GI: Structure and Regulation Flashcards
What parts of the GI tract does the vagus nerve innervate?
Esophagus
Stomach
Small Intestine
Upper Colon
What does the pelvic nerve innervate?
Descending colon
Sigmoid colon
Rectum
Anal canal
What is the pathway of the vagovagal reflex?
Information from receptors relayed to CNS via vagus nerve afferents
Response is carried back to GI tract via vagus nerve efferents
Describe sympathetic innervation to the GI tract
Nerve fibers synapse outside GI tract in prevertebral ganglia
A few innervate blood vessels and secretory cells directly
What is the enteric nervous system?
Made up of motor, sensory, and interneurons
Networks formes by mysenteric plexus and submucosal plexus
Relays information to and from guy via extrinsic system
What are the roles of the myenteric and submucosal plexuses respectively?
Myenteric - mostly controls motility
Submucosal - mostly controls secretion
What is gastrin?
Secreted from G cells in stomach
Released in response to protein digestion, distension of stomach, and vagal stimulation
Stimulates HCl secretion by parietal cells in stomach
What is Zollinger-Ellison Syndrome?
Hypersecretion of gastric acid due to continuous release of gastrin from a gastrinoma in the small intestine or pancreas
Patients develop duodenal ulcers, diarrhea, and steatorrhea
What is cholecystokinin (CCK)?
Secreted from I cells of proximal small intestine
Released in response to small peptides, AAs, fatty acids and monoglycerides
Stimulates gallbladder contraction and pancreatic enzyme secretion
Inhibits gastric emptying
Signal for satiety
What two peptides can stimulate CCK secretion?
CCK-releasing peptide - secreted by paracrine cells within epithelium into lumen
Monitor peptide - secreted by pancreas
Both released in response to neural input
In presence of meal, protected from degredation by trypsin, in absence, degraded
What is secretin?
Released by S cells of proximal small intestine in response to acid
Stimulates bicarb and water secretion in pancreas and liver
Increases bile production
Inhibits gastric acid secreiton by parietal cells
What is glucose-dependent insulinotropic peptide (GIP)?
Secreted by K cells in proximal small intestine
Released in response to fatty acids, glucose, and to a lesser extent AAs
Stimulates insulin release from pancreas
What is motilin?
Released cyclically about every 90 minutes from M cells in stomach and small intestine
Stimulates migrating myoelectric complex in stomach and intestine
Released abolished by eating
What is guanylin?
Secreted by intestines
Binds to guanylyl cyclase
Increases fluid secretion by increasing Cl- secretion
What is somatostatin?
Paracrine secreted by D cells throughout GI tract in response to acid in lumen
Inhibits gastric acid secretion and gastrin release
Inhibits release of all GI hormones
