Tissues: Epithelium

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Tissues Epithelium

• Summer Scholars 2007

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Definition of tissues

• Tissue a group of cells (and their
  extracellular products) that share a similar
  structure or function.

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Basic Tissue Types

• All 200 cell types can be grouped into these
  main tissue types.
• Each organ is made up of several tissue types.
• Epithelial tissues
• Connective tissues
• Muscle tissues
• Nervous tissues
• Blood and lymphatic tissues (also considered CT)

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Epithelial Tissues

• Cover surfaces of the body.
• Line tubes within the body.
• Form various glands.

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Common characteristics shared by all epithelia

• 1. Form continuous sheets or tubes, 1 to many
  cells thick.
• 2. Consist of closely packed cells with very
  little intercellular matrix.

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Common characteristics shared by all epithelia

• 3. Extensively interconnected by cell-cell
  junctions.

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Terminal Bars represent cell-to-cell attachment
sites
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Common characteristics continued

• 4. Cells are polar with structurally and
  functionally distinct surface domains apical,
  basal, lateral.
• 5. Supported by a basal lamina, a basement
  membrane that cells use for structural support
  and attachment.

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lumen
apical portion of a cell
basal portion of a cell
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Common characteristics of epithelium

• 6. Avascular
• 7. Dependent on diffusion of dissolved gases and
  metabolites.
• 8. Continually renewed by mitosis.
• Intestinal epithelium half-life 4-6 days
• Skin epidermis half-life 2-4 weeks

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Classification of Epithelia must be in this order

• 1. Number of cell layers
• Simple one cell layer resting on the basal
  lamina
• Stratified gt1 cell layer thick, only basal
  layer rests on basal lamina
• Pseudostratified looks stratified, but all
  cells are actually in contact with BL.
• 2. Shape of the most superficial layer of cells
• Squamous flattened in shape
• Cuboidal cube-shaped or square
• Columnar rectangular or elongated with respect
  to the basal lamina
• 3. Surface specializations
• Ciliated or non-ciliated
• Keratinized or non-keratinized
• Brush border (microvilli) or stereocilia
• Goblet cells

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Simple squamous epithelium of capillaries
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kidney tubules
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Human kidney
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Duodenum
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Esophagus
classify this epithelium
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Thick skin
keratin
Stratified Squamous Epithelium
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Trachea
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Epididymis
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Bladder
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Functions of Epithelial Tissues

• Protection
• Containment
• Transport
• Absorption
• Secretion
• Sensation