lecture 15- Intro to GI tract physiology Flashcards
list the layers of the gut tract will from outer to inner
serosa –> longitudinal smooth muscle layer –> myenteric plexus –> circular smooth muscle layer –> meissner’s plexus –> submocusa –> mucosa
what is the serosa continuous with
mesentery (pathway for blood vessels to gut tube)
what is the serosa replaced with when it is absent
replaced with adventitia connecting to abdominal wall
what does the submucosa incorporate
blood vessels and submucosal plexus
what does the mucosa support
supports simple columnar epithelium with goblet cells which lines entire gut tract
what collectively forms the enteric nervous system of the gut tract
myenteric and meissner’s plexuses
how does the enteric nervous system operate autonomously
via intrinsic regulation and sensory reflexes
what do parasympathetics typically do to GI tract activity
increases it
what do sympathetics typically do to GI tract activity
decreases it
what are the neurons of the enteric nervous system supported by
intrinsic glial cells
where is the myenteric plexus located
between longitudinal and smooth muscle layers
what is the myenteric plexus primarily controlling
intestinal smooth muscle and participates in tonic and rhythmic contractions
what does the meissner’s plexus mainly control
GI secretion, absorption and local blood flow
what is meissners plexus concerned with
controlling function within inner wall of each minute segment of the intestine
what is the usual stimulus for propulsive movements
distension
what plexus is required for propulsive movements
myenteric
what reflex is involved in receptive relaxation
vagovagal reflex
what is the receptive relaxation initiated by
stomach distension
what increases the distensibility of proximal end of stomach during receptive relaxation
CCK
what is mixing and digestion in stomach stimulated by
vagus nerve increases gastric contractions; sympathetic decreases gastric contractions
what is the gastroileal reflex mediated by
extrinsic ANS and gastrin
what senses food and releases serotonin during peristaltic contractions
enterochromaffin cells in intestine
where does most colonic water absorption occur
in proximal colon
what does the valsalva maneuver result in
increased abdominal pressure
where do slow waves originate
in interstitial cells of canal (pacemakers)
what do spike potentials excite
muscle contraction
what are spike potentials responsible for
opening calcium channels and smaller number of sodium channels in GI smooth muscle cells
what factors cause depolarization
stretching of muscle;
stimulation by acetylcholine (parasympathetic);
stimulation by specific GI hormones
what factors cause hyperpolarization
norepinephrine and epinephrine; stimulation of sympathetic nerves
what are some causes of tonic contractions
continuous repetitive spike potentials, hormones and continuous entry of calcium ions
what reflexes are integrated entirely within the gut wall enteric nervous system control
much of GI secretion, peristalsis, mixing contractions and local inhibitory effects
what reflexes are from the gut to the pre vertebral sympathetic ganglia and then back to GI tract
transmit signals long distance to other areas of gut tract, cause evacuation of the colon (gastrocolic reflex), inhibit stomach motility and secretion (enterogastric reflex), and empty ileal contents into the colon (colonileal reflex)
what reflexes are from the gut to the spinal cord or brain stem and then back to GI tract
reflexes from stomach and duodenum to brainstem and back to stomach control gastric motor and secretory activity, pain reflexes cause general inhibition of the entire GI tract, defecation reflex extend from the colon to the rectum to the spinal cord and back
what are the 4 official GI hormones
gastrin, CCK, secretin, GIP
where does all biologic activity of gastrin occur
in the 4 C-terminal aa
what is stimulus for secretion of gastrin
small peptides and aa in stomach lumen, dissension of stomach, vagal stimulation mediated by GRP
what inhibits secretion of gastrin
acid from stomach and somatostatin
what are the actions of gastrin
stimulates gastric acid secretion by parietal cells and stimulates mucosal growth by stimulating synthesis of RNA and new protein
when does Zollinger-Ellison syndrome occur
from gastrin secreting non-beta cell tumors of pancreas
what is CCK homologous to
gastrin
where is the biologic activity of CCK
C-terminal heptapeptide
what is the stimulus for secretion of CCK
small peptides and aa, fatty acids and monoglycerides
what is the site of secretion of CCK
I cells of duodenum, jejunum and ileum
what is secretin homologous to
glucagon
what is the stimulus for secretion of secretin
acid and fat in lumen of duodenum
what is the site of secretion of secretin
S cells of duodenum, jejunum and ileum
what stimulates pepsin secretion
secretin
what is GIP homologous to
secretin and glucagon
what is the stimulus for secretion of GIP
only GI hormone released in response to protein,fat and carb. released in response to orally administered glucose
what is the site of secretion of GIP
K cells of duodenum and jejunum
what are the actions of GIP
stimulates insulin release and inhibits gastric acid secretion by parietal cells
what is the stimulus for secretion of motilin
fat, acid and nerve action
what is the site of secretion of M cells
duodenum and jejunum
what are the actions of motilin
stimulates gastric and intestinal motility. secreted during fasting
what contributes to the slow emptying of cyme into the small intestine
stretching of stomach wall due to increased food volume promotes increased emptying of stomach due to local myenteric reflexes in the wall
what factors are continually monitored in the duodenum and can initiate enterogastric inhibitory reflexes
degree of distension, presence of any degree of irritation of the duodenal mucosa, degree of acidity of duodenal chyme, presence of certain breakdown products in the chyme
what is the most potent hormone in controlling the duodenum
CCK
what are the 2 types of movement in the intestine
mixing and propulsive contractions
irritation of _____ can cause powerful and rapid peristalsis
intestinal mucosa
what intensifies peristalsis and emptying of ileal contents into cecum immediately after a meal
gastroileal reflex
what are the principal functions of the colon
absorption of water and electrolytes from chyme. storage of fecal matter until it can be expelled
what are haustrations produced by
produced by large circular constrictions plus contractions of the teniae coli
