GI Motility

Question 1

Majority of chewing muscles innervated by

Answer 1

cranial nerve V

CN V - trigeminal nerve

Question 2

what do reticular areas of the brain stem nuclei control

Answer 2

rhythmical chewing

Question 3

what acts as a lubricant in chewing

Answer 3

mucin - glycoprotein

Question 4

how do you digest carbs

Answer 4

with salivary amylase

Question 5

how do you digest fats

Answer 5

lipases

Question 6

three stages of swallowing

Answer 6

• a voluntary oral stage
• a pharyngeal stage
• an oesophageal stage

Question 7

stages of the oral phase

Answer 7

1. Food voluntarily moved posteriorly into the pharynx by tongue then,
2. The trachea is closed
3. The oesophagus is opened
4. A fast peristaltic wave initiated by the nervous system of the pharynx forces the bolus of food into the upper esophagus

Question 8

Pharyngeal Phase

Answer 8

• Initiated by voluntary movement of food into
the back of the mouth
– Detected in ring area around the pharyngeal opening
• Excitation of involuntary pharyngeal sensory receptors to elicit the swallowing reflex

Question 9

The motor impulses from the swallowing center to the pharynx and upper esophagus that cause swallowing are transmitted successively by

Answer 9

CN V, CN IX, CN X, CN XII

Question 10

1° Peristalsis

Answer 10

• Continuation of peristaltic wave that begins in the pharynx and spreads into the esophagus during the pharyngeal stage of swallowing
• Continuous wave passes from pharynx to stomach in about 8-10s

Question 11

2° Peristalsis

Answer 11

• Result from distention of the oesophagus by retained food
• Waves continue until all food has emptied into the stomach
• Initiated by:
– intrinsic neural circuits in myenteric
nervous system
– reflexes that begin in pharynx

Question 12

• Peristaltic waves in upper/striated region

Answer 12

– controlled by skeletal nerve impulses from the glossopharyngeal (CN IX) and vagus nerves (CN X)

Question 13

• In lower 2/3, consists of smooth muscle

Answer 13

– strongly controlled by the vagus nerves (CN X) that act through connections with the oesophageal myenteric nervous plexus

Question 14

mixing in the stomach

Answer 14

• Mixing waves - weak peristaltic constrictor waves - begin in the mid/upper portions of the stomach wall, move toward antrum every 15-20s
– Initiated by gut wall ICC (basic electrical rhythm / slow waves)
• Waves become more intense (body➔antrum)
– force the antral contents under high pressure toward
the pylorus
• Play important role mixing the stomach contents
– Antral contents squeezed upstream through peristaltic ring towards body of stomach, not through the pylorus
• Peristaltic constrictive ring + upstream squeezing action (retropulsion) important mixing mechanism in the stomach

Question 15

what is emptying promoted by

Answer 15

intense peristaltic contractions in stomach antrum

Question 16

what is emptying of the stomach opposed by

Answer 16

by pylorus - contraction under influence of nervous + hormonal signals from stomach + duodenum

Question 17

Regulating factors: Gastric and Duodenal of stomach emptying

Answer 17

Regulating factors: Gastric and Duodenal – stomach volumegastric emptying
– Enterogastric inhibitory reflex
1. Distentionofduodenum
2. Irritation of the duodenal mucosa
3. Acidity/osmolalityofduodenalchyme
4. Presenceofdigestionproductsinchyme e.g., proteins/fats

Question 18

Regulating factors: Hormonal of stomach emptying

Answer 18

– Stimulus mainly fats

– CCK most potent hormone

Question 19

Segmentation Contraction

Answer 19

• Chyme induced extension of GI wall➔stretch➔localised concentric contractions (spaced along intestine, short lasting)➔segmentation
  • Frequency of segmentation determined by frequency of slow waves
  • Become weak when the excitatory activity of the enteric nervous system is blocked by atropine
  • slow waves in smooth muscle cause the segmentation contractions
  • However not effective without background excitation from myenteric nerve plexus

Question 20

Activity increased after a meal: peristalsis

Answer 20

– Chyme entry into duodenum➔duodenal wall stretch
– Gastroenteric reflex (from stomach distension via myenteric plexus)
– Gastrin, CCK, insulin, motilin, serotonin increase motility
– Secretin, glucagon decrease motility

Question 21

Haustrations

Answer 21

mixing movements

• similar to segmentation movements
• combined contraction of circular and longitudinal smooth muscle

Question 22

modified peristalsis

Answer 22

– Constrictive ring occurs (usually in transverse colon) in response to distension
– 20cm of colon distal to constrictive ring lose haustrations and contract as a unit
– Fecal material moves en masse down the colon
– Contraction develops progressively over 30secs
– Relaxation occurs over next 2-3mins
– Another mass movement then occurs

Question 23

Sensation of need to defecation felt

Answer 23

when feces moved into rectum

Question 24

Gastrocolic and Duodenocolic Reflexes

Answer 24

• Facilitate mass movements after meals
• Due to distention of stomach and duodenum
• Transmitted via autonomic nervous system as inhibited when extrinsic autonomic nerves to the colon removed
• Irritation in the colon can also initiate intense mass movements

Question 25

Defecation

Answer 25

• Rectum usually empty of faeces
• Anal canal tightly closed via
contraction of anal sphincters
• Gas or faeces in the rectum stimulates stretch receptors in its wall initiating the rectosphincteric reflex
– reflex relaxation of the smooth muscle of the internal anal sphincter and contraction of the striated muscle of the external anal sphincter
• Defecation is a reflex activity but is subject to conscious control