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GI Final - MSI Spring > GI Motility class > Flashcards

GI Motility class Flashcards

1
Q

What do circular muscle contractions decrease?

A

diameter of the segment

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2
Q

What do longitudinal muscle contractions decrease?

A

the length of the segment

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3
Q

Esophagus, stomach (antrum), small intestine and all tissues involved in mixing and propulsion have what type of muscle contractions?

A

phasic

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4
Q

What are slow waves?

A

are depolarization and repolarization of the membrane potential
originates in the interstitial cells of Cajal

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5
Q

NE (increases/decreases) the amplitude of slow waves

A

decreases

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6
Q

Where is the swallowing center located?

A

in the medulla

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7
Q

Food in the mouth is detected by somatosensory receptors near ______

A

the pharynx

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8
Q

Afferent info from the mouth is carried to the medulla via what nerves during the swallowing reflux?

A

vagus and glossopharyngeal nerves

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9
Q

In the circuit involved in the swallowing reflex, what do the efferent signals connect to?

A

input to striated m of the pharynx and upper esophagus

*Food in pharynx-> afferent sensory input via vagus/gloss->swallowing center (medulla)->brain stem nuclei->efferent input to pharynx

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10
Q

Describe the oral phase during swallowing

A

the only voluntary phase
striated m
tongue forcing bolus towards pharynx which contains high density of somatosensory receptors

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11
Q

What receptors initiate the involuntary swallowing reflux in the medulla?

A

somatosensory receptors

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12
Q

Is the pharyngeal phase voluntary or involuntary? what type of muscle is involved?

A

involuntary

straited m - pharynx and upper part of esophagus

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13
Q

What are the actions during pharyngeal phase?

A

Passage of food through pharynx into esophagus
soft palate rises and closes of nasopharynx
epiglottis covers opening of larynx
UES relaxes
Swallowing reflex inhibits respiratory center
ends with peristaltic wave initiated in pharynx

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14
Q

The esophageal phase is controlled by what 2 things?

A

swallowing reflex - responsible for closing UES

and ENS

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15
Q

During the esophageal phase, there are two types of peristaltic waves. Describe the primary peristaltic wave

A

Continuation of pharyngeal peristalsis
controlled by medulla
CANNOT occur after vagotomy

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16
Q

During the esophageal phase, there are two types of peristaltic waves. Describe the secondary peristaltic wave

A

Occurs if primary contraction fails to empty the esophagus or when gastric contents reflux into the esophagus
induced by distention
repeats until bolus gone
Swallowing center and ENS involved
Can happen in absence of oral and pharyngeal phases and after vagotomy

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17
Q

Mid and lower esophagus consists of _____ muscle and are strongly controlled by what?

A

smooth

vagus nerves that act through the myenteric nervous system

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18
Q

If vagus nerve is cut, how can secondary peristaltic waves occur?

A

myenteric plexus becomes excitable enough after several days to cause 2ndary waves

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19
Q

When does gastroesophageal reflux occur?

A

when intra-abdominal pressure is increased

seen in obesity and pregnancy

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20
Q

What three parts of the upper GI tract are above atmospheric pressure and why?

A

UES and LES - High pressure because they are closed
Below the diaphragm (pressures in the body of the esophagus are similar to those within the body cavity in which the esophagus lies)
Fundus - because there is some contraction

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21
Q

The intrathoracic location of the esophagus poses a challenge. Keeping air out of the esophagus at the upper end and keeping acidic gastric contents out of the lower end. How are the problems solved?

A

both UES and LES are closed, except when food bolus is passing from pharynx to esophagus to stomach

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22
Q

The opening of the LES is mediated by what?

A

peptidergic fibers of the vagal nerve

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23
Q

How does the vagal input on the LES relax the sphincter?

A

release of vasointestinal peptide (VIP)

Role of nitric oxide (NO) a neurotransmitter involved in relaxation of LES has been proposed

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24
Q

Gastroesphageal reflux disease (GERD) happens in 1/10 people. What happens with GERD and what are some symptoms?

A

Abnormal relaxation of LES
Backwash of acid, pepsin, and bile into esophagus
Heartburn, chest pain, dysphagia, acid reflux,

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25
Q

What can GERD lead to?

A

stricture of esophagus
Asthma
Chronic sinus infection
Barrett’s esophagus

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26
Q

What is achalasia?

A

Impaired peristalsis
Lack of LES relaxation during swallowing and back up of food
Causes: lack of VIP or enteric system has been knocked out
Elevation of LES resting pressure
Damage to nerves maybe due to immune system
WEIGHT LOSS occurs!

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27
Q

What happens during receptive relaxation in the orad region of the stomach?

A

to receive the food bolus in the stomach the pressure decreases and the volume of the orad region increases
Vagovagal reflux

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28
Q

Describe the activity in the orad region of the stomach

A

Minimal contractile activity
little mixing of ingested food
CCK decreases contractions and increase gastric distensibility

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29
Q

In what region of the stomach is most of the mixing and digestion of food is taking place?

A

caudad region

30
Q

What happens during the primary contractile even in the caudad region of the stomach?

A

From mid stomach to pylorus there are peristaltic contractions. as the contractions approach the pylorus, they increase in both force and velocity (max freq 3-5 w/m)
the phase lag decreases as the wave approaches the antrum
the wave of contraction closes the pylorus and gastric contents are propelled back to stomach (retropulsion)

31
Q

What is the effect of parasympathetic and sympathetic stimulation on gastric contractions during mixing and digestion of food? WHat other hormones have the same effects?

A

PS - via vagus, increases AP and force of contractions
Gastrin and motilin - similar to PS

SP - decreases AP and force
Secretin and GIP

32
Q

What is the rate of gastric emptying increased by?

A

decrease distensibility of the orad
increase force of peristaltic contractions of caudad stomach
decrease tone of pylorus
increase diameter and inhibition of segmenting contraction of prox duodenum

33
Q

How long does gastric emptying take?

A

3 hours

34
Q

Why is gastric emptying closely regulated?

A

to provide adequate time for neutralization of gastric H in the duodenum and sufficient time for digestion and absorption
receptors lie in small intestines

35
Q

What are factors that inhibit gastric emptying?

A

relaxation or orad
decrease force of peristaltic contractions
increase tone of pyloric sphincter
segmentation contractions in intestine

36
Q

Info from the duodenal receptors to the gastric sm m is carried by neurons of what?

A

submocosal and myenteric plexuses - respond to physical and chemical properties

37
Q

What are H+ inhibitory effects mediated by?

A

intrinsic neural reflex involving interneurons in the myenteric plexus

38
Q

What is gastroparesis?

A

Slow emptying of stomach/paralysis of stomach
20% of type 1 diabetics
Damage to vagus n. - idiopathic and HBG
Symptoms fullness, weight loss, nausea, vomiting

39
Q

Large particle of undigested residue remaining in stomach are emptied by what?

A

migrating myoelectric complexes
motilin
90 min intervals
feeding inhibits MMCs

40
Q

Absence of MMCs in stomach have been associated with what?

A

gastroparesis

41
Q

Segmentation contractions serve to…..

A

mix the chyme and expose it to pancreatic enzyme and secretions
produces no forward, propulsive movement along small intestine (back and forth)

42
Q

Peristaltic contractions serve to ….

A

propel the chyme towards the large intestines

43
Q

How do peristaltic contractions work?

A

Behind bolus: circular m contracts and longitudinal m relaxes
In front: circular m relaxes and longitudinal m contracts
work in opposition
are reciprocally innervated

44
Q

Slow waves in stomach can induce a weak contraction. slow waves in the intestines ….

A

DO NOT initiate contractions and spike potentials (AP) are necessary for muscle contractions to occur
Slow wave freq sets max freq of contractions

45
Q

There is a gradient in the maximal frequency of the contractions along the SI. What are the slow wave freqs?

A

duodenum - 12 c/m
jejunum - 10 cycles/m
ileum - 8 c/m
Decrease in freq towards the ileocecal junction

46
Q

From the stomach, what is released to initiate the peristaltic reflex in SI?

A

serotonin (5-HT) is released by ECCs and binds to receptors in IPANs which then initiate the relfex

47
Q

What hormones can stimulate contractions in the SI?

A 
serotonin (stored in large quantities in small bowel)
Certain PGs
Gastrin
CCK
motilin
insulin
48
Q

What hormones can inhibit contractions in the SI?

A

epinephrine, released from adrenal glands
secretin
glucagon

49
Q

What coordinates the vomit reflex?

A

medulla

vagal and sympathetic afferent nerve fibers

50
Q

What are the order of events of vomiting reflex?

A 
reverse peristalsis in SI
relaxation of stomach and pylorus
forced inspiration to increase abdominal pressure
movement of larynx
relaxation of LES
closure of glottis
forceful expulsion
51
Q

What allows flow of contents from ileum into colon?

A

distention of ileum causes relaxation of sphincter

52
Q

What prevents passage of contents from colon to ileum ?

A

distention of colon causes contraction of sphincter

53
Q

What are the main functions of lg intestine?

A

absorption of water and vitamins and conversion of digested food into feces

54
Q

Where is the ENS of the lg intestine concentrated?

A

beneath teneae

55
Q

What is the PNS of the colon?

A

vagus nerve and pelvic nerves

56
Q

What is the SNS of the colon?

A

SMG, IMG,
hypogastric plexus: distal rectum and anal canal
Somatic pudendal nerves: external anal sphincter

57
Q

What are the major excitatory mediators?

A

ACh and substance P

58
Q

What are the major inhibitory mediators?

A

VIP and NO

59
Q

Where does segmentation contractions occur in lg intestine?

A

cecum and ascending colon

appear, disappear, and form again at another location w/i lg intestine

60
Q

What do mass movements do in lg intestines?

A

move content over long distances and stimulate defecation reflex

61
Q

What does poor motility of lg intestine cause?

A

greater absorption and hard feces in transverse colon and cause constipation

62
Q

Rectum is usually (full/empty)

A

empty

63
Q

Frequency of segmentation contractions in rectum’s upper region (greater than\less than) sigmoid colon

A

greater than

64
Q

What is the rectosphincteric reflex?

A

as rectum fills, sm m wall of rectum contracts and internal anal sphincter relaxes
Controlled partly by ENS
Reinforced by neurons in spinal cord

65
Q

Why does the rectosphincteric reflux not result in defecation?

A

voluntary external anal sphincter by puborectalis m

66
Q

What is the gastroileal reflex?

A

(gastroenteric)

gastric distention relaxes ileocecal spincter

67
Q

What is the gastro and duodeno-colic reflexes?

A

distention of stomach/duodenum initiates mass movments (ANS)

68
Q

What type of reflex is the ileocelcal sphincter?

A

intestino-intestinal reflex (short reflex)
generally inhbitory
involving only ENS

69
Q

What is hirschsprung disease?

A

megacolon
ganglion cells absent
VIP levels low - Sm m contstriction, loss of coordinated movement
Present at birth
No bowel movment
Jaundice, vomit, poor feeding, swollen belly
Tx: remove colon w/o ganglia

70
Q

What is diverticular disease?

A

small sacs of intestinal lining that bulge outward at weak spots
excess pressure in colon
Can occur anywhere in colon (descending colon)
If diverticulum becomes infected = diverticulitis
Symp: abdominal pain, swelling, bloating, diarrhea
Increases with age (about 50% > 60 and ~100% > 80)
Tx: dietary and lifestyle interventions

GI Final - MSI Spring (11 decks)

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