3.3 Sphincters

• What does the upper esophageal sphincter separate?

  Pharynx and upper part of esophagus
• What type of muscle is the upper esophageal sphincter composed of?

  Striated muscle
• What is the resting pressure of the upper esophageal sphincter?

  Highest of all GI sphincters
• What mechanism involves the oropharynx and UES?

  Swallowing mechanism
• Which part of the brain controls the swallowing center?

  Medulla
• Which cranial nerves are involved in swallowing?

  CN V, IX, X, XII
• How are respiration and deglutition related?

  They are closely integrated
• What happens to the UES during inspiration?

  It is closed, diverting air away
• What occurs during swallowing regarding the glottis?

  Closure of glottis and inhibition of respiration
• What separates the esophagus from the stomach?

  Lower esophageal sphincter
• What type of muscle composes the lower esophageal sphincter?

  Specialized smooth muscle
• What are the primary functions of the lower esophageal sphincter?

  Permit food movement and prevent reflux
• What happens to LES pressure during deglutition?

  It reduces to intragastric pressure
• When does relaxation of the LES occur?

  After UES returns to resting pressure
• What maintains the resting tone of the lower esophageal sphincter?

  Intrinsic myogenic properties and cholinergic regulation
• What mediates relaxation of the lower esophageal sphincter?

  Vagus nerve and smooth muscle properties
• What condition results from reduced resting LES pressure?

  Gastroesophageal reflux
• What is achalasia?

  Defect in LES relaxation causing dilation
• What does the pyloric sphincter separate?

  Stomach from duodenum
• What regulates gastric emptying?

  Pressure of the pyloric sphincter
• What is a characteristic of the pyloric sphincter?

  It is a short and poor barrier
• What does the ileocecal sphincter separate?

  Ileum and cecum
• What maintains positive resting pressure in the ileocecal sphincter?

  Control by vagus nerve and sympathetic nerves
• What happens to the ileocecal sphincter during ileum distention?

  It relaxes
• What causes contraction of the ileocecal sphincter?

  Distention of proximal colon
• How is ileal flow into the colon regulated?

  By luminal contents and pressure
• What does the anal sphincter consist of?

  Internal and external sphincters
• What type of muscle is the internal anal sphincter composed of?

  Circular and longitudinal smooth muscle
• What controls the internal anal sphincter?

  Involuntary control
• What reflects the resting tone of the internal anal sphincter?

  High resting pressure of overall anal sphincter
• What type of muscle does the external anal sphincter contain?

  Only striated muscle
• How is the external anal sphincter controlled?

  By both voluntary and involuntary mechanisms
• What initiates the rectosphincteric reflex?

  Distention of the rectum
• What happens if defecation is not desired?

  Continence is maintained by external sphincter contraction
• What occurs when defecation is desired?

  Relaxation of external sphincter and contraction of abdominal muscles
• How does the body facilitate defecation?

  Flexure of hips and descent of pelvic floor
• What happens if a delay in defecation is needed?

  Voluntary contraction of external anal sphincter occurs
• What can override reflexes initiated by rectal distention?

  Voluntary contraction of external anal sphincter