Simple Columnar Epithelium

At a glance

Tall, single-layer epithelium with basal nuclei and apical modifications (microvilli, mucin, cilia depending on site).
Balances secretion and absorption: GI tract, gallbladder, Müllerian tract.
Goblet cell density and surface structures (villi, pits, folds) define region; check for orderly, uniform nuclei.
Usual markers: CK7/CK20 pattern depends on site (gastric CK7+, colon CK20+/CDX2+), MUC profile varies.

Colon

Architecture

Straight crypts lined by columnar absorptive cells + many goblet cells.
Why: colon reclaims water/electrolytes but must move formed feces → needs lubrication.

Apical

Shorter microvilli than small bowel.
- Why: absorption, but less surface needed.

Cells

Absorptive colonocyte
- Why: Na⁺/water uptake.
Goblet (very numerous)
- Why: stool lubrication.

IHC / phenotype

CK20+, CDX2+ (strong, diffuse).
- Why: classic colorectal signature.
MUC2+ (goblets).
- Why: intestinal mucin.
CK7− (most colon).
- Why: separates from upper GI, pancreatobiliary, Müllerian.

Function

Dehydrate fecal stream + protect surface from mechanical/chemical injury.
Why: final segment of digestion.

Gallbladder

Architecture

Tall, uniform columnar cells, no goblet cells, on mucosal folds.
Why: concentrates bile, doesn’t need mucus mix.

Apical

Numerous microvilli.
- Why: ↑ surface to reabsorb water/electrolytes from bile.

Junctions

Tight junctions.
- Why: prevent bile from leaking back and injuring wall.

IHC / phenotype

CK7+, CK19+
- Why: biliary/ductal pattern.
CK20− (usually)
- Why: not intestinal.
MUC1+ (apical)
- Why: biliary-type mucin.
CDX2− (unless metaplastic).
- Why: intestinal metaplasia is abnormal.

Function

Concentrate and store bile; withstand bile acids.
Why: tall columnar with tight junctions is optimal.

Gastric / Foveolar

Architecture

Single layer of mucus-secreting columnar cells lining surface + pits.
Why: stomach must protect itself from acid/pepsin, not absorb.

Cytoplasm

Apical mucin droplets (neutral → MUC5AC).
- Why: make thick, bicarbonate-rich gel.

Junctions

Tight junctions high.
- Why: stop back-diffusion of acid.

IHC / phenotype

CK7+, CK20− (usually)
- Why: upper-GI pattern.
MUC5AC+ (surface/foveolar)
- Why: gastric surface mucin.
MUC6+ deeper/antral glands.
- Why: pyloric/Brunner-like mucin.
CDX2− (unless intestinal metaplasia).
- Why: helps spot metaplasia.

Function

Barrier, mucus, bicarb.
Why: main job is self-protection, not transport.

Generalities

1. Architecture

Single continuous layer of tall epithelial cells (one cell thick, height > width)

Why: taller cell = more cytoplasm = room for organelles → good for secretion, absorption, and complex apical specializations.

Cells aligned so nuclei form a basal/infra-nuclear row (oval nuclei at same level)

Why: gives the “picket fence” look and shows the epithelium is well polarized.

Apical surface to lumen / cavity; basal surface to basement membrane

Why: classic vector transport arrangement — take from lumen, process, send basally.

Supported by an intact basement membrane

Why: tall cells need a stable base (they’re top-heavy) and BM guides regeneration.

2. Cytologic Features

Nucleus oval, euchromatic, usually basal 1/3

Why: pushes most of the cytoplasm apically where secretory vesicles or microvilli sit.

Cytoplasm moderate to abundant, often pale to eosinophilic

Why: secretory/absorptive roles need rER, Golgi, mitochondria.

Apical cytoplasm may contain mucin droplets (goblet cells) or secretory vesicles

Why: many columnar epithelia combine lining + mucus protection.

Cells relatively uniform in size/shape in normal sites

Why: variation suggests dysplasia, metaplasia, or repair.

3. Polarity and Apical Specializations

Apical domain with microvilli (“brush/striated border”) — small intestine, proximal colon, gallbladder

Why: ↑ surface area → ↑ absorption/secretion.

Apical glycocalyx over microvilli

Why: holds enzymes, protects surface from autodigestion.

Apical cilia (motile) in some sites — uterine tube, small bronchioles

Why: move fluid/ova/mucus in one direction.

Apical secretory cap in goblet cells

Why: mucus to lubricate and make a chemical barrier on top of columnar epithelium.

4. Junctional Complexes

Apical tight (occluding) junction / zonula occludens

Why: seals the paracellular space so lumen contents must go through the cell (transcellular) → essential in gut, biliary, uterine.

Proteins: claudins (define permeability), occludin, JAMs

Why: let different organs set different “tightness.”

Just below: zonula adherens (E-cadherin + catenins, linked to actin)

Why: keeps cells laterally attached so peristalsis, gallbladder contraction, or uterine motion doesn’t tear the sheet.

Spot desmosomes (macula adherens)

Why: extra mechanical strength, especially in GI where chyme/feces drag over the surface.

Basal hemidesmosomes/integrins to BM

Why: tall cells + peristalsis → need a strong anchor.

This “tight → adherens → desmosome” belt is a classic for simple columnar and is more developed than in many simple squamous linings.

5. Basement Membrane

Continuous BM (type IV collagen, laminin, nidogen, HSPGs)

Why: supports tall cells and separates them from immune cells/vessels in lamina propria.

Closely opposed to vascular lamina propria

Why: absorbed nutrients or secreted hormones must reach blood quickly (intestine, uterus).

6. Cytoskeleton

Apical actin core in microvilli (with fimbrin, villin)

Why: keeps microvilli erect and allows rapid remodeling.

Subapical terminal web of actin

Why: anchors tight/adherens junctions so the seal is stable.

Intermediate filaments: simple epithelial keratins (CK8, CK18, CK19)

Why: tells you on IHC that this is simple glandular/columnar, not squamous.

Microtubules

Why: vesicle trafficking (apical secretion, basolateral delivery of transporters).

If ciliated: axonemal 9+2 microtubule structure + dynein arms

Why: motility for ovum/mucus.

7. Immunohistochemistry (general columnar / glandular profile)

Positive (generic):

CK8/18, CK19

Why: simple/glandular epithelial cytokeratins.
EMA

Why: epithelial membrane/glandular surfaces.
CK7 (many upper GI, biliary, pancreatic, Müllerian)

Why: ductal / upper GI / gynecologic pattern.

Often Negative / Variable:

CK20 (negative in stomach/gallbladder/uterus; positive in colon)

Why: good for site assignment.
CDX2 (negative in non-intestinal; positive in intestinal-type columnar)

Why: enteric differentiation.

Negative for endothelial (CD31, vWF), mesothelial (WT-1, calretinin), squamous HMWK

Why: separates this from other flat/tall linings.

We will add site-specific panels in the site cards (below).

8. Vascularity and Nutrition

Epithelium itself is avascular

Why: epithelial rule.

Lamina propria right under it is highly vascular + lymphatic

Why: to take up absorbed material (intestine) or support high turnover (uterus, stomach).

In villous/mucosal folds: CT cores push up between columnar cells

Why: shortens diffusion distance for a tall, metabolically active epithelium.

9. Functional Correlation

Absorptive (intestine, GB)

Why: microvilli + tight junction belt = controlled, high-capacity uptake.

Secretory / protective (stomach, colon goblet cells, endocervix)

Why: tall cell can house mucin granules and secrete to coat the surface.

Transport / ciliated (uterine tube, some respiratory)

Why: same architecture, different apical machinery.

Barrier (all)

Why: apical tight junctions stop pathogens, bile acids, sperm, or uterine contents from passing between cells.

10. Regeneration and Injury

Mitotically active in lower third / crypts / glands

Why: columnar epithelia have to keep replacing shed or acid-damaged cells.

If BM intact → fast resurfacing by upward migration

Why: stem/transit cells move up and re-epithelialize.

If BM damaged (ulcer): granulation tissue first, then re-epithelialization from the edges

Why: no scaffold = slower, may scar.

11. Typical Anatomic Correlates (to expand separately)

Stomach surface/foveolar epithelium
- CK7+, MUC1/5AC+, CK20−
- Why: mucus/protective, not absorptive.
Small intestine (enterocyte + goblet)
- CK8/18+, CK20+, CDX2+
- Why: absorptive + intestinal differentiation.
Colon
- CK20+, CDX2+, lots of goblets
- Why: absorptive (water) + lubrication.
Gallbladder
- Tall columnar with dense microvilli, CK7+, CK20−
- Why: concentrate bile.
Uterus / oviduct (ciliated + secretory)
- CK7+, PAX8+, ER/PR+
- Why: Müllerian columnar.
Large ducts (pancreatic, biliary, salivary)
- CK7+, CK19+, MUC1+
- Why: ductal columnar.

Müllerian / Uterine / Oviduct

Architecture

Single layer of ciliated and nonciliated secretory columnar.
Why: must move gametes/embryo and provide nutritive fluid.

Apical

Cilia on ciliated cells.
- Why: directional transport toward uterus.
Microvilli on secretory/peg cells.
- Why: secretion.

Hormone dependence

Height, ciliation, secretion vary with cycle.
- Why: match transport to ovulation.

IHC / phenotype

CK7+
- Why: Müllerian.
PAX8+
- Why: Müllerian/renal/thyroid TF, here supports Müllerian.
ER+, PR+
- Why: hormonally responsive.
WT1−, calretinin− (helps vs mesothelium in pelvis).
CDX2−, CK20−
- Why: not intestinal.

Function

Propel ovum/zygote, secrete supportive fluid, protect peritoneal cavity.
Why: ciliated + tight = ideal for reproductive tract.

Small intestine

Architecture

Tall columnar absorptive cells + interspersed goblet cells on villi and crypts.
Why: need to absorb a lot (enterocytes) but also protect/lubricate (goblets).

Apical

Dense microvilli → brush border + glycocalyx.
- Why: huge surface + enzymes (disaccharidases, peptidases) right where absorption happens.

Cells

Enterocyte (absorptive): tall, basal nucleus, clear brush border.
- Why: main transcellular route for nutrients.
Goblet cell: mucin cap, narrow base.
- Why: mucus film protects from chyme.
(In crypts: Paneth, stem, enteroendocrine — but surface is still columnar.)

Junctions

Very tight apical belt.
- Why: force nutrients to go through the cell → selective absorption.

IHC / phenotype

CK8/18+, CK20+, CDX2+ → intestinal differentiation.
- Why: distinguishes from gastric/biliary.
MUC2+ in goblet cells.
- Why: intestinal-type mucin.
Villin+ (apical) often used.
- Why: marks brush border.

Function

Absorb sugars, AAs, lipids; secrete protective mucus.
Why: this is the high-capacity digestive lining.