Chapter 2 of 5 - Histology Course
Epithelial Tissue in Histologic Sections
Epithelia form barriers and glands. On H&E, look for apical specializations, basement membrane cues, nuclear stratification, and whether the tissue is lining a lumen (surface) or forming secretory units.
Structure and Function
Epithelial cells are polarized: an apical surface (lumen or environment), lateral junctions, and a basal surface anchored to the basement membrane region. Simple epithelia line ducts and cavities where diffusion or absorption dominates; stratified types protect high-abrasion surfaces (skin, oral mucosa, urethra in places).
When you practice identification, name two features before moving on: layer count (one layer versus many) and surface cell shape (flattened versus cube versus column). Exceptions like pseudostratified columnar reward careful nuclear counting against the basement membrane.
Classification at a Glance
The table below is a lecture-style map. On real slides, oblique sectioning can make simple epithelium look thicker; use nuclear alignment and basement membrane contact to resolve ambiguity.
| Layers | Surface shape | Example locations (typical) |
|---|---|---|
| Simple | Squamous | Alveoli, glomerular capsule, vessel lining |
| Simple | Cuboidal or columnar | Kidney tubules, gallbladder, intestinal lining (with microvilli brush border in places) |
| Stratified | Squamous (keratinized or non-) | Epidermis, esophagus, oral mucosa (context-dependent) |
| Stratified | Transitional | Urinary tract (relaxed versus distended appearance) |
| Pseudostratified | Columnar (often ciliated) | Respiratory tract epithelium with goblet cells |
Reading Stratified Epithelium (Base to Surface)
In stratified squamous sections, the deepest cells are often more cuboidal and mitotically active; superficial cells flatten as they differentiate. This vertical flow mirrors the epidermis conceptually, even outside skin.
Basal layer
Stem-like cells, strong basophilia, attach to basement membrane
Intermediate layers
Transition in nuclear density and cytoplasm volume
Superficial layer
Squamous, sometimes keratinized or nucleated depending on site
Junctions and Polarity (Why It Matters)
Lateral junctions (tight, adherens, desmosomes) hold epithelial sheets together under mechanical stress. The basal side anchors to matrix via integrins linked to basement membrane components. In exams, "polarity" often means apical specializations (cilia, microvilli) visible as a brush border or striated border at high power.
Hematoxylin (oxidized forms bind tissue)
(6aS,11bR)-7,11b-dihydro-6H-indeno[2,1-c]chromene-3,4,6a,9,10-pentol
Hematoxylin is the core dye used before mordanting in H&E. It highlights nuclei and other basophilic structures, giving epithelial layers sharp nuclear detail on slides.
Formula
C16H14O6
Mol. Weight
302.28 g/mol
Normal breast histology with H&E: epithelial cells surround lumens in acinar arrangements; basement membrane and myoepithelial context are visible at higher magnification.
Mikael Häggström, M.D., Wikimedia Commons, CC BY 4.0
Quick Check
Which epithelium lines many airways and appears 'stratified' but is actually a single layer of cells of differing heights?
Fill in the Blank
Glandular epithelium that keeps a connection to the surface is called________; glands without a surface connection are branched or unbranched acinar or tubular structures depending on morphology.
Quick Check
You are viewing a lining epithelium with multiple cell layers and flattened cells at the free surface. The best name for the layering pattern is:
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