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Associate Degree Nursing Physiology Review


Gastrointestinal (GI) Motility




GI Motitility In the Mouth and Esophagus
GI Motitility In the Stomach
GI Motitility In the Small Intestine
GI Motitility In the Large Intestine
Regulation of GI Motility


Gastrointestinal motility refers to the contraction of the smooth muscles of the gastrointestinal tract.

The gastrointestinal tract is commonly divided into 5 parts: the mouth, esophagus, stomach, small intestine, and large intestine (colon). These parts are separated from each other by special muscles called sphincters which normally stay tightly closed and which regulate themovement of food and food residues from one part to another.

Each part of the gastrointestinal tract has a unique function to perform in digestion, and as a result each part has a distinct type of motility. When the motility is not appropriate for its specific function in digestion, it can cause symptoms such as bloating, vomiting, constipation, or diarrhea which are associated with sensations such as pain, bloating, fullness, and urgency to have a bowel movement.


GI Motitility In the Mouth and Esophagus

The swallowing or deglutition that occurs in the mouth and upper part of the esophagus can be divided into 3 phases:

1. Voluntary Phase

  • A bolus, or mass of food, is formed in the mouth
  • The bolus pushed by the tongue against the hard palate, forcing the bolus toward the posterior part of the mouth and into the oropharynx

2. Pharyngeal Phase

  • Is a reflex that is initiated when a bolus of food stimulates tactile receptors in the oropharynx
    1. The soft palate is elevated, which closes the passage between the nasopharynx and oropharynx (the vestibular folds and vocal cords close and the epiglottis is tipped posteriorly so that it covers the opening into the larynx)
    2. The pharynx elevates to receive the bolus of food from the mouth
    3. Three pharyngeal constrictor muscles then contract in successsion, forcing the food through the pharynx. At the same time the upper esophageal spincter relaxes, and food is pushed into the esophagus

3. Esophageal Phase

  • This phase takes about 8 seconds and moves food from the pharynx to the stomach
  • Muscular contractions collectively called peristalsis occur in the walls of the esophagus
    1. The circular esophageal muscles ahead of the bolus of food relaxes, allowing the digestive tract to expand
    2. A wave of strong contractions of the circular muscles behind the bolus of food occurs
    3. The bolus is propeled through the esophagus
    4. The lower esophageal sphincter in the esophagus relaxes as the peristaltic waves approach the stomach
    5. The presence of food in the esophagus stimulates the enteric plexus, which controls peristalsis through local reflexes;
    6. Motor impulses pass along the efferent fibers of the vagus nerve (CN X) to the striated and smooth muscles within the esophagus, which stimulates their peristaltic contractions


GI Motitility In the Stomach

  • Two types of movement (motility) occur in the stomach: peristalsis and segmentation (mixing)
  • The contractions occur about every 20 seconds and proceed from the body of the stomach toward the pyloric sphincter.
  • About 20% of the contractions in the stomach are peristaltic waves
    • Waves of peristalsis begin as gentle muscular contractions near the lower esophageal sphincter and continue down the stomach toward the pyloric sphincter
    • As the contractile waves near the distal end of the stomach, they become much stronger and more forceful; this results in thoroughly mixed chyme before it passes through the pyloric sphincter
    • As the peristaltic wave passes through the partly opened pyloric sphincter, it causes the chyme to move through it in a back and forth fashion. This serves to break up the larger materials left in the chyme
  • About 80% of the contractions in the stomch are segmentation contractions-relatively weak contractions that thoroughly mix ingested food with stomach secretions to form chyme
    • The more fluid part of the chyme is pushed toward the pyloric sphincter.
    • The more solid part is pushed back toward the body of the stomach
  • The neural mechanisms that stimulate stomach secretions also increase stomach motility. The major stimulus is distension (stretching) of the stomach wall
  • Increased stomach motility increases stomach emptying

GI Motitility In the Small Intestine

  • It takes about 3-5 hours for chyme to move through the small intestine
  • The small intestine undergoes segmental contractions and peristaltic waves
  • Segmental contractions occur for short distances only along the small intestine
  • Peristaltic waves occur for variable distances to cause the chyme to move along the small intestine.
  • Local reflexes are the most important regulators of contractions in the small intestine
  • The ileocecal sphincter (between the ileum and cecum-beginning of the large intestine) remains contracted most of the time.
  • When the cecum is full, increased constriction of the sphincter prevents chyme from entering

GI Motitility In the Large Intestine

  • It takes about 18-24 hours for material to pass through the large intestine
  • The large intestine undergoes mass movements (strong peristaltic contractions in the circular muscles in large parts of the transverse and descending colon) about 3 or 4 times each day
    • Each mass movement extends over 20 cm of the colon and moves the colon contents a considerable distance toward the anus
    • Mass movements are stimulated by irritation or distention of the colon, local reflexes in the enteric plexus, and intense parasympathetic stimulation
    • Mass movement is responsible for the sudden distension of the rectum that triggers defecation.
  • The circular muscles contract simultaneously with the teniae coli (3 bands of smooth muscle from the longitudinal muscle of the colon) of the colon wall to cause constriction and shortening of the colon. This results in the formation of haustra
    • Haustra are pouches formed in the colon wall along its length, giving the colon a puckered appearance
    • Local reflexes regulate haustra formation
  • The thought or smell of food, distention of the stomach, and the movement of chyme into the duodenum can stimulate the gastrocolic and duodenocolic reflexes (local relexes that can stimulate mass movements in the stomach and duodenum, respectively)
  • The defecation reflex removes undigested feces from the body
    • It is a spinal reflex triggered by distension of the rectum
    • The smooth muscle of the internal anal sphincter relaxes
    • Peristaltic contractions in the rectum push material toward the anus
    • At the same time, the external anal sphincter is consciously relaxed if the situation is appropriate
    • Defecation can be added by conscious abdominal contractions and foced expiratory movements against a closed glottis (Valsalva maneuver)
    • Stress can increase intestinal motility and cause psychosomatic diarrhea or constipation


Regulation of GI Motility

GI motility is regulated in 3 ways:

  1. Reflexes that originate outside the digestive system (called long reflexes)
  2. Reflexes that originate inside the digestive system (called the enteric nervous system or short reflexes )
  3. Gastrointestinal (GI) Peptides
    • GI peptides excite or inhibit motility and can cause
      • altered peristaltic activity
      • contraction of the gallbladder for bile release
      • regulated gastric emptying to maximize digestion and absorption
    • GI Peptides include
      • Cholecystokinin (CCK)
        • Is a hormone secretted by endocrine cells of the small intestine and by neurons in the brain and gut
        • It stimulates gallbladder contraction for bile release
        • It inhibits gastric emptying
        • It promotes intestinal motility
      • Secretin
        • Is a hormone secreted by endocrine cells in the small intestine
        • It inhibits gastric emptying
      • Motilin
        • Is a hormone secreted by endocrine cells in the small intestine
        • It stimulates migrating motor complex
      • Glucagon-Like Peptide I
        • Is a hormone secreted by endocrine cells in the small intestine
        • It slows gastric emptying


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This material is based upon work supported by the Nursing, Allied Health and Other Health-related Educational Grant Program, a grant program funded with proceeds of the State’s Tobacco Lawsuit Settlement and administered by the Texas Higher Education Coordinating Board.