GI Motility - Fan 2/18/16

Question 1

role of organ in digestion/motility:

mouth

Answer 1

chewing/mastication

Question 2

role of organ in digestion/motility:

esophagus

Answer 2

swallowing

Question 3

role of organ in digestion/motility:

stomach

Answer 3

digestive period: receptive relaxation, accomodation, gastric emptying

interdigestive period: MMC (migrating myoelectric complexes)

Question 4

role of organ in digestion/motility:

small intestine

Answer 4

digestive period: segmentation (for optimal digestion/abs)

interdigestive period: peristalsis (MMC)

Question 5

role of organ in digestion/motility:

large intestine

Answer 5

haustral shuttling (storage of feces)

mass movement (defecation)

Question 6

role of organ in digestion/motility:

rectum

Answer 6

defecation

Question 7

organs involved in function:

mechanical digestion/breaking food down into smaller particles

Answer 7

mouth

stomach

Question 8

organs involved in function:

storage

Answer 8

stomach

small intestine

Question 9

organs involved in function:

mixing of luminal contents

Answer 9

mouth

stomach

small intestine

Question 10

organs involved in function:

housekeeping

Answer 10

stomach, small intestine: MMC

large intestine: defecation

Question 11

“aboral”

Answer 11

downward

onward

orthograde

Question 12

resident and transit time through GI tract

Answer 12

• mouth/esoph: seconds
• stomach/sm int: DIGESTIVE PERIODS
  
  • ​stomach: 2-4h
  • sm intestine: 2-4h
• stomach/sm int: INTERDIGESTIVE PERIOD
  
  • ​empty stomach/sm int: migrating myoelectric complex cycles (approx 1.5h/cycle) for 10-18 hours
• large intestine: 42-52 hours (8-12h min)
  
  • defecation: seconds-minutes

Question 13

SWALLOWING

phases

organs involved

Answer 13

1. oral phase: involuntary or voluntary control
2. pharyngeal phase: involuntary reflex
3. esophageal phase: involuntary reflex

mouth, pharynx, esophagus, stomach, resp system - actions coordinated by CNS

Question 14

key events of swallowing

Answer 14

• pharynx rapid sequential contraction
• upper eso sphincter relaxes, then contracts
• esophageal slow peristaltic wave
• lower eso sphincter relaxes, then contracts
• fundus and body of stomach relax: happens early on in swallowing, in prep to receive bolus

Question 15

what happens when primary eso peristalsis fails?

Answer 15

if something gets stuck in esophagus, secondary eso peristalsis takes over, starting a contractile/peristaltic wave just above the stuck bolus (not all the way up at the upper eso sphincter!)

Question 16

LES overshooting

Answer 16

lower eso sphincter contraction aims to prevent reflux

Question 17

general mechanisms to prevent reflux

Answer 17

• high tone of lower eso sphincter
• secondary eso peristalsis (acitvation of chemoreceptors)
• pinching of LES by diaphragm
• 2 reflexes
  
  • LES contracts in response to gastric pressue increase and abd pressure increase

*

Question 18

mechanisms to prevent reflux: infants

Answer 18

only have pinching of LES by diaphragm as anti-reflux mechanism

• have to be careful squeezing babies, also have to burp them to decrease the pressure/volume of stomach post meal

Question 19

mechanisms to prevent reflux: pregnant women

Answer 19

only have secondary peristalsis as anti-reflux mechanism

• LES tone knocked out by hormonal changes
• diaphragm elevated due to pregnancy
• gastric/abd pressure constantly elevated due to preg: hard to activate the pressure reflexes

Question 20

problems with LES contraction

Answer 20

insufficient/weak: GERD

• heartburn

excessive/strong: esophageal achalasia

• overactive, excitatory neurons
• abnormal muscle overgrowth
• difficulty swallowing

Question 21

roles of stomach (and its parts) in gastric motility

Answer 21

DIGESTIVE PERIOD

• proximal stomach: storage
  
  • receptive relaxation (during swallowing)
  • accomodation (significant increase in volume without huge wall tension increase due to elasticity of sm muscle)
• distal stomach: mixing/grinding
  
  • mixing, size reduction, emptying via contraction

INTERDIGESTIVE PERIOD

• housekeeping

Question 22

gastric contractions during digestive period

Answer 22

serve the function of mixing, size reduction, and emptying via…

• propulsion: mixing/size red, emptying 0-3.7x/min
• antral systole: grinding, shearing, retropulsion for net effect of mixing/size red

Question 23

control of gastric emptying

Answer 23

promoted by

• proximal stomach tone
• distal stomach peristalsis

inhibited by

• pyloric sphincter tone
• duodenal contraction

Question 24

gastric emptying: stomach

Answer 24

• food enters stomach, triggers stomach distension, stretch receptors hit vagal afferent-CNS-vagal efferents which come through and release Ach and gastrin
• also, peptides/a.a.s trigger gastrin secretion
• in total, stomach contraction triggered

Question 25

gastric emptying: duodenum

Answer 25

* presence of acid → secretin production * presence of FAs, a.a.s/peptides → CCK production * presence of glucose → GIP production all three of these neuroendrocine secretions will have joint effect of... 1. duodenal contraction 2. inhibition of gastrin secretion [either directly or through somatostatin] contraction of the duodenum, in turn, triggers stretch receptors in duodenum for joint effect of... 1. duodenal contraction 2. inhibition of stomach contraction

Question 26

interdigestive period: "housekeeping"

Answer 26

**migrating myoelectric complexes** [as compared to digestive motility] * stronger * intermittent/in waves [vs. constant] * pylorus is open [vs. closed or close to it] * sm intestine undergoes peristalsis [vs segmentation - slow, nonperistaltic] * fx: remove undigestible material and prevent bacterial growth [vs. optimize digestions/abs] * mediated by **motilin**

Question 27

pyloric contraction

Answer 27

pylorus kept small during digestive period because you **don't want everything emptying into small intestine all at once** * ​clinically: dumping syndrome

Question 28

small intestinal motility | (muscles and functions)

Answer 28

1. **muscularis externa:** intraluminal mixing and propulsion via _segmentation_ to optimize digestion/abs. also _housekeeping via MMC_ 2. **muscularis mucosae, villus muscle:** facilitate _absorption_ and _lymph flow_

Question 29

segmentation

Answer 29

aka slow movement main fx: **separation and recombo of chyme boluses** _​effects two means of digestion_ * **luminal digestion:** mixing of chyme with secretions (enzymes, alkaline fluid, bile) * **membrane digestion:** moving chyme to cell membranes toward... * digestive enzymes: membrane digestion * transporters/carriers: **absorption**

Question 30

ECA

Answer 30

**electrical control activity** (unique to gut smooth muscle) * aka: slow waves, basal electric rhythm * origin: pacemaker cells (interstitial cells of Cajal, ICC) * made spontaneously, constantly * conducted to smooth muscle cells via gap jx * modulated (not originated) by motor neurons in muscle and by endocrine secretions

Question 31

frequency of ECAs in GI tract

Answer 31

stomach: 3.7 x/min duodenum: 12 x/min ileum: 10 x/min colon: 3 x/min

Question 32

ECA action potential events

Answer 32

1. **depolarization:** Na, Ca influx 2. **plateau phase:** Na, Ca influx; K efflux 3. **repolarization:** K efflux large ECAs with spike potentials cause muscle contraction = **ERA: electric response activities** * excitatory neuroendocrine factors can lead to higher levels of Ca, spike potentials

Question 33

modulation of ECAs by neuroendocrine factors

Answer 33

**excitatory factors:** Ach, gastin **inhibitory factors:** norepi, nitric oxide

Question 34

relationship between ECAs and ERAs

Answer 34

and ERA is an ECA that is strong/spiked enough to actually initiate contraction * excitatory mediators increase ERA/ECA ratio * inhibitory mediates decrease ERA/ECA ratio

Question 35

neuroendocrine control of peristalsis

Answer 35

peristalsis involves circular and longitudinal muscle layers oppositely relaxing/contracting * **constricted** part of tract * inhibitory neuroendocrine activity/**relaxation of longitudinal m** * excitatory neuroendocrine activity/**contraction of circular m** * **relaxed** part of tract * inhibitory neuroendocrine activity/**relaxation of circular m** * excitatory neuroendocrine activity/**contraction of longitudinal m**

Question 36

how is peristaltic motility coordinated?

Answer 36

**interneurons** * presence of bolus triggers receptors that communicate with interneurons * distension triggers baroreceptors * content might also trigger osmoreceptors, chemoreceptors * interneurons communicate with motor neurons * proximal motor neurons: excitatory neuroendo: **contraction** * distal motor neurons: inhibitory neuroendo: **relaxation** generates a pressure gradient for the bolus to move down

Question 37

describe the various contractile behaviors associated with physiological states of * segmentation * MMC * diarrhea/vomiting

Answer 37

* _segmentation_: short distance propulsion * _MMC_: intermed distance propulsion * _diarrhea/vomiting_: long distance propulsion (opposite directions)

Question 38

reflexive relaxation/contraction of ileocecal sphincter

Answer 38

relaxes/contracts based on distention of regions immediately proximal and distal * distention in distal ileum leads to sphincter relaxation * movement of chyme into cecum * distention in proximal cecum leads to sphincter constriction * prevents reflux

Question 39

overview of large intestinal motility

Answer 39

1. **haustral shuttling** (segmenting, nonperistaltic contractions) to slow fecal stream 2. **reabs** of water and electrolytes (700mL water into cecum, all but 100-300 reabs) 3. periodic **peristalsis** to move feces along 4. rare **mass movement** to move stool into rectum 5. **defecation** (100-300mL) if defecation does NOT occur - get retrograde propulsion!

Question 40

reflexes involved in defecation

Answer 40

1. **involuntary:** stool distends rectum 2. **involuntary:** reflexive contraction of rectum, relaxation of int anal sph, contraction of ext anal sph: movement of stool into anal canal 3. brain receives signals of awareness, which then makes it your **voluntary** call to hold off (contract EAS) or defecate (relax EAS)

Question 41

constipation factors and mechanisms: ## Footnote **diet low in insoluble fiber**

Answer 41

* insufficient stim of baroceptors * loss of benefical microbes that come with a high fiber diet

Question 42

constipation factors and mechanisms: ## Footnote **insufficient fluid intake**

Answer 42

* lack of baroceptor stimulation [low volume] * dry feces

Question 43

constipation factors and mechanisms: excessive delay of defecation

Answer 43

* dry feces (excessive reabs?) * low stim of baroceptors [low volume]

Question 44

constipation factors and mechanisms: ## Footnote **narcotics**

Answer 44

* inhibition of fluid secretion, leading to low stim of baroceptors [low vol] * increased sphincter tone

Question 45

constipation factors and mechanisms: ## Footnote **physical inactivity**

Answer 45

* decreased baroceptor stim due to decreased food intake * decreased GI neuroendo secretion (associated with exercise)

Question 46

constipation factors and mechanisms: ## Footnote **antibiotics**

Answer 46

* disruption of microbiome and associated ENS activities

Question 47

constipation factors and mechanisms: ## Footnote **old age**

Answer 47

combination of * reduced food intake * reduced ENS neuroendo activity, physical activity

Question 48

gastroileal reflex

Answer 48

stimulatory * entry of food into stomach → relaxation of ileocecal sph, emptying of ileum

Question 49

gastrocolic reflex duodenalcolic reflex

Answer 49

stimulatory * entry of food into empty stomach **or** chyme into duodenum → increases aboral propulsive movement in colon

Question 50

colonocolonic reflex

Answer 50

stimulatory * distention in one part of colon → relaxation of another part * ultimately favors aboral movement

Question 51

duodenogastric reflex

Answer 51

inhibitory, physiological * duodenal distension → delayed gastric emptying

Question 52

ileogastric reflex

Answer 52

inhibitory, physiological * distention of ileum → delayed gastric emptying

Question 53

intestinointestinal reflex

Answer 53

inhibitory * overdistention of one part of intestine → general inhibition of instestinal muscle activity

Question 54

colonic-intestinal reflex

Answer 54

inhibitory * overdistention of colon → general inhibition of intestinal muscle activity

Question 55

peritoneo-intestinal reflex

Answer 55

inhibitory * handling of GI tract during surgeries and/or intestinal irrigation → general inhibition of intestinal muscle activity

Question 56

adynamic ileus

Answer 56

occurs due to * obstruction * bacterial overgrowth * abdominal surgery results in triggering of **intestino-intestinal reflex, colonic-intestinal reflex, peritoneo-intestinal reflex** which is why you ask patients to fast until GI motility is regained!