Lecture 3: Gastrointestinal Motility

Question 1

Name the three things that motility accomplishes

Answer 1

Grinding, mixing, breakdown of fragments and ingested food

Question 2

Contractile tissue of GIT is composed of:

Answer 2

Smooth muscle
Striated muscle in pharynx, upper 1/3 of esophagus, external anal sphincter

Question 3

What type of smooth muscle allows for very smooth muscle contractions?

Answer 3

Unitary smooth muscle

Question 4

Unitary smooth muscles cells are __________ coupled via __________

Answer 4

Electrically; gap junctions

Question 5

Circular muscle decreases ________ of that segment

Answer 5

Diameter

Question 6

Longitudinal muscle decreases ________ of that segment

Answer 6

Length

Question 7

Periodic contractions followed by relaxation

Answer 7

Phasic contractions

Question 8

What type of contractions maintain a constant level of contraction or tone without regular relaxation?

Answer 8

Tonic contractions

Question 9

Where do phasic contractions take place?

Answer 9

Esophagus, gastric antrum, SI

Question 10

Where do tonic contractions take place?

Answer 10

Upper region of stomach, lower esophageal region, ileocecal and internal anal sphincters

Question 11

T/F: Slow waves always bring membrane potential to threshold

Answer 11

False

Question 12

T/F: Slow waves are always present

Answer 12

True

Question 13

T/F: APs are always present

Answer 13

False

Question 14

What happens when a slow wave causes an AP?

Answer 14

Contraction

Question 15

What determines direction and velocity of contractions?

Answer 15

Slow waves

Question 16

What is the frequency of slow waves in the stomach?

Answer 16

3 per minute

Question 17

What is the frequency of slow waves in the duodenum?

Answer 17

12 per minute

Question 18

T/F: Frequency of slow waves is not influenced by neural or hormonal input

Answer 18

True

Question 19

What ion causes the depolarizing phase and maintenance of the plateau of slow waves?

Answer 19

Calcium

Question 20

What ion is responsible for repolarization of slow waves?

Answer 20

Potassium

Question 21

Name the 3 phases of swallowing

Answer 21

Oral phase
Pharyngeal phase
Esophageal phase

Question 22

Oral phase, voluntary or involuntary?

Answer 22

Voluntary at first then becomes involuntary

Question 23

Name the phase of swallowing:
Tongue forces bolus toward pharynx, lots of receptors, then involuntary swallowing takes over

Answer 23

Oral phase

Question 24

Name the phase of swallowing:
Involuntary, propel bolus from mouth through pharynx to esophagus in 4 steps

Answer 24

Pharyngeal phase

Question 25

Name the phase of swallowing: Controlled by swallowing reflex AND enteric nervous system Propels bolus through esophagus to stomach After bolus enters esophagus, swallowing reflex closes sphincter

Answer 25

Esophageal phase

Question 26

In pharyngeal phase, what pulls up so that food cannot move into nasopharynx?

Answer 26

Soft palate

Question 27

In pharyngeal phase, what moves to cover the opening to the larynx?

Answer 27

Epiglottis

Question 28

In pharyngeal phase, when the larynx moves up against the epiglottis, what is covered?

Answer 28

Trachea

Question 29

In pharyngeal phase, what relaxes so food can pass from pharynx to esophagus?

Answer 29

Upper esophageal sphincter

Question 30

In pharyngeal phase, what propels the bolus through the sphincter?

Answer 30

Peristaltic wave

Question 31

What is the esophageal phase controlled by?

Answer 31

Swallowing reflex and enteric nervous system

Question 32

In the esophageal phase, after the bolus enters the esophagus, what reflex closes the sphincter?

Answer 32

Swallowing

Question 33

In the esophageal phase, what pushes the bolus down?

Answer 33

Primary peristaltic wave

Question 34

In the esophageal phase, what happens if the esophagus is still distended (food still in it) after the primary peristaltic wave?

Answer 34

Secondary peristaltic wave

Question 35

Why is esophageal motility needed?

Answer 35

To propel bolus from pharynx into the stomach

Question 36

What is the action of the primary peristaltic contraction?

Answer 36

Creates high pressure area behind bolus

Question 37

What opens as the peristaltic wave and bolus reach it?

Answer 37

Lower esophageal sphincter

Question 38

What is the lower esophageal sphincter mediated by?

Answer 38

Vagus nerve and VIP

Question 39

Why is the bolus allowed to move into the stomach?

Answer 39

Lower pressure than in esophagus

Question 40

What difference is there between the upper and lower esophagus?

Answer 40

Pressure difference

Question 41

Where in the esophagus is pressure lower?

Answer 41

Upper

Question 42

What are the three muscle layers of the stomach?

Answer 42

Outer longitudinal Inner circular Inner oblique

Question 43

What region of the stomach is thin walled?

Answer 43

Orad

Question 44

What region of the stomach is thick walled for stronger contractions?

Answer 44

Caudad

Question 45

The orad stomach relaxes due to

Answer 45

Relaxation of lower esophageal sphincter

Question 46

What does relaxation of the orad stomach do to pressure and volume of the stomach?

Answer 46

Decreases pressure Increases volume

Question 47

What reflex is involved in the relaxation of the stomach?

Answer 47

Vasovagal

Question 48

For the vasovagal reflex, what is carried on the vagal nerve?

Answer 48

Both afferent and efferent limbs

Question 49

Name the three components of gastric motility

Answer 49

Relaxation of orad region Contractions Gastric emptying

Question 50

What is the purpose of contractions in gastric motility?

Answer 50

Reduce bolus size and mix with gastric secretion

Question 51

What do gastric secretion consist of?

Answer 51

HCl and Pepsin

Question 52

Describe the path of the contraction waves of gastric motility (begin and move towards where)

Answer 52

Begin in middle of body Move distally along caudal stomach towards pylorus

Question 53

When waves are propelled back and further decrease particle size, what is this called?

Answer 53

Retropulsion

Question 54

For slow waves, neural input and hormones can't alter frequency, but can alter

Answer 54

Contraction strength

Question 55

Force of contractions can be increased via

Answer 55

PSNS, gastrin, motilin

Question 56

Force of contractions can be decreased via

Answer 56

SNS, secretin, GIP

Question 57

Migrating myoelectric complexes are mediated by

Answer 57

Motilin

Question 58

What causes migrating myoelectric complexes to occur, and how often?

Answer 58

During fasting state at about 90 minute intervals

Question 59

What does gastric emptying consist of?

Answer 59

Chyme entering small intestines

Question 60

How often do slow waves occur in duodenum?

Answer 60

12 per minute

Question 61

How often do slow waves occur in ileum?

Answer 61

9 per minute

Question 62

What coordinates segmentation and peristaltic contractions in the SI?

Answer 62

Enteric nervous system

Question 63

Parasympathetic innervates the SI via what

Answer 63

Vagus nerve

Question 64

Sympathetic innervates SI via

Answer 64

Celiac and superior mesenteric ganglia

Question 65

Parasympathetic innervations will do what to contraction strength?

Answer 65

Increase

Question 66

Sympathetic innervations will do what to contraction strength?

Answer 66

Decrease

Question 67

What muscle do segmental contractions occur in? (SI)

Answer 67

Circular muscle

Question 68

What is the purpose of segmental contraction?

Answer 68

Mix chyme expose to pancreatic enzymes

Question 69

Describe movement of segmental contractions

Answer 69

Back and forth movement to mix, but NO forward movement

Question 70

T/F: Segmental contractions contain forward movement

Answer 70

False

Question 71

What kind of contraction propels chyme toward LI?

Answer 71

Peristaltic contractions

Question 72

What kind of muscle involved in peristaltic contractions?

Answer 72

Circular and longitudinal

Question 73

Where does the contraction occur in relation to the bolus?

Answer 73

Contraction behind bolus, relaxed in front of bolus

Question 74

What kind of cells sense the bolus?

Answer 74

Enterochromaffin cells

Question 75

What triggers the peristaltic reflex for moving chyme?

Answer 75

Bolus sensed by enterochromaffin cells

Question 76

Explain the course of events that trigger the vomiting reflex

Answer 76

Information from vestibular system Back of throat GIT and chemoreceptor trigger zone in 4th ventricle? Vomiting center in medulla Vomiting reflex

Question 77

Explain the events of the vomiting reflex

Answer 77

Reverse peristalsis in SI Relaxation of stomach and pylorus Increased abdominal pressure Movement of larynx up, relaxation of lower esophageal sphincter, closure of glottis Forceful expulsion

Question 78

During retching, what remains closed

Answer 78

Upper esophageal sphincter

Question 79

During retching, what remains open

Answer 79

Lower esophageal sphincter

Question 80

What opens to allow contents from SI into cecum?

Answer 80

Ileocecal sphincter

Question 81

Describe the course of contents through colon

Answer 81

Ascending, transverse, descending, sigmoid colon to rectum and anal canal in ruminants in pigs

Question 82

What do ruminants and pigs have that horses, cats, and dogs don't?

Answer 82

Sigmoid colon

Question 83

Segmentation contraction occurs in which parts of LI?

Answer 83

Cecum and proximal colon

Question 84

Segmentation contractions in cecum and proximal colon are associated with what?

Answer 84

Haustra

Question 85

Define haustra

Answer 85

Saclike segments

Question 86

Do dogs, rats, carnivores, ruminants have haustra?

Answer 86

No

Question 87

Do guinea pigs, rabbits, pigs, humans, monkeys, horses have haustra?

Answer 87

Yes

Question 88

The mass movements in the LI have what goal?

Answer 88

Move contents over long distances

Question 89

How often do mass movements in the LI occur?

Answer 89

1-3 times a day

Question 90

External anal sphincter is _______ contracted until defecation

Answer 90

Tonically

Question 91

What contracts to create pressure on the external anal sphincter?

Answer 91

Smooth muscle

Question 92

Retosphincteric reflex

Answer 92

When internal anal sphincter relaxes when rectum fills

Question 93

Gastrocolic reflex

Answer 93

Distention of stomach increases motility of colon

Question 94

Gastrocolic reflex is afferent where and efferent where?

Answer 94

Afferent in stomach Efferent in colon