BIO 304 · Human Anatomy & Physiology
Epithelial Tissue Classification
Tissues · Module 3
A reference for the Epithelial Tissue video. Epithelium covers, lines, and secretes. Every epithelium gets named twice: by shape of cell, and by how many layers thick.
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- Classify any epithelium by cell shape (squamous, cuboidal, columnar) and number of layers (simple, stratified, pseudostratified).
- Match each epithelium to a representative location and primary function.
- Distinguish exocrine from endocrine glands and name the three modes of exocrine secretion.
Click any image to enlarge.
By Shape & Layers
Cell shapes
- Squamousflat, scale-like cells; thin barrier for diffusion
- Cuboidalcube-shaped; secretion and absorption
- Columnartall column-shaped; absorption, secretion, sometimes cilia
Layering
- Simpleone cell layer; thin enough for transport
- Stratifiedmultiple cell layers; protection against abrasion
- Pseudostratifiedone layer but nuclei at different heights, looks layered
- Transitionalchanges shape with stretch; only in urinary tract
Common types & where
- Simple squamousalveoli, capillary endothelium · gas/fluid exchange
- Simple cuboidalkidney tubules, gland ducts
- Simple columnarGI tract lining · absorption + mucus
- Pseudostratified ciliated columnarupper airway · mucus + cilia escalator
- Stratified squamousskin epidermis, esophagus, vagina · abrasion
- Transitional (urothelium)bladder, ureters · stretch without leaking
Glandular Epithelium
Gland types
- Exocrinesecretes through a duct to a surface (sweat, salivary, mammary)
- Endocrineductless; secretes hormones into bloodstream (thyroid, adrenal)
- Unicellular glanda single secretory cell (goblet cell → mucus)
- Multicellular glandorganized acini and ducts (pancreas, salivary)
Modes of secretion
- Merocrineexocytosis only; cell intact (sweat glands, salivary, pancreas)
- Apocrineapical portion of cell pinches off (mammary, some sweat)
- Holocrinewhole cell ruptures; replaced (sebaceous glands)
Universal features
- Apical surfacetop, faces lumen or surface; may have cilia or microvilli
- Basal surfacebottom, sits on basement membrane
- Avascularno blood vessels in the tissue; nourished by diffusion
- High regenerationcontinuous turnover (gut lining renews every 3-5 days)
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