HISTO PRELIMS

• Histology

  is the study of tissues, its structure, and functions
• Tissues


  a group of cells that have similar structure and that function together as a unit
• Cells

  smallest structural and functional unit of an organism

  The simplest unit of living matter.
• Extracellular Matrix

  helps cells attach to, and communicate with, nearby cells, and plays an important role in cell growth, cell movement, and other cell functions body text
• Tissue Preparation

  Fixation

  Dehydration & Clearing

  Infiltration

  Embedding

  Trimming

  Staining
• Fixation

  Treatment of tissue with chemical agent

  Small pieces of tissue are placed in solution of chemicals that cross-link proteins and inactivate degrative enzymes, which preserve cell and tissue structure
• Dehydration & Clearing

  Removal of water from tissue sample

  Clearing the alcohol
• Infiltration

  Uniformly distributing the support medium throughout the tissue

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

  Infiltration of tissue sample with paraffin
• Trimming

  Cutting a fixed tissue or organ to create a flat surface with correct orientation
• Staining

  Applying dyes on the tissue sections to see and study patterns and physical characteristics of cells
• Basic Dyes

  M- Methylene Blue

  A - Alcian Blue

  T- Toluidine blue

  H- Hematoxylin
• Acid Dyes

  E- EOSIN

  O - Orange G

  A - Acid Fuchsin
• Microscope

  an optical instrument that is used to observe tiny objects, often objects that cannot be seen at all with the naked eye
• Different Types of Microscope

  Brightfield Microscope

  Darkfield Microscope

  Phase-Contrast Microscope

  Fluorescence Microscope

  Polarizing Microscopy

  Electron Microscopy
• Brightfield Microscope

  Used to observe the morphology of microorganisms such as bacteria, protozoa, fungi, and algae in unstained and stained state
• Darkfield Microscope

  Unstained organisms are observed against a dark background
• Phase-Contrast Microscope

  Can be used to observe unstained living organisms
• Fluorescence Microscope

  Fluorescent dye attached to the organism
• Polarizing Microscopy

  Allows the recognition of stained or unstained structures made of highly organized subunits
• Electron Microscopy

  Transmission and scanning electron microscopes are based on the interaction of tissue components with beams of electrons
• 2 types of Electron Microscope

  Transmission electron microscope

  Scanning electron microscope
• Epithelial Tissue

  Tissue in which cells are bound tightly together, structurally, and functionally to form a sheet like or tubular structure

  It is a selective barrier that protects tissues and is often involved in absorption or secretion

  Covering, lining and protection, absorption secretion and excretion, contractility
• Surface of Epithelium

  Apical Surface

  Lateral Surface

  Basal Surface
• Apical Surface

  For transcytosis and pinocytosis
• Lateral Surface

  Where the tight junctions are present
• Basal Surface

  Exocytosis
• CHARACTERISTICS OF EPITHELIAL TISSUE

  Tightly packed cells

  Avascular

  Cell shows polarity

  Rest on abasement membrane
• FUNCTIONS OF EPITHELIAL TISSUE

  Protection

  Absorption

  Secretion

  Exchange

  Excretion
• 6 types of junctions

  Zonula Adherens/ Anchoring Junctions

  Macula Adherens / Desosome

  Hemidesmosome

  Zonula Occludens/ Tight Junctions

  Gap Junctions/Communicating Junctions

  Basement Membrane
• Zonula Adherens/ Anchoring Junctions

  Chains that mechanically binds adjacent epithelial cells

  Site of adhesion

  Transmembrane glycoprotein
• Macula Adherens / Desosome

  Junctional type resembles a single "spot-weld"

  Disk shaped structure at the surface of one cell that is matched with an identical structure at the surface of the adjacent cell

  Transmembrane glycoprotein
• Hemidesmosome

  Bind the cell to basal lamina

  Transmembrane protein = Integrin
• Zonula Occludens/ Tight Junctions

  Seals to prevent the flow of materials between the cells

  Forming two functional compartments
• Gap Junctions/Communicating Junctions

  Channel for communication between adjacent cells

  Intercellular communication

  Protein: Connexin
• Basement Membrane

  Semi solid structure that allows the diffusion of materials from the underlying connective tissue.

  Lifeline of Epithelial cells

  Forming two functional compartments
• Cell Adaption

  Regeneration

  Metaplasia

  Anaplasia
• Regeneration

  Ability to replace itself
• Metaplasia

  Adaptive transformation wherein a normal tissue is replaced by another normal tissue
• Anaplasia

  Normal to abnormal tissue; malignant transformation

  Atrophy

  Hypertrophy

  Hyperplasia

  Metaplasia