PHYS: GI Motility

Question 1

What is aclasia?

Answer 1

failure of esophagus to relax

Question 2

What happens when a food bolus reaches the back of the mouth?

Answer 2

reflexive swallowing contraction

Question 3

What starts the wave of food down the esophagus?

Answer 3

primary peristalsis

Question 4

What is the relative pressure at the upper esophageal sphincter?

Answer 4

pressure in esophagus > atmospheric pressure

Question 5

What is the role of the UES?

Answer 5

when a bolus is swallowed, it opens to allow food to pass from the pharynx to exophagus

Question 6

What stimulates the closure of the UES after a swallow?

Answer 6

pressure in the esophagus increases to close UES and the peristaltic wave begins

Question 7

What is the pressure between the UES and diaphragm?

Answer 7

pressure < atmosphetic pressure (intrathoracic pressure is negative, making the esophageal tube flaccid)

Question 8

What keeps the food moving between the UES and diaphragm?

Answer 8

peristaltic wave

Question 9

What is the pressure after the diaphragm?

Answer 9

pressure > atmospheric pressure

Question 10

What happens when the food bolus reaches the diaphragm?

Answer 10

LES relaxes as vagus releases VIP (increases NO for SM relaxation)

Question 11

What occurs even BEFORE the relaxation of the LES to prepare for movement of the bolus into the stomach?

Answer 11

relaxation of the orad stomach

Question 12

What structures are responsible for swallowing?

Answer 12

pharynx and the upper 1/3 of the esophagus (striated skeletal muscle–> voluntary)

Question 13

What innervates the pharynx and the upper 1/3 of the esophagus?

Answer 13

directly innervated by vagus nerve (opposed to SM which must have the vagal stimulus relayed through myenteric ganglia)

Question 14

List the 3 main phases of swallowing.

Answer 14

1) oral phase
2) pharyngeal phase
3) esophageal phase

Question 15

Where does the oral phase of swallowing originate?

Answer 15

swallowing center of the medulla

Question 16

What stimulates the oral phase of swallowing?

Answer 16

sensory information (ex. food in the mouth) is detected by somatosensory receptors located near the pharynx→ vagus and glossopharyngeal nerves carry information to medullary swallowing center→ motor output to striated muscle of pharynx and upper esophagus.

Question 17

True or false: the swallow reflex is voluntary?

Answer 17

FALSE (involuntary)

Question 18

What occurs during the pharyngeal phase of swallowing?

Answer 18

propel food bolus from moth to esophagus (soft palate up, epiglottis covers larynx and prevents food food from entering trachea), UES relaxes, primary peristalsis begins at pharynx.

Question 19

What controls the esophageal phase of swallowing?

Answer 19

controlled partly by swallowing reflex and partly by enteric nervous system

Question 20

What happnes during the esophageal phase of swallowing?

Answer 20

food is propelled into the stomach

Question 21

What is a secondary peristaltic wave?

Answer 21

wave that is stimulated if there is food left behind and “cleans up” after the primary wave

Question 22

What is receptive relaxation?

Answer 22

the orad stomach relaxes before LES relaxation then relaxes more and more as more food comes in

Question 23

What type of reflex is receptive relaxation?

Answer 23

vago-vagal reflex

Question 24

Describe the vago-vagal reflex in receptive relaxation.

Answer 24

both afferent (mechanoreceptors sense distention of stomach and relays it to CNS) and efferent (information to smooth muscle wall of orad stomach to relax after stimulated by VIP) limbs of the reflex are located in the vagus nerve.

Question 25

What is one of the underlying problems that causes GERD?

Answer 25

failure of secondary peristalsis to eliminate acid in the esophagus (and this remaining acid causes erosion)

Question 26

What other things can predispose to GERD?

Answer 26

- Failure of LES closure - Pregnancy - Hiatal hernia (part of stomach goes into thorax and negative pressure sucks up gastric acid)

Question 27

What are the "pacemaker cells of the stomach"?

Answer 27

Interstitial cells of Cajal

Question 28

Where are the interstitial cells of Cajal located?

Answer 28

myenteric plexus

Question 29

How do the interstitial cells of Cajal work?

Answer 29

These depolarize due to cyclic opening of Ca2+ channels (like the SA node), spread the depolarization through low-resistance gap junctions, and continuously produce slow waves

Question 30

What do slow waves of interstitial cells of Cajal lead to?

Answer 30

1) tonic contractions (subthreshold slow waves that do not lead to APs) 2) phasic contractions (if membrane is depolarized to threshold and AP occurs).

Question 31

What determines the strength of the phasic contraction?

Answer 31

The greater the number of APs that occur on top of the slow waves, the stronger the phasic contraction!

Question 32

True or false: the frequency of slow waves is always constant.

Answer 32

TRUE

Question 33

True or false: the amplitude of slow waves is always constant.

Answer 33

FALSE: amplitude of slow waves is greater in the lower stomach

Question 34

What do neuronal and hormonal activity alter in regards to slow waves?

Answer 34

nothing! they alter the frequency of APs (and thus the force of phasic contractions)

Question 35

What leads to increased frequency of APs and strength of gastric contractions?

Answer 35

- Outside digestive processes (gastrin and motilin) | - Strong parasympathetic activity (lots of food)

Question 36

What leads to decreased frequency of APs and strength of gastric contractions?

Answer 36

- Outside digestive processes (secretin and GIP) | - Sympathetic stimulation

Question 37

What portions of the stomach are included in the "orad area"?

Answer 37

fundus and proximal body of the stomach

Question 38

Waht types of glands are located in the "orad stomach"?

Answer 38

oxytinic glands

Question 39

What is the role of the "orad area"?

Answer 39

storage

Question 40

What portions of hte stomach are included in the "caudad area"?

Answer 40

distal portion of the body and the antrum

Question 41

Which is thicker, the orad or caudad area of the stomach? Why?

Answer 41

caudad area (oblique SM in antral layer of stomach gives it an incrased thickenss compared to body/fundus)

Question 42

What is the role of the"cauded area"?

Answer 42

Mixing | Emptying

Question 43

Where do waves of contraction of the stomach begin?

Answer 43

middle of the body of the stomach and move distally along the caudad stomach (increasing in strength as they approach the pylorus)

Question 44

Why is the chyme not immediately pushed into the duodenum with contracton of the stomach?

Answer 44

the contraction closes the pylorus

Question 45

What is retropuslion?

Answer 45

most of the gastric contents are propelled back into the stomach for further mixing/reduction of particle size after being pushed into the duodenum

Question 46

Why does the rate of gastric emptying need to remain pretty constant?

Answer 46

to allow for adequate gastric H+ neutralization and digestion/absorption of nutrients

Question 47

What are symptoms of slow emptying?

Answer 47

fullness loss of appetite nausea

Question 48

What are symptoms of increased gastric emptying?

Answer 48

diarrhea | duodenal ulcer

Question 49

Do gastric ulcers SLOW or SPEED gastric Emptying?

Answer 49

SLOW

Question 50

Do hypertonic solutions SLOW or SPEED gastric Emptying?

Answer 50

SLOW

Question 51

Do hypotonic solutions SLOW or SPEED gastric Emptying?

Answer 51

SLOW

Question 52

Do isotonic solutions (that cannot be broken down) SLOW or SPEED gastric emptying?

Answer 52

SPEED

Question 53

Do solid foods SLOW or SPEED gastric Emptying?

Answer 53

SLOW

Question 54

Do fats SLOW or SPEED gastric Emptying? Why?

Answer 54

SLOW (stimulate CKK when it reaches duodenum→ decrease pressure of orad stomach, slows gastric emptying, increase pressure in duodenum to push back on pylorus)

Question 55

Do liquids SLOW or SPEED gastric Emptying?

Answer 55

SPEED

Question 56

Does high acidity SLOW or SPEED gastric Emptying? Why?

Answer 56

SLOW (detected by duodenal H+ receptors→ enteric nervous system interneurons deliver message to gastric SM→ slow emptying time to permit time for neutralization by pancreatic HCO3-)

Question 57

Does a vagotomy SLOW or SPEED gastric Emptying?

Answer 57

SLOW

Question 58

How long does it typically take a meal to be emptied from the stomach?

Answer 58

2.5-3 hours

Question 59

True or false: the small intestine has a greater slow wave frequency than the stomach.

Answer 59

TRUE (declines as you get closer to the ileum)

Question 60

What is the relative slow wave frequency of the small intestine?

Answer 60

7-8 contractions per minute

Question 61

What are the two types of small intestine contractions that can occur?

Answer 61

Segmental contractions | Peristaltic contractions

Question 62

What is the role of segmental contractions?

Answer 62

mixing the chyme

Question 63

How do segmental contractions work?

Answer 63

wave occurs in the middle of the bolus and sends it in two different directions and relaxation allows it to come back together (no net forward movement)

Question 64

What is the role of peristaltic contractions?

Answer 64

propel the chyme toward the large intestine

Question 65

How do peristaltic contractions work?

Answer 65

contraction occurs at a point behind bolus to push it forward (but not continuous down the entire length).

Question 66

What stimulates a peristaltic contraction?

Answer 66

enterochromaffin cells of the intestinal mucosa sense the food bolus and release serotonin to stimulate a peristaltic reflex (contraction behind bolus and relaxation in front of bolus)

Question 67

True or false: amplitudes are constant in the small intestine.

Answer 67

TRUE

Question 68

What controls whether or not contractions occur?

Answer 68

"spiking"

Question 69

Waht is a migrating motor complex?

Answer 69

contractions that occur every 90 minutes in fasting individuals to remove any residual chyme int he small intestine by propelling it down toward the colon

Question 70

What controls migrating motor complexes?

Answer 70

nervous stimulation of motilin

Question 71

What happens when the material in the small intestine reaches the cecum and proximal colon (distention of colon)?

Answer 71

iliocecal sphincter contracts to prevent reflux into the ileum

Question 72

What relaxes the tonically contracted iliocecal sphincter?

Answer 72

distention of hte ileum

Question 73

What type of reflex is the iliocecal reflex?

Answer 73

intramural reflex (contained within the walls of the terminal ileum and proximal colon)

Question 74

What is the role of the large intestine?

Answer 74

store, absorb water, and evacuate material from the body

Question 75

What is "mass movement"?

Answer 75

the haustra (pouches) disappear over a significant segment of the colon and a peristaltic contraction occurs

Question 76

How often do colon contractions occur?

Answer 76

2-3 times during the day

Question 77

What keeps the internal anal sphincter tonically contracted?

Answer 77

dorsal root segments

Question 78

What is the retrosphincteric reflex?

Answer 78

when material reaches the rectum, the pressure increases and the internal anal sphincter relaxes—causing an urge to defecate (external sphincter automatically contracts (due to autonomic nervous system))

Question 79

If you do not defecate immediately after getting the urge (from material in the rectum), what happens?

Answer 79

internal sphincter will contract and the urge to defecate goes away

Question 80

What happens when defecation is convenient?

Answer 80

Voluntary relaxation of the external sphincter via the pudendal nerve and valsalva maneuver will cause defecation