INTRODUCTION TO HISTOLOGY

• Cadavers


  Dead human body specifically prisoners and used for medical school to study the uncleaned bodies
• Histology


  Studying normal tissues
• Histopathology


  Studying abnormal tissues
• Anatomy


  Connected to histology
• Cell


  • Basic morphologic and functional unit of all living things
  • Perform all of life function
  • Human cells are eukaryotic cells with common basic cell structure (cell membrane, cytoplasm, nucleus)
• Tissue


  Collection of cells formed tissues
• Preparation of tissues for study


  1. Tissue slices or "sections" that can be examined visually with transmitted light

  2. Preserved so that the tissue on the slide has the same structural features it had in the body
• Collection/extraction of sample


  Receiving or collecting a sample is the first thing to do before an examination
• Labelling


  Most important step to prevent mixing with other samples
• Fixation


  Using formalin (37% formaldehyde) to cross-link proteins and inactivate degradative enzymes, which preserve cell and tissue structure
• Dehydration


  Tissue is transferred through a series of increasingly concentrated alcohol solutions, ending in 100%, which removes all water
• Clearing


  Alcohol is removed in organic solvents in which both alcohol and paraffin are miscible
• Infiltration


  Tissue is then placed in melted paraffin until it becomes completely infiltrated with this substance
• Embedding


  Paraffin-infiltrated tissue is placed in a small mold with melted paraffin and allowed to harden
• Blocking


  Cell blocks play an increasingly important role as they yield tissue sections
• Trimming


  The resulting paraffin block is trimmed to expose the tissue for sectioning (slicing) on a microtome
• Sectioning


  To permit thin sectioning, fixed tissues are infiltrated and embedded in a material that imparts a firm consistency
• Staining


  1. Hematoxylin and eosin (H&E) is the most common staining method

  2. Basophilic: cell components with net negative charge have affinity for basic dyes

  3. Acidophilic: cationic components stain more readily with acidic dyes

  4. Counterstain: single dye applied separately to distinguish additional features

  5. Periodic acid–Schiff (PAS): stains carbohydrate-rich structures purple/magenta

  6. Lipid-soluble dyes (Sudan black): useful for diagnosing metabolic diseases

  7. Metal impregnation: using silver salts to visualize certain ECM fibers and cellular elements
• Mounting


  • Protects the sample by holding it in place during imaging and preventing it from drying out
  • Allows for long-term sample storage
• Proper labeling (number coded)


  Very critical to the interpretation of results, relied upon to correctly diagnose patients
• Automated tissue processing

  1. Fixation

  2. Dehydration

  3. Clearing

  4. Infiltration
• Organs


  Formed when tissues are joined or combined
• Organ systems


  • Cardiovascular
  • Respiratory
  • Lymphatic
  • Reproductive
  • Nervous
  • Endocrine
  • Integumentary
  • Digestive
  • Urinary
  • Musculoskeletal
  • Immune