Epithelium Notes Review

Vocabulary flashcards covering key concepts about epithelium, its forms, functions, structures, and related tissues from the lecture notes.

Epithelium

Avascular tissue that covers body surfaces, lines body cavities, and forms glands; serves as a barrier between external environment and underlying connective tissue.

Avascular

Lacks blood vessels; nourished by diffusion from underlying tissues.

Four basic tissue types

Epithelium, Connective tissue, Muscle, Nervous tissue.

Functions of epithelium (general)

Protection, secretion, absorption, diffusion, friction reduction, cleaning, and sensation.

Basement membrane

Structure anchoring epithelium to connective tissue; composed of basal lamina (epithelial) and reticular lamina (connective tissue).

Basal lamina

Glycoprotein-rich layer secreted by epithelial cells; anchors the epithelial basal layer.

Reticular lamina

Part of the basement membrane secreted by connective tissue cells.

Endothelium

Simple squamous epithelium lining the heart, lumen of blood vessels, and lymphatic vessels.

Mesothelium

Simple squamous epithelium lining body cavities and covering the outer surfaces of most internal organs.

Surface epithelium

Epithelium that covers external surfaces and lines vessels/cavities; includes transport epithelium.

Glandular epithelium

Epithelium that forms glands; secretes substances into ducts (exocrine) or into blood (endocrine).

Simple squamous epithelium

One cell layer thick; flattened cells; lines air sacs, heart and vessel linings; enables diffusion/filtration and secretion of lubricants.

Simple cuboidal epithelium

One cell layer; cube-shaped cells; lines ducts and secretory portions of glands and kidney tubules; secretes and absorbs.

Simple columnar epithelium

One cell layer of tall cells; lines absorptive/secretory surfaces (stomach, intestines); often with microvilli and goblet cells.

Goblet cell

Unicellular mucous gland; produces mucus.

Pseudostratified columnar epithelium

Single layer of cells of varying height; nuclei at different levels; some cells do not reach surface; often ciliated with goblet cells.

Cilia

Motile apical projections that move substances across the surface (e.g., in trachea).

Microvilli

Brush-border projections that increase surface area for absorption (intestinal mucosa, renal tubules).

Stereocilia

Long, non-motile microvilli; found in epididymis and sensory organ of inner ear.

Keratinization

Dry-surface epithelium where superficial cells are dead and keratin-filled, e.g., epidermis.

Non-keratinized stratified squamous epithelium

Stratified squamous with nucleated superficial cells; found in esophagus and anal canal.

Stratified squamous epithelium

Many cell layers; protects against abrasion; apical layers may be keratinized or non-keratinized.

Stratified cuboidal epithelium

Rare; typically two layers; lines excretory ducts of glands.

Stratified columnar epithelium

Rare; two or three layers; lines large ducts of glands.

Transitional epithelium (urothelium)

Specialized stratified epithelium lining urinary tract; can stretch as organs distend; changes apparent layers with fixation.

Urothelium

Transitional epithelium of renal pelvis, ureters, bladder, and urethra.

Stratified squamous epithelium (true layers)

Multiple layers; protects against abrasion; keratinized in skin, non-keratinized in moist surfaces.

Tight junctions

Fusion of intramembranous particles; seal membranes to block passage between cells.

Zona adherens (adherens belt)

Adhesive belt junction; cadherins mediate cell-to-cell adhesion in Ca2+ presence.

Desmosomes (macula adherens)

Discontinuous junctions holding cells together; tonofilaments anchor to cytoskeleton; give spiny appearance.

Gap junctions

Conduits between adjacent cells allowing passage of ions and small molecules.

Embryonic germ layers and epithelia

Ectoderm forms epidermis and related epithelia; Mesoderm forms serosae and endothelium; Endoderm forms epithelia lining hollow organs.

Endocrine vs Exocrine glands

Exocrine glands secrete into ducts; endocrine glands secrete into the bloodstream.

Polarization of epithelial cells

Cells have distinct apical, lateral, and basal surfaces with specialized structures.