Histology Introduction and Tissue Study

Histology Introduction

• Histology is the study of tissues, a branch of anatomy
• It examines the tissues of the body and how they form organs
• It considers all aspects of tissue biology, focusing on how cell structure and arrangement optimize functions specific to each organ.

Cells and Extracellular Matrix

• Cells are the basic structural and functional units of the body
• Extracellular matrix (ECM) is a productive matrix, composed of:
  • Ground substance (GS)
  • Fibers.
• ECM functions to support cells, carry nutrients, and remove waste products.
• Cells produce ECM locally and are influenced by matrix molecules.

Tissue Preparation for Study

• Tissue preparation is necessary to study tissues in their natural states because of their small size.
• Tissue is preserved through a process called fixation, to prevent degradation from enzymes and microorganisms.
• Processes for preparation include:
  • Fixation
  • Dehydration
  • Clearing
  • Infiltration
  • Embedding
  • Sectioning
  • Mounting
• Tissue is then typically sectioned into thin slices using a microtome, and then mounted on slides for examination.
• Frozen sections are useful for rapidly analyzing tissue samples prior to complete medical procedures, especially for those samples containing lipids or very sensitive enzymes.
• A cryostat is a type of microtome used for frozen sections

Tissue Staining

• Staining is used to make tissues visible under a microscope because they are colorless.
• Dyes stain materials selectively, often using acidic or basic characteristics.
• Staining methods include:
  • H&E (Hematoxylin and Eosin)
  • Trichrome stains
  • Van Gieson stain
  • Periodic acid-Schiff (PAS) stain
  • Sudan black stain
  • Silver/gold methods
  • Orcein
• Examples of stains and what they highlight are included in the image descriptions.

Microscopy

• Light microscopy and electron microscopy are the two main techniques for observing tissue samples.
• Light microscopy uses light to view stained tissues, and is further subdivided into various methods.
• Electron microscopy uses beams of electrons and allows for a much higher resolution than light microscopy.
• Two major types are Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM).
• Bright-field microscopy is a common light microscopy technique used to examine stained tissue samples.

Other Key Concepts

• Biopsies are tissue samples taken from the body for analysis.