Week 1: GI motility Intro

Question 1

Phases of deglutition/swallowing

Answer 1

1. buccal phase
   - voluntary, oral/buccal. Mastication and sucking
   - tongue forces bolus of food towards pharynx
2. pharyngeal phase
   - involuntary. soft palate and uvula fold forward and cover nasopharynx. Epiglottis folds over larynx
3. Esophageal phase
   - involuntary. upper esophageal sphincter (UES), (tonically contracted at rest), relaxes and opens to allow food to pass
   - LES opens to allow food to enter the stomach

Question 2

Esophageal phase

Answer 2

• Primary peristalsis: primary function is to keep esophagus empty. 3-4 cms/sec, 6-8 secs, <80mmHg. more powerful than secondary peristalsis.
• secondary peristalsis: function is to strip distal part of esophagus of contents and to keep refluxate in the stomach. Assoc. with esophageal distention.

Question 3

esophageal motor activity

Answer 3

• UES and LES at rest are tonically contracted. Maintained by vagal stimulatory fibers vis ENS (enteric nervous system)
• swallow induced relaxation mediated by vagal inhibition (release of VIP, NO)

Question 4

Receptive relaxation of the stomach

Answer 4

• initiate by swallowing
• mechanoreceptors in pharynx stimulated, transmitted to dorsal vagal complex, efferent fibers to inhibitory motor neurons in ENS. Results in relaxation of stomach to increase volume.

Question 5

Peristalsis in stomach

Answer 5

• there are low amplitude contractions along body toward the antrum to mix and move food down stomach.
• initiated by interstitial cell of Cajal (ICC)-pacemaker cells. 3/min
• force of contraction determined by number of action potentials, the more action potentials the higher the amplitude
• Antrum has powerful contractions to break down food into smaller pieces.

Question 6

Factors that delay gastric emptying

Answer 6

• increased acidity, fat, amino acids, hypertonicity and distension of duodenum leads to secretion of hormones and neural stimulation to delay gastric emptying
• means need more time for absorption and digestion
  1. Neural
  2. Endocrine

Question 7

Motility patterns of the gut

Answer 7

1. Fed pattern/digestive state
   - segmentation, low to moderate amplitude non-propagative contractions
   - to mix nutrients (chyme and digestive enzymes). Doesn’t occlude the lumen
   - 2-4 hours post prandial period
   - frequency set by pacemaker cells (ICC)
   - manometry pattern: jumbled, random.
2. Migrating motor complex of inter digestive state (housekeeping)
   - cyclical, 3 phases
   - up to 12 cycles/min
   - allows movement of large particles through bowel
   - sweeps undigested material to large intestines, prevents bacterial buildup

Question 8

Small intestines motility: Phases of migrating motor complex

Answer 8

Phase I -interdigestive state
-quiet period. resting phase to recover muscle strength.
Phase II -increasing activity
-similar to fed state, 30-60mins, for mixing
Phase III -clustered contractions
-highest amplitude of small bowel contractions
-10-20mins duration
-propagating and propulsive contractions
-every 60-90 minutes
-inhibited by fed state

Question 9

Patterns of colonic motility

Answer 9

1. Segmental activity
   - single contractions and group contractions
   - majority of daily motor activity. activity Increases from ascending to sigmoid colon.
   - increases with age
2. Propagated activity
   - low amplitude propagative contractions (LAPCs): poorly studied, transport of liquid and gases
   - high amplitude propagative contractions (HAPCs): infrequent. 0-6 times/day. Assoc. with borborygmus and defecatory stimulus. More active in daytime.

Question 10

Mass movement of colon

Answer 10

1. food in stomach and chyme in duodenum stimulates mass movement on colon
2. mass movements integrated by enteric plexus
3. propel contents towards rectum
4. Feces in rectum stimulates parasympathetic and local reflexes that result in defecation

Question 11

Gastrocolic response

Answer 11

• reproducible response. Signals bypass small intestines and stimulates the colon
• within 1-3 minutes following a meal, there’s colonic activation
• mainly segmental contractions but also increase in LAPCs and HAPCs
• postprandial colonic motility influenced by caloric content and meal composition: fats and carbs stimulate, proteins inhibit

Question 12

Rectal motor complex

Answer 12

rectrum slows and stops contractions

• 2-3/min
• duration >3 minutes
• independent from small bowel activity and colonic activity
• rise in anal canal pressure
• function: avoid rectal stasis and preserve nocturnal fetal continence

Question 13

Phases of defecation

Answer 13

1. Involuntary first phase
   -colonic contents transported towards rectrum
   increased rectal distention and pressure
   -relaxation of internal anal sphincter
2. Voluntary second phase
   -increased intra abdominal pressure
   -pelvic floor relaxes and descends
   -straightening of anorectal angle
   -relaxation of external sphincter
   -expulsion of contents
   Up to 1 hour prior, increase in HAPCs often precedes defecation

Question 14

Rectoanal reflexes

Answer 14

• rectoanal inhibitory reflex (RAIR): relaxation of internal rectal sphincter muscle that goes back up to basal tone in response to rectal distention
• anal cough reflex: EAS contracts with coughing, sneezing and standing
• cutaneoanal reflex (anal wink): touch outside of anus, EAS contracts