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5.2: Epithelial Tissues

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    53571
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    Epithelial Tissues

    Epithelial tissues are found on the surfaces of all organs inside and out of the human body and as such, epithelial tissues have one edge not connected to other cells, the apical surface. The other end of an epithelial tissue (the basal surface) is attached to a basement membrane that is partly produced by the epithelial cells. Underlying the basement membrane are connective tissues. Carefully examine the diagram below to become familiar with recognizing different types of epithelial tissues and their positions in relationship to the basement membrane and the underlying connective tissues. Epithelial tissues do not contain blood vessels and as such are avascular. Connective tissues are usually highly vascular and so the nearby connective tissue provides essential nutrients (from the blood) to the epithelial tissue.

    Diagrams show the distinction between epithelial cells on the surface, connective tissue under the epithelial cells, and the basement membrane separating the epithelial tissue and the connective tissue.

    Epithelial tissues are described using a 2-word naming system:

    1. First word: simple, stratified, or pseudostratified (these terms indicate the number of cell layers - see figure below)
    2. Second word: squamous, cuboidal, columnar, or transitional (these terms indicates the cell shape - see figure below)

    For example, examining the diagram below, the tissue shown in the bottom left corner would be called "stratified squamous" since the cells are flat (squamous) and there are more than two cell layers (stratified). The top second from the left on the diagram would be called, "simple cuboidal" since there is one cell layer (simple) and the cells are cube-shaped (cuboidal). There are some epithelial tissues that look like they are stratified, but they are in fact a single layer of cells - these tissues are called pseudostratified or "false/fake stratified." The tissue in the figure below on the top right is therefore called, "pseudostratified columnar." Simple epithelial tissues are only one cell layer thick to enable absorption, diffusion, or secretion of materials across the tissue. Stratified epithelial tissues have multiple cell layers primarily to protect the tissues underlying them.

    Diagram shows the differences between simple epithelial with one cell layer, pseudostratified with one cell layer that looks like it might be two cell layers but it is not, and stratified epithelial tissues with two or more cell layers. Differences in cell shapes is also shown: squamous are flat, cuboidal are cube-shaped, and columnar are column-shaped.

    Carefully examine the tables showing examples of different types of epithelial tissues and examples of where each type may be found:

    Simple Epithelial Tissues

    Simple Epithelial Tissues

    Examples of Where they are Found

    simple squamous

    Image shows simple squamous epithelia in kidney tissue.

    • inner lining of blood vessels
    • alveoli in the lungs
    • inner lining of lymphatic vessels
    • inner lining of the heart
    • inner lining of glomerular capsule in the kidneys
    • inner lining of some kidney tubules
    • serous membranes

    simple cuboidal

    lumen (inner space) of kidney tub le basement membrane lumen (inner space) of kidney tubule cuboidal connective tissue

    • inner lining of some kidney tubules
    • inner lining of ducts

    simple columnar

    Microscopic image shows simple columnar epithelium.

    • inner lining of the majority of the digestive tract
    • inner lining of ducts
    • lower respiratory tract

    Pseudostratified Epithelial Tissue

    Pseudostratified Epithelial Tissue

    Examples of Where it is Found

    pseudostratified columnar

    Microscopic image shows pseudostratified columnar epithelium with goblet cells, cilia, and basement membrane

    • inner lining of the epididymis (tube that carries sperm)
    • inner lining of upper respiratory tract

    Stratified Epithelial Tissues

    Stratified Epithelial Tissues

    Examples of Where they are Found

    stratified squamous

    Microscopic image shows stratified squamous epithelium.

    • skin surface
    • inner lining of the vagina
    • inner lining of the oral cavity and esophagus

    stratified cuboidal

    Microscopic image shows stratified cuboidal epithelia.

    • uncommon
    • inner lining the ducts of some glands (e.g. sweat glands)

    stratified columnar

    Microscopic image shows stratified columnar epithelium.

    • uncommon
    • inner lining of the ducts of large glands

    transitional - broad cells as shown below when not stretched; cells become smaller when stretched (more like stratified squamous)

    Microscopic image shows stratified columnar epithelium.

    • inner lining of urinary tract (ureters, urinary bladder, urethra)

    Attributions


    This page titled 5.2: Epithelial Tissues is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline.

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