GI motility and regulation

Question 1

Describe the two major types of motility in the GI tract, their function in digestion and the differences between them.

Answer 1

Segmentation- Isolated contraction, not coordinated with movement above and below, propels contents in both directions. When contracting area relaxes, the contents flow back into the original segment with the result that mixing has occurred without net propulsion. the predominant motor activity in the intestines, helping to ensure proper digestion and absorption.
Peristalsis coordinated contractions of adjacent segments in a proximal to distal manner, resulting in net propulsion of contents. A bolus of food in lumen induces distention of the intestinal wall. This leads to formation of a contractile ring ~2-3 cm proximal to bolus. The contractile ring moves towards the bolus, pushing it distally. At the same time, the intestine relaxes distal to the bolus (called receptive relaxation, produced by the pressure of the proximal bolus). This coordination requires nerves of the myenteric plexus. In the stomach, peristalsis occurs when the BERs are coordinated by vagal input in such a way that contraction of a distal segment follows just after contraction of the immediately preceding segment. Note that following a vagotomy, BERs are still observed, but they become disorganized and coordinated peristaltic movements are abolished.

Question 2

Explain how the sympathetic and parasympathetic systems communicate with intestinal smooth muscle.

Answer 2

para–> vagus nerves

Question 3

Describe the characteristics of the basic electrical rhythm (BER) of the small intestine and its relation to smooth muscle contractile activity.

Answer 3

are intrinsic property of muscle cells in a given region (myogenic). addition of ACh causes apps to fire at each peak. muscle contracts at the frequency set by the BER

Question 4

List the stimulus that initiates the swallowing sequence and the events that follow. Identify the point at which the swallowing sequence switches from voluntary to involuntary.

Answer 4

swallowing starts voluntarily- tongue separates a portion of the food and moves it back to the pharynx–> soft palate is pushed upward, upper constrictor contracts–> actions close off the nasopharynx (at this point swallowing is a reflex). respiration is briefly inhibited, larynx rises and glottis closes tp prevent bolus from entering trachea. UES relaxes and the coordinated contraction of the middle and lower constrictor muscles propel the bolus into the esophagus

Question 5

Explain the mechanism of esophageal motility and peristalsis, and the role of the upper and lower esophageal sphincters in this process.

Answer 5

upper 1/3 of the esophagus consists of skeletal muscle, and remainder is smooth muscle . wave of parietals pushes bolus ahead to lower esophageal sphincter (5 sec) LES relaxes just before bolus arrives. Bolus propelled into the stomach

Question 6

Describe the storage, digestion, and motility roles of the stomach.

Answer 6

storage- receptive relaxation (some vagus input)
retropulsion- contractions outrun bolus pushing food back up into body.
chyme- digestive juice

Question 7

List the phases of the migrating motility complex (MMC)].

Answer 7

b/n meals process that sweeps gut. process occurs every 90 min. at anytime 40 cm are involved. involvement of a region lasts 10-15 minutes. each wave is proceeded by an increase in serum hormone motilin. eating terminates the process

Question 8

Compare and contrast the colonic motor activity during a “mass movement” with that during haustral shuttling and the consequence of each type of colonic motility.

Answer 8

haustra- segmentation contractions that mix and dry the chyme

mass mvt- forward propulsion, giant migrating contraction

Question 9

Describe the sequence of events occurring during defecation, differentiating those that are under voluntary control from those under involuntary control.

Answer 9

filling of rectum with stool causes relaxation of internal sphincter and voluntary contraction of external sphincter

Question 10

gastrin

Answer 10

hormone secreted in response to the presence of food in the stomach, increases peristaltic contractions and decreases pyloric tone. combo of distention and gastrin increases the rate of gastric emptying

Question 11

what sequesters iron from bacteria

Answer 11

lactoferrin

Question 12

poor forming antimicrobial secreted in saliva

Answer 12

lysozyme