Motility of the GI Tract

Question 1

Slow waves

Answer 1

Depolarization and repolarization of the membrane potential. Does not, on its own, equal an AP.

Question 2

Phasic contraction definition:

Where does it occur?

Answer 2

Periodic contractions followed by relaxation.

Esophagus, antrum, SI.

Question 3

Tonic contractions definition:

Where does it occur?

Answer 3

Constant contraction w/o regular periods of relaxation.

Orad of stomach, lower esophagus, ileocecal and anal sphincters.

Question 4

What can stimulate an AP in the gut? (3)

Answer 4

Stretch
ACh
Parasympathetics

Question 5

What can stimulate repolarization in the gut? (2)

Answer 5

NE

Sympathetics

Question 6

What does the submcosal plexus control?

Answer 6

GI secretions and local blood flow.

Question 7

What does the Myenteric plexus (Auerbach’s) control?

Answer 7

GI movement.

Question 8

ICCs (Intestinal cells of Cajal)

Answer 8

Pacemaker cells of GI SM.

Propagate slow waves.

Question 9

What nerve innervates most muscles of mastication?

Answer 9

CN 5, trigeminal n.

Question 10

Oral phase of mastication is:

Answer 10

Voluntary.

Question 11

Pharyngeal phase of mastication (5)

Answer 11

1. Soft palate pulled upward.
2. Epiglottis moves.
3. UES relaxes.
4. Peristaltic contractions initiated in pharynx.
5. Food propelled thru UES.
   INVOLUNTARY

Question 12

Esophageal phase is controlled by (2):

Answer 12

Swallowing reflex and ENS.

Question 13

Who controls the involuntary swallowing reflex?

Answer 13

Medulla

Question 14

Involuntary swallowing reflex (5)

Answer 14

Food in pharynx –> vagus/glossopharyngeal n. –> medulla –> brainstem nuclei –> motor output to pharynx

Question 15

Primary peristaltic wave (3)

Answer 15

Continuation of pharyngeal peristalsis.
Controlled by medulla.
Cannot occur post vagotomy.

Question 16

Secondary peristaltic wave (4)

Answer 16

Occurs if primary wave does not empty esophagus or if reflux occurs.
Medulla and ENS involved.
Can occur w/o oral and pharyngeal phases.
Can occur post vagotomy.

Question 17

What occurs in achalasia?

Answer 17

The LES does not fully relax during swallowing, causing a buildup of food.
LES resting pressure is elevated.

Question 18

What can cause achalasia?

Answer 18

Lack of VIP or ENS has been affected.

Damage for nerves in esophagus.

Question 19

Physiology of GERD

Answer 19

LES has abnormally low pressure (it weakens) from lower motor problems. Acid, pepsin and bile can get into esophagus.

Question 20

3 layers of muscle of the stomach

Answer 20

Circular
Longitudinal
Oblique

Question 21

Where does receptive relaxation occur?

How does it affect pressure and volume of that region?

Answer 21

Orad region.
Decreases pressure and increases volume of orad region.
Vasovagal reflex.

Question 22

What occurs does not occur in the orad region?

Answer 22

It does not have contractile ability; therefore, little mixing of food occurs.

Question 23

What is the affect of CCK on contraction and gastric distensibility?

Answer 23

Decreases contractions

Increases gastric distensibility.

Question 24

Peristalitic contraction of the stomach occurs at:

Answer 24

Mid-stomach to pylorus

Question 25

What happens to the force/velocity of the contractions as the approach the pylorus? What is the max. freq. of waves/min?

Answer 25

They increase. | 3-5 waves/min

Question 26

What happens to the gastric contents in caudad region?

Answer 26

"Retropulsion" | Most of it is propelled back into the stomach for further mixing and reduction of particle size.

Question 27

What is the affect of PSNS, gastrin and motilin on AP frequency on force of contractions?

Answer 27

Increases them

Question 28

What is the affect of SNS, secretin and GIP on AP frequency and force of contractions?

Answer 28

Decreases them

Question 29

How long does gastric emptying take?

Answer 29

3 hrs

Question 30

What increases the rate of gastric emptying? (5)

Answer 30

Decreased orad distensibility. Increased force of peristaltic contractions of the caudad region. Decrease tone of pylorus. Increased diameter. Inhibition of segmenting contractions of proximal duodenum.

Question 31

What inhibits the rate of gastric emptying? (4)

Answer 31

Relaxation of orad (increased in distensibility). Decreased force of peristaltic contractions. Increased tone of pyloric sphincter. Segmentation contractions in intestine.

Question 32

Why is gastric emptying closely regulated?

Answer 32

To allow enough time for neutralization of gastric H+ in duodenum and enough time for absorption/digestion.

Question 33

Entero-Gastric reflex

Answer 33

Negative feedback from duodenum which slows the rate of gastric emptying.

Question 34

What happens when there is acid in the duodenum?

Answer 34

Stimulates secretin release and inhibitions stomach motility by gastrin inhibition.

Question 35

What happens when there is fat in the duodenum?

Answer 35

Stimulates CCK and GIP which inhibit stomach motility.

Question 36

What happens when there is hypertonicity in the duodenum?

Answer 36

An unknown hormone inhibits gastric emptying.

Question 37

Gastroparesis

Answer 37

Slow emptying of stomach/paralysis of stomach in the absence of mechanical obstruction.

Question 38

Most common cause of gastroparesis: | What else can cause it?

Answer 38

DM | Damage to vagus n.

Question 39

Migrating myoelectric complex (MMC)

Answer 39

Empties large undigested particles in the stomach.

Question 40

MMCs (4)

Answer 40

Periodic, bursting peristaltic contractions. Occur at 90 min invervals during fasting. Motilin plays a significant role in mediating it. Inhibited during feeding.

Question 41

Segmental contractions

Answer 41

Back-and-forth movements that do not produce a forward movement along SI.

Question 42

When is there slow wave activity?

Answer 42

ALWAYS

Question 43

What sets the max. freq. of contractions?

Answer 43

Slow waves

Question 44

Slow wave freq. in the: Duodenum: Jejunum: Ileum:

Answer 44

D - 12 cycles/min J - 10 cycles/min I - 8 cycles/min

Question 45

How does serotonin affect the peristaltic reflex?

Answer 45

It is release by enterochromaffin cells and binds to IPAN receptors, initiating the peristaltic reflex.

Question 46

``` Hormonal control of contractions Serotonin Prostaglandins Epi Gastrin, CCK, Motilin, insulin secretin, glucagon ```

Answer 46

``` Serotonin : + Prostaglandins : + Epi : - Gastrin, CCK, Motilin, insulin : + Secretin, glucagon : - ```

Question 47

Vomiting reflex is controlled by:

Answer 47

Medulla

Question 48

Events of vomiting (7)

Answer 48

``` Reverse peristalsis. Stomach and pyloric relaxation. Increased abdominal pressure. Movement of larynx. LES relaxes. Glottis closes. Gastric contents thrown up. ```

Question 49

What does distention of the ileum do the sphincter? | Distention of the colon?

Answer 49

Relaxes it to allow the flow from ileum to colon. | Constricts sphincter, preventing backflow into the SI.

Question 50

Taeniae coli

Answer 50

3 flat bands of longitudinal fibers that run from cecum to rectum in the longitudinal muscle.

Question 51

Internal anal sphincter is: | External anal sphincter is:

Answer 51

Involuntary (SM) | Voluntary (skeletal muscle)

Question 52

Haustras

Answer 52

Small pouches that give the LI its segmented appearance. | They are NOT fixed.

Question 53

ENS innervation of the LI

Answer 53

Concentrated beneath teneae coli. | Innervate muscle layers.

Question 54

PSNS innervation of LI Vagus n. Pelvic ns.

Answer 54

Vagus n.: cecum, ascending and transverse colon. | Pelvic ns.: sacral portion of spinal cord, descending and sigmoid colon, rectum.

Question 55

SNS innervation of LI (T10-L2) Superior mesenteric ganglion: Inferior mesenteric ganglion: Hypogastric plexus:

Answer 55

Superior mesenteric ganglion: proximal regions Inferior mesenteric ganglion: distal regions Hypogastric plexus: distal rectum and anal canal

Question 56

Somatic pudendal ns. innervate:

Answer 56

External anal sphincter

Question 57

Mass movements

Answer 57

Occur over long distances. 1-3x day Stimulate defecation reflex. Propels fecal content into rectum.

Question 58

What happens to the wall of the rectum and the internal anal sphincter when the rectum fills with feces?

Answer 58

SM wall of rectum contracts and the internal anal sphincter relaxes.

Question 59

Vagovagal reflex

Answer 59

Stimulatory reflex

Question 60

Intestino-intestinal reflex

Answer 60

Inhibitory reflex

Question 61

Gastroileal (gastroenteric) reflex

Answer 61

Negative feedback from duodenum will slow rate of gastric emptying.

Question 62

Gastro and duodeno-colic reflexes

Answer 62

Distention of stomach/duodenum initiates mass movements

Question 63

Rectosphincteric (defecation) reflex

Answer 63

Rectal distention initiates defecation