Peristalsis in the Small Intestine

Small Intestine Motility

• When a portion of the small intestine becomes distended with chyme, a type of movement called segmentation contractions occurs.
• The purpose of segmentation contractions is to mix chyme with digestive enzymes and increase the surface area for absorption.
• Segmentation contractions chop the chyme into smaller particles at a rate of about 12-15 times per minute.
• During segmentation contractions, the intestine appears beaded or segmented in appearance.
• Mixing movements in the small intestine involve localized concentric contractions at intervals along the intestine, which aids in mixing chyme with digestive enzymes.
• The primary function of mixing movements is to increase the surface area for absorption.
• The maximum frequency of segmentation contractions is determined by the electrical slow wave activity of the intestine.
• On average, chyme moves through the small intestine at a rate of 1-2 mm/sec.

Peristaltic Movements

• Peristaltic movements involve a wave-like contraction that helps propel chyme through the small intestine.
• The primary function of peristaltic movements is to propel chyme through the small intestine towards the large intestine.
• Peristaltic contractions are initiated by the gastroenteric reflex, which is mediated by the neurotransmitter acetylcholine.
• It typically takes 3-5 hours for chyme to travel from the pylorus to the ileocecal valve.
• The main trigger for the occurrence of the peristaltic rush is the presence of irritative substances in the small intestine.

Ileocecal Valve and Sphincter

• The ileocecal valve and sphincter prevent backflow of cecal contents into the small intestine.
• The ileocecal valve closes and prevents backflow when the cecum is distended.
• The degree of contraction of the ileocecal sphincter and the intensity of peristalsis in the terminal ileum are controlled by the enteric nervous system.

Migratory Motor Complex (MMC) Movements

• MMM movements occur during the interdigestive period and help clear the small intestine of residual particles.
• MMM movements start in the stomach and progress downward through the small intestine, occurring every 90-120 minutes.
• During MMM movements, the ileocecal sphincter relaxes, allowing residual particles to enter the cecum.

Other Factors Affecting Motility

• Irritation in the cecum causes a decrease in motility in the terminal ileum.
• An inflamed appendix causes a decrease in motility in the terminal ileum and an increase in tone of the ileocecal sphincter.
• Gastrin, CCK, and serotonin increase motility in the small intestine through the gastroenteric reflex.
• Secretin inhibits small intestinal motility.