Histology Overview and Microtechnique

Histology

• The study of the structure of cells, tissues, and organs in relation to their function.
• The human body is organized in a hierarchical manner: cells, tissues, organs, and systems.

Cells

• The basic, structural units of all living organisms.
• Vary in size, shape, and function.
• Each cell consists of a nucleus and cytoplasm.
• Require microscopes for examination due to their small size (4-200 micrometers).

Tissues

• Composed of similar or related cells that work together for a specific function.
• Four basic types:
  • Epithelium
  • Connective tissue
  • Muscular tissue
  • Nervous tissue

### Organs

• Formed by the assembly of different tissues.
• Examples include the stomach, lung, and liver.
• Each organ has a specific function.

Systems

• Composed of different organs that work together for a common purpose.
• Examples include the digestive, respiratory, and excretory systems.

### Microtechnique

• Methods used to prepare tissues for microscopic examination after staining.
• The paraffine technique is the most common.
• Steps include:
  • Fixation
  • Dehydration
  • Embedding
  • Sectioning
  • Staining
  • Mounting

Histological Staining

• Hematoxylin & eosin (H&E) is the most common stain:
  • Hematoxylin: a basic dye that stains acidic components blue (basophilic), like the nucleus, ribosomes, and rough endoplasmic reticulum.
  • Eosin: an acidic dye that stains basic components red (acidophilic), like cytoplasm.
• Some structures require special stains that are not visible with H&E.

Microscopy

• Importance of a microscope: magnifies small objects and reveals their fine details (resolution).
• Light microscopes: use daylight or electric lamps as a source of light.