Introduction to Histology and Histochemistry

A set of vocabulary flashcards covering the basics of histology, its history, organizational levels, and the detailed steps involved in tissue processing and decalcification.

Histology

Derived from the Greek histos (meaning tissue) and logia (meaning study of or knowledge), it is the microscopic study of normal tissues.

Robert Hooke

The first person to observe cells in 1665; he observed thin slices of cork that appeared as little boxes which he called cells.

Rudolf Virchow

Scientist who stated in 1855 that new cells arise from the division of pre-existing cells and that chemical reactions for life occur inside the cell.

Mathias Schleiden and Theodor Schwann

Proposed in 1883 that all plants and animals were composed of cells, which were the basic building blocks of life.

Cell

The smallest basic structure of higher organisms capable of independent existence.

Tissue

A group of cells of similar function & origin that form functional units.

Biopsy

An examination of tissue taken from a living body.

Autopsy

An examination of post-mortem tissue.

Necropsy

An examination of tissue taken from a dead animal.

Whole mount

A histological preparation of an entire animal, such as a fungus or parasite, measuring between $0.2-0.5\,mm$.

Microtomes

Special instruments with an automatic mechanism used for cutting very thin sections of hardened tissue.

Fixation

The preservation of tissue to avoid autolysis and putrefaction using substances like Formaldehyde or Osmium Tetraoxide.

Dehydration

The removal of water from tissue by using a graded series of alcohol, specifically $70\%$, $95\%$, and $100\%$.

Clearing

The removal of alcohol from the tissue using a paraffin solvent, such as Xylene, which makes the tissue appear clear.

Xylene

A clearing agent and paraffin solvent used to remove alcohol from tissue sections.

Wax Impregnation

The process of replacing xylene with paraffin by immersing the tissue in melted paraffin at approximately $55^{\circ}C$.

Embedding

The process of placing tissue in a mold filled with media like paraffin wax, ester wax, or cellulose nitrate to obtain a solid block.

Hematoxylin

A basic dye used in staining to identify basophilic structures such as DNA and RNA.

Eosin

An acid dye used to highlight acidophilic (eosinophilic) structures like mitochondria and collagen.

Coverslipping

Covering a stained section with a thin piece of glass to protect the tissue from scratches and preserve it for a long period.

Decalcification

A process of complete removal of calcium salt from tissues like bone and teeth following fixation to allow for easier cutting.

EDTA

A decalcifying agent that removes calcium safely and slowly, but is considered expensive in large amounts.