MOTILITY

Question 1

What happens in the small intestine?

What two types of waves allow this to occur?

Answer 1

Digestion (fat, protein, carbs, absorption of breakdown products) and absorption - vitamins, nutrients, water, electrolytes

Optimized by

• Segmentation waves: brings chyme into close contact w villi & maximizes mixing of chyme w enzymes and bile
• Peristaltic waves: move content slowly toward the colon, enabling absorption by including contact with segments

Question 2

___ & ___ absorbed in the upper small intestine

___ & ___ absorbed in teh terminal ileum

Answer 2

Calcium & iron - upper small intestine

Vitamin B12 & bile salts - terminal ileum

Question 3

Segmentation’s ring-like contractions are

• generated by ___ nerves
• occur at sites where ___

Answer 3

• Generated by enteric nerves
• Contractions occur at sites of distension
  
  • –> squeeze & split the distending bolus in half so half of it is ‘orad’ and the other half is ‘caudad’
  • –> distends adjacent segments of the bowel
  • –> process repeats over and over, maximizing mixing of chyme w enzymes & bile

Question 4

Peristaltic waves occur due to

Answer 4

Bolus is propelled toward colon due to inherent differences in basic electrical rhythms between the

• duodenum (12/min),
• jejunum (10/min)
• ileum (8/min)

These differences ensures that chyme gets moved caudally to the slower contracting segments until emptied into the colon

Question 5

Which occurs more frequently - peristaltic or segmental contractions?

Answer 5

Segmental contractions

Question 6

Power propulsion

Answer 6

Abnormal peristaltic contractile response to irritation that moves material too rapidly over long stretches of bowel –> diarrhea

Question 7

Ileocolic reflex - what brings it on? what is it? what inhibits it?

Answer 7

• Initiated by the residual products distending the terminal ileum
• Relaxation of the ileocecal valve -> contents flow into cecum (first part of colon)
• Inhibited by cecum distension –> ileocecal valve closes

Important for maintaining bacterial gradient between colon and small bowel

Question 8

What happens if you didn’t have your ileo colic reflex?

Answer 8

Bacteria would enter & thrive in the nutrient-rich small bowel –> diarrhea, bloating, gas, weight loss, B12 deficiency

Question 9

Migrating motor complex (fasted state)

Answer 9

• Begins 2 hrs post-meal
• Antrum produces a perstaltic wave that sweeps through the entire small inestine and ends in the ileocecal valve 2 hrs later.
  
  • This cycle repeats itself every 2 hours as long as a meal is not digested
• “Housekeeping”:
  
  • Removes particles larger than 2mm from the stomach
  • Clears residual chyme from the small bowel into colon to prevent bacteria in small intestine

Question 10

What abolishes the MMM?

Answer 10

Eating –> fed state abolishes the MMM wherever it is within its 2 hr cycle by liberating gastrin or CCK

Question 11

The changes in fluidity of feces is determined by what organ?

Answer 11

Colon (4-5ft long)

• cecum
• ascending colon
• transverse colon
• descending colon
• rectum
• anus

Question 12

Two purposes of colon

Answer 12

• Absorption of water & electrolytes (90% of 2L presented to it)
  
  • Leaves 200 cc for softening stool
• Elmination of undigestible solids (feces)

Question 13

Two types of mixing movements in the colon

Answer 13

Haustrations: maximize electrolyte & water absroption; segmental contractions bringing feces in close contact w colonic epithelium

Mass movements: move feces distally for excretion; peristaltic

Question 14

Defecation reflex

Answer 14

Vasovagal reflex initiated by rectal distension that results in release of nitric oxide to relax the internal anal sphincter –> feces and gas can enter the anal canal

Question 15

Sensory signals in the anal canal tell you if it’s solid, liquid or gas in there.

If you consciously decide to maintain continence, what happens?

Answer 15

Ach is released to raise the pressure/contract the skeletal-muscled external anal sphincter & puborectalis muscle.

Question 16

When you maintain continence (keep feces in rectum), how do you overcome rectal discomfort?

Answer 16

Rectal muscles undergo nitric oxide-mediated receptive relaxation ^{(like the fundus after a meal)}

–> reduced retal pressure

–> internal anal sphincter can contract again, so you don’t need the voluntary contraction of the external anal sphincter & puborectalis muscles

Question 17

Puborectal muscles

Answer 17

A rein on the rectum.

Contraction impedes feces from entering anal canal

Relaxation straightens outthe rectum

Question 18

Gastroscopic reflex

Answer 18

Food entering the stomach signals the colon to produce a mass movement

–> movement forces material into the rectum

–> distension produces the defecation reflex

Question 19

Gastrolienal reflex

Answer 19

Food entering the stomach signals the distal small bowel to empty remaining ileal chyme into the right colon