Lesson 2

• Connective tissues (CT)


  A group of tissues which connects or binds other tissues in the body
• Connective Tissue


  • Mechanical support
  • Medium for exchange of nutrients & waste products
  • Energy store and thermal insulation
  • Defensive functions (Barrier, Engulf bacteria, Antibodies)
• Connective Tissue


  • Predominantly intercellular material (matrix)
  • Cells widely spaced
  • Development from mesoderm, neural crest (head region)
  • Few blood vessels supply
• Connective Tissue

  Classification based on matrix, cells, fibres
• Connective Tissue


  • Characterized by an abundance of extracellular material with a paucity of cells
• Major Groups of Connective Tissue

  • CT proper
  • CT special types: cartilage, bone, blood & hemopoietic tissue (myeloid & lymphoid)
• Connective Tissue Proper

  • Found all over the body
  • Envelopes muscles
  • Binds body parts together but allows some degree of movement
  • Forms the stroma or supporting framework of various organs
  • Serves as a venue for the exchange of gases & substances between the other basic tissues & blood
  • Provides the cells needed to defend the body against invading organisms & harmful substances
• Cartilage


  • Consists of a network of closely packed collagen fibers and elastic fibers
  • Cells of mature cartilage are called chondrocytes
• Hyaline Cartilage

  • Bluish-white in color
  • Consists of fine collagen fibers and many chondrocytes
  • Location: End of long bones, anterior ends of ribs, nose, parts of larynx, trachea, bronchi, bronchial tubes
  • Function: Provides small surface for movement at joints, flexibility, and support
• Elastic Cartilage


  • Strongest form of cartilage
  • Chondrocytes located within a threadlike network of elastic fibers within extracellular matrix
  • Location: Pinna of ear, top of larynx
  • Function: Provides strength, elasticity, and maintains the shape of certain organs such as the external ear
• Fibro Cartilage


  • Strongest form of cartilage
  • Chondrocytes scattered among the bundle collagen fibers within the extracellular matrix
  • Location: Intervertebral disc
  • Function: Covers and protects bony structures of the body
• Structure of Cartilage

  • Hyaline Cartilage
  • Elastic Cartilage
  • Fibro Cartilage
• Bone (Osseous Tissue)
• Blood
• CT Composition

  • Consists of cells & ECM
  • Cells are scattered individually in the ECM
  • Presence of blood vessels & nerve fibers
• Extracellular Matrix (ECM)


  • Ground Substance: Amorphous, homogenous, transparent, hydrated gel consisting mainly of water with proteoglycans, mineral salts & glycosaminoglycans
  • Proteoglycans are the main structural constituent with Glycosaminoglycans (GAGs)
• Five types of Glycosaminoglycans

  • Hyaluronic acid (most abundant)
  • Keratan sulfate
  • Chondroitin sulfate
  • Dermatan sulfate
  • Heparan sulfate
• Five types of Glycosaminoglycans

  • hyaluronic acid (most abundant)
  • keratan sulfate
  • chondroitin sulfate
  • dermatan sulfate
  • heparan sulfate
• Hyaluronic acid (HA)


  A naturally occurring glycosaminoglycan found throughout the body's connective tissue
• Hyaluronic acid (HA)


  • Main component of what gives skin structure, responsible for plump and hydrated look
• Three types of Extracellular Fibers (ECF)

  • collagen
  • elastic
  • reticular
• Composition of Connective Tissue

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


  • Large fibers made of the protein collagen, promote tissue flexibility, present in all CTs, appear pink in H & E prep but blue in Masson trichrome stain, have tensile strength, most abundant CHON in the body, PROCOLLAGEN is the molecular precursor of a collagen fiber
• Elastic Fibers (EFs)


  • Fine fibers about 1 um in diameter, branch and anastomose, pinkish-yellow in H & E stain but blue-black in orcein stain, have lesser tensile strength than collagen fibers but flexible and recoil back to their original length due to elastin CHON, abundant in specific body parts, formed by fibroblasts, smooth muscle cells, and mesenchymal cells
• Reticular Fibers (RFS)


  • Contain collagen type III, very fine fibers that branch and anastomose, appear black in silver stain, sparse in most CTs but main ECFs in specific organs, excreted by reticular cells
• Cells in Connective Tissue

  • Resident Cells: fibroblasts/fibrocytes, reticular cells, adipose cells, mast cells, resident macrophages
• Fibroblasts (fbs) & Fibrocytes (fcs)

  • Fbs are the most abundant cells in most CTs, produce precursors of fibers, larger with irregular cytoplasmic processes, capable of mitosis; Fcs are resting FBs, smaller, not actively synthesizing CT elements, acidophilic cytoplasm
• Reticular cells


  • Specialized FBs that synthesize precursors of type III collagen, abundant in specific tissues and organs, slightly larger than typical FBs
• Adipose/fat cells

  • Store lipids mainly triglycerides, predominant in adipose tissue, mature fat cells do not divide, nucleus and organelles pushed to one side by fat droplet
• Mast cells


  • Abundant in specific body parts, large ovoid cells with centrally located spherical nuclei
• Signet ring cell


  • Found on 1 side on H & E stain
• Mature fat cells DO NOT divide, if needed, can be sourced from mesenchymal cells or pre-fat cells
• Mast cells

  • Abundant in GIT, respiratory tract, underneath the skin & blood vessels; come from bone marrow
  • Large, ovoid cells w/ centrally located spherical nuclei & numerous cytoplasmic granules
  • Dark purple in toluidine blue stain
  • Contains heparin (anticoagulant), histamine (stimulates Sm M cells of the lungs) & some proteases
  • Involved in inflammation & immediate-type hypersensitivity rn (allergic or anaphylactic shock)
  • Plays a role in wound healing & pathogen defense
  • Similar to basophils except that basophils are smaller, mobile, have a shorter life span, inability to divide & come from different progenitor cells
• Macrophages

  • Phagocytes that differentiate from monocytes & are widely distributed all over the body
  • Play a major role in the body's inflammatory response by engulfing & digesting invading microorganisms
  • Ingest & destroy not only bacteria but also dead or dying cells & senescent tissue elements
  • Found in lungs (pulmonary alveolar macrophages), liver (kupffer cells), CT (histiocytes/fibroblasts)
  • On mobility: can be fixed or free in CTs
  • Become activated by certain stimuli & increase their functional activity
• Visiting cells in Connective Tissue

  • Inflammatory macrophages
  • Plasma cells
  • Leukocytes (WBCs)
• Plasma cells


  • Abundant in lamina propria of digestive tract where it is accessible to foreign proteins & bacteria
  • Differentiate from WBCs called B lymphocytes (B cells)
  • Produce immunoglobulins (antibodies) in response to an antigen (foreign to the body: bacteria, viruses etc) & destroy the latter
  • Slightly bigger than RBC & blue on H & E stain with eccentric nucleus ("cartwheel appearance")
  • Terminally differentiated cell incapable of cell division
• Leukocytes/WBCs


  • Produced in the bone marrow
  • Reach the CT by escaping from the blood capillaries by amoeboid movement
  • Gather in inflamed & infected areas of the body
• Classification of Connective Tissue Proper

  • Loose CT (Areolar CT)
  • Dense CT
• Loose CT (Areolar CT)

  • More abundant in the body & cellular than dense
  • Comprises the hypodermis (subcutaneous tissue) of skin, tunica adventitia of old vessels & lamina propria & submucosa of the digestive, respiratory & urogenital tracts
  • Highly vascular & abundant in extracellular substance
• Areolar Connective Tissue


  • Forms a loose network in intracellular material
  • Consists of collagen, elastic fibers, reticular fibers and several kinds of cells
  • Location: Below the skin, fills space between muscles, supports blood vessels and nerves in the alimentary canal
  • Functions: Gives strength, elasticity and support to tissue