GB 1003: Histology and Embryology I - Histology and Its Methods of Study

Practice vocabulary flashcards covering tissue preparation, fixation, staining methods, light and electron microscopy, and cytochemical techniques from GB 1003 Histology and Its Methods of Study.

Histology

The study of tissues and how they are arranged to form organs, derived from the Greek word "histo," meaning tissue or web.

Histo

The Greek root word meaning tissue or web.

Extracellular Matrix (ECM)

A noncellular component composed of macromolecules (such as collagen fibrils and basement membranes) that provides structural support and facilitates nutrient transport and waste removal for cells.

Fixation

The tissue preparation step in which small tissue pieces are placed in chemical solutions that preserve structure by cross-linking proteins and inactivating degradative enzymes.

Dehydration

The process of transferring tissue through a series of increasingly concentrated alcohol solutions, ending in $100\%$, to remove all water.

Clearing

The step in tissue preparation where alcohol is replaced by an organic solvent (such as toluene) in which both alcohol and paraffin are miscible, making the tissue translucent.

Infiltration

The step where cleared tissue is placed in melted paraffin at $52^\circ\text{C}-60^\circ\text{C}$ until it becomes completely permeated with the substance.

Embedding

The step in which paraffin-infiltrated tissue is placed into a small mold with melted paraffin and allowed to harden.

Trimming

The process of slicing away excess paraffin from a hardened block to expose the embedded tissue specimen for sectioning.

Microtome

A precision mechanical instrument with a steel knife used for slicing paraffin-embedded tissue blocks into sections generally between $1\,\mu\text{m}$ and $10\,\mu\text{m}$ thick for light microscopy.

Ultramicrotome

A specialized cutting device equipped with a glass or diamond knife used to cut resin-embedded specimens into ultra-thin sections less than $1\,\mu\text{m}$ thick for transmission electron microscopy.

Autolysis

The process of tissue digestion and breakdown by intracellular enzymes and bacteria that begins immediately after an organ is removed.

Formalin

A widely used light microscopy fixative consisting of a buffered isotonic solution of $37\%$ formaldehyde that stabilizes proteins by reacting with their amine ($\text{NH}_2$) groups.

Glutaraldehyde

A dialdehyde fixative used in electron microscopy that preserves ultrastructural detail by cross-linking amine ($\text{NH}_2$) groups of tissue proteins.

Double-Fixation Method

A preparation procedure for electron microscopy involving initial fixation with buffered glutaraldehyde followed by secondary fixation with osmium tetroxide.

Osmium Tetroxide

A specialized fixative and heavy metal stain used in electron microscopy to preserve and stain membrane lipids and proteins.

Epoxy Resins

Embedding plastics that harden via cross-linking polymerizers without high heat, avoiding tissue shrinkage and allowing ultra-thin sectioning for transmission electron microscopy.

Micrometer ($\mu\text{m}$)

A unit of histologic measurement equal to $1/1000\,\text{mm}$ or $10^{-6}\,\text{m}$.

Nanometer ($\text{nm}$)

A unit of measurement equal to $0.001\,\mu\text{m}$, $10^{-6}\,\text{mm}$, or $10^{-9}\,\text{m}$.

Angstrom ($\text{\AA}$)

A unit of measurement equal to $0.1\,\text{nm}$ or $10^{-4}\,\mu\text{m}$.

Basophilic Components

Anionic, negatively charged cellular and tissue structures (such as nucleic acids) that bind readily to basic dyes.

Acidophilic Components

Cationic, positively charged cellular and tissue structures (such as proteins, mitochondria, and collagen) that bind readily to acidic dyes.

Basic Dyes

Cationic staining compounds—including toluidine blue, alcian blue, and methylene blue—that form electrostatic linkages with negatively charged tissue molecules.

Acidic Dyes

Anionic staining compounds—including eosin, orange G, and acid fuchsin—that form electrostatic linkages with positively charged tissue components.

Hematoxylin

A dye that acts like a basic dye, staining basophilic components such as DNA and nuclei blue or purple.

Eosin

An acidic counterstain that stains acidophilic structures such as cytoplasm, mitochondria, and collagen fibers pink.

Trichrome Stains

Special staining combinations (e.g., Mallory and Masson trichromes) used to distinguish extracellular matrix components and connective tissue fibers better than H&E.

Feulgen Reaction

A specific cytochemical technique that uses mild hydrochloric acid to hydrolyze deoxyribose, followed by Schiff reagent, to selectively stain and quantify DNA.

Periodic Acid-Schiff (PAS) Reaction

A histochemical reaction that converts 1,2-glycol groups in sugars into aldehyde residues, which react with Schiff reagent to stain glycogen, glycoproteins, and mucin magenta.

Glycosaminoglycans (GAGs)

Long-chain anionic polysaccharides present in proteoglycans of the extracellular matrix that do not react with PAS but bind strongly to basic dyes like alcian blue.

Sudan Black

A lipophilic dye used to stain intracellular lipid droplets and lipid-rich structures, typically applied to frozen sections to avoid lipid extraction by solvents.

Silver Salts

Metal impregnation agents used to visualize delicate extracellular matrix fibers and cellular processes, particularly in nervous tissue.

Bright-Field Microscopy

The standard optical microscopy method in which ordinary transmitted light passes through a stained, thin tissue specimen to create an image.

Condenser Lens

The optical component in a light microscope that collects and focuses a beam of light directly onto the specimen.

Objective Lens

The primary optical magnifying lens positioned closest to the specimen that projects an enlarged image toward the eyepiece and determines resolution.

Eyepiece (Ocular Lens)

The lens system nearest the observer's eye that further magnifies the image formed by the objective and projects it onto the retina or a detector.

Resolving Power

The smallest distance between two points at which they can still be distinguished as separate objects, with a maximal limit of $0.2\,\mu\text{m}$ for standard light microscopes.

Fluorescence

The physical phenomenon in which a substance absorbs light of a specific wavelength and subsequently emits light of a longer wavelength.

Fluorescence Microscopy

A microscopic method where specimens are irradiated with ultraviolet (UV) light, causing fluorescent compounds to emit visible light that appears brilliant against a dark background.

Acridine Orange

A fluorescent dye that binds nucleic acids, causing nuclear DNA to fluoresce yellow and cytoplasmic RNA to emit orange light.

DAPI (4',6-diamino-2-phenylindole)

A fluorescent stain that binds specifically to DNA, emitting a characteristic blue fluorescence to visualize cell nuclei.

Fluorescein-Phalloidin

A fluorescently labeled conjugate that binds specifically to actin microfilaments, visualizing their distribution as green fluorescence.

Transmission Electron Microscope (TEM)

An electron microscope that directs an electron beam (accelerated between $60\,\text{kV}$ and $120\,\text{kV}$) through an ultra-thin section to reveal ultrastructural internal details.

Scanning Electron Microscope (SEM)

An electron microscope that scans a focused electron beam sequentially across a metal-coated specimen surface, producing high-resolution, shadowed 3D surface images.

Electron-Lucent

Areas in a transmission electron micrograph through which electrons pass freely with minimal interaction, appearing bright.

Electron-Dense

Dense regions or areas binding heavy metal ions in a TEM specimen that absorb or deflect electrons, appearing dark.

Primary Cell Culture

An in vitro culture of live cells isolated directly from normal or pathologic animal tissues by mechanical or enzymatic dispersion.

Permanent Cell Lines

Cultured cell populations that have become immortalized through transformation, enabling continuous in vitro proliferation beyond normal finite cellular lifespans.

Enzyme Histochemistry

A method used to identify and localize cellular structures by incubating cryostat tissue sections with a substrate and marker compound to form an insoluble, visible precipitate at the site of enzyme activity.

Indirect Immunocytochemistry

An immunological detection method using an unlabeled primary antibody against a target antigen, followed by a labeled secondary antibody that binds the primary antibody, thereby amplifying the visible signal.