I. Epithelial Tissue

A. Common Characteristics
1) Individual cells are closely attached to each other at their margins to form tight sheets
2) No extra-cellular matrix
3) No vascularization
4) Arranged so that there is a(n):
        -apical surface (free surface)
        -basal region (closely anchored to the underlying CT)

B. Functions
1) Protection:  covers body and lines all body cavities;  provides a protective shield for underlying tissues
        (e.g.  epidermis)
2) Absorption:  in some parts of the body it takes in certain materials (e.g. digestive tract)
3) Secretion:  in some parts of the body epi. tissue is specialized to secrete certain products
        E.g. small intestine:  some cells are specialized to secrete mucus
4) Excretion:  in the kidney cells rid the body of materials
5) Surface transport:  cilia on cells in the lungs move mucus and particles up and out
6) Sensory functions:  Ex. taste buds in the mouth

C. Three main shapes of cells at the apical/free surface
1) squamous:  thin and flat
2) cuboidal:  small cubes in cross section
3) columnar:  tiny columns

D. Layering
1) simple:  one layer of cells
2) stratified:  cells arranged in two or more layers
3) pseudostratified:  falsely appear to be layered


    Simple squamous epithelium        Stratified squamous epithelium
    Simple cuboidal epithelium          Pseudostratified squamous epithelium
    Simple columnar epithelium        Transitional epithelium
 

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Simple Squamous Epithelium
Epithelial tissue
One layer of thin, flat cells
Looks like fried eggs from the side.  The nucleus looks like the yolk.
Functions:
    Makes a very thin membrane that is good for the indiscriminate passage of molecules (diffusion, filtration)
    Also, makes a very smooth surface that is good for lining structures that require very little friction or drag
Found:
     renal corpuscle in kidney
     lines arteries and veins
     capillaries
     alveoli of lungs
     lines chambers of the heart
     lines serous membranes

Photo taken by Dr. S. Desai

Green arrows indicate nuclei of simple squamous epithelial cells of the parietal layer of Bowman's capsule in a renal corpuscle in the cortex of the kidney.

    Simple squamous epithelium        Stratified squamous epithelium
    Simple cuboidal epithelium          Pseudostratified squamous epithelium
    Simple columnar epithelium        Transitional epithelium

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Stratified Squamous Epithelium
Epithelial tissue
Many layers of flat cells
Two types:
    Keratinized:  waterproof
    Unkeratinized:  not waterproof
Found
     Keratinized:
        skin
        scalp
        bottom of feet
        rectum
     Unkeraitinized
        mouth
        lining of nose
        vagina
        esophagus

Photo taken by Dr. S. Desai

Blue bracket indicates all of the layers of stratified squamous epithelial cells that make up the epidermis of the skin.  You will learn the different layers when you cover the Integumentary System.

    Simple squamous epithelium        Stratified squamous epithelium
    Simple cuboidal epithelium          Pseudostratified squamous epithelium
    Simple columnar epithelium        Transitional epithelium

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Simple Cuboidal Epithelium
Epithelial Tissue
One layer of cube shaped cells
More picky than simple squamous epi., and does not take as much wear as simple columnar epi.
Function:
    Good for reabsorption and secretion
Found
    kidney
    convoluted tubules
    collecting ducts
    ascending loop of Henle
    choroid plexus of brain
    surface of ovaries
    Thyroid gland

Photo taken by Theresa Carrera

Simple cuboidal epithelium (two cells indicated by black box) make up the tubules in the kidneys (shown in cross section and indicated by the black oval).  You will notice many tubules in this view.
 

Photos taken by Dr. S. Desai

Here the tubules are shown in longitudinal section.  You can see the single layer of cube shaped cells of each tubule.

    Simple squamous epithelium        Stratified squamous epithelium
    Simple cuboidal epithelium          Pseudostratified squamous epithelium
    Simple columnar epithelium        Transitional epithelium

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Simple Columnar Epithelium
Epithelial tissue
One layer of long thin cells
Thick and built to take more wear and tear than simple squamous and simple cuboidal epithelia.
Functions:
    Absorption and secretion (with microvilli)
    Surface transport (with cilia)
Found
     small intestine
     stomach
     large intestine
     glands
     ducts
     uterus
     uterine tubes

Photo taken by Dr. W. Coons

Simple Columnar Epithelium (indicated in the black box) lining the stomach.

    Simple squamous epithelium        Stratified squamous epithelium
    Simple cuboidal epithelium          Pseudostratified squamous epithelium
    Simple columnar epithelium        Transitional epithelium

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Pseudostratified Ciliated Columnar Epithelium (PSCCE)
Epithelial tissue
Looks stratified, but is not;  has cilia; cells are long and thin, like columnar
Nuclei do not line up like in simple columnar epithelium
Functions:
    Makes and secretes mucus
    Surface transport
Found
     trachea
     bronchi
     nasal cavities
     auditory tube

Photo taken by Theresa Carrera

PSCCE (indicated by black bracket) lining the trachea

    Simple squamous epithelium        Stratified squamous epithelium
    Simple cuboidal epithelium          Pseudostratified squamous epithelium
    Simple columnar epithelium        Transitional epithelium

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Transitional Epithelium
Epithelial Tissue
Many layers of cells the flatted when the tissue is stretched.
Look like stratified squamous epi. when stretched and stratified cuboidal when relaxed.
Found
    ureters
    bladder
    superior urethra

Photo taken by Theresa Carrera

Transitional epithelium (400x)  The blue bracket indicates the transitional epithelium when the bladder is contracted (not distended).

Photo taken by Theresa Carrera

Transitional epithelium (400x) the light blue bracket indicates the transitional epithelium when the bladder is distended (full).

    Simple squamous epithelium        Stratified squamous epithelium
    Simple cuboidal epithelium          Pseudostratified squamous epithelium
    Simple columnar epithelium        Transitional epithelium

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Designed and constructed by
M. E. Janowski-Bell, Ph.D.
Assistant Professor of Biology
Victoria College
tarantula@victoriacollege.edu