Colonic Motility Flashcards
Functions of phasic contractions in large intestine
. Optimal absorption of H2O and electrolytes
. Net aboral movement of contents
. Storage and orderly evacuation of feces
Tenia Coli
. 3 bands of concentrated longitudinal smooth m. That begin at the cecum and end at the rectum
. At rectum the bands spread out and form a longitudinal m. Layer of uniform thickness
Haustra
. Bulges in colon wall where the longitudinal m. Layer is thin
. Periodic contractions of circulating m. Then pulls the bulges into pouches or haustra
. Not fixed, appear and disappear is different locations
. Inc. SA available for absorption
Innervation of colon
. CN X innervates enteric neurons in cecum, ascending colon, and transverse colon (parasym.)
. Pelvic nn. W/ cell bodies in sacral parasym. Nucleus in sacral spinal cord, innervate enteric neurons in descending colon, sigmoid colon, and rectum
. SNS innervate entire colon
. Enteric neurons in myenteric and submucosal plexuses innervate smooth m. And mucosa of entire colon
. Enteric neurons innervate internal anal sphincter, pelvic nn. Innervate internal sphincter via enteric neurons
. Pudendal n.: somatic motor to striated m. Of external anal sphincter
Haustral shuttling
. Individual haustra appear and disappear randomly bc contractions of tenia coli and circular m
. Luminal contents displaced in both directions
. No net movement of chyme
. Mixing movements thoroughly mix contents and aid in absorption of H2O and electrolytes
Haustral propulsion
. Few adjacent haustra contract sequentially
. contents in 1 haustra are displace aborally to an adjacent haustra
. Net movement 5-10 cm
Multi haustral propulsion
. Combined contraction of many haustra
. Net aboral movement of intestinal contents over a moderate distance
Haustral retropulsion
. Few adjacent haustra contract sequentially
. Contents of 1 haustra are displaced backward to an adjacent haustra
Mass movement
. Simultaneous, very strong contractions of circular m. And tenia coli
. Contractions move the colonic contents over long distance
. Mass movements are infrequent in healthy adults and occur 1-3 times per day after the ingestion of a meal as part of the gastrocolonic reflex
Phasic contractions in prox. Colon
. Haustral propulsion
. Multihaustral propulsion
. Frequent haustral retropulsion
. Not much haustral shuttling
Phasic contractions in colonic regions
. Haustral shuttling
. Frequent haustral retropulsion
. Not much haustral or multihaustral propulsion
. Slow transit in distal colon which minimizes. Challenges to continence while maximizing proximal colon mixing
Rectum
. Fecal material enters rectum during a mass movement
. Can temporarily store feces
. After initial accommodation, subsequent haustral retropulsion returns fecal material to sigmoid colon
Internal anal sphincter control
. Rectoanal inhibitory reflex (short and long neural reflex)
. Distension of rectal smooth m. Relaxes the internal anal sphincter
External anal sphincter control
. Sphincter has a high basal tone (pudendal n.)
. Voluntarily constricted or relaxed
Rapid component of gastrocolonic reflex
. Gastric distension causes long neural reflex through parasympathetic vagus (afferent) and pelvic (efferent) nn.
Slow component of gastrocolonic reflex
. Gastric distension inc. release of gastrin from G cells in gastric mucosa (short neural reflex)
. Hormone gastric inc. colonic motility
Gastrocolonic reflex
. Has rapid and slow components
. Accounts for urge to poo 30 min after eating
.mass movement after a meal are facilitated by this reflex
Pressure in rectum
. Inc. As result of fecal matter moving in from mass movement
. Inc. pressure in rectum Causes relaxation of internal anal sphincter (rectoanal inhibitory reflex)
. Fecal material enters the anal canal and its presence is consciously sensed by the individual
Outcomes of inc. rectal pressure
. Retention of fecal contents
. Elimination of fecal contents
Retention of fecal contents
. If circumstances are not appropriate for defecation the external anal sphincter is not voluntarily relaxed by the individual
. Eventually smooth m. Relaxes to accommodate fecal material
. As rectal pressure dec. the rectal anal inhibitory reflex is no longer activated and tone of internal anal sphincter returns to normal
. Haustral retropulsion resumes clearing rectum of fecal material
Elimination of fecal contents
. When circumstances are appropriate both short and long neural reflexes and pudendal n. Participate in defecation
Short neural reflex for defecation
. Enteric IPANS are stimulated by presence of fecal material
. Enteric motor neurons inc. haustral propulsion in descending colon. Sigmoid, and rectum
. Inc. intraluminal pressure in those areas
. Relax internal anal sphincter
Long neural reflex of defecation
. Parasympathetic afferent nn. Are activated by presence of fecal material
. PNS pelvic efferent nn. Innervating the ENS of the descending, sigmoid, and rectum inc. haustral propulsion and inc. intraluminal pressure against the fecal material
. Internal anal sphincter promote relaxation
Somatic nerve involvement in defecation
. Involved in taking a deep breath, closure of glottis, contraction of abdominal mm. To force fecal contents downward and relaxation of pelvic mm.
. Squatting and relaxation of puborectalis m. Dec. angulation of the anal canal facilitating defecation