Lecture 26: Intestinal Motility Flashcards
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
What are the two types of phasic contractions in the small intestines?
1) Segmentation
2) Peristalsis
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
____: mixing movements of small intestine
Segmentation
True or False: Segmentation is propulsive
False - it is non-propulsive
___: the basic propulsive movement
Peristalsis
Small intestinal peristaltic contractions consist of a wave of smooth m contraction that propels luminal contents toward the ___
colon
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
What two molecules increase intestinal motility?
Gastrin (hormone made from G cells) and Ach
What four molecules decrease intestinal motility?
1) Epi and NE
2) Opioids
3) Somatostatin (paracrine released from endocrine cells of GIT)
What is the pattern of small intestinal motility like during fasting (interdigestive period)?
MMC (Migrating Motor Motility Complex)
____: 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)
True or False: The MMC occurs in the colon and orad stomach
False - it does not
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
Which phase of the MMC pattern is the longest and has no contractile activity?
Phase 1
Which phase of the MMC pattern consists of random and irregular peristaltic contractions?
Phase 2
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
What happens to indigestible particles remaining in the stomach during phase 3 of the MMC?
Emptied into duodenum and forced toward colon
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!!!!!
In Phase 1 MMC, __ slow waves produce an AP, therefore there is __ contractions
no; no
In Phase 2 MMC, ___% of slow waves produce AP bursts in SM, with SM contractions
50%
True or False: In Phase 3 MMC, ALL slow waves make AP bursts in smooth muscle with accompanying smooth muscle contractions
True
___, a hormone released from endocrine cells of the proximal small intestine, may be responsible for the MMC
Motilin
The concentration of ___ is directly related to frequency of peristaltic contractions
Motilin
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?
- Tenia coli
- Haustra
- 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
