page_title: Gastrointestinal wall
section_title: Muscular layer
hierarchical_section_title: Gastrointestinal wall / Structure / Muscular layer
caption_attribution_description: English: 3D Medical Animation still shot of Muscular layers of stomach
context_page_description: The gastrointestinal wall of the gastrointestinal tract is made up of four layers of specialised tissue. From the inner cavity of the gut outwards, these are:
  Mucosa
  Submucosa
  Muscular layer
  Serosa or Adventitia
  The mucosa is the innermost layer of the gastrointestinal tract. It surrounds the lumen of the tract, and comes into direct contact with digested food. The mucosa itself is made up of three layers: the epithelium, where most digestive, absorptive and secretory processes occur; the lamina propria, a layer of connective tissue, and the muscularis mucosae, a thin layer of smooth muscle.
  The submucosa contains nerves including the submucous plexus, blood vessels and elastic fibres with collagen, that stretches with increased capacity but maintains the shape of the intestine.
  The muscular layer surrounds the submucosa. It comprises layers of smooth muscle in longitudinal and circular orientation that also helps with continued bowel movements and the movement of digested material out of and along the gut. In between the two layers of muscle lies the myenteric plexus.
  The serosa/adventitia are the final layers.
context_section_description: The muscular layer (also known as the muscularis propria ) consists of two layers of muscle, the inner and outer layer. The muscle of the inner layer is arranged in circular rings around the tract, whereas the muscle of the outer layer is arranged longitudinally. The stomach has an extra layer, an inner oblique muscular layer.  Between the two muscle layers are the myenteric or Auerbach's plexus. This controls peristalsis. Activity is initiated by the pacemaker cells (interstitial cells of Cajal). The gut has intrinsic peristaltic activity (basal electrical rhythm) due to its self-contained enteric nervous system. The rate can of course be modulated by the rest of the autonomic nervous system.
  The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch.
  The coordinated contractions of these layers is called peristalsis and propels the food through the tract. Food in the GI tract is called a bolus (ball of food) from the mouth down to the stomach. After the stomach, the food is partially digested and semi-liquid, and is referred to as chyme. In the large intestine the remaining semi-solid substance is referred to as faeces. The circular muscle layer prevents food from travelling backward and the longitudinal layer shortens the tract.
  The thickness of the muscular layer varies in each part of the tract:
  In the colon, for example, the muscular layer is much thicker because the faeces are large and heavy, and require more force to push along. The outer longitudinal layer of the colon thins out into 3 discontinuous longitudinal bands, known as taeniae coli (bands of the colon). This is one of the 3 features helping to distinguish between the large and small intestine.
  Occasionally in the large intestine (2-3 times a day) there will be mass contraction of certain segments, moving a lot of faeces along. This is generally when one gets the urge to defecate.
  The pylorus of the stomach has a thickened portion of the inner circular layer: the pyloric sphincter. Alone among the GI tract, the stomach has a third layer of muscular layer. This is the inner oblique layer, and helps churn the chyme in the stomach.
caption: Muscular layers of the stomach wall.
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