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Physiology > GI Motility > Flashcards

GI Motility Flashcards

1
Q

What is the term used to refer to contraction and relaxation of walls and sphincters of GIT?

A

motility

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2
Q

What does motility accomplish?

A
  • propel digesta
  • mixing
  • grinding
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3
Q

Contractile tissue of GIT is composed of?

A
  • smooth muscle
  • striated muscle in pharynx, upper 1/3 of esophagus, external anal sphincter
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4
Q

What is the smooth muscle type of the GIT?

A

unitary smooth muscle

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5
Q

Contraction of circular muscle does what?

A

Shortening of ring of smooth muscle (decrease diameter)

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6
Q

Contraction of longitudinal muscle does what?

A

Shortening in longitudinal direction (decrease length)

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7
Q

What are phasic contractions?

A

Periodic contractions followed by relaxation

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8
Q

Which organs have phasic contractions?

A
  • esophagus
  • gastric antrum
  • small intestine
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9
Q

What do phasic contractions do?

A

mixing and propulsion

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10
Q

What are tonic contractions?

A

maintain a constant level of contraction or tone without regular relaxation

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11
Q

What regions of the GIT have tonic contractions?

A
  • upper region of stomach
  • lower esophagus
  • ileocelcal and internal anal sphincters
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12
Q

What determines the movement of digesta?

A

slow waves of GIT

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13
Q

What are the three functions of chewing (mastication)?

A
  • mix food with saliva to lubricate
  • reduces size of food particles
  • mixes ingested carbohydrates with salivary amylase
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14
Q

Chewing has an involuntary and voluntary component. What initiates the involuntary component?

A

initiated by food in mouth and mechanoreceptors in mouth relay to brainstem

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15
Q

Chewing has an involuntary and voluntary component. What does the voluntary do?

A

can override the reflex chewing of involuntary component at any time

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16
Q

What are the three phases of swallowing (deglutition)?

A
  • oral phase
  • pharyngeal phase
  • esophageal phase
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17
Q

Reflex swallowing is controlled by what?

A

swallowing center in medulla

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18
Q

Is swallowing initially voluntary or involuntary?

A

voluntary

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19
Q

The pharyngeal phase of swallowing has four steps. Describe them.

A
  • soft palate pulled up which narrows passage so bolus can not move to nasopharynx
  • epiglottis covers opening to larynx, larynx moves against epiglottis and covers opening to trachea
  • upper esophageal sphincter opens so food moves from pharynx to esophagus
  • peristaltic wave propels bolus
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20
Q

The esophageal phase of swallowing is controlled by what?

A

swallowing reflex AND enteric nervous system

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21
Q

What is the receptor path for reflex swallowing?

A

receptors near pharynx detect and send info via vagus an gloospharyngeal nerves to swallowing center in medulla

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22
Q

Describe the oral phase of swallowing.

A

tongue forces bolus toward pharynx which has a lot of receptors and triggers involuntary swallowing to start

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23
Q

What is needed to propel bolus from pharynx to stomach?

A

esophageal motility

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24
Q

What are the four steps of esophageal motility?

A

-upper esophageal sphincter open to allow bolus into esophagus, then closes
- primary peristaltic contraction creates high pressure area behind bolus
- as peristaltic wave and bolus reach lower esophageal sphincter, it opens. we also get receptive relaxation of upper region in stomach
- secondary perstaltic wave clears esophagus and any remaining food

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25
Q

The pressure difference between the upper and low esophagus creates the need for what?

A

sphincters

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26
Q

What mediates the opening of the lower esophageal sphincter?

A

vagus nerve and VIP

27
Q

What are the three components of gastric motility?

A
  • relaxation of orad region in stomach
  • contractions reduce bolus size and mix gastric secretions
  • gastric emptying which is when chyme (digests) enters small intestine
28
Q

Gastric emptying has what type of regulation?

A

hormonal regulation

29
Q

What are the three muscle layers of the stomach?

A
  • outer longitudinal
  • middle circular
  • inner oblique
30
Q

What type of innervation is found in the stomach?

A

extrinsic and intrinsic

31
Q

Describe receptive relaxation and its effects.

A
  • relaxation of orad stomach caused by relaxation of lower esophageal sphincter
  • reduces pressure, increases volume of stomach
  • vagovagal reflex involved
32
Q

What are the components of mixing and digestion?

A
  • contractions, mixing in caudad region
  • waves begin in middle of stomach body
  • retropulsion (digesta propelled back)
  • slow waves
  • migrating myoelectric complexes mediated by motilin
33
Q

Slow wave frequency cannot be altered by neural input or hormones, but strength can be. What can cause an increase in strength? Decrease?

A
  • increase force via PSNS, gastrin, motilin
  • decrease force via SNS, secretin, GIP
34
Q

What are the three goals of small intestinal motility?

A
  • mix chyme with enzymes and secretions
  • expose nutrients to intestinal mucosa for absorption
  • propel chyme into large intestine
35
Q

In what part of the small intestine are slow waves more frequent?

A

duodenum

36
Q

What is the parasympathetic innervation of small intestine and its effect?

A

via vagus nerve to increase contraction strength

37
Q

What is the sympathetic innervation of small intestine and its effect?

A

via celiac and superior mesenteric ganglia to decrease contraction strength

38
Q

What nervous system coordinates segmentation and peristaltic contractions of the small intestine?

A

enteric nervous system

39
Q

What is the function of segmentation contraction in small intestine?

A
  • mix chyme (digesta) and expose it to pancreatic enzymes
40
Q

Describe segmentation contractions.

A

back and forth movement to mix, no forward movement

41
Q

What is the function of peristaltic contractions in small intestine?

A

propel chyme toward large intestine

42
Q

Describe peristaltic reflex for moving chyme.

A

bolus is sensed by enterochromaffin cells

43
Q

Why do we need circular and longitudinal muscles working together for peristaltic contractions in the small intestine?

A

contraction is behind bolus, relaxed in front of bolus

44
Q

List the events of vomiting reflex.

A
  • reverse peristalsis in small intestine
  • relaxation of stomach and pylorus
  • increased abdominal pressure
  • movement of larynx up, relaxation of lower esophageal sphincter, closure of glottis
  • forceful expulsion
45
Q

What causes vomiting reflex?

A
  • information from vestibular system, back of throat, GIT and chemoreceptor trigger zone in 4th ventricle which does to vomiting center in medulla to trigger vomiting reflex
46
Q

Describe retching.

A

upper esophageal sphincter remain closed, lower open, contents return to stomach when retch over

47
Q

What are the sac like segments that help with mixing in a side to center fashion?

A

haustra

48
Q

Segmentation contractions occur where?

A

cecum and proximal colon

49
Q

What species do not have haustra?

A
  • dogs
  • rats
  • carnivores
  • ruminants
50
Q

What species do have haustra?

A
  • guinea pigs
  • rabbits
  • pigs
  • humans
  • monkeys
  • horses
51
Q

Haustra is associated with what type of contractions?

A

segmentation contractions

52
Q

What species do not have a sigmoid colon?

A
  • dog
  • cat
  • horse
53
Q

In what species does the ascending colon form a spiral colon?

A

pigs

54
Q

What allows contents to enter the cecum?

A

ileocecal sphincter opening

55
Q

What is the gastrocolic reflex?

A

distension of stomach increases motility of colon

56
Q

What are the mediators of the gastrocolic reflex?

A

CCK and gastrin

57
Q

What is the purpose of mass movements in the large intestine?

A

move contents over long distances for water reabsorption and into rectum

58
Q

What occurs for defecation?

A
  • rectum fills and smooth muscle wall contracts
  • internal anal sphincter relaxes
  • external anal sphincter tonically contracted until defecation, then it relaxes for defecation to occur
59
Q

What is a unique feature of GI smooth muscle?

A

slow waves in GIT

60
Q

Describe slow waves of GIT.

A
  • oscillating depolarization and repolarization of cell membrane potential of smooth muscle cells
  • slow waves may or may not bring cell to threshold for AP to occur
61
Q

What is the origin of slow waves in GIT?

A

interstitial cells of Cajal in myenteric plexus

62
Q

What is the pacemaker for GI smooth muscle?

A

interstitial cells of cajal in myenteric plexus

63
Q

What is the mechanism of the depolarizing phase and maintenance of plateau for slow waves?

A

opening of Ca channels maintain plateau

64
Q

What is the mechanism of the repolarization phase for slow waves?

A

opening of K channels

Physiology (18 decks)

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