone


  • Constitutes about 95% of organic substance
  • Synthesized from vesicles of rough endoplasmic reticulum
  • Occurs as cross striated fibers 50-70 μm in diameter
  • Predominantly Type I collagen
  • Has greater degree of intermolecular bonding compared to collagen from other tissues
• Ground Substance in Bone

  • Mucopolysaccharide cement substance in which collagen fibrils are embedded
  • Synthesized from vesicles of Golgi apparatus
  • Contains chondroitin sulfate, keratin sulfate, and hyaluronic acid