Histo

• Connective tissue


  Composed of cells and extracellular matrix characterized by an abundance of extracellular material and a relative paucity of cells
• All of the connective tissue in the body are derived from mesoderm, except for some in the head that are derived from ectoderm
• Connective tissues are classified into two major groups

  • Connective tissue proper
  • Special types of connective tissue (Cartilage, Bone, Blood, Hematopoietic Tissue)
• Connective tissue (proper)


  • Found all over the body
  • Acts as "Glue" that binds body parts together
  • Forms the stroma, which means supporting framework
• Other functions of connective tissue

  • Envelops muscle
  • Acts as an avenue for the passage of blood vessels and nerves
  • Serves as a venue for the exchange of gases and substances between blood and basic tissues
  • Provides arena needed to defend the body against invading organism
• Ground substance


  An amorphous, homogenous, transparent, and hydrated gel. It consist mainly in water that is stabilized by proteoglycans, hyaluronic acid, mineral salts, and glycoproteins
• Proteoglycans


  Main structural constituents and are responsible for the gelatinous character of the ground substance of connective tissue
• Glycosaminoglycans (GAG)


  Attached covalently in a radiating substances. Examples: Hyaluronic acid – Most abundant GAG in the ground substance of connective tissue
• Extracellular Fibers


  • Collagen fibers (Collagenous Fibers)
  • Elastic fibers
  • Reticular fibers

  
• Collagen fibers (Collagenous Fibers)


  • Present in all connective tissues, although in differing amounts
  • Made up of collagen
  • Collagenous connective tissue (Ordinary connective tissue) – most commonly occurring type of connective tissue in the body, THE MAIN EXTRACELLULAR FIBERS
  • Colorless in vivo, when present in abundant amounts, as in tendons, imparts WHITE COLOR
  • 2 – 10 um in diameter
  • Appears pink in H&E prep because they are ACIDOPHILIC
  • Most common types of collagen are Types I, II, III
  • Collagen fibers are made up of collagen type I
  • Collagen fibers are slightly flexible but inelastic

  
• Formation of collagen fibers

  1. Procollagen – precursor of collagen fiber

  2. Synthesized by fibroblast and mesenchymal cells

  3. Tropocollagen are formed from three procollagen, these will aggregate to form collagen microfibrils

  4. Collagen microfibrils will group together in parallel fashion to form collagen fibers

  
• Elastic fibers


  • Fine fibers that average 1.0 um in diameter
  • Imparts yellow color to fresh tissue
  • Highly insoluble protein that is responsible for elasticity of elastic fibers
  • Resistant to boiling and hydrolysis by acids and can be hydrolyzed by elastase
• Formation of elastic fibers

  1. Elastogenesis – secrete microfibrils, then aggregate to form bundles

  2. Tropoelastin – precursor protein of elastin

  3. Elastin that forms the elastic lamellae in arteries is synthesized by smooth muscle cells
• Reticular fibers (Reticulin fibers)


  • Also made up of collagen
  • Type III collagen
  • They are very fine (0.5-2.0 um in diameter)
  • Tend to branch and anastomose
  • Referred to as ARGYROPHILIC FIBERS
  • React positively with PAS reagent

  
• Formation of reticular fibers

  Same as collagen fibers but precursors are synthesized and excreted into intercellular matrix by specialized fibroblast called RETICULAR CELLS

  
• Cells in connective tissue

  • Resident cells (Mesenchymal cells, fibroblast and fibrocytes, reticular cells, adipose cells, mast cells, and resident cells)
  • Visiting cells (Inflammatory macrophages, plasma cells, and Leukocytes (WBCs))

  
• Mesenchymal cell


  • Multipotential stem cells
  • Stem cells of most connect tissue (fibroblast and fibrocytes, reticular cells, adipose cells, reticular cells etc)
  • Abound in the embryo and in the umbilical cord
  • Light Microscope: Cannot be distinguished from fibroblast
  • Electron Micrographs: Have coarser chromatin and less developed cytoplasmic organelles than fibroblast
• Fibroblast and fibrocytes


  • Fibroblast are the most abundant cells in most connective tissue
  • Responsible for producing and maintaining most extracellular components of connective tissue
  • Synthesize organic compounds and precursors of collagen and elastic fibers
  • Capable of Mitosis
  • Fibrocytes are considered idle or resting
  • Smaller and have fewer processes than fibroblasts
  • Cytoplasm are acidophilic and nucleus are compact and dark
  • Also called Reticular cells
• Reticular cells


  • Synthesized the precursor of type III collagen that make up reticular fibers
  • Slightly larger than typical fibroblast
  • Most numerous cells in the reticular tissue

  
• Macrophages


  • Phagocytes that are derived from monocytes
  • Light Microscopy: Cytoplasm is slightly basophilic and appears "frothy"
  • Ingest and destroy not only bacteria and exogenous particulate but also dead or drying cells, and senescent tissue elements
  • Classified either, Resident or inflammatory
  • Resident macrophages – those inhabit a given site (not immunologically active)
  • Inflammatory macrophages – those response to a stimulus and are (immunologically active)
• Plasma cells


  • Slightly bigger than RBC
  • Strongly basophilic cytoplasm and eccentric nucleus
  • Nucleus has "Clock-face" or "Cartwheel" appearance
  • B lymphocytes (B cells) – produces antibody
  • Has a lifespan of 10 to 20 days
• Leukocytes or White Blood Cells

  • Nucleated cells in blood
  • Five types: Neutrophils, Basophils, Eosinophils, Monocytes and Lymphocytes
  • Produced in the bone marrow, EXCEPT Lymphocytes
  • In connective tissue, they exhibit AMOEBOID MOVEMENT

  
• Types of connective tissue

  • Collagenous
  • Adipose
  • Reticular
  • Elastic
  • Mucous
• Types of collagenous connective tissue

  • Loose connective tissue
  • Dense connective tissue

  
• Dense collagenous connective tissue

  • Characterized by scanty intercellular ground ground substance
  • Dense irregular – collagen fibers run in various direction
  • Dense regular – collagen fibers are arranged in the definite pattern

  
• Loose collagenous connective tissue

  • A.K.A Areolar Connective Tissue, Areolar Tissue
  • Characterized by high vascularity and abundance of extracellular substance
• Adipose tissue


  • A connective tissue in which the predominant cellular element is the fat of adipose cell
  • Represents the largest energy storage site of the body
  • Male : 12% - 14%; Females : 20% - 25%
  • Function: Serves as storage, thermal insulator, and shock absorber
  • Two types: Yellow (white) – store lipid in the form of single fat vacuole, Brown – store lipids in the form of droplets
  • White adipose tissue synthesize and secrete hormones, notably leptin (satiety hormone)
  • Adipose tissue – considered as endocrine tissue
  • The main function of fat cells in brown adipose tissue is to produce heat (thermogenesis)

  
• Reticular fibers (Reticulin fibers)


  • Forms the stroma of supporting framework of the liver, myeloid tissue, pancreas, lymph tissues and organs

  
• Mucous tissue


  • Abundance of amorphous and jelly-like ground substance
  • The ground substance of mucous tissue is mainly hyaluronic acid
  • Common in embryo
  • Example: Wharton's jelly – the connective tissue present in the umbilical cord

  
• Blood


  • Loose Connective tissue
  • Composed of Extracellular material (Plasma) and cellular elements or formed elements (RBCs, WBCs, and Platelets)

  
• Functions of blood


  • Transports oxygen from the lungs and nutrients from the GI tract
  • Carries CO2
  • Deliver substances (hormones, proteins, etc)
  • Defends the body against microorganisms and toxic substances

  
• Blood comprises 8% of a person's body weight, and is slightly alkaline with a normal pH of 7.4
• Plasma


  Yellowish and translucent top layer, comprises about 54% of the volume
• Buffy coat


  Grayish white film formed by platelets and WBC
• RBC


  Bottom layer accounts 45%
• Stroma


  • Supporting framework of the liver, myeloid tissue, pancreas, lymph tissues and organs
• Mucous tissue


  Abundance of amorphous and jelly-like ground substance
• Ground substance of mucous tissue

  Mainly hyaluronic acid
• Mucous tissue is common in embryo
• Blood


  Loose Connective tissue