Green - GI Tract: Structure And Function Flashcards
Reflex found in GI tract in which afferent and efferent impulses travel via the vagus nerve
Vagovagal reflex
Fat in feces
Steatorrhea
Small tumor in the small intestine or pancreas that produces high levels of gastrin
Gastrinoma
Cells in GI tract that release histamine
Enterochromaffin-like cells
Intrinsic nervous system of GI tract that is separate from the CNS
Enteric nervous system
In extrinsic nervous system, the vagus nerve innervates:
Parasympathetic innervation
Esophagus, stomach, small intestine and upper colon
In extrinsic nervous system, pelvic nerve innervates (parasympathetic innervation)
Descending colon
Sigmoid colon
Rectum
Anal canal
The _______ plexus and ________ plexus form networks of the enteric nervous system
Myenteric
Submucosal
The enteric nervous system innervates:
Blood vessels, smooth muscle, secretory cells, and endocrine cells
The enteric nervous system relays info to and from the gut via
The extrinsic system
Myenteric plexus is found thru/o GI tract and mostly controls
Motility
The submucosal plexus is found predominantly in the intestines and mostly controls
Secretion
Extrinsic control of muscles dominates in
Esophagus
Stomach
Defecation
Enteric control of muscles dominates in
Small intestine
Large intestine
3 different subtypes of gastrointestinal peptides
Hormones
Paracrines
Neurocrines
Gastrin is secreted from ?
G cells in stomach
Gastrin is released in response to ?
Peptides and amino acids from protein degradation
Distention of stomach
Vagal stimulation
Gastrin acts to ?
Stiimulate HCl secretion by parietal cells of stomach
Patients with ______ hypersecrete gastric acid due
to continuous release of gastrin into blood from gastrinoma in small intestine
or pancreas; they develop duodenal ulcers, diarrhea, and steatorrhea (excess fat in stools)
Zollinger-Ellison Syndrome
Cholecystokinin is secreted from ?
I cells of the proximal small intestine
Cholecystokinin is released from I cells in the proximal small intestine in response to ?
small peptides, AA’s, fatty acids, monoglycerides (containing 8 or more carbons) that bind to I cells
CCK releasing peptide
Monitor peptide
Monitor peptide is released from the ?
Pancreas
CCK-releasing peptide is secreted by ?
Paracrine cells w/in epithelium into lumen of small intestine
In the absence of a meal, what happens to both CCK releasing peptide (from paracrine cells) and monitor peptide (from pancreas)
They are both degraded by trypsin
Functions of cholecystokinin (CCK)
stimulates gallbladder contraction and pancreatic enzyme secretion;
potentiates pancreatic bicarbonate secretion stimulated by secretin inhibits gastric emptying – reason fatty meals empty more slowly than non- fat meals
signal for satiety
Explain what secretin does
Secretin is released by S cells in the proximal small intestine in response to acid. It stimulates the pancreas and liver to release bicarbonate and water, which both neutralizes the acid and decreases acid production in parietal cells. It also increases bile production
Explain glucose dependent insulinotropic peptide (GIP)
GIP is secreted in the proximal small intestine by K cells as a response to glucose and fatty acids (and a lesser extent amino acids) it stimulates the release of insulin from the pancreas.
Explain motilin
Motilin is released cyclically every 90 minutes from the upper small intestine and stimulates a migrating myoelectric complex in the stomach and small intestine. Release of motilin is abolished by eating.
Explain the paracrine factor somatostatin
Secreted by D cells throughout the entire small intestine in response to acid in the lumen. Somatostatin inhibits the release of all GI hormones. It also inhibits gastric acid secretion and the release of gastrin
Explain the GI role of Histamine:
Histamine is secreted in the acid producing portions of the stomach by enterochromaffin-like cells. It causes increased gastric acid secretion both directly and by potentiating the effects of gastrin and ACh.
Explain vasoactive intestinal peptides actions (VIP
VIP is release from nerves in the mucosa and intestinal smooth muscle. It’s main action is to cause smooth muscle relaxation. It also stimulates intestinal and pancreatic secretion.
Explain how Gastrin-Releasing peptide works
GRP (bombesin) is released from nerves in the gastric mucosa secondary to vagal stimulation. GRP then causes the release of gastrin.
Explain the actions of enkephalins
Enkephalins are released from the gastric mucosa and the smooth muscle of the GI tract. They cause the contraction of GI smooth muscle, especially the lower esophageal, pyloric, and iliocecal sphincters. Enkephalins also inhibit the secretion of fluid and electrolytes (stopping diarrhea)
GI smooth muscle slow waves are generated by ?
Interstitial cells of Cajal
Are slow waves action potentials?
No
Periodic changes in resting membrane potential of smooth muscle cells.
Potential rhythmicity depolarizes and polarizes
Also called basic electrical rhythm
Characteristic of GI smooth muscle
Slow waves
