Histology Guide

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Chapter 2 - Epithelium

Epithelium forms continuous sheets of cells that line internal surfaces and cover the external surface of the body. It acts as a selective barrier that protects tissues. A basement membrane separates the epithelium from underlying connective tissue.

Epithelium is classified based on three criteria:

Epithelial cells are polarized:

Epithelium does not contain blood vessels and receives nourishment via diffusion from the underlying connective tissue.

Glands are formed by the down growth of an epithelium into the underlying connective tissue.

It is not necessary to learn the names of specific tissues for this chapter, but rather learn to recognize variations in epithelia.

Simple Squamous Epithelium

Simple squamous epithelium consists of a single layer of flattened cells in contact with the basement membrane. The thinness of these cells facilitates the selective transfer of materials (e.g., gases, fluids or nutrients) across the epithelium.

Simple Cuboidal Epithelium

Simple cuboidal epithelium consists of a single layer of cuboidal cells. This epithelium is often associated with absorption, secretion or excretion of waste matter.

Simple Columnar Epithelium

Simple columnar epithelium consists of a single layer of cells that are taller than they are wide. This epithelium is often associated with absorption or secretion.

Small Intestine

Gallbladder

Pseudostratified Epithelium Epithelium

Pseudostratified epithelium appears to be stratified because the nuclei of the epithelial cells are at different levels, but every cell is in contact the basement membrane. The epithelial cells vary in height.

Stratified Squamous Epithelium

Stratified squamous epithelium has multiple layers of cells becoming flattened as they move from the basal layer to the apical layers. It provides protection from abrasion and is keratinized on the external surface of the body.

Cilia and Microvilli

Cilia and microvilli are two specializations frequently found on the lumenal surface of simple columnar epithelia.

Intercellular Junctions

Lateral specializations between individual epithelial cells of an epithelium. Those near the apical surface are Known as the junctional complex by Electron Microscopy | Histology and terminal bar by light microscopy.

Examples of intercellular junctions in the simple columnar epithelium of the small intestine.