Lecture 26: Intestinal Motility Flashcards by Katlyn Heneghan

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

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

1) Segmentation
2) Peristalsis

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

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

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____: mixing movements of small intestine

Segmentation

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True or False: Segmentation is propulsive

False - it is non-propulsive

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___: the basic propulsive movement

Peristalsis

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

colon

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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

ahead; behind

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What two molecules increase intestinal motility?

Gastrin (hormone made from G cells) and Ach

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What four molecules decrease intestinal motility?

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

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

MMC (Migrating Motor Motility Complex)

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____: 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

MMC (Migrating Motor Motility Complex)

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

False - it does not

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

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

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

Phase 1

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

Phase 2

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

Phase 3

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

Emptied into duodenum and forced toward colon

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

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

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

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

no; no

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

50%

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

True

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

Motilin

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

Motilin

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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

True

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

brainstem

What six factors can induce vomiting?

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)

How does distension of the stomach/duodenum induced vomitting?

Serotonin is released from enterochromaffin cells of upper small intestine Afferent vagal nerves are activated by serotonin

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

vagal afferent nerves

What are the first four steps of the vomiting reflex?

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

What are steps 5-7 of the vomit reflex?

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

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

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

What are unique features of the colon?

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

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

Tenia coli

What is the function of haustra in the colon?

Increase SA for absorption

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

True

What types of nerves innervate the colon?

Autonomic

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

1) Cecum 2) Ascending Colon 3) Transverse colon

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

Pelvic Nerves

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

1) Descending Colon 2) Sigmoid Colin 3) Rectum

Which nerves innervate the ENTIRE colon?

Sympathetic nerves

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

True

Which n innervates external anal sphincter?

Pudendal n. (somatic, alpha motor n)

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

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

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?

Haustral Shuttling

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! ???

Haustral Propulsion

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

Haustral Retropulsion

___ are propulsive contractions that move colonic contents over LONG distances

Mass movement

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

True

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

Cecum, Ascending Colon, and Transverse Colon

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

True

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

- Haustral Retropulsion - Haustral Shuttling

What two phasic contractions occur in the rectum?

- Haustral Retropulsion - Mass movements fill rectum

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

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

True or False: Haustral Retropulsion maximizes proximal mixing

True

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. Distal Colon

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

B. Haustral Retropulsion

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

False - increases!

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

Gastrocolonic Reflex

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

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

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

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

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?

Gastrin - Increases colonic motility by activation of receptors on smooth m cells

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

C. Both Long and Short

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

relaxes

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 ___

constricted relaxed

Why is the rectum usually empty?

Huastral retropulsion moves fecal matter back into sigmoid colon

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

Mass movement

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

increases; internal anal sphincter

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

Recto-Anal Inhibitory Reflex

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

External sphincter is consciously restricted more tightly

Can the rectum act as a temporary storage organ?

Yes

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

short and long

How does the pudendal n affect external anal sphincter

Consciously relaxes it

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 ___

parasympathetic efferent increase haustral propulsion relaxation

Increased ___ can reduce transit time

dietary fiber