Colonic Motility Flashcards
Phasic contractions of the colon are optimized for
Water and electrolyte absorption and storage and evacuation of feces
Tenia Coli
3 bands of longitudinal muscle from cecum to rectum
Haustra
bulges of colon wall where longitudinal muscle is thin, increases SA of colon
IAS
circular smooth muscle
EAS
striated muscle
Parasympathetic innervation to colon - VAGUS
cecum, ascending colon, and transverse colon
Parasympathetic innervation to colon - PELVIC
descending colon, sigmoid colon, rectum
PUDENDAL n
somatic motor innervation to EAS
Sympathetic innervation to colon
innervate ENTIRE colon
Innervation of the IAS
Pelvic n indirectly via enteric neurons
5 types of phasic contractions in the colon
Haustral shuttling, haustral propulsion, multihaustral propulsion, haustral retropulsion, mass movement
Haustral shuttling
Mixing of contents for absorption of water and electrolytes, (NON-PROPULSIVE), tenia coli and circular muscle contractions cause random appearance and disappearance of haustra
Haustral propulsion
few adjacent hausfrau contract sequentially for aboral displacement of contents (5-10cm movement)
Multihaustral propulsion
Contraction of many hausfrau, aboral movement of 18-20cm
Haustral retropulsion
adjacent haustra contract in an oral direction, and contents move backward 5-20cm
Mass movement
gastrocolonic reflex; strong contraction of MANY circular muscle and tenia coli, aboral movement >30cm; after ingestion of meal
Common motility pattern of proximal colon
haustral propulsion, multihaustral propulsion, haustral retropulsion
Common motility pattern of distal colon
Haustral shuttling, haustral retropulsion
Purpose of common motility patterns
slow transmit in distal colon to increase absorption and minimize incontinence
Mass movements effect on normal motility patterns
cause strong aboral contractions, initiated by TRANSVERSE, descending or sigmoid colon
MMC in colon
DOES NOT EXIST :( :(
Rectum motility
fecal material enters during a mass movement, can be stored and sent back to sigmoid via retropulsion
Rectoanal inhibitory reflex
distention of the rectal smooth muscle causes IAS relaxation (long and short neural pathways)
EAS
HIGH basal tone (pudendal n) - voluntary
Gastrocolonic Reflex
food enters stomach and causes increased colonic motility
Fast component of Gastrocolonic Reflex
gastric distention - long neural reflex - PNS (vagal and pelvic) activity
Slow component of Gastrocolonic Reflex
gastric distention - increased gastrin release - short neural reflex - increased colonic motility
The urge to defecate often occurs
30 min after a meal due to gastrocolonic reflex and MASS movements
rectum is generally empty because
mass movement and filling leads to defecation (lax IAS), or retropulsion
Rectum as temporary storage
if defecation is not appropriate, the rectum can store the feces -> rectal SM relaxes –> rectal pressure decreases –> IAS constricts –> haustral retropulsion into sigmoid colon
What causes IAS to relax
PNS to myenteric inhibitory neurons –> increased NO
Hirschsprung’s Disease
ENS absent in distal colon/rectum, failure of phasic contractions or relaxation of IAS
Pressures during defecation
rectum: HIGH, IAS: medium, EAS: low
Defecation involves ______________ neural reflex
long and short
Short neural reflex functions to
Increase haustral propulsion, increase intra-luminal pressure, and relax the IAS
Short neural reflex for defecation is activated by
IPAN activation by rectal distention
Long neural reflex functions to
Increase haustral propulsion, increase intra-luminal pressure, and relax IAS
Muscles active to defer defecation
puborectalis, EAS contract = narrow anorectal angle and increase pressure
Defecation
puborectalis and EAS relaxed via pudendal n, widen the anorectal angle and relieve pressure
Somatic and PNS act on various structures during defecation
Valsalva maneuver and relaxation of pelvic muscles
Constipation definition
> 2 stools/week, straining, hard stools, feeling of incomplete evacuation
Slow-Transit Constipation (STC)
increased transit time from proximal to distal colon
Cause for Slow-Transit Constipation
weak mass movement contractions, uncoordinated activity in distal colon resisting aboral movement
Pelvic Floor Dysfunction
prolonged storage of feces in rectum
Casuses of Pelvic Floor Dysfunction
Muscular hypertonicity of EAS (paradoxical contraction or incomplete relaxation), or hypotonicity of rectum
transit time in the colon
1.5-4 days
Fiber decreases transit time to
<30 hrs
How fiber works
draws water into stool, increases stool weight, stretching of colon = motility, absorbs organic materials
Fiber can absorb organic materials like
lipids, bile acids, and cholesterol
ICC are more active in
a colon of a healthy patient than one who is constipated
Hemorrhoids
acute lower GI bleed due to strained passage of hard stools or frequent diarrhea
Colonic lesions
acute lower GI bleed due to ulcerative colitis, colon cancer or polyps, or infections
Diverticulosis
acute lower GI bleed due to outpouchings of the colon wall
