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Colin GI > Phys GI Motility > Flashcards

Phys GI Motility Flashcards

1
Q

Where is the Meisner’s plexus located?

A

Meisner’s (aka Submucosal Plexus) is located in the submucosa, deep to the circular smooth muscle layer

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2
Q

Where is the Auerbach’s Plexus located?

A

Auerbach’s (aka Myenteric plexus) is located between the longitudinal smooth muscle layer and the deeper circular smooth muscle layer

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3
Q

What are the Interstitial cells of Cajal?

A

The pacemaker cells, they spontaneously set the slow wave activity of the GI tract

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4
Q

Are slow waves APs?

A

Slow waves are NOT APs

APs occur when the depolarization of the slow wave moves the membrane potential to or above threshold

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5
Q

When does the mechanical response occur in relation to an AP?

A

Mechanical response occurs soon after AP

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6
Q

What are phasic contractions, and which organs display this mechanical motion?

A

Phasic contractions are periodic contractions followed by relaxation

Esophagus, small intestine, antrum of stomach, any tissues involved in mixing and propulsion of

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7
Q

What are tonic contractions, and which structures display this mechanical motion?

A

Maintain a constant level (pressure) of contraction without regular periods of releaxation

Orad stomach, lower esophageal, ileocecal junction, internal anal sphincter

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8
Q

How do you explain a change in force of contraction with slow waves/APs?

A

Slow waves may not reach threshold. Thus no contraction

Slow waves may just reach threshold causing 1-2 APs, causing a weaker force of contraction

Slow waves may exceed the threshold causing several APs to occur, causing a strong force of contraction

The greater the number of APs fired from a slow surpassing threshold, the greater the force of contraction

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9
Q

What signals cause an increase in slow wave membrane potential/number of APs?

A

Acetylcholine (neurotransmitter; parasympathetics)
Stretch receptor activation
Gastrin
Motilin

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10
Q

What signals causea decrease in slow wave membrane potential/number of APs?

A

Norepinephrine (neurotransmitter; sympathetics)
Secretin
GIP

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11
Q

What is the main function of the Mesiner’s plexus?

A

Meisner’s plexus (Submucosal plexus) is primarily responsible for controlling GI secretions and local bloodflow

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12
Q

What is the main function of the Auerbach’s plexus?

A

Auerbach’s plexus (Myenteric plexus) is primarily responsible for GI motility

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13
Q

Is mastication voluntary or involuntary?

A

Mastication is both voluntary and involuntary

There is a mastication reflex

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14
Q

What innervates the muscles of mastication?

A

5th cranial nerve

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15
Q

What are the three motor phases of swallowing?

A 
Oral Phase (voluntary)
Pharyngeal Phase (involuntary)
Esphageal Phase (involuntary)
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16
Q

What happens during the Pharyngeal phase of swallowing?

A 
Soft palate is pulled downward
Epiglottis moves
Upper Esophageal Sphincter relaxes
Peristaltic contractions initiated in the pharynx
Food propelled through UES
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17
Q

Describe the swallowing reflex

A

Afferent signals from the pharynx follow the vagus/glossopharyngeal nerves to the medulla.

Efferent signals from the medulla go back to the pharynx causing initiation of peristalitic waves

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18
Q

What are the 2 forms of esophageal Peristaltic waves?

A

Primary peristalsis - Continuation of pharyngeal peristalsis, controlled by the medulla, requires vagus nerve
- Cannot happen after vagotomy

Secondary Peristalsis - Occurs if primary peristalsis fails. Medulla and ENS involved, but does not require the vagus nerve
- Can happen after a vagotomy

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19
Q

What is the purpose of the UES and LES?

A

UES prevents air from entering the upper esophagus

LES prevents gastric acid from entering the lower esophagus

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20
Q

What is Achalasia?

A

Impaired peristalsis of the esophagus and impairment of LES ability to relax

Causes food to accumulate in the esophagus, resulting in regurgitation and chest pain

Caused by lack of VIP secretion, knockout of ENS, damage to esophageal nerves

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21
Q

What is GERD?

A

Gastroesophageal Reflux Disease

Weakening of the LES, allowing stomach contents into the esophagus, causing irritation (heart burn)

22
Q

What are the regional sections of the stomach?

A 
Cardiac
Fundus
Body
Antrum
Pylorus
23
Q

What do I mean when i say orad vs caudad region?

A

Orad - toward to oral cavity

Caudad - toward the tail

24
Q

What are the three muscle layers of the stomach from most exterior to most interior?

A

Longitudinal
Circular
Oblique

25
Q

How does Receptive relaxation of the stomach work?

A

Vagovagal reflex

Distention causes vagus nerve afferents to brain stem, which send back efferent signal down the vagus nerve again, signaling relaxation of LES and stomach to allow gastric filling

26
Q

How does CCK (cholecystokinin) contribute to relaxation of the stomach?

A

CCK decreases stomach contractions, which promotes gastric distention

27
Q

What part of the stomach primarily does the mixing and digesting, and how does this occur?

A

The caudad region of the stomach does the mixing and digesting

The peristaltic contraction begins in the mid body of the stomach and continues down to the pylorus in a wave.

The contractile force and velocity increase as it approaches the pylorus

Max frequency - 3-5 contractions per min

28
Q

Why do the stomach contents get propelled back after a wave of peristaltic contractions toward the pylorus?

A

The peristaltic wave contraction forces the Pyloric sphincter to close. The wave presses the contents into the closed sphincter, causing it be propelled back into the stomach (retropulsion)

29
Q

What increases the rate of gastric emptying?

A

Decreased distensibility of the orad region of the stomach

Increased force of peristaltic contractions of caudad stomach

Decreased tone of the pylorus

Increased diameter of proximal duodenum

Decreased segmenting contractions of the proximal duodenum

30
Q

How long does gastric emptying normally take?

A

3 hours

31
Q

What factors inhibit gastric emptying?

A

Increased tone of pylorus

Increased distensibility of the orad region

Decreased diameter of the duodenum

Increased amount of segmentation contractions of the duodenum

Decreased force of caudad wave contractions

32
Q

Why would the stomach reduce the time it takes to empty its contents?

A

To give more time for digestion to occur and to allow more time for the the duodenum to neutralize acid from stomach.

33
Q

What is the enterogastric reflex?

A

Negative feedback from the duodenum, slowing the rate of gastric emptying

Acid in duodenum detected by chemoreceptors causes release of secretin, which inhibits gastric motility via Gastrin inhibition

Fats in the duodenum signal the release of CCK and GIP, which inhibit stomach motility

Distension in the duodenum causes the release of an unknown hormone, causing inhibition of gastric motility

34
Q

What is Gastroparesis?

A

Slow emptying of stomach or paralysis of stomach in absence of mechanical obstruction

Associated with diabetes mellitus (mostly type 1)

Can be caused by injury to vagus nerve

Causes fullness, nausea, vomiting, weight loss, abdominal bloating and discomfort

35
Q

What is the Migrating Myoelectric Complex?

A

MMC is a periodic burst of peristaltic movement (causes the rumbling of stomach)

Occur at 90 minute intervals during fasting

The purpose of this is to move larger undigestable material through GI tract

DOES NOT OCCUR DURING FEEDING

36
Q

What is the difference between segmentation contractions and peristaltic contractions?

A

Segmentation generates back and forth movements of chyme

Persitaltic generates propulsion of chyme by reciprocally innervating the circular and longitudinal muscles

37
Q

How does slow wave frequency change over the course of the small intestine?

A

It slows. Dudodenum has the greatest frequency, jejunum is slower, and ileum is slowest

38
Q

What is IPAN and how does it work?

A

Intrinsic Primary Afferent Neuron

Afferent neuron that sends signals from stimulated mucosa

Enterochromaffin cells in the mucosa sense secrete Serotonin (5-HT), which initiates IPANs to conduct the peristaltic reflex

39
Q

What signals initiate excitatory smooth muscle contraction and which initiate inhibition of muscle contraction?

A

Contraction: ACh and Signal P

Inhibition: NO and VIP

40
Q

What signals promote GI motility?

A 
Serotonin
Gastrin
CCK
Motilin
Insulin
41
Q

What signals inhibit GI motility?

A

Glucagon
Norepinephrine/Epinephrine
Secretin

42
Q

How does the vomiting reflex work?

A

Vagus and sympathetic afferents from the stomach and duodenum signal the medulla

Efferent signaling from the medulla causes:

  • Reverse peristalsis
  • Stomach and pylorus relaxation
  • Relaxation of LES
  • Closure of glottis
  • Forced inhalation (increases abdominal pressure)
  • Forced expulsion of gastric contents
  • Movement of larynx
43
Q

What portions of the large intestine does the vagus nerve innervate?

A

Cecum, ascending colon, transverse colon

44
Q

What portions of the large intestine does the Pelvic nerves innervate?

A

S2 - S4

Descending colon, sigmoid colon, rectum

45
Q

What nerve innervates the external anal sphincter?

A

The Somatic Pudendal Nerves

46
Q

How does the rate of Large Intestine Motility affect the state of fecal matter?

A

More rapid movement of large intestine causes reduced reabsorption of fluids, resulting in diarrhea

Slower movement of colon causes increased reabsorption of fluids, resulting in hard feces and constipation

47
Q

What is the rectosphinteric reflex?

A

As large intestine distends with feces, the internal anal sphincter relaxes, preparing for defecation

48
Q

What is Hirschprung Disease?

A

Ganglion cells absent from segment of colon

Causes constriction (inability to relax colon, loss of coordianted movements) and accumulation of fecal matter in colon

Like achalasia, but of the colon not the esophagus

49
Q

What is the intestino-intestinal reflex?

A

Inhibitory reflex. If part of small intestine is distended, it inhibits GI motility

50
Q

What is the Gastroileal reflex?

A

Gastric distention causes the ileocecal junction to relax, promoting movement of small intestine contents into large intestine

51
Q

What is the Gastrocolic Reflex?

A

Distention of stomach promotes GI motility

52
Q

What is Duodenocolic reflex?

A

Distention of duodenum promotes GI motility

Colin GI (10 decks)

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