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Gastro > GI Motility (Johnson/Costanza) > Flashcards

GI Motility (Johnson/Costanza) Flashcards

1
Q

All contractile muscle in the GI tract is smooth muscle except …

A

pharynx, upper 1/3 esophagus, and external anal sphincter

**these are striated

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2
Q

The smooth muscle of the gastrointestinal tract is _____ smooth muscle, in which the cells are electrically coupled via _____

A

unitary smooth muscle coupled via gap junctions

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3
Q

what is the significance of the gap junctions that connect the smooth muscle of GI tract?

A

allow for low resistance pathways to propagate AP quickly so that there are coordinated contractions

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4
Q

defn tonic vs phasic contractions

A

phasic: period of contraction then relaxation
Tonic: constant low level confraction

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5
Q

in what part of GI tract are tonic contractions found?

A

upper stomach and lower esophageal, ileocecal, and internal anal sphincters

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6
Q

in what part of GI tract are phasic contractions found?

A

esophagus, gastric antrum, and small intestine

***all tissues involved in mixing and propulsion.

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7
Q

are slow waves a type of action potential

A

NO

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8
Q

slow waves are oscillating depolarization and repolarization of _____ in gastric smooth muscle

A

membrane potential

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9
Q

what lags behind the electrical activity of a slow wave?

A

mechanical response (i.e contraction/tension)

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10
Q

what determines the frequency of contraction of GI smooth muscle?

A

freq of AP which is dept on the freq of slow waves

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11
Q

feq of slow waves in stomach

A

3/min

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12
Q

feq of slow waves in duodenum

A

12/min

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13
Q

effect of neuronal input on slow waves

A

not not affect the slow waves!! (they do effect the production of APs and the strength of the muscle contraction)

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14
Q

the “pacemaker of the GI smooth muscle”

A

interstitial cells of Cajal

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15
Q

transmits cyclic depolarizations/respolarization of smooth muscle via gap junctions

A

interstitial cells of Cajal

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16
Q

What is the biochem mechanism behind the sloq waves? (i.e. what ions are involved)

A

depolarization due to Ca influx

repolarization due to K efflux

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17
Q

cyclic depolarizations that do not reach threshhold cause

A

weak tonic contractions (i.e. no relaxation)

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18
Q

depolarizations that achieve threshold result in

A

phasic contraction

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19
Q

what is the result of increasing the number of APs on top of the slow wave depolarization

A

increase the duration of the PHASIC contraction

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20
Q

drives the frequency of slow waves

A

the pacemaker cells (interstitial cells of Cajal)

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21
Q

where are the interstitial cells of Cajal found?

A

myenteric plexus

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22
Q

first steps in the processing of ingested food as it is prepared for digestion and absorption

A

chewing and swallowing

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23
Q

three functions of cheming

A

(1) It mixes food with saliva, lubricating it (facilitate swallowing)
(2) it reduces the size of food particles (facilitates swallowing)
(3) it mixes ingested CHO with salivary amylase to begin CHO digestion

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24
Q

Initiated by food in the mouth. Sensory information is relayed from mechanoreceptors in the mouth to the brain stem which orchestrates a reflex oscillatory pattern of activity to the muscles in the mouth

A

involuntary component of chewing

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25
Q

In involuntary chewing, food in the mouth is detected by… and carried to the …which orchestrates …

A

mechanoreceptors → the brain stem → reflex oscillatory pattern of activity to the muscles in the mouth

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26
Q

can override involuntary or reflex chewing at any time

A

voluntary chewing

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27
Q

in the mouth swallowing is (voluntary or involuntary)

A

voluntary

**from then on down it is involuntary

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28
Q

what controls/coordinates involuntary swallowing

A

swallowing center in the medulla

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29
Q

brain stem controls…

medulla controls…

A

brain stem controls chewing (involuntary)

medulla controls swallowing (involuntary)

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30
Q

in involuntary swallowing, food in the mouth is detected by… and carried by … to the …

A

somatosensory receptors near the pharynx → Vagus and glossopharyngeal (IX and X) → medulla

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31
Q

What are the phases of swallowing? What happens in each?

A

oral → pharyngeal → esophageal

oral: tongue forces a bolus of food back toward the pharynx (where somatosensory receptors are found that will initiate the involuntary swallowing reflex)

pharyngeal:
(1) The soft palate is pulled upward to prevent reflux into the nasopharynx.
(2) The epiglottis moves to cover the opening to the larynx, (∴ breathing is inhibited) and the larynx moves upward against the epiglottis
(3) The upper esophageal sphincter relaxes, allowing food to into the esophagus.
(4) A peristaltic wave of contraction is initiated in the pharynx to propel food through the open upper esophageal sphincter.

esophageal: swallowing reflex closes the sphincter so food cannot reflux into the pharynx and then a primary peristaltic waves propels food along (secondary wave will be initiated if primary does not move all the food)

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32
Q

controls esophageal phase of swallowing

A

swallowing reflex and enteric nervous system

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33
Q

primary vs secondary peristaltic wave

A

Primary is coordinated by the swallowing reflex
Secondary occurs if primary does clear the esophagus of food.
Secondary is mediated by the enteric nervous system and is initiated by the continued distention of food in the esophagus.

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34
Q

initiates the secondary peristaltic wave

A

continued distention of the esophagus by food that was not cleared

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35
Q

how does the primary peristaltic contraction move food down the esophagus?

A

As each segment of esophagus contracts, it creates an area of high pressure just behind the bolus, pushing it down the esophagus. Each sequential contraction pushes the bolus further along. If the person is sitting or standing, this action is accelerated by gravity.

36
Q

What happens as the food bolus approaches the lower esophageal sphinceter

A

Vagus nerve releases VIP (a vasovagal reflex, i.e. afferent and efferent fibers are in the vagus N) → relaxation of lower esophageal sphincter

37
Q

the pressure of the intrathoracic esophagus is equal to

A

the intrathoracic pressure

38
Q

the abdominal pressure is > or < the intraesophageal pressure. Significance?

A

adb > esophagus = the gastic contents will want to travel from high to low pressure (stomach to esophagus)

***Conditions in which intra-abdominal pressure is increased (e.g., pregnancy or morbid obesity) may cause gastroesophageal reflux, in which the contents of the stomach reflux into the esophagus.

39
Q

atmospheric pressure is > or < the intraesophageal pressure. Significance?

A

atm > esophagus = air will want to travel from high to low (atm to esophagus)

40
Q

What prevents gastric contents and air from entering into the esophagus (with their pressure gradients)

A

upper and lower esophageal sphincters

41
Q

What is receptive relaxation? Why is it important?

A

At the same time that the lower esophageal sphincter relaxes, the orad region of the stomach also relaxes. This decreases the pressure in the orad stomach and facilitates movement of the bolus into the stomach.

42
Q

At the lower esophageal sphincter’s resting tone, the pressure at the sphincter is (lower or higher) than the pressure in the esophagus or in the orad stomach.

A

higher

43
Q

describe the muscle layers of the stomach

A

outer longitudinal layer, a middle circular layer, and an inner oblique layer

44
Q

how does the thickness of the muscle wall change?

A

it increases from proximal to distal stomach

45
Q

describe the innervation to the stomach

A
  1. extrinsic innervation by the autonomic nervous system

2. intrinsic innervation from the myenteric plexus and submucosal plexuses

46
Q

What are the anatomic divisions of the stomach

A

fundus, body, antrum

47
Q

___ region of the stomach is proximal and contains …

A

orad region: fundus and proximal portion of the body

48
Q

___ region of the stomach is distal and contains …

A

caudad region: distal portion of the body and the antrum

49
Q

orad or caudad region has thicker wall and stronger contractions. Why?>

A

caudad to mix and propel food into small intestine

50
Q

the orad region relaxes when …

A

the lower esophageal sphincter distends (receptive relaxation, a vasovagal reflex) → mechanoreceptors in stomach sense this and send info to CNS via vagus N → efferent info sent back to stomach smooth muscle via vagus N → post gang release of VIP → smooth muscle of orad relaxes

51
Q

what breaks down bolus into chyme

A

contractions of thick muscular wall of caudal portion of stomach + gastric secretions

52
Q

Gatric contractions … as they approach the pylorus

A

increase in strength

53
Q

what is retropulsion?

A

the wave of contractions in the caudad region also closes the pylorus as they move the bolus down → causes most of the gastric contents to be propelled back into the stomach for further mixing and reduction in size

54
Q

What increases the frequency of action potentials and the force of gastric contractions?

A

parasympathetic stimulation, gastrin, motilin

55
Q

What decreases the frequency of action potentials and the force of gastric contractions?

A

sympathetic stimulation, secretin, and GIP

56
Q

What are migrating myoelectric complexes?

A

during fasting, periodic contractions (every 90 mins) that clear the stomach and small intestines of residual food/chyme products

57
Q

What mediates migrating myoelectric complexes?

A

motilin

58
Q

The rate of gastric emptying must be closely regulated to provide adequate time for …

A
  1. neutralization of gastric H+ in the duodenum (maintain pH)
  2. digestion to appropriate size (< 1mm3)
  3. absorption of nutrients
59
Q

isotonic contents empty (more or less) rapidly than either hypotonic or hypertonic contents

A

more rapidly

60
Q

major factors slow or inhibit gastric emptying

A

presence of fat and low pH

61
Q

if there is high fat content in the stomach, how is gastric emptying time increased?

A

CCK is secreted

  • *the mechanism was not in the book
  • *in duodenum
62
Q

if there is high [H+] in the stomach, how is gastric emptying time increased?

A

H+ receptors activated and relay this information to gastric smooth muscle via interneurons in the myenteric plexus → increased time for bicarb neutralization (why secretin dec force of contractions)
**in duodenum

63
Q

frequency of slow waves in the ileum

A

9 waves/min

64
Q

Parasympathetic innervation of the SI occurs via

A

vagus N

65
Q

Sympathetic innervation of the SI originates in the …

A

celiac and superior mesenteric ganglia.

66
Q

Neurocrines released from parasympathetic peptidergic neurons of the small intestine include:

A

VIP, enkephalins, motilin

67
Q

what type of contraction in the SI mixes chyme

A

segmentation contractions

68
Q

what type of contraction in the SI propels chyme

A

peristaltic contractions

69
Q

where do the contractions occur in segmental vs peristaltic contractions in the SI

A

segmentation: within a bolus or chyme to split it in half (will then relax to allow it to merge back together → repeat)
peristaltic: contractions occur behind chyme and relaxations occur in front → propels it forward

70
Q

he neurotransmitters and involved in the orad contractions in peristaltic contractions of the SI are?
caudad relaxation?

A

ordad contraction: ACh and substance P

caudad relaxation: VIP and NO

71
Q

Where in the brain is the vomiting center?

A

medulla

72
Q

Describe the innervation of the vomiting reflex

A

vestibular system → medulla → throat, GI, chemoreceptor trigger zone in 4th ventricle

73
Q

Describe the motor events of the vomiting reflex

A
  1. reverse peristalsis that begins in the SI
  2. relaxation of the stomach and pylorus
  3. inspiration to increase abdominal pressure
  4. relaxation of the lower esophageal sphincter
  5. forceful expulsion of gastric, and sometimes duodenal, contents
74
Q

What is retching

A

vomiting but the upper esophageal sphincter is closed so the gastric contents return to the stomach

75
Q

After the contents of the small intestine enter the cecum and proximal colon, _____ to prevent reflux into the ileum

A

the ileocecal sphincter contracts

76
Q

___ contractions occur in the cecum and proximal colon are are mediated by ____

A

segmentation mediated by haustra

77
Q

occur in the colon and function to move the contents of the large intestine over long distances, such as from the transverse colon to the sigmoid colon

A

mass movements

78
Q

how frqeuntly do mass movements occur?

A

1-3 times per day

79
Q

makes the fecal contents of the large intestine semisolid and increasingly difficult to move

A

water absorption (in the distal colon)

80
Q

What is the rectosphincteric reflex?

A

As the rectum fills with feces, the smooth muscle wall of the rectum contracts and the internal anal sphincter relaxes

81
Q

why does defecation not occur with the ectosphincteric reflex?

A

the external anal sphincter is still contracted – it is under voluntary control (striated muscle)

82
Q

once the rectum fills to ___% of its capacity, there is an urge to defecate

A

25

83
Q

he intra-abdominal pressure created for defecation can be increased by a

A

valsalva maneuver (expiring against a closed glottis)

84
Q

What is the gastrocolic reflex?

A

Distention of the stomach by food increases the motility of the colon and increases the frequency of mass movements in the large intestine

85
Q

What is the innervation controlling the gastrocolic reflex?

A

The afferent limb in the stomach is mediated by the parasympathetic nervous system.
The efferent limb of the reflex, which produces increased motility of the colon, is mediated by the hormones CCK and gastrin.

Gastro (25 decks)

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