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September 15, 2010

Intrinsic appreciation of the body’s layers facilitates paradigm shifts in medicine’s approach to health and disease management. 

Understanding how the human body works (and what is going on when it doesn’t work) requires an understanding of how it’s put together.  Not only do we need to know the locations of the various organs and tissues, we must also appreciate the elegant structure that provides the functional capabilities of the organs.

Many of the body’s tissues are built with a series of layers.  Each layer provides a specific function which has benefit to the organism.

  • Skin
    • Epidermis (meaning “above the dermis”):  dead flat (“squamous”) epithelial cells lying on top of each other in a growing pile that flakes off daily, expanding outward from its growth base.  It is this layer that makes skin water-tight and provides a barrier function against would-be microbial invaders. 
    • Dermis, made primarily of tough collagen providing tissue strength to the skin and also houses sensory nerves.  Glands extending from the epidermis penetrate into the dermis.
  • Intestine
    • Mucosa: The epithelium (mucosa) of the gastrointestinal tract  is continuous with the epithelium (epidermis) of the skin, joining it on either end at the mouth and the anus.  The type of cell changes however, where the esophagus (the “swallowing tube”) meets the stomach.  Instead of the flat squamous cells, the lining turns into columnar cells.  These cells, in addition to providing the barrier function, also possess many digestive, absorptive, and secretory functions. 
    • Lamina propria, which provides an immunologic defense layer. 
    • Muscularis externa, which propels food and waste through the intestinal tract.
    • Serosa: connective tissue covering, often fused with the peritoneum, whose smooth moist surface allows the intestines to contract freely within the peritoneal cavity.
  • Blood vessels
    • Intima: the inner surface providing a smooth surface.  If this surface is injured, blood clotting is stimulated by the underlying collagen and its negative charges
    • Media, containing collagen, elastic tissue, and, often, muscle fibers enabling changes in caliber of the blood vessel
    • Adventia, made up of connective tissue and housing nerves that control the blood vessel’s reactions
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