Lecture 3: Epithelial Cells and Surface Specialisations

Vocabulary practice flashcards covering epithelial tissue classification, embryonic origins, functional characteristics, cell surface specialisations, renewal rates, and clinical correlations.

Epithelial tissue

One of four basic tissue types that make up organs; a thin, continuous protective layer of avascular cells covering both internal and external body surfaces, including blood vessels, functioning in protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception.

Ectoderm-derived epithelium

Epithelial tissues originating from the embryonic ectoderm, primarily comprising the epidermis on exterior body surfaces.

Endoderm-derived epithelium

Epithelial tissues originating from the embryonic endoderm that line interior spaces opening directly to the exterior, such as the gastrointestinal tract, respiratory tract, genitourinary tract, and external acoustic meatus.

Mesoderm-derived epithelium

Epithelial linings originating from the embryonic mesoderm that line interior closed cavities, including the pericardial sac, pleural sacs, peritoneum, blood vessels, and lymphatic vessels.

Epithelial classification criteria

The three diagnostic morphological criteria used to classify epithelial tissues: the number of cell layers (simple vs. stratified), the shape of the surface cells (squamous, cuboidal, or columnar), and any apical surface specialisations.

Simple squamous epithelium

A single layer of flattened, scale-like epithelial cells whose thinness and high permeability provide an efficient barrier for rapid diffusion, filtration, and gas exchange.

Endothelium

A specialised simple squamous epithelial lining that lines the lumen of the heart, blood vessels, and lymphatic vessels, facilitating fluid, waste, and nutrient exchange while reducing friction.

Mesothelium

A simple squamous epithelium covering the serous membranes of closed body cavities—including the pericardium, pleura, and peritoneum/viscera—specialised for tissue lubrication and fluid exchange.

Simple cuboidal epithelium

A single layer of polygonal cells with roughly equal height and width, containing a central spherical nucleus and abundant cytoplasm to house organelles for active ion transport, secretion, and absorption.

Thyroid follicular epithelium

A simple cuboidal epithelium bounding spherical follicles that synthesises thyroglobulin, stores it extracellularly in the central colloid, and reprocesses it to release thyroxine directly into blood capillaries.

Simple columnar epithelium

A single layer of epithelial cells whose height is significantly greater than width, providing extensive cytoplasm for protein synthesis, organelle storage, barrier integrity, and robust absorptive or secretory functions.

Crypts of Lieberkühn

Tubular intestinal glands in the mucosa of the colon lined by simple columnar epithelium and mucus-secreting goblet cells that function in nutrient and fluid absorption.

Stratified squamous non-keratinised epithelium

A multilayered, renewable protective epithelium with flattened, nucleated surface cells that shields underlying tissue from mechanical friction and abrasion while remaining moist, such as in the mouth, oesophagus, and vagina.

Vaginal epithelial glycogen

Intracellular glycogen stored within stratified squamous non-keratinised cells of the vagina that serves as a nutrient substrate for resident lactobacilli to generate lactic acid, preserving an acidic pH protective against pathogens.

Transitional epithelium (urothelium)

A specialized stratified urinary tract epithelium lining from renal calyces to the proximal urethra that distends and recoils reversibly without tearing, while providing an impermeable barrier against toxic chemicals.

Microvilli

Minute, non-motile finger-like apical membrane projections that amplify plasma membrane surface area to maximize density of transport proteins, ion channels, receptors, and enzymes for absorption and secretion.

Lacteal

A specialized lymphatic capillary situated within the core of an intestinal villus that absorbs emulsified fats and dietary lipids.

Stratified squamous keratinised epithelium

A durable multilayered epithelium whose outer layers lose their nuclei and cytoplasm to become compacted squames of keratin, forming a tough, waterproof barrier on the epidermis and distal anal canal.

Stratum corneum

The outermost non-living, cornified layer of stratified squamous keratinised epithelium that minimizes transepidermal water loss, prevents microbial/toxin penetration, and protects against ultraviolet damage and mechanical trauma.

Pseudostratified ciliated columnar epithelium

An epithelial tissue wherein all cells contact the basement membrane, but not all extend to the free surface, causing cell nuclei to align at varying depths and giving a false appearance of multiple layers.

Mucociliary escalator

A coordinated airway clearance mechanism where motile cilia beat synchronously at $12\,\text{Hz}$ within a watery periciliary fluid layer to propel a viscoelastic mucus blanket carrying trapped particles upward toward the pharynx.

Goblet cell

A modified, mucus-secreting epithelial cell lacking apical cilia and bearing microvilli, which exocytoses mucin granules that hydrate to lubricate and protect luminal surfaces.

Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)

An epithelial chloride channel whose defect disrupts normal ion and water efflux across membranes, leading to dehydrated, excessively viscous mucus that blocks airways, pancreatic ducts, and reproductive tracts.

Club (Clara) cells

Non-ciliated, dome-shaped epithelial cells of terminal bronchioles that secrete uteroglobin and surfactant-like lipids, metabolize inhaled toxins via smooth endoplasmic reticulum cytochrome P450 enzymes, and act as regenerative stem cells.

Microfold (M) cells

Specialised gut epithelial cells overlying intestinal lymphoid nodules (Peyer's patches) that endocytose luminal antigens and microorganisms to deliver them to underlying dendritic cells, macrophages, and lymphocytes within a basal pocket.

Stereocilia

Long, non-motile, actin-based apical microvillar projections that serve as mechanosensory transducers in inner ear hair cells and mediate fluid and residual sperm body reabsorption in the male epididymis and vas deferens.

Airway ciliagenesis renewal duration

The physiological timeframe of $2\text{ to }4\,\text{days}$ required for damaged respiratory epithelial cells to regenerate cilia following acute insult.

Tracheal epithelial renewal rate

The normal physiological turnover timeframe of $1\text{ to }2\,\text{months}$ for the replenishment of tracheal epithelial cells.

Alveolar epithelial renewal rate

The physiological turnover timeframe of approximately $8\,\text{days}$ for alveolar pneumocytes in healthy lung tissue.

Chronic bronchitis

Persistent bronchial inflammation characterized by productive cough and excess mucus persisting for at least 3 months across 2 successive years, featuring goblet cell hyperplasia, loss of ciliated cells, and airway narrowing.

Emphysema

A chronic pulmonary pathology characterized by abnormal, permanent enlargement and destruction of airspaces distal to terminal bronchioles without fibrosis, causing loss of alveolar elastic recoil.

Asthma

A chronic airway disease characterized by variable expiratory airflow limitation, smooth muscle bronchospasm, mucus obstruction, and airway hyperresponsiveness to triggers such as cold air, exercise, stress, or allergens.