Epithelium histology
Epithelium, glands and cell junctions: histology for FCPS Part 1
Types of epithelium and where each is found, surface specialisations, cell junctions and blistering diseases, and gland types for FCPS Part 1. Each epithelium is matched to its job so organ-identification questions become logical.
One of the most tested topics in past papers
Epithelium matches its job
Epithelium is named by the number of layers and the shape of the surface cells. Thin cells suit exchange, tall cells suit absorption and secretion, many layers suit friction, and transitional cells suit stretch.
| Type | Job | Examples |
|---|---|---|
| Simple squamous | Diffusion, filtration | Alveolar lining (type I pneumocytes), endothelium, mesothelium, parietal Bowman capsule, thin limb of loop of Henle |
| Simple cuboidal | Secretion, absorption | Thyroid follicles, kidney tubules, ovarian surface, small gland ducts |
| Simple columnar | Absorption, secretion | Stomach, small and large intestine, gallbladder, endocervix; ciliated in the uterine tube |
| Pseudostratified ciliated columnar with goblet cells | Mucociliary clearance | Nasal cavity, trachea, bronchi (respiratory epithelium) |
| Pseudostratified columnar with stereocilia | Absorption of fluid | Epididymis, vas deferens |
| Stratified squamous non-keratinised | Wet friction | Mouth, oesophagus, vagina, ectocervix, cornea, anal canal below the pectinate line |
| Stratified squamous keratinised | Dry friction, waterproofing | Epidermis |
| Stratified cuboidal or columnar | Large ducts | Sweat and salivary gland ducts, parts of male urethra, conjunctiva |
| Transitional (urothelium) | Stretch, impermeable to urine | Renal pelvis, ureters, bladder, proximal urethra |
- All cells of pseudostratified epithelium touch the basement membrane, but not all reach the surface, so nuclei sit at different heights.
- In the airways, goblet cells and cartilage fade out distally: goblet cells are absent from terminal bronchioles, where club (Clara) cells take over.
- Urothelium lines the whole urinary tract from renal pelvis to proximal urethra, so urothelial carcinoma is often multifocal (field change); after a bladder tumour the upper tracts are imaged too. Bladder squamous carcinoma arises from squamous metaplasia (stones, catheters, schistosomiasis).
Metaplasia in exam stems
| Site | Change | Cause |
|---|---|---|
| Lower oesophagus | Squamous to intestinal-type columnar with goblet cells (Barrett) | Acid reflux; columnar lining above the GE junction |
| Bronchi | Ciliated columnar to squamous | Smoking |
| Cervix | Columnar to squamous (transformation zone) | Normal; site of CIN |
| Gallbladder | Columnar to gastric or intestinal type | Chronic cholecystitis |
- In chronic bronchitis (productive cough for 3 months in 2 consecutive years), the sputum comes from hypertrophy of submucosal mucous glands (raised Reid index, gland thickness over wall thickness, above 0.4) and goblet cell hyperplasia.
Surface specialisations
| Structure | Core | Function | Site |
|---|---|---|---|
| Microvilli (brush border) | Actin microfilaments | Absorption; carry enzymes | Small intestine, PCT |
| Cilia | Microtubules (9+2) with dynein arms | Beat to move mucus or ova | Respiratory tract, uterine tube, ependyma |
| Stereocilia | Actin; long non-motile microvilli | Absorption; mechanosensation in the ear | Epididymis, vas deferens, inner ear hair cells |
- Disaccharidases such as lactase sit in the brush border membrane. Flattening of villi and damage to microvilli (coeliac disease, gastroenteritis) causes secondary lactose intolerance.
- Primary ciliary dyskinesia (Kartagener syndrome): dynein defect, giving bronchiectasis, sinusitis, male infertility (immotile sperm) and situs inversus in about half.
- Telling vas deferens from epididymis: both have stereocilia, but the vas has a small star-shaped lumen and a very thick three-layered smooth muscle wall; the epididymis has a wide round lumen with sperm and a thin muscle coat.
Cell junctions
| Junction | Protein | Function | Disease link |
|---|---|---|---|
| Tight junction (zonula occludens) | Claudins, occludin | Seals the paracellular space; blood–brain barrier | Clostridium perfringens enterotoxin targets claudins |
| Adherens junction (zonula adherens) | E-cadherin to actin | Cell–cell adhesion belt | Loss in diffuse gastric and lobular breast carcinoma |
| Desmosome (macula adherens) | Desmogleins, keratin filaments | Strong spot welds | Pemphigus vulgaris (anti-desmoglein 3): flaccid intraepidermal blisters, Nikolsky positive |
| Hemidesmosome | Integrins, BP180 and BP230 | Anchor cells to the basement membrane | Bullous pemphigoid: tense subepidermal blisters in the elderly |
| Gap junction | Connexins | Electrical and chemical coupling | Present in cardiac and smooth muscle, absent between skeletal muscle fibres |
Basement membrane
- Basal lamina (lamina lucida and lamina densa, made of type IV collagen, laminin, perlecan) plus a reticular lamina (type III collagen) from connective tissue.
- In the alveolar wall the basement membranes of type I pneumocyte and capillary endothelium are fused, making the air–blood barrier very thin.
- In the glomerulus, type IV collagen and negatively charged heparan sulphate block protein by size and charge; antibodies to type IV collagen cause Goodpasture (linear IgG).
- Breaching the basement membrane separates invasive carcinoma from carcinoma in situ.
Myoepithelial cells
Contractile epithelial cells between the luminal cells and basement membrane of breast ducts, sweat glands and salivary glands; they squeeze secretion out (oxytocin in the breast). Stains: p63, smooth muscle actin, calponin. A preserved myoepithelial layer means in situ disease (DCIS) or a benign lesion such as sclerosing adenosis; loss means invasion.
Glands
| Classification | Types and examples |
|---|---|
| Route | Exocrine (ducts) versus endocrine (blood) |
| Shape | Tubular, acinar, tubuloacinar; simple or compound (branched ducts) |
| Mode of release | Merocrine: exocytosis (pancreas, salivary, eccrine sweat). Apocrine: apical cytoplasm lost (mammary lipid, axillary apocrine sweat). Holocrine: whole cell breaks down (sebaceous glands) |
| Product | Serous (watery enzymes: parotid), mucous (mainly sublingual), mixed (submandibular) |
- Goblet cells are unicellular mucous glands. Paneth cells, at the base of small intestinal crypts, have eosinophilic granules containing lysozyme and defensins (antimicrobial).
- Parotid epithelium comes from ectoderm (stomodeum); submandibular and sublingual are usually described as endoderm. Pleomorphic adenoma, the commonest salivary tumour, looks mixed but is a single epithelial-myoepithelial tumour.
- The submandibular gland wraps around the posterior free border of mylohyoid, with a large superficial part and small deep part.
- Greater vestibular (Bartholin) glands are mucous glands in the posterolateral vestibule (5 and 7 o'clock) whose duct blockage forms a cyst or abscess; male homologue: bulbourethral glands.
Remember Thin for exchange, tall for absorption, layers for friction, transitional for stretch.
Exam trap Pemphigus attacks desmosomes; pemphigoid attacks hemidesmosomes.
Exam trap Stereocilia are actin-cored microvilli, not cilia; true cilia have a 9+2 microtubule core.
How FCPS asks about this
- Simple squamous epithelium: alveolar lining, endothelium, mesothelium.
- Core of the brush border and why lactose intolerance follows mucosal damage: actin; lactase sits in the brush border.
- Cells secreting lysozyme and defensins: Paneth cells at the crypt base.
- Star-shaped lumen, stereocilia, thick three-layered muscle: vas deferens.
- Stains for myoepithelial cells deciding invasion: p63 and smooth muscle actin.
- Imaging the upper tract after bladder cancer: urothelium lines pelvis and ureters.
- Sebaceous gland secretion: holocrine; gap junctions present in cardiac and smooth muscle.
Test yourself on this topic
5 of the 62 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A smoker with three months of hoarseness has squamous cell carcinoma of the right true vocal cord. Which epithelium normally lines the true cords?
Answer: Non-keratinised stratified squamous
Most of the larynx is lined by respiratory (pseudostratified ciliated columnar) epithelium, but the true vocal cords, which face constant friction, are covered by non-keratinised stratified squamous epithelium. This is why squamous cell carcinoma, often preceded by leukoplakia, is the usual cancer of the glottis. The vocal cords also have very sparse lymphatics, so early glottic cancer rarely spreads to nodes and hoarseness appears early.
Vocal cord epithelium
- True cords: non-keratinised squamous
- Rest of larynx: respiratory epithelium
- Glottic SCC: early hoarseness
- Few lymphatics: late nodes
Remember Friction surfaces get squamous epithelium.
Exam trap Supraglottic cancers present later and spread to nodes early because that region is rich in lymphatics.
Why the other options are wrong
- Pseudostratified ciliated columnar Lines most of the larynx, but not the true cords.
- Keratinised stratified squamous Normal on skin; keratinisation on the cord is abnormal (leukoplakia).
- Stratified cuboidal Lines sweat gland ducts.
- Transitional epithelium Lines the urinary tract.
A man develops painful oral erosions and flaccid skin blisters that spread when pressed (positive Nikolsky sign). Antibodies are directed against which structure?
Answer: Desmoglein in desmosomes
Cell junctions: tight junctions (zonula occludens; claudins, occludin) seal the paracellular route; adherens junctions (cadherins linked to actin); desmosomes (macula adherens; desmoglein, desmocollin, linked to keratin) bind cell to cell; gap junctions (connexons) allow ions to pass (cardiac muscle, smooth muscle); hemidesmosomes (integrins) attach cells to the basement membrane. Pemphigus vulgaris: IgG against desmoglein 3 (and 1) → acantholysis, intraepidermal flaccid blisters, mucosal involvement, Nikolsky positive. Bullous pemphigoid: antibodies to hemidesmosomes → tense subepidermal blisters, mucosa usually spared.
Junctions and blisters
- Desmosome (desmoglein): cell–cell → pemphigus vulgaris
- Hemidesmosome: cell–BM → bullous pemphigoid
- Gap junction: connexons (heart)
- Tight junction: claudins (barrier)
Remember Pemphigus is between cells; pemphigoid is below them.
Why the other options are wrong
- Hemidesmosome proteins (BP180, BP230) Bullous pemphigoid.
- Gap junction connexons Electrical coupling.
- Tight junction claudins Barrier function.
- Type VII collagen Epidermolysis bullosa acquisita.
Which surfaces are lined by non-keratinised stratified squamous epithelium?
Answer: Oesophagus and vagina
Stratified squamous non-keratinised epithelium lines moist surfaces exposed to abrasion: oral cavity (most parts), pharynx, oesophagus, anal canal below the pectinate line, vagina, ectocervix and cornea. Keratinised stratified squamous epithelium forms the epidermis (thickest on palms and soles). The trachea and bronchi have pseudostratified ciliated columnar epithelium; the small intestine has simple columnar epithelium with microvilli and goblet cells; the bladder has transitional epithelium (urothelium).
Squamous epithelia
- Non-keratinised: oesophagus, vagina, ectocervix, cornea, mouth
- Keratinised: skin
- Simple squamous: alveoli, endothelium, mesothelium
Remember Wet and rubbed: non-keratinised squamous.
Why the other options are wrong
- Skin of the palm Keratinised.
- Trachea and bronchi Respiratory epithelium.
- Small intestine Simple columnar.
- Urinary bladder Transitional.
After pelvic inflammatory disease, a woman has a tubal ectopic pregnancy. Loss of which cells of the tubal lining best explains this?
Answer: Ciliated columnar cells
The uterine tube is lined by simple columnar epithelium with ciliated cells and non-ciliated secretory (peg) cells. Cilia beat towards the uterus and, with peristalsis, carry the fertilised ovum along the tube. Salpingitis destroys ciliated cells and causes adhesions within the mucosal folds, so transport is delayed and the embryo implants in the tube. Smoking also impairs ciliary function and is a risk factor.
Uterine tube lining
- Simple columnar epithelium
- Ciliated cells move the ovum
- Peg cells secrete
- PID destroys cilia: ectopic
Remember Damaged cilia, stuck embryo.
Exam trap The ampulla, not the isthmus, is the commonest site of tubal ectopic pregnancy.
Why the other options are wrong
- Peg (secretory) cells Secrete nutrients for the ovum but do not propel it.
- Smooth muscle cells Peristalsis helps, but loss of cilia is the key change.
- Mesothelial cells Cover the outer serosa, not the lumen.
- Stromal decidual cells Decidua forms in the endometrium, not the normal tube.
A specimen from an orchidectomy contains a highly coiled tube in cross-section, lined by tall pseudostratified columnar cells with long stereocilia, surrounded by a thin layer of smooth muscle, with sperm in the lumen. Which structure is this?
Answer: Epididymis
The epididymis is a single, highly coiled duct, so a section shows many profiles of the same tube. It is lined by tall pseudostratified columnar epithelium with stereocilia, which absorb fluid and help concentrate sperm, and it has a thin circular smooth muscle coat. The vas deferens has the same lining but a very thick three-layered muscular wall and a star-shaped lumen. Seminiferous tubules contain germ cells and Sertoli cells.
Epididymis
- Coiled duct: many profiles
- Pseudostratified with stereocilia
- Thin smooth muscle
- Sperm mature and store here
Remember Thin muscle: epididymis; thick muscle: vas.
Exam trap Stereocilia are absorptive microvilli; they do not propel sperm.
Why the other options are wrong
- Vas deferens Has a much thicker three-layered muscle wall.
- Seminiferous tubule Lined by germ cells and Sertoli cells, not stereocilia.
- Rete testis Lined by low cuboidal epithelium.
- Prostatic urethra Lined by urothelium.
Where this sits in the CPSP syllabus
- Paper 1: General and special histology, Epithelium, glands and cell junctions
- Surgery & Allied, Paper 2: Histology for surgery, Epithelium, glands and cell junctions
Read next
Drug dose pages
Doses, cautions and practical tips for drugs in this chapter.