Introduction to Histology

• Histology: the study of the TISSUES of the body and how these tissues are arranged to constitute ORGANS
• What does the root word "histo" means?

  tissue or web
• Tissues: webs of interwoven FILAMENTS and FIBERS, both cellular and noncellular, with MEMBRANOUS linings.
• Histology involves all aspects of TISSUE BIOLOGY, with the focus on how cell's structure and arrangement OPTIMIZE functions specific to each organ.
• What are the 2 components of tissues?

  Cells and extracellular matrix
• Which component of tissues produce the extracellular matrix?

  Cells
• Cells of the tissues are influenced and sometimes controlled by what molecules?

  Matrix molecules
• The extracellular matrix of tissues consists of what type of molecules?

  Macromolecules
• The macromolecules of the extracellular matrix form COMPLEX STRUCTURES like what?

  Collagen fibrils and basement membranes
• Extracellular matrix: supports the cells and the fluid that transports nutrients to the cells, and carries away their catabolites and secretory products.
• Cells and matrix interact EXTENSIVELY, with many components of the matrix recognized by and attaching to cell surface RECEPTORS.
• Protein receptors: span the cell membranes and connect to structural components inside the cells.
• Cells and ECM form a CONTINUUM that functions together and reacts to STIMULI and INHIBITORS together.
• We study histology to be able to better understand the STRUCTURE and the INNER WORKINGS of the human body in general.
• We study histology to distinguish DISEASED TISSUES from NORMAL SPECIMENS.
• We study histology to understand the PROPER HANDLING of tissue samples.
• We study histology to be able to recognize HISTOLOGIC SECTIONS through their structure.
• What are the steps in TISSUE PROCESSING?

  Fixation, dehydration, clearing, infiltration, embedding, and trimming
• FIXATION: small pieces of tissues are placed in solutions of chemicals that cross-link proteins and inactivate degradative enzymes, which preserves cell and tissue structure.
• During the FIXATION process, what does the solutions of chemicals do in order to PRESERVE the cell and tissue structure?

  Cross link proteins and inactivate degradative enzymes
• Dehydration: The 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: The tissue is then placed in melted paraffin until it becomes completely infiltrated with this substance.
• During the infiltration process of tissue processing, the tissue is placed in what until it becomes completely infiltrated with this substance?

  Melted paraffin
• EMBEDDING: The paraffin-infiltrated tissue is placed in a small mold with melted paraffin and allowed to HARDEN.
• TRIMMING: The resulting paraffin block is trimmed to expose the tissue for sectioning (slicing) on a MICROTOME.
• Similar steps are used in preparing tissue for TRANSMISSION ELECTRON MICROSCOPE, except special fixatives and dehydrating solutions are used with SMALLER TISSUE samples and embedding involves EPOXY RESINS which become HARDER than paraffin to allow VERY THIN sectioning.
• What is used to sectioning PARAFFIN-EMBEDDED tissues?

  Microtome
• What is used to sectioning EPOXY RESIN-EMBEDDED tissues?

  Transmission Electron Microscopy
• What microscope is used for PARAFFIN-EMBEDDED tissues?

  Light microscope
• What microscope is used for EPOXY RESIN-EMBEDDED tissues?

  Transmission Electron Microscope
• Thickness of the cut of PARAFFIN-EMBEDDED tissue?

  1-10 micrometers
• Thickness of the cut of EPOXY RESIN-EMBEDDED tissue?

  less than 1 micrometer
• After each forward move, the tissue block passes over the steel knife edge and a section is cut at a thickness EQUAL to the distance the block advanced.
• Epoxy resin-embedded cells uses an ULTRAMICROTOME with what type of knife?

  Glass or diamond