Histology Guide virtual histology laboratory

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Histology Guide

Chapter 2 - Epithelium

Epithelium are sheets of cells that cover the externel surface and line the internal surfaces of the body. It is classified by the shape of the surface cells and whether it has a single or multiple layers of cells. All epithelia make a basement membrane that forms a boundary between it and the underlying connective tissue.

Epithelial cells are polarized. Basal refers to those cells or parts of cells next to the basement membrane. Apical refers to those cells or parts of cells found next to the free surface or lumen.

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Fig 008 Epithelium

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

A simple squamous epithelium consists of a single layer of flattened cells. It often occurs at sites of metabolite, fluid or gas exchange across or between cells.

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MH 016 Simple Epithelia

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MHS 261 Common Bile Duct

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MHS 227a Eye

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MHS 224 Ovary and Oviduct

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MHS 281 Pavement Epithelium

Simple Cuboidal Epithelium

A simple cuboidal epithelium consists of a single layer of cells of similar height and width. Limited distribution but often found in the lining of ducts.

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MH 016 Simple Epithelia

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MHS 211 Pancreas

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MHS 224 Ovary and Oviduct

Simple Columnar Epithelium

A single columnar epithelium consists of a single layer of cells that are taller than they are wide. Typically associated with secretion or absorption.

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MH 016 Simple Epithelia

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MH 119 Ileum

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MH 120 Ileum

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MHS 219 Jejunum

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MHS 261 Common Bile Duct

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MHS 224 Ovary and Oviduct

Pseudostratified Columnar Epithelium

A pseudostratified columnar epithelium appears stratified because: (1) not all cells reach the apical surface, (2) nuclei are at different levels and (3) cells appear tightly packed. However, it is a specialized type of a simple columnar epithelium because all the cells rest on the basement membrane. It lines the upper respiratory tract.

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MH 016 Simple Epithelia

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MH 135 Larynx

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MH 136 Trachea

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MHS 222 Trachea

Stratified Squamous Epithelium

A stratified squamous epithelium has two or more layers of cells. Only the basal layer of cells rests on the basement membrane. Its name arises from the squamous appearance of the surface layer of cells. The epithelium is keratinized on the external surface of the body to prevent loss of water and protect against abrasion.

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MH 017 Stratified Epithelia

(keratinized and non-keratinized)

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MH 109 Esophagus

(non-keratinized)

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MH 038 Epiglottis

(non-keratinized)

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MH 090 Thin Skin

(keratinized)

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MH 091 Thick Skin

(keratinized)

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MHS 235 Thick Skin

(keratinized)

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MHS 227a Eye

(non-keratinized)

Stratified Cuboidal Epithelium

A stratified cuboidal epithelium consists of two or more layers of cells. Only the cells of the surface layer are cuboidal with subsequent layers varying in shape from cuboidal to polyhedral. Limited distribution found only in the lining of larger ducts.

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MH 109 Esophagus

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MHS 234 Esophagus

Transitional Epithelium

A transitional epithelium consists of multiple layers of cells. The surface layer is composed of much larger, dome-shaped cells (umbrella cells) that change in shape when the epithelium is relaxed or stretched. Found only in the urinary tract.

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MH 018 Transitional Epithelia

(relaxed and stretched bladder)

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MHS 214 Bladder