Small Intestine Function Flashcards
BER
Rate decreases as you move distally
It is a property of the smooth muscle in that region
How are stomach and SI rhythm linked?
By distention reflexes and continuity of the longitduinal layer of muscle across pyloric sphincter
Segmentation due to circular smooth muscle contraction - piramry mixing mvmnt
Chyme moves in both directions but net movement is aboral bc pressure graident established by higher intrinsic rate int he duodenum
Mvmt via short peristaltic waves
How are propulsion and mixing related
Feeding inc molity but can dec propulsive action
Morphine inc tonic tone of gut which dec average size of lumen and dec flow…this results in inc water reabsroptiin and pot constipation
Interdigestive complex
Stimulated by motilin
Causes intermittent periods of contraction
Neural and hormonal regulation
Vagal and celiac/superior mesenteric ganglia - changes of rate of BER
Local reflexes - distention act mechanos which result in ENS reflex to - proximally contract circular layer of smooth muscle (Ach and sub P) and relax distally (VIP and NO) (while contracting long)…mostly through myenteric plexus
Regional reflexes - if sensory upstream then move aborally…if sensor downstream, then dec upstream fxn
Intestinointestinal reflex Gastroenteric reflex Ileogastric Gastroilial Gastrocolic
Extrinsic innervation…overdistension of one part causes relaxation of the raminader
Gastric distension inc intestinal peristaltic activity
Distension of ileum dec gastric motility and gastric emptying
Inc in stomach motility cause inc ileal motility and inc emtytihng of intestine
Inc stomach fxn leads to inc colonic activity…resulting in MMC contraction which triggers urge to defacate
Hormonal
Gastrin - positive effect ot inc motility
CCK - weak gastrin-like action…also competes with gastrin receptors
Secretin - dec stomach secretions except pepsinogen
Villi movements
Musc mucosa contracts irregularly about 3 times/min
Individual villi also contract
Both stmulated by local reflexes from tactile and distension…villikinin from mucsoal cells
Countercurrent exchange - hypoxia at tip leads to inc cell turnoved…ischemic bowel dz
Ileocecal valve
Normally closed
Short wave into small intestine immediately orad to vavle causes relaxation
As chyme flow into cecum, distension causes contraction
Tone and opening of the ICV are controlled by intramural plexus supplemented by gastroileal reflex
This regulates absorption
INtestinal secretions
Most of serous from proximal intestine due to rapidly inc osmolarity bc of carb digestion by pancreatic amylase
Mucus - released by golbet cells by processes of exfoliation and exocytosis…inc by PNS, secretin, tactile reflexes…low level by SNS
Electrolytes - plasma ultrafiltrate with neutral pH…serves as vehile for reabsorption….inc during digestive phase
Hormones - GEP cells in the intertinal mucosa release secretin (inc electrolyic) and CCK (inc enzymatic and bile salt release)
Enzymatic secretion of small intestine
Enteropeptidases
Intestinal amylase
Brush border - peptidases (exopeptidase and endopeptidase)
Diasaccharidases
Lipases
Regulation of intestinal fxn
Dysfunction - cholera toxin leads to excessive secretion due to Cl mediated secretion
Osmotic - pulls water into lumen due to particales and osmolairyt in the lumen
Hypermotile - not enough time to absorb
Hypomotile - not enough mixing to dec sitance for diffusion
Secretory - pumps osmotic particles into the lumen which then draws water
GI digestion and absorption
IC - phagocytosis and lysosome
EC - exocytotic release
BB enzymes
Typical strucutre of absorptive enterocyte - short life span…part of villus structure contains goblet cells…dense array of microvilli on apical membrane….covered by a glycocalyx…unstirred layer of fluid overtop of glycocalyx
