Gastrointestinal Lecture 2 Part 2 Segment-Specific Patterns of Motility (Small & Large Intestines)

Question 1

Peristalsis and segmentation contribution to SI

Answer 1

• Peristalsis makes a minor contribution to motility of the small intestine
• During digestion, segmentation is major contributor to breaking up and mixing chyme

Question 2

Rhythm of segmentation dictated by _______?

Answer 2

Rhythm of segmentation dictated by the BER (basic electrical rhythm); varies

Question 3

What does the migrating myoelectrical complex generate?

Answer 3

Migrating myoelectrical complex generates waves of contraction that moves undigested material to the large intestine after process of digestion and absorption

Question 4

tonic contractions in GI

Answer 4

Tonic contractions are relatively prolonged contractions that can isolate segments of the intestine (slows transit time, increasing time for absorption)

Question 5

What separates the ileum and colon?

Answer 5

Ileocecal valve separates the ileum and colon

Question 6

What are the parts of the large intestine?

Answer 6

• colon
• cecum
• rectum

Question 7

How does the Ileocecal valve open and close?

Answer 7

• Increases in colonic pressure squeeze it closed (back pressure prevents backflow)
• increases in ileal pressure open it

Question 8

Gastroileal reflex

Answer 8

opening of the ileocecal valve in response to food leaving the stomach

Question 9

What do segmentation and peristalsis contribute to?

Answer 9

contribute to mixing and propelling the contents of the colon

Question 10

What are mass action contractions?

Answer 10

• unique to colon
• Simultaneous contraction of large areas of the colon (~10/day)
• Move material through the colon and into the rectum

Question 11

How does defecation happen?

Answer 11

• Increases in rectal pressure caused by mass action contractions initiates defecation reflex and desire to defecate
• Internal anal sphincter under involuntary control (smooth muscle)
  
  • relaxation of internal anal pressure
• External anal sphincter under voluntary control (skeletal muscle)
  
  • contraction of external anal pressure

Question 12

What pressure allows defecation to occur?

Answer 12

At certain pressure (> 55 mm Hg) reflex relaxation of the external anal sphincter is triggered, allowing the feces to be passed

Question 13

How can urge to defecate be delayed?

Answer 13

Urge to defecate can be delayed by voluntary contraction of the external anal sphincter

• Prolonged distension of rectum initiates a reverse movement, driving rectal contents into the sigmoid colon
• Urge to defecate subsides until next mass movement propels feces back into the rectum

Question 14

How can defecation be initiated?

Answer 14

Defecation can be initiated by voluntary straining

• Contraction of abdominal muscles and relaxation of puborectalis combines to lower the pelvic floor, open the anorectal angle and facilitate defecation

Question 15

Which position is best for defecation?

Answer 15

• squatting is easier and faster
• Countries with cultural practice of sitting have increased incidence of hemorrhoids and diverticular disease → angle is more close up and straining causes retention of feces

Question 16

GI motility transit time

Answer 16

• Varies between individuals
  
  • Transit time in adults: > 50 h
  • Transit time in children: ~33 h
• Varies between type of food
• Varies on health status

Question 17

How long does it take for a meal to pass through the GI segments?

Answer 17