Large Intestine Flashcards
Voluntary control of defecation is possible because…
the parasympathetic system at that level is controlled by the pelvic branches instead of the vagus
the ileocecal sphincter relaxes due to…
mechanoreceptors that sense the stretch in the ileum; they also close the sphincter behind it
four types of motility in the large intestine
mixing/segmentation; mass movement; reservoir; defecation
transit time through the large intestine
varies considerably
rectosphincteric reflex
pressure on the inside of the internal anal sphincter causes relaxation of the sphincter muscles and reflexive relaxation of the external anal sphincter
commensal bacteria in the colon perform what function?
breakdown of some indigestible products of the small intestine which can then be digested
hirschsprung’s disease; rate; pathophysiology
1:5000 births; the colon is devoid of enteric neurons which causes a backup of chyme behind that region; this results in megacolon which is normally treated surgically in infancy
ileogastric reflex
distension in the ileum causes lack on contraction in the stomach
gastroileal reflex
distension in the stomach causes movement in the ileum
colonocolonic reflex
distension in the distal colon prevents motility in the proximal colon
gastrocolic reflex
distension in the stomach produces motility in the colon and promotes defecation
emesis is controlled by.. and receives inputs from
the emesis center in the medulla; chemoreceptors in the GI tract and mechano receptors in the throat
chemoreceptor trigger zone is in the ….
fourth ventricle and triggers emesis
retching is characterized by
opening of the LES to allow contents into the esophagus but having the UES stay closed
water secretion in the intestine is coordinated by…
crypt cells via the CFTR channels
water secretion is regulated by
secretagogues:
neural: ACh, VIP and serotonin
para/endocrine: gastrin, CCK, NO
water migration mechanism
Na/K/2Cl transporter brings in Cl
Cl leaves via CFTR
Na and H2O follow paracellularly
water secretion increases with…
muscle contraction; blocked by Immodium which blocks enteric neurons
sodium absorption locations along the GI tract
Na/H duodenum
Na/solute - small intestine
Parallel (Na/H + HCO3/Cl) - ileum and colon (little bit in rectum)
ENaC - colon
Chloride (secretion absorption GI tract)
Passively everywhere by potential difference
anion exchanger ileum and below
Parallel with sodium ileum and colon (little bit in rectum)
Potassium (secretion/absorption in GI tract)
passive paracellular pathways in the small intestine
active secretion in the colon K leak channel
active absorption in the rectum K/H pump
passive secretion in the colon
water moves in the GI tract via
paracellular pathways (instead of aquaporins)
in tight tight junctions, the solution produced is…
hypertonic
things that cannot be absorbed in the lumen have what effect on bowel movements?
increased osmotic pressure leads to more frequent bowel movement - osmotic diarrhea; common with lactose intolerance
