Introduction to Histology & Basic Tissues (Epithelium)

Vocabulary flashcards covering key terms from the lecture on histology preparation, staining, epithelial structure, junctions, classifications, and apical specializations.

Histology

The study of body tissues and their organization within organs, emphasizing how cellular structure optimizes function.

Fixation

First step in slide preparation; stabilizes and preserves tissue architecture by cross-linking or precipitating proteins.

Embedding

Infiltration of fixed tissue with a medium (e.g., paraffin) that allows it to harden for sectioning.

Sectioning

Cutting embedded tissue into thin slices for microscopic examination.

Staining

Application of dyes to tissue sections to enhance contrast and reveal specific structures.

Artifact

Preparation-induced distortion or error seen in histologic sections.

Longitudinal Section

Tissue slice made parallel to the organ’s long axis.

Cross (Transverse) Section

Tissue slice cut perpendicular to the organ’s long axis.

Oblique Section

Tissue slice cut at an angle between longitudinal and cross sections.

Basic Dye

Positively charged stain (e.g., hematoxylin) that binds acidic, anionic tissue components such as nucleic acids.

Acidic Dye

Negatively charged stain (e.g., eosin) that binds basic, cationic tissue components like cytoplasmic proteins.

Basophilia

Affinity of anionic structures (DNA, RNA) for basic dyes, appearing blue-purple.

Eosinophilia (Acidophilia)

Affinity of cationic structures (proteins, collagen) for acidic dyes, appearing pink-red.

Hematoxylin

Basic dye that stains nuclei, ribosomes, and cartilage matrix dark blue or purple.

Eosin

Acidic dye that stains cytoplasm, collagen, and most extracellular fibers pink or red.

H&E Stain

Most common histologic stain combining hematoxylin (nuclei blue) and eosin (cytoplasm pink).

Periodic Acid–Schiff (PAS)

Reaction that stains carbohydrates (glycogen, glycoproteins, mucins) magenta.

Masson Trichrome

Three-dye stain differentiating nuclei (purple), cytoplasm/keratin/erythrocytes (red), and collagen (blue).

Wright–Giemsa Stain

Combination of methylene blue and eosin used on blood or marrow smears; nuclei purple, RBCs pink-orange.

Basement Membrane

Thin extracellular layer underlying all epithelia; acts as support and selective filter.

Basal Lamina

Fine fibrillar portion of the basement membrane directly beneath epithelial cells.

Reticular Lamina

Diffuse, fibrous layer beneath basal lamina containing collagen III fibers.

Cell Polarity

Uneven distribution of organelles and membrane proteins, creating apical, lateral, and basal domains in epithelia.

Tight Junction (Zonula Occludens)

Apical belt-like seal between adjacent cells mediated by claudin and occludin, preventing paracellular diffusion.

Adherens Junction (Zonula Adherens)

Band of strong adhesion below tight junctions mediated by cadherins linked to actin via catenins.

Desmosome (Macula Adherens)

Spotlike anchoring junction containing desmogleins and desmocollins, attaching intermediate filaments.

Gap Junction

Intercellular channels formed by connexons of connexin proteins that permit ion and small molecule passage.

Simple Epithelium

Single layer of cells resting on the basement membrane.

Stratified Epithelium

Two or more cell layers stacked on the basement membrane, mainly protective.

Squamous Cell

Flattened, thin epithelial cell; width greater than height.

Cuboidal Cell

Cube-shaped epithelial cell with equal height and width.

Columnar Cell

Tall epithelial cell whose height exceeds width.

Simple Squamous Epithelium

Single layer of flat cells specialized for exchange; lines blood vessels and alveoli.

Simple Cuboidal Epithelium

One layer of cube-shaped cells; found in kidney tubules and small ducts.

Simple Columnar Epithelium

Single layer of tall cells; lines digestive tract, absorbing and secreting.

Stratified Squamous Keratinized

Multilayer epithelium of skin; surface cells are anucleate squames filled with keratin, preventing dehydration.

Stratified Squamous Nonkeratinized

Multilayer lining of moist cavities (mouth, esophagus, vagina); surface cells retain nuclei.

Stratified Cuboidal Epithelium

Two-layer ducts of sweat and salivary glands.

Stratified Columnar Epithelium

Protective, mucus-secreting lining of conjunctiva and large ducts.

Transitional Epithelium (Urothelium)

Stratified lining of urinary tract; umbrella cells allow distension and protect against urine toxicity.

Umbrella Cell

Large dome-shaped superficial cell of urothelium providing barrier and stretch capacity.

Pseudostratified Columnar Epithelium

Tall, irregular cells all touching basement membrane; nuclei at different levels create stratified appearance (e.g., trachea).

Exocrine Gland

Gland that remains connected to surface epithelium via ducts, secreting onto that surface.

Endocrine Gland

Ductless gland releasing hormones into blood for distant targets.

Merocrine Secretion

Exocytosis of membrane-bound secretory granules; cell remains intact (e.g., salivary glands).

Holocrine Secretion

Entire cell disintegrates to release product and debris (e.g., sebaceous glands).

Apocrine Secretion

Apical cytoplasm pinches off with product (e.g., mammary gland milk fat).

Microvillus

Actin-based apical protrusion increasing surface area for absorption; forms brush border.

Stereocilium

Long microvillus in epididymis and inner ear; involved in absorption or mechanosensation.

Cilium

Microtubule-based motile projection propelling fluid or mucus over epithelial surfaces.

Myoepithelial Cell

Contractile epithelial cell aiding secretion in glands.

Claudin

Transmembrane protein forming tight junction strands.

Occludin

Transmembrane protein partnering with claudin in tight junctions.

Cadherin

Calcium-dependent adhesion molecule of adherens junctions and desmosomes.

Catenin

Cytoplasmic protein linking cadherins to actin filaments in adherens junctions.

Connexin

Protein subunit of gap junction channels.

Connexon

Hexameric assembly of connexins forming a gap junction pore.