Gastrointestinal Motility. GI smooth Muscle. Smooth muscle makes up all the contractile tissue of the GI tract with the exception of the pharynx, upper one third of the esophagus, and the external anal sphincter.
Oscillations of the resting membrane potential cause spontaneous depolarization (spike potentials) if above the threshold potential
Pressure profile across the lower esophageal sphincter
Pressure changes from negative intrathoracic pressure to positive below the LES
Rare condition of spastic constriction of LES and loss of peristalsis in lower esophagus.
Treated with balloon dilation or surgery of the LES.
MOTILITY OF CAUDAD AREA After a meal contractions occur at rates of 3 to 5 per min.
FUNCTION OF SMALL INTESTINE
•Mixes contents with digestive enzymes
•Reduces particle size and solubilizes contents
•Exposes contents to absorptive surfaces
FUNCTION OF LARGE INTESTINE
•Storage of feces
•Absorption of water and any remaining nutrients
Phases: I – quiescent; II irregular activity; III-intense peristalsis
Haustra disappear and reform during and after contractions of 20 to 60 seconds.
LARGE INTESTINAL STRUCTURE
• Gastrointestinal smooth muscle cells contract as a unit because of anatomic and electrical coupling.
• Smooth muscles may contract for a few seconds (phasic), or contractions may last from minutes to hours (tonic).
• Material moves through the gastrointestinal (Gl) tract from regions of higher to regions of lower intraluminal pressure.
• Primary peristaltic contractions are initiated in the esophagus by swallowing and are responsible for moving most material through the esophagus; secondary peristaltic contractions initiated by distension and local reflexes remove any “leftover” material.
•The principal motility function of the orad (proximal) stomach is receptive relaxation, to store ingested materialmediated by a vagovagal reflex.
• The principal activity of the caudal (distal) stomach is mixing, grinding and emptying.
•Gastric contractions are triggered by regularly (3-5/ min) occurring depolarizations called slow waves.
•Small intestinal motility is characterized by brief, irregular contractions that are interrupted during fasting approximately every 90 min by a wave of intense contractions that sweeps the entire length of the small intestine. After a meal, these migrating motility complexes are replaced by segmental and short peristaltic contractions.
• Contractions in the small intestine are initiated by spike potentials that are superimposed on slow waves.
• The ileocecal sphincter relaxes when the ileum is distended and contracts when the colon distends, thus allowing material to enter the colon and preventing reflux.
• The principal movements of the proximal colon are weak peristaltic contractions that permit storage of contents and absorption of most remaining water
• Two or three times a day, a peristaltic wave, termed a mass movement, propels a significant amount of material into the distal colon or rectum. Distension of the rectum triggers the rectosphincteric reflex.