Exam 3 (Lecture 7) - Motility Patterns of Stomach and Small Intestine

Question 1

What are the main functions of the stomach?

Answer 1

1) Mixer/grinder
- churning motions to change semi-solid food bolus to chyme

2) Storage vat

3) Control rate of chyme delivery to duodenum

Question 2

List the smooth muscular layers encountered in the stomach.

Answer 2

1) Outer longitudinal smooth muscle
2) Middle circular smooth muscle
3) Inner oblique smooth muscle

Question 3

Is the muscular activity in these areas of the stomach weak or strong? What is the function of these tonic contractions?

Answer 3

Fundus:
- muscle activity is weak
- tonic contractions shape the gastric wall to its contents and
provide gentle propulsion of material into the pyloric antrum

Body/Pyloric Antrum:
- strong waves of peristalsis
- propel ingesta
- mix and grind ingesta

Question 4

What is the associated muscular reflex in these areas of the stomach? How does this reflex work?

Answer 4

Fundus:
- Adaptive Relaxation/Accomodation
- Major muscular reflex of the fundus
- Vagal activity suppresses muscular contractions and leads to
adaptive relaxation as food boluses enter the stomach w/o
an increase in intraluminal pressure
- Storage area with little mixing

Body/Pyloric Antrum
- Intense slow wave activity and muscular contractions are frequently present

Question 5

Describe the 4 steps involved in these areas of the stomach (A-D on diagram).

Question 6

How does vagal (X) stimulation affect motility in these two areas of the stomach?

Answer 6

Fundus:
- Vagal activity suppresses muscular contractions and leads to
adaptive relaxation as food boluses enter the stomach
without an increase in intraluminal pressure

Pyloric Antrum:
- Vagal stimulation causes intense peristaltic activity mediated by
Ach

Question 7

During the cephalic phase of digestion, vagal stimulation on the stomach is stimulated by events occurring in two locations: ________ and __________.

Answer 7

1) CNS
2) Stomach

Question 8

How do sensory receptors in the stomach create a positive feedback loop to enhance gastric motility? Suppress gastric motility?

Answer 8

As food enters the stomach, vagal activity increases.

Increased gastrin secretion.
- Positive feedback (stimulate) loop starting with sensory
receptors in the stomach
- Increases gastric motility and secretion of HCl and pepsinogen

Gastric motility is suppressed when pH decreases and inhibits gastrin release.

Question 9

The rate at which the stomach empties is regulated by the contents of the ___________.

Answer 9

Duodenum

Question 10

How are reflexes named? Describe the enterogastric reflex. What are the afferent receptors in the duodenum stimulated by?

Answer 10

Reflexes are named based on:
- site of origin of the afferent stimulus
- site of the efferent response

Enterogasgtric Reflex:
- Duodenum controls the rate of gastric emptying
- Rate of gastric emptying must match the SI digestion and
absorption rate
- Certain types of food can be digested and absorbed more
rapidly than others

Afferent Receptors in Duodenum Stimulated By:
- Low pH
- High osmolarity
- Fat

Question 11

How is stomach emptying inhibited?

Answer 11

Afferent receptors of the GI reflexes located in the duodenum are stimulated by low pH, high osmolarity, and fat in the duodenal lumen.

These conditions stimulate vagal, enteric neuronal, and hormonal reflexes that inhibit stomach emptying.

Question 12

How are the inhibitory influences of the stomach removed?

Question 13

How are the GI reflexes named?

Answer 13

1) Site of origin of the afferent stimulus
2) Site of the efferent response

Question 14

Name the 2 phases of small intestine motility. When do each of these phases occur?

Answer 14

1) Digestive Phase
- After food intake

2) Interdigestive Phase
- When digestive tract is mostly empty

Question 15

Name the two motility patterns of the digestive phase.

Answer 15

1) Propulsive
2) Nonpropulsive

Question 16

Describe nonpropulsive motility.

Answer 16

Segmentation results from localized contractions of circular muscle.

Portions of small intestine, usually 3 to 4 cm long, contract tightly, dividing the gut into segments of constricted and dilated lumen.

Within a few seconds, the constricted portions relax and new areas constrict.
- Action tends to “milk” gut contents back and forth within the
small intestine, mixing them with digestive juices and circulating
them over the absorptive mucosal surfaces
- Slows down the aboral movement of material because of
closure of the intestinal lumen in contracted segements

Question 17

Describe propulsive motility.

Answer 17

Peristaltic contractions that migrate down the gut in phase with the slow waves.

Digestive phase peristaltic contractions pass over short segments of intestine and then fade out.

Ingesta are pushed down the small intestine for a short distance and then subjected to additional segmentation contractions and mixing activity.

Question 18

Describe the interdigestive phase of small intestine motility and the importance of the migrating motility complex (MMC). What interrupts the MMC?

Answer 18

MMC is the basic motor activity in the gut during a fasting or interdigestive state.

Characterized by waves of powerful peristaltic contractions that sweep over a large length of the small intestine.

Waves produced by MMC.

MMC begins the pyloric antrum as groups of slow waves that stimulate intense action potential and muscular contraction activity.

The complex migrates down the small intestine at the rate of the slow waves.

Some of the MMCs fade out before reaching the ileum, but some travel the entire length of the small intestine.

** Meal consumption interrupts the MMC.

Question 19

MMC lasts 80 minutes to 2 hours and consists of how many phases? What is the trend for the time it takes per phase and types of contractions moving from phase I to phase III?

Answer 19

3 Phases:
- Phase I (60-70 minutes) = no contractions
- Phase II (20-30 minutes) = intermittent and irregular
contractions
- Phase III (3-10 minutes) = strong peristaltic contractions, start
from the caudal esophagus/stomach and migrate caudally to
colon

Trend:
- Moving from Phase I to Phase III
- Less time
- Stronger contractions

Question 20

How does the MMC work as a housekeeping function?

Answer 20

Serves to push undigested material out of the small intestine.

Important in controlling the bacterial population in the upper gut.

Helps to impede the migration of bacteria from the ileum to the duodenum.
- duodenum harbors relatively small population of bacteria and
the population increases toward the ileum

Question 21

Define ileus. Describe what occurs during ileus.

Answer 21

Absence of peristalsis.

Small intestinal bowel loops become distended and fluid-filled.
- small intestinal edema

Decreased intestinal/stomach sounds (borborygmi)

Absence of the ileocecal noise dorsally behind the right costal arch.