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Physiology II > Lecture 26: Intestinal Motility > Flashcards

Lecture 26: Intestinal Motility Flashcards

1
Q

What are the three purposes of phasic contractions of the small intestine during the digestive period?

A

1) Mix chyme with digestive secretions
2) Expose luminal contents to enterocyte brush border, where dig enzymes/transporters are anchored
3) Ensure net movement of chyme towards colon

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2
Q

What are the two types of phasic contractions in the small intestines?

A

1) Segmentation
2) Peristalsis

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3
Q

During the digestive period, which neural reflexes control frequency of phasic contractions? What is it in response to?

A

Short neural reflexes
- In response to luminal nutrients and smooth muscle distension

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4
Q

____: mixing movements of small intestine

A

Segmentation

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5
Q

True or False: Segmentation is propulsive

A

False - it is non-propulsive

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6
Q

___: the basic propulsive movement

A

Peristalsis

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7
Q

Small intestinal peristaltic contractions consist of a wave of smooth m contraction that propels luminal contents toward the ___

A

colon

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8
Q

Peristalsis involves relaxation of circulation m and contraction of longitudinal m __ of the chyme, as well as contraction of circulation muscle and relaxation of long muscle ___the chyme

A

ahead; behind

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9
Q

What two molecules increase intestinal motility?

A

Gastrin (hormone made from G cells) and Ach

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10
Q

What four molecules decrease intestinal motility?

A

1) Epi and NE
2) Opioids
3) Somatostatin (paracrine released from endocrine cells of GIT)

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11
Q

What is the pattern of small intestinal motility like during fasting (interdigestive period)?

A

MMC (Migrating Motor Motility Complex)

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12
Q

____: acts as a housekeep, sweeping undigested/unabsorbed luminal contents from gastric antrum and small intestine into the large intestine to prevent bacterial OVERGROWTH in SMALL INTESTINE

A

MMC (Migrating Motor Motility Complex)

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13
Q

True or False: The MMC occurs in the colon and orad stomach

A

False - it does not

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14
Q

The MMC pattern of motility will be replaced by segmentation and peristalsis under which condition? Which neural reflex is involved?

A

Person eats, before chyme enters stomach
- Long parasympathetic neural reflex

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15
Q

Which phase of the MMC pattern is the longest and has no contractile activity?

A

Phase 1

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16
Q

Which phase of the MMC pattern consists of random and irregular peristaltic contractions?

A

Phase 2

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17
Q

Which phase of the MMC pattern consists of 3-6 minutes of intense peristaltic contractions, with strong propulsions of luminal contents toward large intestines?

A

Phase 3

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18
Q

What happens to indigestible particles remaining in the stomach during phase 3 of the MMC?

A

Emptied into duodenum and forced toward colon

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19
Q

During each phase of the MMC, what changes? what stays the same?

A

% of slow waves associated with smooth muscle contractions differs in each phase

FREQUENCY of slow waves stays the same!!!!!

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20
Q

In Phase 1 MMC, __ slow waves produce an AP, therefore there is __ contractions

A

no; no

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21
Q

In Phase 2 MMC, ___% of slow waves produce AP bursts in SM, with SM contractions

A

50%

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22
Q

True or False: In Phase 3 MMC, ALL slow waves make AP bursts in smooth muscle with accompanying smooth muscle contractions

A

True

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23
Q

___, a hormone released from endocrine cells of the proximal small intestine, may be responsible for the MMC

A

Motilin

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24
Q

The concentration of ___ is directly related to frequency of peristaltic contractions

A

Motilin

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25
Q

True or False: There is a low plasma concentration of motilin in phase 1, a medium plasma concentration in phase 2, and a high plasma concentration in phase 3

A

True

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26
Q

Vomiting (emesis) is a reflex behavior controlled and coordinate by a central pattern generator in the ___

A

brainstem

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27
Q

What six factors can induce vomiting?

A

1) Distension of stomach/duodenum
2) Emetic chemical (ipecac)
3) Systemic chemical could trigger the CRTZ
4) Activation of tactile receptors in pharynx
5) Vestibular centers
6) Higher brain centers (fear, anticipation, pain)

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28
Q

How does distension of the stomach/duodenum induced vomitting?

A

Serotonin is released from enterochromaffin cells of upper small intestine

Afferent vagal nerves are activated by serotonin

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29
Q

Emetic chemicals can activate chemoreceptive ____ nerves, innervating the gastric/duodenal mucosa

A

vagal afferent nerves

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30
Q

What are the first four steps of the vomiting reflex?

A

1) Reverse peristalsis forces small int. contents from middle of small intestines towards duodenum
2) Stomach relaxes and intestinal contents enter stomach (due to contraction of duodenum and relaxation of pylorus)
3) LES/UES relax (open)
4) Forced INspiration against a closed glottis reduces intra-thoracic (and intra-esophageal) pressure

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31
Q

What are steps 5-7 of the vomit reflex?

A

5) Diaphragm is lowered, increasing intra-abd pressure
6) Abdominal m contract, ejecting gastric content into esophagus
7) Salivary secretions buffer acids in vomit to minimize injury to esophagus

32
Q

Phasic contractions of the large intestine are organized to promote what three things?

A

1) Optimal absorption or water and electrolytes
2) Net aboral (towards rectum) movement of contents
3) Storage and evacuation of feces

33
Q

What are unique features of the colon?

A
  1. Tenia coli
  2. Haustra
  3. Internal/External Anal Sphincter
34
Q

___: bands of concentrated longitudinal smooth muscle that begin at cecum and end at rectum

A

Tenia coli

35
Q

What is the function of haustra in the colon?

A

Increase SA for absorption

36
Q

True or False: Internal anal sphincter contains smooth m while external anal sphincter contains skeletal

A

True

37
Q

What types of nerves innervate the colon?

A

Autonomic

38
Q

The parasympathetic vagus n innervates enteric n in the ___, ___, and ___

A

1) Cecum
2) Ascending Colon
3) Transverse colon

39
Q

___ nerves: Parasympathetic efferent nerves with cell bodies in the sacral parasympathetic nucleus in the sacral spinal cord

A

Pelvic Nerves

40
Q

Which three parts of the colon are innervated by pelvic nerves?

A

1) Descending Colon
2) Sigmoid Colin
3) Rectum

41
Q

Which nerves innervate the ENTIRE colon?

A

Sympathetic nerves

42
Q

True or False: Enteric neurons of the myenteric and submucosal plexuses innervate the smooth m and mucosa of entire colon, respectively.

A

True

43
Q

Which n innervates external anal sphincter?

A

Pudendal n. (somatic, alpha motor n)

44
Q

What are the five patterns of phasic contractions in the colon?

A

1) Haustral shuttling
2) Haustral propulsion
3) Multihaustral propulsion
4) Haustral retropulsion
5) Mass movement

45
Q

In which pattern of phasic contraction in the colon is NO net movement of chyme? However, there is mixing, which aids in absorption of water and electrolytes?

A

Haustral Shuttling

46
Q

In which pattern of phasic contraction in the colon is one haustrum displaced aborally to an adjacent haustrum. There is net movement over a SHORT distance! ???

A

Haustral Propulsion

47
Q

In which pattern of phasic contraction in the colon is the contents of one haustrum displaced toward the ileocecal sphincter to an adjacent haustrum?

A

Haustral Retropulsion

48
Q

___ are propulsive contractions that move colonic contents over LONG distances

A

Mass movement

49
Q

True or False: Mass movements are infrequent in most adults, occur 1-2 times per day after ingestion of meal as part of GC reflex

A

True

50
Q

In what three structures of the colon does the follow occur?
- haustal retropulsion/propulsion
- multi haustral propulsion

A

Cecum, Ascending Colon, and Transverse Colon

51
Q

True or False: Colonic phase contractions in the colon promote water and electrolyte absorption

A

True

52
Q

What two phasic contractions occur in both the descending and sigmoid colon?

A
  • Haustral Retropulsion
  • Haustral Shuttling
53
Q

What two phasic contractions occur in the rectum?

A
  • Haustral Retropulsion
  • Mass movements fill rectum
54
Q

True or False: Each region of the large intestine has predominate pattern of phasic contraction. These motility patterns change, however, based on food intake and fasting

A

False - Each region of the large intestine has predominate pattern of phasic contraction. These motility patterns PERSISTS, regardless of food intake or fasting

55
Q

True or False: Haustral Retropulsion maximizes proximal mixing

A

True

56
Q

In the ___ colon, material in the lumen has changed from liquid to semi solid state. Contractile activity slows flow of fecal matter into rectum.
A. Distal Colon
B. Proximal Colon

A

A. Distal Colon

57
Q

_____ ____ prevents fecal material from entering the rectum
A. Haustral Shuttling
B. Haustral Retropulsion
C. Haustral Propulsion

A

B. Haustral Retropulsion

58
Q

True or False: Colonic motility and frequency of mass movements decrease after a meal enters into stomach

A

False - increases!

59
Q

Which reflex accounts for the urge to defecate ~30 min s/p a meal?

A

Gastrocolonic Reflex

60
Q

In the rapid component of the gastrocolonic reflex, gastric distension activates a _____ reflex through ___ and ___ nerves

A

long neural reflex; parasympathetic vagal (afferent) and pelvic (efferent) nerves

61
Q

How does an increased in pelvic n activity affect colonic motility? How?

A

Increase in pelvic n activity increases colonic motility via: activation of enteric motor neurons

62
Q

In the slow component of the gastrocolonic reflex, gastric distension activates a neutral reflex to increase release of ____, a hormone from G cells in the gastric mucosa.

What affect does this hormone have on colonic motility? How?

A

Gastrin

  • Increases colonic motility by activation of receptors on smooth m cells
63
Q

What type of neural reflexes are involved in the recto-anal inhibitory reflex?
A. Long Neural Reflexes
B. Short Neural Reflexes
C. Both Long and Short

A

C. Both Long and Short

64
Q

In the recto-anal reflex, distension of the rectum ___ internal anal sphincter

A

relaxes

65
Q

When the external anal sphincter is distended and defecation is not appropriate, the sphincter ____

When rectum is distended and defecation is appropriate, the sphincter is ___

A

constricted
relaxed

66
Q

Why is the rectum usually empty?

A

Huastral retropulsion moves fecal matter back into sigmoid colon

67
Q

What type of movement strongly propels fecal material towards the rectum?

A

Mass movement

68
Q

As fecal matter enters the rectum, rectal pressure ____, which causes a reflex relaxation of the ______ sphincter

A

increases; internal anal sphincter

69
Q

____Reflex: Increased rectal pressure causes a reflex relaxation of internal anal sphincter

A

Recto-Anal Inhibitory Reflex

70
Q

What happens to the external anal sphincter if circumstances are not appropriate for defecation?

A

External sphincter is consciously restricted more tightly

71
Q

Can the rectum act as a temporary storage organ?

A

Yes

72
Q

When circumstances are appropriate, both __ and __ neural reflexes and pudendal n participate in defecation

A

short and long

73
Q

How does the pudendal n affect external anal sphincter

A

Consciously relaxes it

74
Q

In defecation, the Long Neural Reflex is described as: activation of ____ afferents by rectal distension

Parasympathetic pelvic ___ nerves innervation myenteric motor neurons of the
a. distal colon/rectum increase ____
b. internal anal sphincter cause ___

A

parasympathetic
efferent

increase haustral propulsion
relaxation

75
Q

Increased ___ can reduce transit time

A

dietary fiber

Physiology II (23 decks)

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