Epithelial tissue (classification according to the function)
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Introduction[edit | edit source]
Epithelial tissue covers the body surfaces and lines internal cavities. While we often classify epithelium by shape and layers, another helpful approach is by function. Since different epithelia perform different jobs, grouping them like this makes it easier to understand why they look the way they do under the microscope.
1. Protective Epithelium[edit | edit source]
This type protects underlying tissues from mechanical stress, pathogens, and dryness.
Examples[edit | edit source]
- Stratified squamous keratinised – epidermis of skin
- Stratified squamous non-keratinised – oesophagus, oral cavity
- Transitional (urothelium) – bladder (protects against urine)
Key Features[edit | edit source]
- Many layers
- Basal cells more cuboidal; surface cells flatten
- In skin, the upper keratin layer adds water resistance
2. Absorptive Epithelium[edit | edit source]
Specialised for taking up nutrients, ions or water.
Examples[edit | edit source]
- Simple columnar with microvilli – small intestine
- Simple cuboidal – kidney tubules
Key Features[edit | edit source]
- Large apical surface (often microvilli = “brush border”)
- Plenty of mitochondria for active transport
- Tight junctions to prevent leakage
3. Secretory Epithelium[edit | edit source]
These epithelia produce mucus, enzymes, hormones or other fluids.
Examples[edit | edit source]
- Simple columnar mucous cells – stomach
- Simple cuboidal – thyroid follicles (colloid secretion)
- Pseudostratified epithelium with goblet cells – respiratory tract
Key Features[edit | edit source]
- Clear vesicles in mucous cells
- Basally located nuclei
- Well-developed ER and Golgi apparatus in protein-secreting cells
4. Ciliated Epithelium[edit | edit source]
Designed to move fluid or particles on the surface.
Examples[edit | edit source]
- Pseudostratified ciliated – respiratory passages
- Simple columnar ciliated – uterine tubes
Key Features[edit | edit source]
- Apical cilia with microtubules (9+2 arrangement)
- Coordinated movement to transport mucus or ovum
5. Sensory Epithelium[edit | edit source]
Contains specialised receptor cells.
Examples[edit | edit source]
- Neuroepithelium – olfactory mucosa
- Hair cells – inner ear
- Taste buds – tongue papillae
Key Features[edit | edit source]
- Specialised receptors
- Close connection with afferent nerve endings
Bibriography
RNDr. Lucie Fraser Lantová, Ph.D. Institute of Histology and Embryology epithelial tissue1
junqueira
