Histology of connective tissue, bone and cartilage

• Connective tissue

  • is one of the most abundant and widely distributed tissues in the body.
  • is responsible for providing & maintaining form in the body.
  • It supports, binds tissue parts and is the packing material of the body.
• General characteristics of Connective tissue

  1. Connective tissue possess a relatively large amount of intercellular substance.
  2. They usually do not occur on the surface.
  3. It functions through its extra-cellular components.
  4. They are usually fibrous and vascular.
  5. They all developed from embryonic mesenchyme.
• Fill in the blank

  A) Areolar tissue

  B) white

  C) Yellow

  D) tendon

  E) regular

  F) irregular

  G) Loose

  H) Specialised

  I) Compact

  J) Hyaline

  K) Fibrous

  L) Elastic

  
• Functions of Connective tissues

  1. Mechanical function – provide the connecting & supporting tissues of the body.
  2. Nutritional function – the inter-cellular substance is responsible for nutritional exchange.
  3. Defensive function – Blood leucocytes & histiocytes defend the body against bacteria and foreign bodies.
• Components of adult connective tissue

  1. Cells
  2. Proteinaceous fibers
  3. Amorphous ground substance
• Fill in the blank: Cell of connective tissue

  A) Mesenchyme cell (embryonic)

  B) Fibroblast

  C) Macrophage

  D) Leucocyte

  E) Plasma cell

  F) Mast cell

  G) Fat cell (signet)

  
• All supportive tissue of the body arise from mesenchymal cells except neuroglia, thymus, chromatophores which arise from neural crest cells.
• Fibroblast – Most common.

  • have large active nuclei and eosinophilic cytoplasm that tapers off in both directions along the axis of the nucleus, often referred to as “spindle-shaped.”
  • They appear as flattened, irregular, polyhedral cell with long tapering cytoplasmic processes
  • cytoplasm is pale with a nucleus large, pale, ovoid with 1 or 2 nucleoli.
  • They are active cells and are responsible for the formation of fibers & ground substance
• Fibrocyte

  • are inactive cells.
  • They are much smaller, spindle –shaped with fewer cytoplasmic processes.
  • Nucleus is smaller & darker. Cytoplasm is eosinophilic
• Macrophages

  • are characterized by its great capacity for pinocytosis & phagocytosis.
  • They are important agents of defense by acting as scavengers. When several cells are grouped together and engulf large particles – they are called “foreign body giant cells”.
  • 2 types of Macrophage - fixed & wandering macrophage. (they are different phases of the same cell)
• 2 types of Macrophage

  1. Fixed macrophages

  • are spindle-shaped with an ovoid or indented reniform nucleus & condensed cytoplasm with coarse granules.
  • Inactive forms of macrophage are called “histiocytes”.

  2. Wandering or free macrophage

  • have irregular outline with unusually short & blunt cytoplasmic processes.
  • The nucleus is usually round. Nucleoli is not obvious
• Fill in the blank

  A) Fixed

  B) Free

  
• Fill in the blank

  A) Kupffer cells

  B) Central nervous system

  C) Osteoclasts

  D) Alveolar

  E) Langerhans

  
• Plasma cells

  • They are few in normal tissue.
  • They are large, ovoid cells with a deeply basophilic cytoplasm.
  • Nucleus is large & spheroidal and eccentric in position with cart-wheel appearance of chromatin.
  • Function: production of antibodies.
  • (Infection → antigen → B lymphocyte → plasma cell → antibodies)
• Mast cells

  • They are large ovoid cells present along the small blood vessels.
  • Cytoplasm contains numerous coarse, deeply basophilic secretory granules.
  • Nucleus is small, pale & spheroidal and located centrally.
  • Function: produces heparin & histamine. (dilates the blood vessels as part of the inflammatory response, the body’s action to injury or infection).
  • Mast cells can also kill bacteria
• Adipose cells or fat cells

  • They are normal components of areolar tissue.
  • They are cells that have become specialized for storing neutral fat.
  • They occur single or in clusters between collagen fibers.
  • They are found below the skin and around organs such as heart and kidneys.
  • They are large cells with a thin rim of cytoplasm and the inconspicuous nucleus is pushed to one side giving a signet ring appearance to the cell.
• Function of adipose tissue

  1. Nutrition : food reserve by storage of fat
  2. Lessens motion and act as soft cushion
  3. Supporting function : act as lubricant allowing smooth movement
  4. Conservation of heat
• Fibers of connective tissue

  • Fibers in the extracellular matrix strengthen and support the connective tissues.
• There are 3 kinds of connective tissue fibers that occur in adult connective tissue.

  1. Collagen fibers : are very strong and resist pulling forces, but they are not stiff, which promotes tissue flexibility.
  2. Elastic fibers : smaller in diameter than collagen fibers.
  3. Reticular fibers : provide support and strength or supporting framework os many soft organs such as spleen and lymph nodes. These fibers also help form the basement membrane
• Collagen fibers are white fibers with a structure that consists of colorless compound fibers composed of a variable number of finer collagen fibrils which run in wavy parallel courses.
• Collagen fibers occur in bundles lying parallel to one another.
• Fibrils are unbranched and usually seen in bundles.
• Collagen fibers run in the same plane and same direction.
• Fibrils are acidophilic with longitudinal striations.
• Collagen fibers are the most numerous fiber in connective tissue.
• Collagen fibers are found whenever great strength is required, combined with flexibility and resistance to a stretching force, such as in tendons and ligaments.
• Collagen fibers are flexible but inelastic and have great tensile strength.
• Collagen fibers have a low refractive index.
• Collagen fibers are composed of protein, specifically collagen, which is the most abundant protein in the body, making up 25% of total protein.
• Collagen fibers stain pink when viewed under a microscope using H&E staining.
• Elastic fibers

  1. Type – Yellow fibers
  2. Structure - Elastic fibers are thinner than collagen fibers. They do not have longitudinal striations. Fine fibers branch and anastomose forming an irregular network. Fibers run in all directions. There are no fibrils. They are seen as brilliant, highly refractile fibers.
  3. Distribution - Found in places where strength is required combined with the ability to be stretched and return to its original form. E.g blood vessels, lung elastic ligaments
  4. Elasticity - They are capable of stretching to one and a half times their length
• Fill in the blank

  A) Elastic fiber

  B) Collagenous fiber

  
• Fill in the blank

  A) Collagen fibers

  B) Elastic fibers

  C) Collagen fibers

  
• Fill in the blank

  A) Elastic fiber

  
• Chemical composition - Protein (elastin); resistant to boiling, dilute acids & alkali
• Staining reaction - Van Gieson→ yellow
• Elastic fibers are of a different type from collagen fibers and have a different structure.
• Distribution: Found in places where strength is required combined with the ability to be stretched and return to its original form, examples include blood vessels and lung elastic ligaments.
• Elasticity: They are capable of stretching to one and a half times their length.
• Refractive index: High.