GI physiology: stomach, small/large intestine Flashcards
What are the 3 layers and function of stomach smooth muscle?
longitudinal=>outer, for peristalsis
circular=> for mixing
oblique=> inner
What structures can the stomach be divided into?
fundus, body, antrum
how and where does receptive relaxation occur?
mediated by VIP occurs in fundus
how is the receptive relaxation work as the stomach fills?
a vagovagal-mediated receptive relaxation occurs allowing storage
Before reaching the small intestine, what happens to the bolus of swallowed food?
it is macerated and mixed w/ HCl, mucus, and pepsin => chyme => discharged at controlled rate
How much chemical digestion occurs in the stomach?
very small amount
How and where does the pacemaker of the stomach work?
w/in greater curvature produces basal electric rhythm (BER) of 3-5 waves/min
What controls the magnitude of the gastric contractions?
increased by PANS;
decreased by SANS
define migrating motor complexes (MMC)
propulsive contractions initiated during fasting that begin in stomach and move undigested material from stomach and small intestine into colon
what mediates the migrating motor complexes?
motilin => repeat every 90-120min
why are migrating motor complexes important for general health?
this is a housekeeping function that lowers the bacterial count in the gut
what is the pylorus
continuous w/ circular muscle layer;
acts as “valve” to control gastric emptying
What limits the movement of chyme into duodenum and promotes retropulsion?
pyloric sphincter contraction at time of antral contraction
define retropulsion WRT gastric emptying
mixing by forceful regurgitation of antral contents back into fundus
What delays gastric emptying?
- fat/protein in duodenum stimulating CCK release=> increases gastric distensibility
- H+ in duodenum via neural reflexes
- stomach contents that are hypertonic or hypotonic
what is the primary role of the small intestine?
digestion and absorption of nutrients via specialized villi on epithelial surface
What is the order of structures of the duodenum?
duodenum=> proximal pyloric end
jejunum
ileum
Mucus production occurs throughout the GI tract. What produces it in the small intestine?
Brunner glands=> duodenum Goblet cells => throughout intestine
What are the functions of mucus?
lubrication of GI tract;
binding bacteria;
trapping Ig
What may INCREASE rate of mucus secretion?
choinergic stimulation;
chemical irritation;
physical irritation
How are gastritis, duodenitis and some peptic ulcer diseases related to small intestine?
any compromise of mucous protection can lead to damage and irritation
regarding intestinal motility, how do small bowel slow waves move?
move caudally in circular smooth muscle => slows more distally
what are the importance of segmentation contractions?
ring-like contractions that MIX INTESTINAL CONTENTS => occur at nodes along intestine
define peristalsis
reflex response initiated by stretching of lumen of gut => propel contents caudally
what modulates peristalsis?
autonomic input;
can occur in isolated loops of small bowel w/ no extrinsic innervation
give the steps to peristalsis occurring
intrinsic control system senses stretch w/ CGRP;
contractile wave initiated by ACh and substance P;
relaxation caudal to stimulus initiated by NO & VIP
what controls the contractions of the small intestine?
PANS increases;
SANS decreases
How is small intestinal contents delivered to large intestine?
gastroileal reflex caused by food in stomach => stimulates peristalsis in ileum =>
relaxes ileocecal valve
Why are small intestinal secretions alkaline?
neutralize acid nature of chyme from pylorus
Since PANS activates peristalsis, what can be given for a dysfxn of PANS leading to constipation?
dopaminergic and cholinergic agents
What muscles constitute the outer layer of the colon?
3 longitudinal bands of muscle => teniae coli
How are haustra created?
colon is longer than teniae coli so haustra are created for them to fit
How is mucus secreted in large intestine?
short, inward-projecting colonic glands => NO VILLI
What are important immunological areas of the colon?
abundant lymphoid follicles => cecum and appendix
Major fxns of colon
reabsorption of fluid and electrolytes;
temporary storage of feces
What promotes movement of chyme in the colon?
peristaltic waves => increase speed distally
What type of contractions are found only in the colon?
mass movement contractions
What is the defecation reflex?
distention of rectum w/ feces
What are important electrolytes that the large colon is responsible for absorbing?
Na+ actively transported w/ water following it;
K+ and HCO3 secreted into colon
in normal feces, what % may be bacterial?
30%
Why are bacteria a large portion of feces?
synthesize VITAMIN K, B-complex vitamins, folic acid;
split urea to NH3;
produce small organic acids from unabsorbed fat and carbohydrate
How does PANS causes defecation feeling?
rectal distention w/ feces activates intrinsic and cord reflexes causing relaxation of internal anal sphincter
What will lead to defecation actually occurring?
pudendal nerve causes external anal sphincter to relax; Valsalva maneuver (increased intra-abdominal pressure) leads to defecation
What controls the gastrocolic reflex and what is its relation to defecation?
PANS=> distention of stomach by food INCREASES FREQUENCY OF MASS MOVEMENTS and produces urge to defecate
