Basics of Epithelial Tissue

Tissue is any group of cells of similar structure that perform a common function.  They also have a nonliving material between the cells called the extracellular matrix which we will discuss in detail later.
There are 4 basic tissue types:

• Epithelial (covering)
• Connective (support)
• Muscle (movement)
• Nervous (control) tissue

Epithelial tissue covers a body surface or lines a body cavity and is present on almost all glands.

Functions of Epithelia

• Protection of underlying tissues
• Sensory reception via nerve endings/receptors
• Diffusion (movement of molecules down their concentration gradients)
• Absorption (taking molecules into cells)
  • Note role of Microvilli in pic above (to absorb)
• Secretion (releasing molecules from cells)
• Ion transport (moving charged ions across the tissue)
• Filtration (removal of molecules from fluid)
• Forms slippery surfaces (production of mucus)
  • Note role of Cilia in pic above (to propel)

Special characteristics of Epithelia

• High Cellularity (cells separated by minimal amounts of ECM)
• Specialized contacts (cells joined by special junctions)
• Polarity (Apical surface differs from basal surface)
• Supported by layer of connective tissue (includes a basement membrane)
• Avascular (has no blood vessels) but innervated (has nerves).  It receives nutrients from underlying connective tissue where capillaries lie.
• Regeneration (lost cells are quickly replaced by mitosis)

How to Classify Epithelia

First name of tissue indicates number of cell layers

• Simple—one layer of cells
• Stratified—more than one layer of cells

Last name of tissue describes shape of cells

• Squamous—cells are wider than tall (plate-like) – “squashed”
• Cuboidal—cells are as wide as tall, like cubes
• Columnar—cells are taller than they are wide, like columns

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