Body Tissues and Epithelial Tissues

A vocabulary set of key terms and definitions related to body tissues, with emphasis on epithelial structure, junctions, surface specializations, and glandular development.

Parenchyma

Functional cells of an organ that perform its specialized tasks.

Stroma

Supportive tissue of an organ; usually connective tissue, except in brain and spinal cord.

Epithelial Tissue

Tissues formed by interactions between cells and extracellular matrix; cover surfaces, line cavities, and form glands.

Basement Membrane

Semipermeable filter between epithelium and connective tissue; consists of basal lamina and reticular lamina.

Basal Lamina

Thin sheet of fine fibrils; mainly Type IV collagen, laminin, nidogen, and perlecan; provides strength and adhesive sites.

Reticular Lamina

Meshwork rich in Type III collagen; anchors basal lamina to connective tissue; involves Type VII collagen for anchoring.

Type IV Collagen

Collagen in basal lamina providing tensile strength.

Laminin

Basal lamina protein that provides adhesive sites for epithelial integrins.

Nidogen

Basal lamina component helping structure and porosity.

Perlecan

Basal lamina heparan sulfate proteoglycan aiding structure and porosity.

Type III Collagen

Main collagen of the reticular lamina meshwork.

Type VII Collagen

Anchoring fibrils that connect basal lamina to reticular lamina and connective tissue.

Cadherin

Calcium-dependent adhesion molecules that mediate cell–cell adhesion at intercellular junctions.

Tight Junction (Zona Occludens)

Apical belt-like junction that seals intercellular space and regulates paracellular diffusion.

Adherens Junction (Zona Adherens)

Anchoring junction forming a belt around cells, linked to actin filaments.

Desmosome

Spot-weld junction connecting intermediate filaments for strong cell adhesion.

Gap Junction

Intercellular channel permitting direct cytoplasmic exchange and signaling between adjacent cells.

Interdigitation

Interlocking lateral cell membranes that increase surface contact between neighboring epithelial cells.

Microvilli

Apical projections supported by actin filaments; increase surface area for absorption.

Stereocilia

Longer, less motile microvilli; found in epididymis and inner ear; contain actin.

Cilia

Microtubule-based apical structures that move substances across epithelia; found in secretory and transport regions.

Apical Surface

Free surface of epithelial cells facing the lumen or exterior; part of epithelial polarity.

Basal Surface

Surface attached to underlying connective tissue; anchors epithelium and receives nutrients from below.

Simple Squamous Epithelium

Single layer of flattened cells; lines vessels and body cavities; permits diffusion and filtration.

Simple Cuboidal Epithelium

Single layer of cube-shaped cells; mitochondria-rich; active transport and secretion common.

Simple Columnar Epithelium

Single layer of tall cells; may have microvilli or cilia; specialized for absorption.

Stratified Epithelium

Two or more cell layers; primarily provides protection against wear and invasion.

Keratinized Stratified Squamous

Outer dead cells rich in keratin; lines dry surfaces like skin.

Non-keratinized Stratified Squamous

Living cells in moist cavities; lines esophagus, mouth, and vagina.

Transitional Epithelium (Urothelium)

Lines the urinary tract; superficial rounded cells with specialized membranes; withstands urine tonicity.

Pseudostratified Epithelium

Appears multi-layered but all cells contact the basement membrane; nuclei at different levels; often with cilia and goblet cells.

Goblet Cells

Unicellular mucous-secreting glands; abundant in intestine and respiratory tract; secrete mucus.

Glandular Development

Glands originate from surface epithelium and invade underlying connective tissue; exocrine glands have ducts; endocrine glands are ductless.

Exocrine Gland

Glands with ducts that secrete onto surfaces or into ducts.

Endocrine Gland

Glands without ducts that secrete hormones directly into the bloodstream.

Merocrine Secretion

Secretory products released by exocytosis; most glands use this mode.

Holocrine Secretion

Secretory product accumulates until the entire cell disintegrates; example: sebaceous glands.

Apocrine Secretion

Secretory product released from the apical portion of the cell with some cytoplasm; example: mammary glands.

Serous Secretions

Protein-rich secretions that are nonglycosylated; glands producing serous products stain well.

Mucous Secretions

Secretions rich in mucins (glycoproteins) that hydrate to form mucus; goblet cells typical; stain poorly.