Introduction to Histology: Processing of Tissues and Cells

Vocabulary flashcards covering the fundamentals of histology, cytology sampling methods, fixation principles, chemical fixatives, tissue processing steps, embedding systems, and microtomy.

Histology

The scientific study of the microscopic structure (microanatomy) of cells and tissues, examining the correlation between structure and function.

Histopathology

The study of diseases of the tissues.

Cytology

The scientific study of cells.

Cytopathology

The branch of pathology that studies and diagnoses diseases at the cellular level.

Cervical Spatula

An instrument designed for collecting cytology samples from cervical cells through scraping or abrasion.

Fine Needle Aspiration

A cytology sampling procedure that utilizes a thin, hollow needle to withdraw cells from a tissue or fluid collection.

Fixation

A histological procedure that confers chemical stability on tissue, stabilizes macromolecules by rendering them insoluble, hardens tissue, prevents autolysis and putrefaction, and maintains lifelike morphology.

10% Buffered Formalin

The most widely used routine histological fixative that stabilizes tissue by fixing soluble proteins to structural proteins, acting as an effective broad preservative.

Carnoy's Fluid

A compound fixative commonly used for cytology specimens consisting of $60\%$ ethanol, $30\%$ chloroform, and $10\%$ acetic acid.

Factors Affecting Fixation

The key physical and chemical variables that alter fixation efficacy: temperature, pH, osmolarity, and tissue volume.

Dehydration

The processing stage that removes fixative and water from a tissue specimen and replaces them with a dehydrating fluid such as ethanol, methanol, or acetone.

Graded Ethanol Series

A sequential dehydration regimen using water through $10\%$, $20\%$, $50\%$, $95\%$, and $100\%$ ethanol to minimize structural distortion from diffusion currents.

Clearing

The step in tissue processing where the dehydrating fluid is replaced with an intermediate reagent that is miscible with both the dehydrant and the embedding wax.

Clearing Agents

Chemical transition fluids used prior to paraffin infiltration, including xylene, toluene, chloroform, benzene, and petrol.

Wax Infiltration

The process of replacing the clearing agent with an embedding medium by immersing tissues in molten wax that solidifies upon cooling.

Paraffin Wax

A substance used during infiltration and embedding to increase hardness, decrease melting point, and improve ribbon formation during sectioning.

Tissue Embedding Station

A dedicated histological workstation equipped with a $4.6\,\text{L}$ paraffin reservoir, mold prewarming chamber, dispensing nozzle, heated workspace, and a cooling plate adjustable to $-15\,^{\circ}\text{C}$.

Microtome

A precision mechanical cutting instrument used to slice embedded tissue blocks into thin sections for microscopic analysis.

Microtomy

The laboratory technique of sectioning paraffin-embedded tissue blocks into ultra-thin slices using a microtome.