<h2>Epithelial<strong> Tissue</strong></h2>
<p>Epithelial tissues are formed by cells that cover surfaces (e.g. skin) and line tubes and cavities (e.g. digestive organs, blood vessels, kidney tubules and airways). Epithelial tissue usually consists of a single <a data-lesson="introduction-to-cell-reproduction" data-subject="biology" data-tutorial="cell-reproduction" href="https://app.ulearngo.com/biology/cell-reproduction/introduction-to-cell-reproduction">cell</a> layer of cells, however in certain cases there may be more than one layer. All <a data-lesson="epithelial-tissues" data-subject="biology" data-tutorial="animal-body-form-function" href="https://app.ulearngo.com/biology/animal-body-form-function/epithelial-tissues">epithelial tissues</a> are free surfaces attached to the underlying layers of a basement membrane.</p>
<p>There are different types of epithelial tissue which are named according to the number of layers they form and the shape of the individual cells that make up those layers. <em>Simple epithelium</em> refers to a <em>single</em> layer of cells. <em>Stratified epithelium</em> refers to <em>two or more</em> layers of cells. Squamous epithelium refers to flattened cells, cuboidal epithelium refers to cells that are cube-shaped and columnar epithelium refers to vertically elongated cells. Ciliated epithelium refers to epithelial cells that contain many tiny hair-like projections.</p>
<div class="ns-tutorial">
<div class="ns-school-defn2">
<h3>Fact:</h3>
<p>Pseudostratified epithelium refers to epithelium consisting of one layer but looking as though it consists of more than one layer.</p>
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<div>
<div class="wp-caption alignnone" style="width: 688px"><img alt="Image" height="318" src="https://data.ulearngo.com/assets/e6604ef6-d31c-47f4-a932-326198fd81b7" width="688"/><p class="wp-caption-text">The different types of epithelial tissue found in mammals.</p></div>
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<h3>General Functions of Epithelial Tissue</h3>
<div>
<ul>
<li>Provides a barrier between the external environment and the organ it covers.</li>
<li>Specialised to function in secretion and absorption.</li>
<li>Protects organisms from microorganisms, injury, and fluid loss.</li>
<li>Excretes waste products such as sweat from the skin.</li>
</ul>
<div class="ns-tutorial">
<div class="ns-school-defn2">
<h3>Fact:</h3>
<p>The skin is the largest human organ.</p>
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<p>The different types of epithelial tissue are classified according to their shape. The major categories we are going to examine are <em>squamous, columnar and cuboidal</em> epithelium. The table presents each of them in detail.</p>
<div>
<table>
<tbody>
<tr>
<td><em>Epithelial tissue type</em></td>
<td><em>Location in body</em></td>
<td><em>Structure</em></td>
<td><em>Function</em></td>
</tr>
<tr>
<td>Simple squamous and stratified squamous</td>
<td>Simple: capillaries, alveoli (in lungs); stratified: skin</td>
<td>Thin and flat cells that are elliptically shaped and lie on basement membrane. Simple squamous epithelium is one-cell thick. Stratified squamous epithelium consists on many layers.</td>
<td>Responsible for diffusion. Thin structure allows for movement of substances across the cells.</td>
</tr>
</tbody>
</table>
</div>
<div>
<table>
<tbody>
<tr>
<td><em>Epithelial tissue type</em></td>
<td><em>Diagram</em></td>
<td><em>Microscopic image</em></td>
</tr>
<tr>
<td>Simple squamous and stratified squamous</td>
<td><img alt="Image" src="https://data.ulearngo.com/assets/3286274a-f6f6-4708-ab1a-e27a5458bfbb"/></td>
<td><img alt="Image" src="https://data.ulearngo.com/assets/69b8e492-16aa-470b-af35-cc74ccd1f827"/></td>
</tr>
</tbody>
</table>
</div>
<div>
<table>
<tbody>
<tr>
<td><em>Epithelial tissue type</em></td>
<td><em>Location in body</em></td>
<td><em>Structure</em></td>
<td><em>Function</em></td>
</tr>
<tr>
<td>Cuboidal</td>
<td>Kidney tubules or glands (regions of the body responsible for excretion).</td>
<td>Cube-like in structure; may occasionally have structures called <em>microvilli</em> on surface to aid absorption.</td>
<td>Serve a protective function against bacteria and the wearing away of certain organs by lining various structures. Also prevent <a data-lesson="water-and-life-2" data-subject="biology" data-tutorial="biology-foundations" href="https://app.ulearngo.com/biology/biology-foundations/water-and-life-2">water</a> loss.</td>
</tr>
</tbody>
</table>
</div>
<div>
<table>
<tbody>
<tr>
<td><em>Epithelial tissue type</em></td>
<td><em>Diagram</em></td>
<td><em>Microscopic image</em></td>
</tr>
<tr>
<td>Cuboidal</td>
<td><img alt="Image" src="https://data.ulearngo.com/assets/6748c3c3-c59c-441c-8b09-ef0c72078c73"/></td>
<td><img alt="Image" src="https://data.ulearngo.com/assets/82f4de15-0ef0-491b-86dc-b0e97193b789"/></td>
</tr>
</tbody>
</table>
</div>
<div>
<table>
<tbody>
<tr>
<td><em>Epithelial tissue type</em></td>
<td><em>Location in body</em></td>
<td><em>Structure</em></td>
<td><em>Function</em></td>
</tr>
<tr>
<td>Columnar</td>
<td>Digestive tract, reproductive organs</td>
<td>Elongated cells, nuclei located at the base of the cell. Cells connected by tight <a data-lesson="intercellular-junctions" data-subject="biology" data-tutorial="cell-structure" href="https://app.ulearngo.com/biology/cell-structure/intercellular-junctions">junctions</a> and receive their nutrients from the basement membrane.</td>
<td>Main function is protective. Prevents against bacterial infection. Can also secrete mucus to protect surface from damage.</td>
</tr>
</tbody>
</table>
</div>
<div>
<table>
<tbody>
<tr>
<td><em>Epithelial tissue type</em></td>
<td><em>Diagram</em></td>
<td><em>Microscopic image</em></td>
</tr>
<tr>
<td>Columnar</td>
<td><img alt="Image" src="https://data.ulearngo.com/assets/2918f378-9152-43e1-8b87-e372ee4885a0"/></td>
<td><img alt="Image" src="https://data.ulearngo.com/assets/99474d1d-19bb-492c-8a24-abaafcb561d4"/></td>
</tr>
</tbody>
</table>
</div>

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Epithelial Tissue

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Epithelial Tissue

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