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SMP - GI > Lecture 2 - Motility > Flashcards

Lecture 2 - Motility Flashcards

1
Q

What is the special type of motility of the interdigestive state? Describe it.

A

Migrating myoelectric complex (MMC) = housekeeping wavelike sequential contractions to sweep undigested material and bacteria into colon active from mid-stomach through terminal ileum

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2
Q

When does the interdigestive state occur?

A

3-4 hours after eating, when the food is past the upper GIT and in the ileum or lower

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3
Q

Describe the phases of the migrating myoelectric complex.

A

4 phases lasting a total of 75 to 120 minutes:

  • Phases I, II, and IV have minor and disregulated contractions
  • Phase III contractions last 10 min/cycle but these sweep material lower in the GIT
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4
Q

What is phase III of the MMC stimulated by?

A

Stimulated by motilin, secreted into blood from the M cells of the duodenum

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5
Q

What allows the enterocytes to be viable for longer?

A

MMC

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6
Q

Describe swallowing.

A
  • Starts as voluntary action with the skeletal muscle in the mouth and pharynx
  • Continues as involuntary action as soon as bolus enters the esophagus as the enteric and ANS systems take over
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7
Q

What are the 2 types of esophageal propulsions? Describe each.

A
  1. Primary esophageal peristalsis: caused by the medullary swallowing center, more of an extrinsic effect due to vagal innervation (ENS is also helping, but not main mechanism)
  2. Secondary esophageal peristalsis: more of an intrinsic effect due to local ENS (but vagus can help) stimulation of salivation and mucus secretions to lubricate stuck bolus of food and contractions
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8
Q

Can smooth muscle disorders in the GIT affect the enteric nerves? Example?

A

YUP

Achalasia: smooth muscle disorder in the lower esophageal sphincter which cannot relax making it hard for food to be propelled to stomach => esophagus dilates => very painful to eat and patients often become anorexic

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9
Q

Achalasia treatment? Side effect? Treatment for side effect?

A

No pharmacological treatment, but we can clip the esophageal sphincter to make it floppy

Side effect: GERD, which can be treated with H2 antagonist to lesser the HCl secretion in the stomach to avoid erosion of the esophagus

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10
Q

What does GERD stand for?

A

Gastroesophageal Reflux Disease

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11
Q

What is gastric accommodation? What to note?

A

As food enters the stomach it will expand and relax due to vagal stimulation causing VIP release so that intraluminal pressure will not increase until 1 L as entered the stomach

This also happens in the duodenum to a certain extent

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12
Q

Other name for gastric accommodation?

A

Receptive relaxation

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13
Q

Describe bariatric surgery.

A

Goal is to reduce the ability of the stomach to accommodate food

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14
Q

What is the antrum?

A

Narrowing of stomach proximal to the pyloris

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15
Q

What helps break down the chyme in the stomach?

A

Contractions of the stomach push the chyme against the antrum, so the chyme will retropulse and break down

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16
Q

What is the rate of gastric emptying dependent on? Describe this.

A

Depends on the types of nutrients in the stomach:

  • Saline meal fastest: carbohydrates
  • Acid meal: proteins need to be broken down by gastric proteases
  • Oleate meal slowest: lipids because small intestine needs more time to get ready to emulsify these
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17
Q

How are contractions generated in the GIT? Is this similar to how contractions are generated in other areas of the body?

A

Different way than from other areas of the body:

  1. RMP is in the form of slow waves = basic electrical rhythm
  2. Various factors cause depolarization of smooth muscle cells
  3. At threshold (-40 mV) spike potentials are generated on top of the slow waves
  4. Ca++ influx in smooth muscle cells through VG channels to bind to calmodulin
  5. Contraction of smooth muscle cells
  6. Plateau due to slow movement of Ca++ and Na+
  7. Repolarization due to delayed increase in K+ conductance
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18
Q

What does the strength of GIT contractions depend on?

A

Depends on the max rate of contractions => depends on max number of spike potentials generated => depends on the basic electrical rhythm of that portion of the GIT

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19
Q

Are spike potentials action potentials?

A

YUP

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20
Q

Is the rate of slow waves aka the basic electrical rhythm the same throughout the GIT?

A

NOPE

Stomach: 3/min
Small intestine: 10-12/min

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21
Q

What causes depolarization of the smooth muscle cells of the GIT?

A
  1. Stretch
  2. ACh from parasympathetic NS
  3. Gastrin from duodenum and antrum
  4. Serotonin
  5. Substance P
  6. Motilin
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22
Q

Other name for substance P?

A

Tachykinin

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23
Q

What causes hyperpolarization of the smooth muscle cells of the GIT? Are these secreted locally or from extrinsic factors?

A
  1. NE
  2. Sympathetics
  3. VIP
  4. NO

Secreted LOCALLY by interneurons

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24
Q

What does VIP stand for?

A

Vasoactive intestinal peptide

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25
Q

2 types of motility in the small intestine? Can both be seen at different areas of the GIT? Which one is more prominent?

A
  1. Peristalsis
  2. Segmentation***

YUP

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26
Q

Describe peristalsis.

A

Circular muscle of the GIT will relax ahead of the bolus and contract behind it due to signals from cholinergic motor interneurons (contraction) and VIP motor interneurons (relaxation)

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27
Q

What happens during vomiting?

A

Reverse peristalsis

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28
Q

Is segmentation or peristalsis more under intrinsic control? What about extrinsic?

A

Segmentation: intrinsic
Peristalsis: extrinsic

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29
Q

Describe segmentation.

A

Contractions of CIRCULAR muscle are generated on either side of the bolus causing both mixing and propulsion and move down the GIT forming different pockets of bolus

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30
Q

Purpose of gallbladder?

A

It concentrates bile and then contracts to release bile into the duodenum to facilitate lipid absorption

31
Q

Regulation of gallbladder?

A
  1. Vagal stimulation mildly relaxes the sphincter of Oddi from gallbladder into duodenum at the beginning of digestion
  2. CCK released in blood + vagal stimulation later in digestion stimulate gallbladder contraction and full relaxation of the sphincter of Oddi
32
Q

What happens to fats in the duodenum?

A

Emulsification and digestion

33
Q

What happens to fats in the jejunum?

A

Micelle formation and absorption

34
Q

What does CCK stand for?

A

Cholecystokinin

35
Q

Motility in the large intestine? Describe each. Which is the predominant form of propulsion?

A
  1. *****Segmental propulsion = taneia coli contract to make sacs (haustrae) in the colon
  2. Mass movements = peristaltic contractions stimulated by GI hormones and vagus nerve in response to chyme in the upper GIT
36
Q

Speed of segmental propulsion in large intestine?

A

SLOW

37
Q

What are the taneia coli?

A

3 bands of longitudinal smooth muscle in the large intestine

38
Q

Which 2 GI hormones stimulate mass movements in the colon?

A
  1. Gastrin

2. CCK

39
Q

Timing of mass movements in the colon? What is this called? Describe it.

A

Gastrocolic reflex = occurs after feeding:

Chyme in the stomach stimulates colonic mass movements through the stimulation of the PNS and gastrin, both of which are stimulated very early in feeding => these both stimulate depolarization of slow waves lower in the GI tract (ileum, ascending and transverse colon), initiating peristaltic-type movements => chyme (and feces) move out of the lower GI tract

40
Q

Where does the vagus innervation end?

A

Proximal 2/3rds of transverse colon = end of midgut

41
Q

What typically stimulates the defecation reflex?

A

Mass movements in colon cause the haustrae to smooth out into a tube and the feces to descend from the colon to the rectum => rectal stretch => mechanoreceptors activate the ENS => signal to the brain with urge to defecate + relaxation of internal rectal sphincter => voluntary contraction of external rectal sphincter => over time the urge to defecate goes away as the rectum relaxes

42
Q

Other name for defecation reflex?

A

Rectosphincteric reflex

43
Q

What happens during defecation?

A

Increased abdominal pressure through the Valsalva maneuver

44
Q

What is Hirschsprung’s disease? Treatment? Other name?

A

Congenital disorder in which the ganglion cells in the myenteric and submucosal plexus are lacking from a portion of the distal colon, rectum, and ALWAYS the internal anal sphincter => feces and gas accumulate proximal to the affected bowel segment causing tremendous distention/hypertrophy of the bowels => internal rectal sphincter cannot relax = mega colon

Treatment = surgery to remove that part of the colon and rectum, and reanastamosis with the external anal sphincter

45
Q

What can constipation lead to?

A

Polyp formation and cancer

46
Q

Usual age of diagnosis for Hirschsprung’s disease?

A

2 months

47
Q

What are the interstitial cells of Cajal?

A

Specialized pacemaker cells located in the wall of the stomach, small intestine, and large intestine that generate the slow waves

48
Q

Can the slow waves of the basic electric rhythm cause contractions of the GIT?

A

Only in the stomach

49
Q

What sets the maximal possible rate of propulsion through the GIT?

A

The basic electric rhythm

50
Q

Motility types in the mouth?

A
  1. Mastication

2. Deglutition = swallowing

51
Q

3 parts of stomach?

A
  1. Fundus
  2. Corpus = body
  3. Antrum
52
Q

What is special about the smooth muscle in the stomach?

A

Oblique muscle layer in addition to the longitudinal and circular layers found in the rest of the GIT

53
Q

Other than in the stomach, where else does gastric accommodation occur?

A

Small intestine

54
Q

What is colonic salvage?

A

Last absorption of Na+ and H2O by the colon through the haustrations that stay formed for long periods of time as they do not have villi

55
Q

2 circumstances where retrograde peristalsis occurs?

A
  1. Vomiting

2. When the defecation reflex is voluntarily stopped

56
Q

Rate of contractions during segmentation?

A

Same rate as slow waves

57
Q

Which can be propagated over longer areas of intestine: peristalsis or segmentation?

A

Segmentation

58
Q

What allows flow of bile into the duodenum?

A
  1. Vagal innervation
  2. CCK
  3. Peristalsis
59
Q

What cells secrete HCl in the stomach?

A

Parietal cells

60
Q

Where are the interstitial cells of Cajal located?

A

Between the longitudinal and circular smooth muscle layers

61
Q

What is the ileogastric reflex? Purpose?

A

Chyme in the ileum => stimulates nerves that innervate the pylorus to increase sphincter tone => reduced amount of chyme leaving the stomach to empty into the duodenum

Purpose: this allows a little more time to clear the lower GI of chyme

62
Q

What produces gastrin in the GIT? In response to what?

A

G cells of the antrum of the stomach and duodenum secrete gastrin in response to stretch and composition of chyme

63
Q

Functions of gastrin?

A
  1. Enhance HCl secretion in stomach

2. Stimulate motility in the ileum and colon

64
Q

When does the MMC stop?

A

As soon as food is in the stomach

65
Q

How are the slow waves of the interstitial cells of Cajal generated? What regulates this?

A

The undulations reflect changes in the resting membrane potential caused by coupling of the muscle to the ICC and a PDGFR-α+ cell (Platelet-derived growth factor receptor), forming a SIP (smooth muscle, ICC, PDGFR-α+ cell) syncytium

The SIP syncytium is regulated by ion channels (primarily potassium and variations in Na+-K+ ATPase activity) and receptor-mediated processes

66
Q

List the layers of the muscles of the stomach from outer to inner.

A
  1. Longitudinal
  2. Circular
  3. Oblique
67
Q

If a slow wave has more spike potentials than another, what does that mean?

A

Force of contraction is stronger

68
Q

Is motilin secreted and active during normal digestion?

A

NOPE, only during MMC

69
Q

What is ileus?

A

Inability of a portion of the SMALL intestine to contract normally and move waste out of the body due to an issue with the ENS

70
Q

Do mass movements ALWAYS stimulate a defecation reflex?

A

NOPE, might not move poop into rectum

71
Q

When do the gastric contractions start?

A

As soon as food enters the stomach (?)

72
Q

What is the MAIN purpose of the gastric contractions: propulsion to duodenum or mixing of the food? Why?

A

Mixing because rate of slow waves is very slow in the stomach (3/min)

73
Q

Are mass movements fast or slow?

A

FAST

SMP - GI (21 decks)

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