GI 6 Flashcards
what is the regulation of intestinal phase?
regulated by distension, acidity and digestive products in the small intestine through short and long reflexes and endocrine signaling
-reduces motility and secretions in the stomach, increases in the intestine
what is intestinal motility influenced by?
primarily by ENS neurons (myenteric plexus)
-slow waves brought to threshold
-distension of stomach
-distension of small intestine
-stimulated by increased parasympathetic input (long reflexes)
Mo cells-motilin (in duodenum)
-possibly stimulated by alkaline pH
what are accessories in intestinal phase?
-secretions: long reflexes
Gi peptides:
-S cells: secretin
-I cells: cholecystokinin
-K cells: glucose dependent insulinotropic peptide (GIP)
-L cells: glucagon-like peptide 1 (GLP-1)
what are the pancreatic secretions?
-begin during the cephalic and gastric phases
-gastrin and parasympathetic neurons
what is a reflex in pancreatic secretions?
-enteropancreatic reflex
when is secretin secretes by S cells? and the primary role?
-stimulated by acid entering the duodenum in the stomach
-primary role in regulation of pH
what is the primary role of secretin?
stimulates bicarbonate (buffer stomach acid) secretion from pancreas
-stimulates bile secretion from liver (secondary)
what is the secondary role of secretin?
inhibition of gastric acid secretion
-inhibits gastric motility and thus gastric emptying into the small intestine
when is cholecystokinin (CCK) by I cells stimulated?
-stimulated by the presence of fatty acids and amino acids in chyme
what are the roles of cholecystokinin?
- regulates pancreatic enzyme secretion
- regulates bile secretion
-also inhibits gastric acid production and emptying
what is the table of the three phases of pancreatic secretion?
what are the roles of GIP secreted by K cells and GLP-1 secreted by L cells?
primarily endocrine function: glucose homeostasis
-inhibit gastric acid secretion and motility
what is the integration of gastric and intestinal phase?
enterogastric reflex (entero=intestine)
-acid, enzymes and digested food results in hyperosmotic chyme that inhibits gastric emptying
how does the large intestine concentrate water?
store and concentrate fecal matter
approximately 1.5L of chyme proceed through ileocecal valve
-valve relaxes as concentration proceeds through ileum
-food in stomach causes contraction of ileum and relaxation of ileocecal valve (gastroileal reflex)
what is the secretion and digestion in the large intestine?
-secretions: minimal and primarily consists of mucus from goblet cells
-digestion: traditionally believed that zero digestion occurs in the large intestine
how are complex things broken down in the large intestine?
indigestible complex carbohydrates, fats and proteins are broken down by bacteria through fermentation processes
-produces lactate and short chain FA’s used by colonocytes for energy production
-produce absorbable vitamins (vit K)
-produce gases (methane, beans)
what is the motility in the large intestine?
- slow segmental contractions (18-24 hrs)
- haustral rolling or churning
-thickened bands of longitudinal muscle layer taenia coli
-creates pouches called haustra (from incomplete longitudinal waves) - mass peristalsis
-gastrocolic reflex, stimulated by food in stomach (2-3 times a day)
what are the two reflexes initiated by distension of the rectum?
short reflex
-local peristaltic waves
long reflex
-relaxation of internal sphincter (smooth muscle), contraction of external
-more forceful peristaltic contractions from parasympathetic input (push further into rectum)
-completed by voluntary relaxation of external sphincter (skeletal) and aided by increased abdominal pressure
