Digestive Histology General Information

The gastrointestinal tract is one long continuous tube from mouthThe opening of the digestive tract where food enters and mastication begins. to anusThe terminal opening of the digestive tract through which feces are expelled..  Each organ through which food moves has the same 4 layers of tissue however the layers are specialized to the purpose of the organ.  

The GI tract or Alimentary Canal

The digestive tract can also be called the GI (GastroIntestinal) tract, or the alimentary canal.  This is the tube through which food moves from oral cavity (mouth) to anus.  Each part of the GI tract is specialized for its designated function.  For example, the stomach has an extra muscle layer to pummel food and the small intestine has tons of little finger-like projections to increase the surface area over which you absorb food.

The Four Layers

Surrounding the lumenThe inside space of a hollow organ or structure. (open space) through which food moves are 4 distinct layers of tissue.  The mucosaThe innermost lining of the digestive tract that contains mucus-secreting cells for protection and a is the deepest, or innermost, layer of epithelial tissue that lines the open space through which food moves.  A layer of connective tissue called the submucosa is superficialNear the surface of the body. to the mucosa.  This layer is rich in glands, capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues., lacteals, and nerves.  Superficial to the submucosa is the muscularis external, a double and sometimes triple layer of smooth muscle that can create alternating contraction to move or pummel food. The most superficial layer of the GI tract that surrounds these other layers is called the serosa.

Terminology

• Bolus – a ball of food
• Mastication – chewing
• Mechanical digestion – the process of tearing and ripping food into smaller pieces
• Chemical Digestion – the process of enzymatic breakdown or emulsification of food
• Peristalsis – alternating contractions of the longitudinal and circular layers of smooth muscle in the muscularis externaA smooth muscle layer of the digestive tract responsible for peristalsis and segmentation. in order to propel food forward through the GI tract
• Chyme – a slurry of food and enzymesProteins that speed up chemical reactions in the body.
• Segmentation – alternating contractions of smooth muscle in the muscularis externa that pummel food without producing forward movementA fundamental property of life involving motion of the body or its parts..