Epithelial Tissues

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1

Epithelial Characteristics:

  • LINES the inside and outside of the body and CREATE GLANDS.
  • Epithelial tissues have very little extracellular matrix and are mostly composed of cells.
  • Composed of layers of closely packed cells that cover organ surfaces, line structures, and form glands.
  • Named by shape of apical cells (cells at the very top)
  • Has distinct tissue surfaces: Free, basal; lateral.
  • Polar
  • Nonvascular (no blood connections)
  • High regeneration capacity.
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Apical surface (free)

Exposed to external environment or internal body space ( lumen).

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Basal (bottom) surface

Surface of an epithelial cell attached to underlying connective tissue.

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Functions of Epithelial Tissues

  • Protecting underlying structures
  • Acting as barriers
  • Secreting substances
  • Absorbing Substances
  • Allows diffusion (movement of objects from one side to another) of gases, filtration of blood, secretion, absorption.
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What are the two classifications of epithelial tissues based on number of cell layers?

  • Simple - 1 layer, inside.
  • Stratified - several layers on top of one another, outside.
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Simple Epithelium

  • Location:
    • One layer of cells in which all cells rest directly on the basement membrane but appear to be arranged in layers.
    • All cells touch the basement membrane.
  • Function:
    • Allows diffusion (movement of objects from one side to another) of gases, filtration of blood, secretion, absorption.
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Stratified Epithelium

Named by shape of apical cells (cells at the very top)

  • Location:
    • Some cells rest on top of others and do not touch basement membrane.
  • Function:
    • Protection, particularly against abrasion.
    • Subjected to wear-and-tear.
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Cell Shapes of Epithelial Tissues

  • Squamous
  • Cuboidal
  • Columnar
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Squamous Cell

Allows diffusion or acts as filter.

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Cuboidal Cell

An epithelial cell who’s the height and width are about equal.

  • Function:
    • Secretion or absorption.
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Columnar

Secretion or absorption.

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Types of Glands

  • Exocrine
  • Endocrine
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Exocrine.

Have contact with the body surface (exterior) by way of a duct.

i.e. sweat, tear, & mammary glands.

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Endocrine.

Have no open contact with the surface and have no ducts and secreted directly to blood.

  • Produce hormones
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Modes of Exocrine Secretion (glands)

  • Holocrine
  • Merocrine
  • Apocrine
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Holocrine

Shedding of entire cells. VERY RARE

  • Cells accumulate a product and then the entire cell disintegrates.
  • Secretion = mixture of cell fragments and synthesized substance
  • Location:
    • Sebaceous (oil) glands of scalp, glands of eyelids.
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Merocrine

Glands have vesicles that release their secretion by exocytosis.

  • No cell destruction during secretion.

Location:

  • Sweat, salivary and tear glands, pancreas, gastric glands, and others
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Apocrine

Primarily merocrine mode of secretion but cells are pinched off. RARE

Location:

  • Axillary sweat glands (armpits), mammary glands
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Simple Squamous Location

Location:

  • Blood and lymphatic capillaries
  • Alveoli of lungs
  • Membranes of body cavities: pleural, pericardial and peritoneal
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Simple Squamous Functions

  • Diffusion
  • Secretion/absorption of Serous fluid in cavities
  • Protection against abrasion/friction (wear & tear)
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Simple Squamous Special Characteristics

  • Cell Shape: Single layer of thin, disc-like flatten cells
  • Nucleus = flattened and hence, CANNOT be seen.
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Simple Cubodial Location

  • Kidney tubules
  • Terminal bronchioles of lungs
  • Glands and their ducts
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Simple Cubodial Functions

  • Secretion and absorption by kidney tubules
  • Movement of particles in mucus by ciliated cells of terminal bronchioles
  • Secretion of cells of glands
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Simple Cubodial Special Characteristics

  • Cell Shape: Single layer of square or rounded cube-like cells.
  • Some have MICRIVOLI (i.e. kidney tubules) or CILIA (i.e. terminal bronchioles of the lungs).
  • Nucleis: Circular, located in center of cell
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Simple Columnar Location

  • Glands
  • Bronchioles of lungs
  • Intestines
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Simple Columnar Functions

  • Cell secretions of the glands
  • Movement of particles out of the bronchioles of the lungs by ciliated cells
  • Absorption by cells of the small and large intestines by microvilli
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Simple Columnar Special Characteristics

  • Cell shape: single layer of tall, narrow cells (rectangles)
  • May contain Goblet Cells that create mucus within non-secretory epithelia.
  • May contain CILIA and may contain GOBLET CELLS.
  • Oval-shaped nucleus in basal half of the cell (lines up nicely).
  • Vertical oriented
  • Usually in basal half of cell.
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Pseudostratified Location

  • Trachea
  • Bronchi of lungs
  • lining of nasal cavity and sinuses
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Pseudostratified Special Characteristics

  • Not all cells reach the free surface (apical free surface), thus creating a false appearance of stratification (looks multilayered)
  • Contains CILIA and may contain GOBLET CELLS.
  • Cell shape: Single layer, tall and short columnar cells
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Pseudostratified Function

  • Synthesize and secret mucus.
  • Move mucus that contains foreign particles out of passages.
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Stratified Squamous Location

  • Keratinized: epidermis of skin
  • Non-Keratinized: Mouth, esophagus, anus, vagina
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Stratified Squamous Function

  • Protections against abrasion, barrier against infection and reduce water loss
  • Protections against abrasion, barrier against infection
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Stratified Keratinized Special Characteristics

  • Cell Shape: Stratified (multiple layers) that are cuboidal in the basal layer with cells becoming increasingly flat/scaly toward to surface.
  • Basal area may be more cuboidal in shape.
  • Can be keratinized (layer of compact dead cells without nuclei).
34

Stratified Non-Keratinized Special Characteristics

  • Cell Shape: Stratified (multiple layers) of all shapes & sizes.
    • Surface cells change from round to flat when stretched.
  • Surface layer of cells are bulging & irregular (like lumpy pillows).
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Stratified Cubodial Location

  • Sweat gland ducts,
  • ovarian follicular cells
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Stratified Cuboidal Special Characteristics

Cell Shape: Stratified (2+ layers of cells), surface cells that are square or rounded (cubed-like).

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Stratified Cubodial Function

  • Secretion
  • Absorption
  • protection from infection
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Stratified Columnar Location

  • Mammary gland ducts
  • Male urethra
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Stratified Columnar Function

  • Secretion of milk components
  • Protection against caustic urine
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Transitional Location

  • Lining of Bladder
  • Ureters
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Transitional Function

  • Expansion and stretching
  • Protection against caustic urine