Epithelial tissue (classification according to the function)

Introduction

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.

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1. Protective Epithelium

This type protects underlying tissues from mechanical stress, pathogens, and dryness.

Examples

• Stratified squamous keratinised – epidermis of skin
• Stratified squamous non-keratinised – oesophagus, oral cavity Transitional (urothelium) – bladder (protects against urine)

Key Features

• Many layers
• Basal cells more cuboidal; surface cells flatten
• In skin, the upper keratin layer adds water resistance

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2. Absorptive Epithelium

Specialised for taking up nutrients, ions or water.

Examples

• Simple columnar with microvilli – small intestine
• Simple cuboidal – kidney tubules

Key Features

• Large apical surface (often microvilli = “brush border”)
• Plenty of mitochondria for active transport
• Tight junctions to prevent leakage

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3. Secretory Epithelium

These epithelia produce mucus, enzymes, hormones or other fluids.

Examples

• Simple columnar mucous cells – stomach
• Simple cuboidal – thyroid follicles (colloid secretion)
• Pseudostratified epithelium with goblet cells – respiratory tract

Key Features

• Clear vesicles in mucous cells
• Basally located nuclei
• Well-developed ER and Golgi apparatus in protein-secreting cells

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4. Ciliated Epithelium

Designed to move fluid or particles on the surface.

Examples

• Pseudostratified ciliated – respiratory passages
• Simple columnar ciliated – uterine tubes

Key Features

• Apical cilia with microtubules (9+2 arrangement)
• Coordinated movement to transport mucus or ovum

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5. Sensory Epithelium

Contains specialised receptor cells.

Examples

• Neuroepithelium – olfactory mucosa
• Hair cells – inner ear
• Taste buds – tongue papillae

Key Features

• Specialised receptors
• Close connection with afferent nerve endings

Bibriography

RNDr. Lucie Fraser Lantová, Ph.D. Institute of Histology and Embryology epithelial tissue1

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