Stratified Squamous Non-Keratinized Epithelium

At a glance

Multilayered squamous epithelium with living surface cells (no thick keratin mat); kept moist by mucus/secretions.
Present in oral cavity, oropharynx, esophagus, true vocal cords, vagina/ectocervix, and distal anal canal.
Expect orderly maturation, glycogenated superficial cells, smooth basement membrane; parakeratosis is minimal/patchy at most.
Basal cells p63/p40/CK5/6+; upper layers lose high-molecular-weight keratins; no broad surface anuclear keratin.

Distal Anal Canal (non-keratinized zone)

1. Location

Segment just above the anal verge, below the rectal columnar mucosa, but not yet fully keratinized perianal skin.
Why: this is a high-friction passage, but still a moist mucosa.

2. Architecture

Stratified squamous, non-keratinized or very thin parakeratin depending on friction.
- Why: has to tolerate passage of stool but remain stretchable.
Basal/parabasal → intermediate → superficial nucleated layer.

3. Transitions

Proximal: to colorectal/rectal columnar mucosa.
Distal: to keratinized epidermis.
Why: anal canal is a classic “junction zone,” so patterns can mix — this matters in small biopsies.

4. Junctions / support

Lots of desmosomes.
- Why: resist shear from stool.
Strong basal attachment.
- Why: prevent mucosal sloughing in defecation.

5. Path/clinical angle

Chronic irritation (constipation, prolapse, hemorrhoids, dermatologic disease) → reactive squamous hyperplasia, sometimes focal keratinization.
- Why: mucosa adapts to increased rubbing.
Important background for anal intraepithelial neoplasia (AIN) and HPV-related lesions — you need to know what normal non-keratinized anal squamous looks like.
- Why: dysplasia here can resemble cervical/vaginal SIL patterns.

Generalities

1. Architecture

Multiple cell layers (more than 2–3)

Why: built for protection against friction/trauma — more layers = more buffer.
Surface cells are squamous but still nucleated and viable

Why: this epithelium lines moist surfaces (mouth, esophagus, vagina); you don’t want a dry, keratinized layer there.
Basal layer of cuboidal to low columnar cells on a basement membrane

Why: these are the progenitor cells → they divide and push cells upward.
Progressive maturation toward surface (basal → parabasal → intermediate → superficial)

Why: as cells move up, they flatten and adjust their junctions so the surface stays intact.

2. Cytologic Features

Basal cells: small, high N:C, darker nuclei

Why: active, dividing compartment.
Suprabasal/intermediate cells: larger, more cytoplasm, still polygonal

Why: transition zone; gives thickness and flexibility.
*Superficial cells: flat, pale cytoplasm, nuclei retained

Why: surface must stay moist and able to slough gently without becoming a dry “skin.”

3. Keratin vs no keratin

No surface keratin layer, no anuclear squames

Why: the surface is constantly bathed in saliva, mucus, or vaginal secretions — keratin would make it too dry and stiff.
May have a very thin superficial condensation in high-friction areas (parakeratin-like)

Why: local adaptation to friction, but still not true orthokeratin as in skin.

4. Polarity / attachment

Apical surface faces a moist lumen (oral cavity, oropharynx, esophagus, vagina, ectocervix).

Why: these sites see food, speech, intercourse, childbirth → need wet + tough.
Basal surface firmly attached to basement membrane via hemidesmosomes

Why: the whole sheet is being rubbed — it must not detach.

5. Junctions

Desmosomes prominent, especially in suprabasal layers

Why: main mechanical glue to resist shear; also explains “prickle cells” in some sections.
Tight junctions present but less dominant than in simple epithelia

Why: protection here is more about mechanical integrity than about super-tight sealing.
Basal cells with hemidesmosomes → BM

Why: anchors the proliferative layer so upward movement works.

6. Basement membrane

Continuous BM (lamina lucida + lamina densa) over lamina propria

Why: supports high turnover and gives a plane for regeneration.
Papillae of CT may project upward (esp. oral mucosa, esophagus)

Why: increases surface area for nutrition in a thick, avascular epithelium.

7. Vascularity / nutrition

Epithelium itself is avascular

Why: like all epithelia.
Nourished from vessels in underlying lamina propria / papillary CT

Why: multiple layers need more diffusion surface → hence CT papillae.

8. Function

Mechanical protection against abrasion

Why: food bolus, teeth, intercourse, pH shifts → top layers can be lost safely.
Keeps surface moist and permeable enough

Why: viable surface cells + mucus/saliva → better for speech, swallowing, sexual function, childbirth.
Barrier to pathogens

Why: multiple layers + desmosomes + mucus on top slow down microbes.

9. Immuno (generic epithelial)

Positive: broad cytokeratins (AE1/AE3), CK5/6 (basal/squamous), p63/p40 (basal/squamous-type TFs).

Why: confirms stratified squamous nature.
Basal layer: p63+, high-molecular-weight keratins (34βE12), CK14

Why: marks the proliferative squamous compartment.
Negative: endothelial (CD31, vWF) and mesothelial panels (WT-1, calretinin, D2-40) in the usual mucosal sites

Why: separates from other flat linings.

10. Regeneration

Basal cells proliferate → cells move upward → desquamate

Why: constant turnover to replace cells lost to friction.
Healing is fast if BM is intact

Why: cells can crawl along it and re-stratify.

11. Typical anatomic sites

Oral cavity (most of it)
Oropharynx
Esophagus
True vocal cords
Vagina and ectocervix
Distal anal canal (non-keratinized zone)

Oral/Pharyngeal/Esophageal Type

1. Location

Lining mucosa of cheeks, soft palate, floor of mouth, ventral tongue, inner lip.
Oropharynx (areas exposed to both food and air).
Esophagus (upper to lower, until the gastric junction).
Why: these are transit or contact surfaces that receive mechanical stress from food, teeth, speech and sometimes gastric reflux, but they must remain moist and sensate.

2. Overall architecture

Many cell layers, usually 20 or more in thicker zones such as the esophagus.
Basal layer on a basement membrane, then parabasal, then intermediate layers, then a superficial layer that is flattened but still nucleated.
Why: multiple layers give mechanical insurance, so superficial cells can be lost without exposing connective tissue.

3. Basal layer

Cells: small, cuboidal to low columnar, high nuclear to cytoplasmic ratio, basophilic cytoplasm.
Attachments: hemidesmosomes to the basement membrane.
Markers: p63 positive, p40 positive, CK5/6 positive, high molecular weight keratins positive.
Why: this is the proliferative compartment that renews the epithelium, so it must be firmly attached and able to divide.

4. Parabasal / suprabasal layers

Cells become larger, more polygonal, cytoplasm increases.
Prominent desmosomes produce an intercellular bridge appearance in well fixed tissue.
Nuclei remain centrally located, usually bland and round to oval.
Why: this zone provides thickness, flexibility and most of the mechanical strength. Desmosomes here are very important because this is the level that is exposed to shear from the food bolus.

5. Intermediate layer

Cells can accumulate some glycogen, especially in the esophagus and some oral sites.
Intercellular spaces are small because of many desmosomes.
Why: a slightly hydrated, glycogenated middle layer helps the epithelium stay flexible and respond to changing friction.

6. Superficial (surface) layer

Cells are flattened (squamous), cytoplasm becomes lighter, nuclei are still present and often a bit pyknotic but not lost.
No stratum corneum and no orthokeratin.
In areas of very high friction, a very thin parakeratin-like surface can appear, but this is still considered non-keratinized in routine mucosa.
Why: surface must stay moist and able to desquamate gradually. Losing the nucleus and forming a thick keratin layer would make this mucosa dry and less useful for swallowing and speech.

7. Junctions

Desmosomes are abundant, especially in suprabasal and intermediate layers.
- Why: they are the main resistance mechanism against lateral shear from food and tongue movement.
Tight junctions exist apically but are not the main feature.
- Why: this epithelium is about mechanical protection more than about forming a very tight chemical barrier, unlike small intestine or stomach.
Basal hemidesmosomes attach to the basement membrane.
- Why: the whole sheet is pushed and rubbed, so the basal cells must not detach.

8. Basement membrane and lamina propria

Continuous basement membrane separates the epithelium from the underlying connective tissue.
Lamina propria in the oral cavity and esophagus often has upward projecting papillae that interdigitate with epithelial ridges.
- Why: this increases the contact area for diffusion, which is important because the epithelium is thick and avascular.
- It also improves mechanical anchoring, so mucosa does not slide.
In the esophagus, the lamina propria is relatively loose and allows folding of the mucosa.
- Why: the lumen must distend for a food bolus.

9. Vascular supply

Capillary loops rise into the connective tissue papillae just below the epithelium.
Why: multiple layers of cells need oxygen and nutrients, and diffusion distance must be kept short.

10. Function

Mechanical protection
- Thick, stratified structure lets the surface lose cells to friction, food, accidental biting or dental appliances without ulceration.
Moist surface
- Saliva and mucous secretions can adhere to viable superficial cells, which improves lubrication and bolus formation.
Barrier to pathogens
- Several cell layers, intact desmosomes and a saliva layer with IgA reduce microbial penetration.
Sensory role support
- Keeping the surface viable, not keratinized, preserves the environment needed for taste and for oral sensory receptors.

11. Site specific notes

Oral cavity: often slightly thicker, flexible, sometimes shows minor parakeratin where chewing is intense.
- Why: adaptation to mastication and dentures.
Oropharynx: exposed both to food and to air, so it stays clearly non-keratinized to keep the surface lubricated.
Esophagus: more uniform stratified non-keratinized, good for a large passing bolus, and capable of reactive thickening (acanthosis) in chronic irritation such as reflux.

12. Immunohistochemistry (what is useful to a resident)

Basal/suprabasal: p63 positive, p40 positive, CK5/6 positive, high molecular weight keratins positive.
- Why: confirms native squamous mucosa and helps identify squamous dysplasia or invasive squamous carcinoma when it arises.
Negative for endothelial markers (CD31, vWF) and mesothelial panel (WT-1, calretinin).
- Why: rules out other flat linings when tissue is small or crushed.
In biopsies with suspected columnar metaplasia (Barrett esophagus), the loss of this squamous profile and the gain of columnar markers is the diagnostic shift.

13. Regeneration and injury

If the basement membrane is intact, re-epithelialization is rapid, from basal cells at the edge.
- Why: high mechanical turnover sites are set up to repair quickly.
Chronic irritation can cause:
- Acanthosis (thickening of spinous layer),
- Papillomatosis (accentuated papillae),
- Focal surface keratinization.
- Why: the mucosa adapts to higher friction or low-grade chemical injury.

14. Transitions

At the lips, this epithelium transitions to keratinized skin at the vermilion.
At the gastroesophageal junction, it transitions abruptly to simple columnar gastric-type mucosa.
- Why: different environments require different barrier strategies.

True Vocal Cords

1. Location

Mucosa directly over the true vocal folds (not the false cords).
Why: this area vibrates at high frequency and can rub against the opposite cord → needs a tough but still moist lining.

2. Architecture

Stratified squamous, non-keratinized (or very minimally para-keratinized in heavy voice users).
- Why: protects from mechanical trauma of phonation but keeps the surface pliable.
Basal → parabasal → intermediate → superficial, nucleated.
- Why: classic non-keratinized maturation.

3. Basal layer

Cuboidal to low columnar, p63+/p40+/CK5/6+.
Firm hemidesmosomal attachment.
Why: cords stretch and vibrate → epithelium must not shear off.

4. Superficial layer

Flattened, still nucleated, thin.
Why: vibrations need a flexible, non-brittle surface to keep the mucosal wave.

5. Lamina propria (Reinke space)

Very loose, delicate superficial lamina propria under the epithelium.
Why: this layer must move independently → if it scars (smoking, intubation), voice changes.

6. Path/clinical angle

Chronic irritation (smoke, reflux, voice abuse) → focal hyperplasia, acanthosis, even focal keratinization.
- Why: local adaptation to increased friction.
Dysplasia and early SCC often start here on this squamous background.
- Why: it’s a high-turnover, high-stress squamous patch.

Vagina / Ectocervix

1. Location

Vagina (from hymenal ring to vaginal fornices).
Ectocervix / exocervix (the part of the cervix projecting into the vagina, before the squamocolumnar junction).
Why: these are contact/mucosal surfaces exposed to friction, microtrauma, microflora, and variable pH, so they need a tough but still moist epithelium.

2. Overall architecture

Stratified: basal → parabasal → intermediate → superficial.
Surface cells remain nucleated and viable.
No true keratin layer.
Why: the lumen must stay lubricated and distensible (intercourse, childbirth), so you can’t have a dry, keratinized cap like skin.

3. Hormone dependence (key difference from oral/esophagus)

Under estrogen (reproductive age): epithelium is thick, nicely stratified, with large intermediate/superficial layers full of glycogen.
- Why: estrogen drives squamous maturation upward. More mature cells = better protection + more glycogen for lactobacilli.
Low estrogen (prepubertal, postpartum, postmenopausal): epithelium becomes thin, mostly basal/parabasal cells, little glycogen.
- Why: without estrogen, cells don’t mature up → epithelium loses its thick protective top → mucosa becomes more fragile and easily inflamed.

4. Basal layer

Small, cuboidal to low columnar cells, high N:C ratio, basophilic.
Strongly attached to basement membrane by hemidesmosomes.
Immuno: p63+, p40+, CK5/6+, HMWK+.
Why: this is the proliferative pool. It must be anchored (to resist friction) and capable of supplying all upper layers.

5. Parabasal layer

Slightly larger cells, round to oval nuclei, still relatively high N:C.
In atrophic vaginitis, these cells can reach the surface.
Why: when maturation fails (low estrogen), you start seeing “young” cells exfoliate — that’s why Pap tests in atrophic women show many parabasal cells.

6. Intermediate layer

Bigger polygonal cells, more cytoplasm, begin to accumulate glycogen (PAS positive, diastase-sensitive).
Why: this is the estrogen-responsive expansion zone; it gives thickness and supplies glycogen to the lumen once cells desquamate.

7. Superficial layer

Flattened, still nucleated, cytoplasm pale or vacuolated from glycogen.
No anuclear squames.
Why: cells must remain viable to maintain a moist, protective surface; at the same time, they are “loaded” so that, when shed, they feed lactobacilli.

8. Glycogen → flora → pH

Desquamated superficial cells rich in glycogen → lactobacilli metabolize → lactic acid → pH ~4.0–4.5.
Why: acidic pH inhibits many pathogens and helps maintain normal vaginal flora.
In low estrogen states: less glycogen → fewer lactobacilli → higher pH → more infections.
- Why: epithelium isn’t feeding the flora properly.

9. Junctions

Desmosomes well developed through mid/superficial layers.
- Why: resist friction during intercourse and childbirth.
Hemidesmosomes basally.
- Why: prevent sloughing of the whole sheet.
Tight junctions present but not the main protective feature.
- Why: the key job here is mechanical and microbial, not fine control of solute flux.

10. Basement membrane + lamina propria

Continuous BM over a vascular, elastic lamina propria.
- Why: needs to stretch and recoil.
Lamina propria may have rich venous plexuses.
- Why: contributes to vaginal lubrication and engorgement during sexual arousal even though there are no mucous glands in the vagina itself.
In ectocervix: lamina propria is denser and blends with cervical stroma.
- Why: cervix must also provide structural support to the uterus.

11. Function

Mechanical protection from intercourse, tampon use, pelvic exams, minor trauma.
- Why: stratification allows superficial loss without ulcer.
Microbial/ecologic role via glycogen → lactobacilli → lactic acid.
- Why: turns the epithelium into a “feeder” for protective flora.
Maintain moisture and elasticity (viable surface, no keratin).
- Why: needed for sexual function and childbirth.
Barrier to ascending infection (multiple viable layers + acidic environment).
- Why: protects upper genital tract.

12. Immunohistochemistry / diagnostic angles

Normal squamous mucosa: p63+, p40+, CK5/6+, HMWK+ (basal and parabasal strongest).
- Why: confirms squamous lineage in small/fragmented cervical/vaginal biopsies.
HPV-related SIL (LSIL/HSIL): loss of normal maturation + expansion of immature cells upward; HSIL often shows strong, block-type p16.
- Why: you compare to the expected fully maturing non-keratinized squamous.
CK7-/+ pattern helps separate from endocervical lesions in some settings.
- Why: ectocervix is squamous, endocervix is glandular.

13. Injury / repair

Fast re-epithelialization if BM is intact (e.g. post-trauma, postpartum).
- Why: basal cells spread and divide along the existing BM.
If BM/stroma damaged (deep lacerations): healing may lead to scarring or adhesions.
- Why: loss of the “flat guide” makes regeneration less orderly.

14. Transition zone (SCJ)

At the squamocolumnar junction, non-keratinized squamous meets mucus-secreting columnar endocervical epithelium.
- Why: this is a physiologic meeting of two environments (vaginal acidic vs cervical mucus).
Metaplasia here (reserve cells → squamous) is common.
- Why: acidic vaginal environment can “request” a tougher squamous cover.
This is the site for HPV infection and most cervical precancers.
- Why: actively remodeling, exposed epithelium is more susceptible.

15. Special clinical/path notes

Atrophic vaginitis: thin, fragile, parabasal-rich epithelium, higher pH, more infections.
- Why: low estrogen.
Pregnancy: can see increased glycogen and sometimes more exuberant squamous maturation.
- Why: hormonal changes.
Radiation / chronic infection: may cause squamous atrophy, ulcer or scarring.
- Why: high-turnover epithelium is radiosensitive.