Lecture 38 11/15/23

Question 1

What movements fall into GI tract motility?

Answer 1

-propulsive
-retentive
-mixing

Question 2

What is transit time?

Answer 2

time it takes for ingesta to travel from one portion of GI tract to another

Question 3

What are the functions of GI movements?

Answer 3

-propel ingesta from one location to the next
-retain ingesta at a given site for digestion, absorption, or storage
-break up food material and mix it with digestive secretions
-circulate ingesta so it comes in contact with digestive/absorptive surfaces

Question 4

What are the characteristics of slow waves?

Answer 4

-slow, rhythmic movements
-slow changes in resting membrane potential
-NOT action potentials/do not cause contraction
-frequency varies by location
-determine maximum rate of muscle contractions

Question 5

What are the characteristics of the interstitial cells of Cajal?

Answer 5

-pacemaker cells
-generate slow waves
-form network between smooth muscle layers
-connected by tight junctions

Question 6

What happens when excitatory peptides, like acetylcholine, are released into an area of GI tract?

Answer 6

increase in cell membrane potential and contraction

Question 7

What happens when inhibitory peptides, like norepinephrine, are released into an area of GI tract?

Answer 7

decreased cell membrane potential and no contraction

Question 8

What is the overarching function of propulsive movements?

Answer 8

move food forward through the GI tract

Question 9

What are the characteristics of contraction during peristalsis?

Answer 9

-contractile ring behind bolus
-relaxation of muscle in front of bolus

Question 10

What are the potential stimuli for peristalsis?

Answer 10

-distension of gut
-physical or chemical irritation of gut lining
-strong parasympathetic NS signals

Question 11

What are the functions of mixing movements?

Answer 11

-grinding/mixing food material with digestive enzymes
-allowing food to come in contact with gut mucosa for absorption

Question 12

What are the characteristics of prehension?

Answer 12

-process of getting food into the mouth
-involves coordination of small, voluntary muscles of the face/lips/tongue

Question 13

What are the characteristics of chewing/mastication?

Answer 13

-first act of digestion
-breaks food down small enough to pass through esophagus
-moisten and lubricate food by mixing with saliva

Question 14

What are the four phases of swallowing/deglutition?

Answer 14

-oral preparatory phase
-oral propulsive phase
-pharyngeal phase
-esophoageal phase

Question 15

What are the characteristics of the oral preparatory phase of swallowing?

Answer 15

-voluntary
-food enters oral cavity
-chewing
-bolus formation

Question 16

What are the characteristics of the oral propulsive phase of swallowing?

Answer 16

-voluntary
-tongue elevates and propels bolus to pharynx

Question 17

What are the characteristics of the pharyngeal phase of swallowing?

Answer 17

-involuntary
-bolus in caudal pharynx stimulates mechanoreceptors
-soft palate elevates to seal nasopharynx
-epiglottis covers trachea and stops respiration
-pharyngeal wave occurs as upper esophageal sphincter relaxes/opens

Question 18

What are the characteristics of the esophageal phase of swallowing?

Answer 18

-involuntary
-bolus passes into esophagus
-esophagus contracts sequentially
-lower esophageal sphincter relaxes
-bolus enters stomach

Question 19

What are the three segments of the esophagus?

Answer 19

-upper esophageal sphincter
-body
-lower esophageal sphincter

Question 20

What is primary peristalsis of the esophagus?

Answer 20

-peristaltic wave from pharynx to stomach
-initiated by swallowing

Question 21

What is secondary peristalsis of the esophagus?

Answer 21

secondary wave that occurs if food does not reach stomach following first wave

Question 22

Why is the lower esophageal sphincter typically tightly closed?

Answer 22

prevent gastric reflux

Question 23

What are the characteristics of lower esophageal sphincter relaxation?

Answer 23

-mediated by vasoactive intestinal peptide
-occurs when food bolus distends area just orad to sphincter muscle

Question 24

Why does the stomach have an additional inner oblique layer of muscle?

Answer 24

to help the stomach have more powerful contractions for grinding/mixing food

Question 25

What are the motor functions of the stomach?

Answer 25

-food storage -mechanical breakdown of food/mixing -release of chyme at a controlled rate

Question 26

What type of motility is seen in the proximal region of the stomach (cardia, fundus, first 1/3 of body)?

Answer 26

sustained tonic contractions that allow for storage

Question 27

What type of motility is seen in the distal region of the stomach (distal 2/3 of body, antrum)?

Answer 27

phasic propagating contractions that allow for grinding of food

Question 28

What are the characteristics of the vago-vagal reflex?

Answer 28

-response to presence of food in stomach -leads to gastric hormone release

Question 29

What is the post-prandial period?

Answer 29

digestive period after food intake

Question 30

What occurs directly after food intake?

Answer 30

weak peristaltic waves in the stomach that move the food towards the antrum

Question 31

What happens once food reaches the antrum of the stomach?

Answer 31

-more powerful contractions -shearing/grinding of food particles

Question 32

What happens once food reaches the pylorus?

Answer 32

-pylorus tightens -only small food particles can enter duodenum

Question 33

What factors impact the rate of gastric emptying?

Answer 33

-water content -nutrient composition -nutrient acidity -nutrient osmolality -temperature -intestinal feedback

Question 34

What are the characteristics of the migrating motility complex?

Answer 34

-fasted motility -clears gut of undigested residue -NOT present in cats and rabbits -cycles every 90 minutes -mediated by GI hormone Motilin

Question 35

What are the phases of the migrating motility complex?

Answer 35

-phase 1/slow waves -phase 2/intermittent contractions -phase 3/intense propulsive motility

Question 36

What are the four components of the vomiting/emetic reflex?

Answer 36

-visceral receptors -vagal and sympathetic afferent neurons -chemoreceptor trigger zone -emetic center

Question 37

Which components of the body provide input to the emetic center?

Answer 37

-vagal and sympathetic afferent neurons -chemoreceptor trigger zone -vestibular apparatus -cerebral cortex

Question 38

What are the physical steps of the emetic reflex?

Answer 38

-relaxation of stomach muscles, closing of pylorus, and relaxation of lower esophageal sphincter -contraction of abdominal muscles -expansion of thoracic cavity while glottis remains closed -opening of lower esophageal sphincter

Question 39

Which species are unable to vomit?

Answer 39

-horses -rabbits -rodents

Question 40

Which movements occur in the small intestine during the post-prandial period?

Answer 40

-non-propulsive movement/mixing -propulsive movement

Question 41

What type of fasted motility is seen in the small intestine?

Answer 41

migrating motility complex

Question 42

What are the characteristics of the ileocolic sphincter?

Answer 42

-prevents colonic contents from moving into ileum -ring of circular muscle that is typically closed -peristaltic activity forces sphincter to open and allow ingesta through

Question 43

What are the characteristics of colonic anatomy?

Answer 43

-varies by species/amount of fermentation occurring -some species have haustra/sacculations

Question 44

What are the functions of the colon?

Answer 44

-water and electrolyte absorption -fecal matter storage -fermentation -evacuation of fecal matter

Question 45

What are the characteristics of mixing activity in the colon?

Answer 45

-important for absorption and fermentation -achieved by segmental and longitudinal contraction -can include retropulsion

Question 46

What are the characteristics of mass movements in the colon?

Answer 46

-move feces down the colon -cause urge to defecate -initiation can occur after meals

Question 47

What are the reflexes that initiate mass movements of the colon?

Answer 47

-gastrocolic reflex/distension of stomach -duodenocolic reflex/distension of duodenum

Question 48

What are the characteristics of the internal anal sphincter?

Answer 48

-smooth muscle -normally contracted -responsible for fecal continence -parasympathetic NS relaxes -sympathetic NS contracts

Question 49

What are the characteristics of the external anal sphincter?

Answer 49

-voluntary striated muscle -innervated by pudendal nerve

Question 50

What must occur for defecation to take place?

Answer 50

-relaxation of internal anal sphincter -peristaltic contractions of rectum