GI 5 Flashcards
3 Main Functions of Small Intestine Contractions
- Mixing food with digestive secretions
- Circulation of foodstuffs
- Net propulsion
Patterns of Small Intestinal Motility
- Segmentation
- Peristalsis
- Migrating Motor Complex
Is segmentation propulsive?
no
segmentation goal
slow down movement of ingesta and retain food in one region to facilitate repeated contact with intestinal mucosa, mix food and secretions/enzymes
Is peristalsis propulsive?
yes
Peristalsis
circular constrictions to move contents aborally; contraction occurs with aboral relaxation
Migrating Motor Complex
during interdigestive phase with intesnse contractions thru stomach and small intestine to push out undigested material
What hormone facilitates the migrating motor complex?
motilin
What pattern of small intestinal motility is responsible for maintaining the regional distribution of gut bacteria?
migrating motor complex (MMC)
What part of the GI has the most microbes?
colon
What part of the GI has the fewest microbes?
stomach
What determines contractile parameters in the small intestine?
slow waves
(frequency, velocity, direction)
Main NT regulator of the enteric nervous system and SI motility?
acetylcholine
What drug can be given to block aceylcholine, thereby slowing the motility of the SI?
atropine
cephalic phase
anticipation of food, before the food enters the stomach
How does the duration of fed motility pattern depend on caloric content?
more calories (and more fat) need more time, inc. segmental contractions, decreases speed of motility
Ileal brake
[distal to proximal] feedback mechanism that controls meal transit in the GI to optimize nutrient digestion and absorption
4 Factors of the Ileal Brake
- Delays gastric emptying
- Delays intestinal transit
- Inhibits secretions (gastric/pancreatic/biliary)
- Increases satiety
How does the ileal brake delay gastric emptying?
decreases frequency of peristalsis in pylorus and duodenum, increases pyloric sphincter pressure
How does the ileal brake delay intestinal transit?
decrease frrequency, number, and distance of peristalsis and propogation
Ileocecocolic junction
space where the small intestine (ileum) enters the large intestine (colon) at the location of the cecum
Ileocolic orifice
one-way valve between ileum and colon to limit reflux and maintain relative sterility of small intestine
4 Functions of Large Intestine Contractions
- Absorb water and electrolytes
- Fermentation of organic matter (species dependent)
- Net aboral movement
- Storage and evacuation of feces
Is movement in the colon fast or slow?
slow (to intensively mix ingesta)
Haustra
small pouches created by the sacculations of the colon (the segments) (not well-defined)
Tenia
outer longitudinal smooth muscle along the colon
Do guinea pig have tenia?
yeah!
What nerves control the external anal sphincter?
somatic nerves (voluntary control)
What nerves innervate the proximal colon?
vagus nerve
What nerves innervate the distal colon?
pelvic nerve
3 Patterns of Colonic Motility
- Segmentation
- Peristatic and Antiperistaltic Waves
- Mass Movements
Peristalsis in the Colon
shallow circular contractions, low propulsion, some backflow across opening of constriction to allow mixing
Pacemaker of the Colon?
Interstitial cells of Cajal (ICC)
Mass Movement
occurs infrequently and usually after a meal at a high amplitude to help move a large amount of feces over significant distance into rectum
Characteristic motor pattern of cecum nd colon?
peristaltic and antiperistaltic contractions
Majority of contractions in the colon are what kind?
Segemental (90%)
Segmental contractions in the Colon
Long lasting circular constrictions that occur simultaneously at adjacent sites and it slowly moves the content aborally
Segmental Contractions in the Small Intestine
short (a few seconds) contractions at various intestinal sites
Do you lose segmental activity during mass movements?
yes
Do you lose haustrations during mass movements?
yes
Gastrocolic reflex
stomach gives signal to the colon to clear out the large intestine to make room for another meal
How frequently do mass movements (giant migrating contractions) occur after a meal and for how long?
Every 15 minutes for 1 hour
Are mass movements the same as migrating motor complex?
NO
Is this a kangaroo?
obviously
Is defecation voluntary or involuntary?
both (dependent on the sphincter - internal is involuntary, external is voluntary)
Muscle Type of Internal Anal Sphincter
smooth muscle
External Anal Sphincter innervation?
pudendal nerve
Muscle Type of External Anal Sphincter
Striated muscle
Which anal sphincter is most responsible for tonic contractions/anal tone?
internal anal sphincter
Retrosphincteric Reflex
signal from rectum to sphincter when stretch receptors are activated - causes peristalsis of rectum and relaxation of internal anal sphincter, signal to CNS to contract external anal sphincter and feel the urge to defecate
Fecal Continence
choose to suppress defecation, rectum and external anal sphincter relax, internal anal sphincter regains tone
Causes of Fecal Incontinence
muscle damage to external anal sphincter,
nerve damage to the nerves that sense stool in rectum or the ones that control the sphincter
Megacolon [in Cats]
constipation/obstipation due to a generalized dysfunction of smooth muscle in the colon (most commonly seen in middle aged cats)
Obstipation
prolonged retention of feces causes inability to pass stool or gas
What are the two distal to proximal feedback reflexes in the intestine?
- Enterogastric reflex
- Ileal brake