[HISTO] Cytology

• Histology vs. Pathology:

  • Histology: The study of normal cells and tissues using a microscope
  • Pathology: Talks about the normal state of the tissue; if it is abnormal, it might be something else
• Histopathology:

  • The study of abnormal/diseased cells and tissues using a microscope
• Cell:

  • Functional unit of all living organisms or life
• Tissue:

  • Aggregate of cells (usually of a particular kind), together with their intercellular substance, that form one of the structural materials of a plant or animal
  • Cells of similar type grouped together performing one function
  • A tissue is not a random group of cells
  • Cells → Tissues → Organ
• Epithelium Tissue:

  • Highly basophilic substance corresponds to numerous cells performing one particular function
• Group of Thyroid Tissues Forming the Thyroid Gland:

  • Sets of tiny cells form epithelial lining
  • Colloid material
• Microscope:

  • An optical instrument that uses a lens or a combination of lenses to produce magnified images of small objects, especially of objects too small to be seen by the unaided eye
• Slide vs. Cover Slip:

  • Slide: A glass or transparent material on which the material (specimen) is placed for examination under the microscope
  • Cover Slip: A small, thin piece of glass used to cover the specimen on/over the microscope slide
• Staining:

  • A technique used to enable better visualization of cells and their parts under the microscope
  • Basophilic vs. Eosinophilic:
  • Basophilic: Attracts basic dyes like hematoxylin (H)
  • Eosinophilic: Attracts acidic dyes like eosin (E)
• Dye: Hematoxylin (H):

  • Stains chromatin in cell nuclei dark blue to black when combined with a mordant
  • Stains rough endoplasmic reticulum, ribosomes, myelin, elastic fibers, collagen, and acid mucins
• Dye: Eosin (E):

  • Stains the extracellular matrix, collagen, and cytoplasm pink
  • Shows the general layout and distribution of cells
• Tissue sectioning:

  • Tissues are cut into very thin sections by a microtome, then placed on a slide
  • Sectioning Techniques:
  • Paraffin: Most commonly used, sections are about one millimeter thin, provides a complete report of the cell condition
  • Frozen: Thicker than paraffin-embedded sections, better in the preservation of antigenicity and lipid retention
  • Resin: Improved morphology because of less tissue shrinkage, microscopic features are more visible
• Giovanni Faber coined the name "microscope" for the compound microscope submitted by Galileo to the Accademia dei Lince
• First detailed account of the microscopic anatomy (histology) of organic tissues based on the use of a microscope was done through Giambattista Odierna's L'occhio della mosca or The Fly's Eye
• Marcello Malpighi, known as the "Father of Histology, Modern Pathology, and Physiopathology," began his analysis of biological structures with the lungs
• Robert Hooke's Micrographia had a huge impact because of its impressive illustrations, and he was the first to describe a cell as a tiny box-like cavity through multiple lenses
• Antonie van Leeuwenhoek, known as the "Father of Microbiology" and "Father of Microscopy," achieved up to 300 times magnification using a single lens or monocular microscope
• August Köhler developed a key principle of sample illumination (Kohler illumination) which is central to achieving or adjusting the theoretical limits of resolution for the light microscope
• Frits Zernike discovered phase contrast in 1953, allowing imaging without stain
• Georges Nomarski discovered differential interference known as contrast illumination in 1955, allowing imaging without stain
• • Fine Adjustment Knob/Fine Focus: used to bring the specimen into sharp focus under low power and high power/magnification
  • Condenser: collects, focuses, and concentrates the light from the light source onto the specimen
  • Iris Diaphragm: slit-like opening that controls the amount of light that reaches the specimen
• Parts of the microscope:

  • Eyepiece Lens/Ocular Lens: the lens at the top that you look through, usually 10x power
  • Tube: connects the eyepiece to the objective lenses
  • Head: Eyepiece + tube
  • Arm: supports the tube/microscope head and connects it to the base
  • Base: the bottom of the microscope used for support, houses the illuminator and other knobs
  • Illuminator: a steady light source up through the bottom of the stage
  • Light/Power Switch: turns the illuminator on/off
  • Stage: the flat platform where you place your slides
• • Mechanical Stage: useful at higher magnifications where very delicate or slow movements of the specimen are required
  • Stage Clips: holds the glass/specimen slides in place
  • Revolving Nosepiece or Turret: holds/houses two or more objective lenses and can be rotated to easily change the power of the magnitude of the objective lenses
  • Objective Lenses: primary optical lenses, almost always consist of 4x, 10x, 40x, and 100x powers
  • Coarse Adjustment Knob/Coarse Focus: moves the mechanical stage up and down to bring the specimen into focus
• Types of microscope:

  • Optical/Light Microscope:
  • Uses light to view specimens not visible to the naked eye such as blood cells
  • Also called High Power/Biological Microscope
  • Upright microscope; also called a Compound Lens Microscope
  • Immersion oil is used to concentrate light and increase the resolution of the specimen image
  • Electron Microscope:
  • Stronger microscope than compound
  • Can achieve resolution down to 0.2 nanometers, up to several hundred thousand times magnification of biological material
  • Uses electrons instead of light for imaging
• Electron Microscope (EM)
• Plays an important role in areas of scientific research
• Offers a much higher range of magnification and resolution over an optical/light microscope
• Most likely used for studying the coronavirus
• Uses electromagnetic or electrostatic lenses and a beam of charged particles (electrons) to view particles in the nanometer scale
• Extensively used in scientific laboratories globally to study biological samples such as cells, microbes, and biopsies
• Generates two-dimensional (2D) and three-dimensional (3D) images
• Requires staining through applying heavy metal salt stain
• Main advantage is higher resolution
• If electrons scatter and produce an image, it is electron-dense; if electrons pass through, it is electron-lucent
• Electron microscope images only come in black and white
• Scanning Electron Microscope (SEM) vs. Transmission Electron Microscope (TEM)
• Scanning EM (SEM): Surface of the specimen only; Electron beams scan over the surface of the sample (Ultrastructures)
• Transmission EM (TEM): Plane section of the specimen; Electron beam passes through thin sample
• SEM produces 3D images, while TEM produces 2D images
• Sample for SEM can be any thickness and is mounted on an aluminum stub, while TEM uses specially prepared thin samples supported on TEM grids