GI Physiology: First Aid & Ninja Nerd Because That Guy Sucks Flashcards
secreted by G cells in the antrum of stomach, duodenum
gastrin
increases H+ secretion
gastrin
increases the growth of gastric muscosa
gastrin
increases gastric motility
gastrin
upregulated by stomach distension/alkalinization, animo acids, peptides, vagal stimulation via GRP
gastrin
down regulated by a pH less than 1.5
gastrin
upregulated by chronic proton pump inhibitor use
gastrin
secreted by D cells in pancreatic islet and GI mucosa
somatostatin
decreases gastric acid and pepsinogen secretion
somatostatin
decreases pancreatic and small intestine fluid secretion
somatostatin
decreases gallbladder contraction
somatostatin
decreases insulin and glucagon release
somatostatin
upregulated by acid
somatostatin
downregulated by vagal stimulation
somatostatin
inhibits secretion of various hormones, encourages homeostasis
somatostatin
(somato-stasis)
secreted by I cells in the duodenum and jejunum
cholecystokinin (CCK)
increases pancreatic secretion
CCK
increases gallbladder contraction
CCK
decreases gastric empyting
CCK
increases spinchter of Oddi relaxation
CCK
upregulated by fatty acids, amino acids
CCK
acts on neural muscarininc pathways to cause pancreatic secretion
CCK
secreted by S cells in the duodenum
secretin
increases pancreatic HCO3- secretion
secretin
decreases gastric acid secretion
secretin
increases bile secretion
secretin
upregulated by acid, fatty acids in lumen of duodenum
secretin
allows pancreatic enzymes to function by neutralizing the gastic acid in the duodenum via increased bicarb production
secretin
secreted by the small intestine
motilin
produces migrating motor complexes (MMCs)
secretin
upregulated in a fasting state
2
motilin
ghrelin*
*don’t think this has been discussed yet, FA pg 380
erythromycin can be used to stimulate peristalsis because it’s a […] receptor agonist
not sure if he discussed this, but useful clinical correlation i think
motilin
FA pg 380
increases smooth muscle relaxation and spinchter relaxation
NO and VIP
secreted from parasympathetic ganglia in spinchters, gallbladder, small intestine
VIP
increases intestinal water and electrolyte secretion
VIP
secreted by parietal cells of stomach
2
gastric acid
intrinsic factor
upregulated by histamine, gastrin, and vagal stimulation
2
gastric acid
intrinsic factor
downregulated by somatostatin, GIP, prostaglandin, and secretin
2
gastric acid and intrinsic factor
vitamin B12 binding protein
intrinsic factor
secreted by chief cells of stomach
pepsin
digests proteins
pepsin
upregulated by vagal stimulation (Ach), local acid
pepsin
pepsinogen is converted to pepsin in the presence of
H+
secreted by muscosal cells in the stomach, duodenum, salivary glands, and pancreas
and Brunner glands in the duodenum
bicarbonate
neutralizes acid
bicarb
upregulated by pancreatic and biliary secretion with secretin
bicarb
trapped in the mucus that covers the gastric epithelium
bicarb
autoimmune destruction of parietal cells can cause
chronic gastritis and pernicious anemia
(lack of gastric acid and intrinsic factor to bind B12)
FA pq 381
somatostatin analog used to treat acromegaly, carcinoid syndrome, VIPoma, and variceal bleeding
octreotide
throwing it back to RC haha
FA pg 380
secreted by K cells in duodenum and jejunum
glucose dependent insulinotropic peptide
GIP
exocrine: decreases gastric H+ concentration
endocrine: increases insulin release
glucose dependent insulinotropic peptide
GIP
upregulated by fatty acids, amino acids, and oral glucose
glucose dependent insulinotropic peptide
GIP
gastin increases acid production primarily through its effects on […] cells, leading to histamine release
enterochromaffin like cells (ECL)
what layer of the alimentary canal contains the myenteric plexus?
muscularis externa
what layer of the alimentary canal contains the submucosal plexus?
submucosa
if a structure has serosa it is
intra or retroperitoneal
intraperitoneal
if a structure has adventitia it is
intra or retro peritoneal
retroperitoneal
for food to move down the gut, the circular muscles need to […] and the longitudinal muscles need to […]
contract/relax
- contract
- relax
ascending fibers in the myenteric plexus work on the […] side of the bolus to push it forward
oral or aboral
oral
what neurotransmitters cause the circular muscles to contract
Ach
what neurotransmitters cause the longitudinal muscles to relax?
NO and VIP
the descending fibers work on the […] side of the bolus to open and relax the next segment
oral/aboral
aboral
what neurotransmitters relax the circular muscles?
NO and VIP
what neurotransmitters contract the longitudinal muscle fibers?
Ach
chemoreceptors are located in the […] plexus
submucosal or myenteric
submucosal
how to chemoreceptors stimulate blood vessels?
cause dilation, more blood flow, increased absorption of nutrients
how to chemoreceptors stimulate the glands in the submucosal plexus?
stimulates glands to secrete secretions into lumen to help digest food
foods rich in fatty acids and H+ stimulate the release os secretin. what 2 functions does secretin have?
- stimulates hepatocytes to produce bile
- stimulates duct cells in acini of pancreas to release bicarb to neutralize acid
food rich in protein stimulates the I cells to produce CCK. what are the 4 functions of CCK?
- gall bladder contractions
- potentiate secretins action on liver
- stimulates pancreatic ductal cells to produce proteases, lipases, and amylase
- relaxes spinchter of Oddi to allow more bile and pancreatic juices into duodenum
food rich in glucose activates K cells to procude GIP. what is the function of GIP?
stimulates pancreas to produce insulin, inhibiting gastric motility
how does the sympathetic nervous system effect the process of the GI tract?
overall: inhibits
decreases motility, blood flow, secretions, absorption
however, contracts spinchters
how does the parasympathetic nervous system effect the process of the GI tract?
overall, induces it
increases motility, secretions, and absorption
however, relaxes spinchters
GLP is secreted by what cells?
L cells in the ileum and large intestine
effects of GLP-1 on stomach
reduces gastric empyting, acid secretion, and motility
describe the vagovagal reflex
- chemoreceptor/stretch receptors transmist signal via afferent fibers to DNV of PNS
- stimulates DNV, sends signal via efferent fibers to activate submucosal and myenteric plexus
parasympathetic response
the vagovagal reflex allows for […] of the stomach
compensation
describe the entero-gastric reflex
- chemo/stretch receptors send signal to prevertebral ganglion (SNS)
- inhibits secretions, dilation, constriction of pyloric spinchter
sympathetic response
the entero-gastric in an inhibitory reflex triggered by what 2 things?
- too much acid in intestines
- too much distension of stomach
describe the defecation reflex
- distension of colon activates chemo/stretch receptors, send signal to sacral plexus (S2-S4)
- sacral plexus sends signal to pelvic splanchinic nerves, which innervate the submucosal and myenteric plexus
- submucosal and myenteric plexus intiate peristaltic waves in descending colon, sigmoid, and rectum
list the layers of the alimentary canal
4
mucosa, submucosa, muscularis externa, serosa
where is the Auerbach plexus located?
myenteric
muscularis externa
where is the Meissner’s plexus found?
submucosa
ascending fibers cause the contraction of the […] and the relaxation of the […] to push food forward
muscle types
- circular muscles
- longitudinal muscles
what receptor is the most powerful stimulator of the submucosal plexus?
chemoreceptors
what is the postganglionic cells bodies of the parasympathetic nervous system?
submucosal and myenteric plexus
which long reflex is activated when there is a high amount of acid in the intestines?
entero-gastric reflex
cells located in the antrum of the stomach
2
D cells
G cells
the vagus nerve can act directly on what cells in the stomach?
D cells and G cells
Ach binds to an M3 receptor on antral D cells, inhibiting the release of
somatostatin
results in an increase of pepsin and HCl secretion
GRP released by the vagus nerve binds to receptors on the G cells to stimulate the release of
gastrin
results in increase of pepsin and HCl secretion
gastrin binds to CCK2 receptors on parietal cells, resulting in
- increased intracellular Ca++
- stimulates proton pump, pushing H+ ions out into lumen and brings K+ in
increases concentration of H+ in lumen
Ach binds to M3 receptors on parietal cells resulting in
- increased intracellular Ca++
- stimulates proton pumps
Histamine binds to the H2 receptor on parietal cells to stimulate
HCl secretion
prostaglandin binds to PGE2 receptors on parietal cells to inhibit
inhibits HCl production
somatostatin binds to SST receptors on parietal cells to inhibit
proton pumps
parietal cells are stimulated by
3
gastrin
Ach
histamine
all end result in increased HCl
parietal cells are inhibited by
2
prostaglandin
somatostatin
inhibit HCl production/proton pumps
chief cells are stimulated by
4
gastrin
histamin
Ach
secretin
stimulate release of pepsinogen
stimulate enterochromaffin like cells (ECL)
2
Ach
gastrin
stimulates release of histamin
inhibit ECLs
1
somatostatin
inhibit release of histamine
the secretion of gastrin stops when the pH of gastric content is below
2
is released as a result of contact of acidic chyme with the duodenmal mucosa
secretin
stimulated by gastric distension and inhibited by presences of excess acid in pyloric antrum
gastrin
stimulates insulin secretion from pancreas
gastrin
the cephalic phase of gastric secretion is controlled by the […] nerves
vagus
3 phases of gastric secretion
- cephalic (1/3 of secretions)
- gastric (2/3)
- intestinal (very little)
describe how contraction moves through the stomach
starts at cardia -> fundus -> antrum -> pylorus
what is it called when 25% of the chyme is pushed back into the corpus of the stomach to continue mixing?
retropulsion
secrete intrinsic factor important for absorbing vitamin B12
parietal cells
when high peptone concentration are sensed by duodenal G cells, the release gastrin into the blood to the parietal cells in the corpus, stimulating the release of
more H+ ions into lumen
peptones are basic
endocrine secretions of the pancreas
insulin
glucagon
exocrine secretions of the pancreas
general
- fluid: bicarb, H20, elctrolytes
- digestive enzymes
secretions that aid in digestion
pancreatic cells that secrete enzymes, Na, Cl and some fluids
acinar
pancreatic cells that modify the fluid secreted by acinar cells, secrete bicarb, and add water to pancreatic juice
ductal cells
fluid secreted by the pancreas contains […] to neutralize the acidic fluid from the stomach
bicarb
describe the flow rate of pancreatic fluid in a fasted state
low flow
* high Cl-
* low bicarb
describe the flow rate of pancreatic fluid in a fed state
high flow
* low Cl-
* high bicarb
the Na and K concentrations of pancreatic fluid are always
isotonic, hypotonic, hypertonic
isotonic
same as plasma
why is bicarb higher in high flow states?
- bicarb is secreted in the small ducts and reabsored in the large ducts
- reabsorption is ineffective at high flow rates
what hormone is the main stimulus for HCO3- release by the pancreas?
secretin
released in response to increased H+ in duodenum
secreted by S cells in duodenum
secretin
major stimuli for release of pancreatic enzymes from acinar cells
CCK
also Ach via vagovagal reflex
- local GI tract reflex circuit
- both afferent and efferent fibers found within the vagus nerve
vagovagal reflex
H+, amino acids, and fats in the duodenum activate the […] reflex and stimulate pancreas to release enzymes
vagovagal
pancreatic enzyme that digests starch
a-amylase
hydrolyzes starch at a1-4 linkages
a-amylase
- secreted by the pancreas in the active form
- functional in small intestine
- elevated in acute pancreatitis
a-amylase
breaks down amylopectin and amylose
a-amylase
what is different about salivary amylase vs. pancreatic?
salivary amylase has an optimal pH of 6 and is inactivated in the stomach
only […] are absorbed by the intestine
carbohydrate form
monosaccarides
after amylase intital breaks down amylopectin and amylose, further digestion occurs at
intestinal brush border by oligosaccharide hydrolases
maltase, sucrase, lastase, etc
rate limiting step of carbohydrate digestion
breakdown at the intestinal brush border
glucose
fructose
galactose
are all…
monosaccharides
hydrolyzes 1 and 3 bonds of triglycerides into fatty acids and monoglycerides
pancreatic lipase
pancreatic enzymes for fat digestion
3
colipase
lipase
phospholipase
assists pancreatic lipase
colipase
- secreted as inactive pro-phospholipase A2
- activated by trypsin
phospholipase A2
pancreatic enzymes that aid in protein digestion
4 big ones
- trypsin
- chymotrypsin
- elastase
- carboxypeptidases
pancreatic enzymes that aid in protein digestion are all secreted as
zymogens
inactive proenzymes
trypsin is secreted as inactive trypsinogen and activated by […]
enterokinase
brush border enzyme
once activated by enterokinase, […] activates all other protein enzymes
trypsin
when pancreatic secretion is blocked, auto-activation of trypsin leads to auto-digestion of pancreatic enzymes causing
clinical correlate
acute pancreatitis
increased amylase and lipase
- found in the gastric glands
- secrete HCl (gastric acid)
parietal cells
- maintains very low pH in stomach
- provides protection against infectious agents
- denatures proteins for breakdown/absorption
gastric acid
stomach cells are protected from gastric acid by
mucous and bicarb secreted by neck cells
hormone from G cells in antrum of stomach
gastrin
binds to CCKb receptor on parietal cells to trigger them to release HCl
gastrin
activates ECL cells which produce histamine to stimulate parietal cells to release more HCl
gastrin
activates G cells to produce gastrin via binding on M3 receptors
Ach
from vagus
the vagus can release […] to stimulate G cells to produce gastrin
GRP
3 stimuli for acid procdution
- direct gastrin
- indirect gastrin (histamine mediated)
- vagus nerve (Ach and GRP)
- muscarinic blocker
- blunts parietal cells stimulation by Ach
- but does not block GRP so not great for acid control
atropine
- necessary for B12 absorption
- released by parietal cells
intrinsic factor
block H+ secretion by parietal cells
proton pump inhibitors
omeprazole, pantoprazole
H+ that is pumped out of parietal cells is formed from what enzyme?
carbonic anhydrase
H+ formed by carbonic anhydrase causes HCO3- to be pumped out of the cell. The increased serum HCO3- after meals if referred to as the
alkaline tide
how does vomiting cause metabolic alkalosis?
- increased production of HCl
- more HCO3- is generated during the production of HCl
hypochloremia as well
a low urinary chloride indicates
vomiting
loss of Cl- in gastric secretions
stimulate secretion of HCl by parietal cells
3
Ach
gastrin
histamine
inhibit secretion of H+ by parietal cells
2
somatostatin
prostaglandins
work via Gq proteins with IP3/Ca second messenger system
2
Ach
Gastrin
work via Gs/i and cAMP second messenger system
histamine, somatostatin, PGs
Gq proteins
2
Ach
Gastrin
Gs/i proteins
3
histamin
prostaglandins
somatostatin
H2 blockers
- cimetidine
- ranitidine
- fomotidine
- nizatidine
decrease HCl production
PGE1 analog that blunts acid production
misoprostol
released by chief cells to digest proteins
pepsin
chief cells release pepsinogen, it is activated to pepsin by
H+
works best at a pH of 1-3
pepsin
what stimulates the release of pepsin?
vagus nerve
- major hormone that stimulates acid secretion in stomach
- produced by antral G cells
gastrin
gastrin is secreted into the […] vein blood and takes physiologic action on […] cells
portal vein
parietal
found in glands of lamina propria in the mucosa layer in antrum
cell type
G cells
found in glands of lamina propria in the mucosa layer in body
cells type
parietal cells
stimulates H+ secretion by parietal cells
gastrin
effects of gastrin
3
- stimulates H+ secretion by parietal cells
- stimulates growth of gastric mucosa
- increases gastric motility
gets stomach ready for digestion
gastrin stimulates […] cells to release histamine, which stimulates parietal cell
ECLs
parietal cell receptors
3
- histamine (most important)
- gastrin
- Ach (vagus)
most important way by which HCl secretion is stimulated
indirect gastrin pathway
gastrin -> ECL -> histamine -> parietal cells
stimuli for increased gastrin secretion
4
- stomach distension
- alkalinazation
- amino acids
- vagal stimulation (GRP)
gastrin secretion is inhibited by
- low pH
- somatostatin
atropine does not block […] mediated gastrin release
GRP
phenylalanine and tryptophan are potent stimuli for […] release
gastrin
- tumors that occur in duodenum or pancreas
- cause excessive acid secretion
- cause hypertrophy/hyperplasia of mucosa
clinical correlate
gastrinoma
gastrin secreting tumors
- abdominal pain that improves with food
- chronic diarrhea
- ulcers in distal duodenum refractory to PPI therapy
- heartburn
clinical correlate
zollinger-ellison syndrome
from gastrinoma
- extremely high gastrin levels
- increased gastrin after secretin administration
would indicated what disease?
gastrinoma
elevated […] levels are a typical finding of pernicious anemia
gastrin
- hormone for gallbladder contraction
- stimulates secretion of pancreatic enzymes
CCK
released by I cells in the duodenum and jejunum
CCK
how does CCK stimulate pancreatic enzyme secretion?
- CCK receptors in vagus nerves
- CCK stimulates vagus -> Ach -> pancreas
- relaxes spinchter of Oddi
- inhibits gastric empyting
CCK
major stimuli for CCK release
3
- fatty acids
- monoglycerides
- amino acids
not triglycerides
hormone to raise pH in small intestine
secretin
released by S cells of duodenum
secretin
released in response to H+ in duodenum and fatty acids in duodenum
secretin
increases HCO3- secretion by pancreatic duct cells
secretin
neutralizes gastric acid, allows pancretic enzymes to function
inhibits gastic H+ secretion by inhibiting gastrin release
secretin
increases bile production
secretin
- promotes pancreatic flow
- water secreted with bicarb and flushes pancreatic enzymes into intestines
secretin
inhibits most GI hormones
somatostatin
released by D cells throughout GI tract
somatostatin
major stimuli for somatostatin release
low pH
major inhibitor for somatostatin release
vagus nerve
thinking about eating decreases somatostatin to prepare digestive tract
how does somatostatin regulate digestion/acid secretion
describe both fed and fasted states
fed: food in stomach -> decreases somatostatin -> hormones are released
fasted: acid in stomach -> increases somatostatin -> hormones inhibited
analog of somatostain used in upper GI varices bleeding
octreotide
reduces splanchnic blood flow
used to treat carcinoid syndrome,
acromegaly,
gastrinoma
octreotide
- stimulates insulin release from pancreas
- blunts H+ secretion
GIP
released by K cells of duodenum/jejunum
GIP
what stimulates the release of GIP?
3
glucose
fatty acids
amino acids
only hormone released in response to fats, protein, and carbs
why is oral glucose metabolized faster than IV glucose?
IV glucose does not stimulate GIP release
- synthesized in neurons
- released in response to action potential onto target cells
VIP
- causes relaxation of the smooth muscle
- raises pH
- inhibits gastric H+ secretion
VIP
similar to secretin
how does VIP raise pH?
stimulates pancreatic HCO3- secretion
important for relaxation of lower esophageal spinchter
VIP
- watery diarrhea (tea colored, odorless)
- hypokalemia
- achlorhydria
clinical correlate
VIPoma
WDHA syndome
rare VIP secreting tumors in pancreatic islet cells
VIPoma
- adult 30-50 years old
- long standing watery diarrhea without blood or pus
- no response to diet change
- high pH in stomach on EGD
- elevated VIP on serum testing
clinical correlate
VIPoma
- released by cells in stomach, intestines, and colon
- promotes motility in fasting state
motilin
highest levels of motilin are found
fed/fasted state
between meals
fasted
binds motilin receptors and used to treat gastroparesis
erythromycin
secreted in antrum
gastrin
secreted in duodenum and jejunum
3
CCK
secretin
GIP
secreted throughout GI tract
3
motilin
VIP
somatostatin
major player in cephalic phase of digestion
vagus nerve
stimulated by thought, sight, and smell of food
vagus
in the cephalic phase, the vagus nerve primarily stimulates
acid secretion by triggering gastrin release
major player in gastric phase
stomach
how does the stomach trigger acid secretion in the gastric phase?
gastric distension, increased gastric pH and amino acids trigger gastrin release
major player in intestinal phase of digestion
small intestine
how does the small intestine trigger CCK, secretin, and GIP release in the intestinal phase?
presence of fatty acids, amino acids, and H+ trigger this release
what does CCK do during the intestinal phase?
3
- gallbladder contraction
- release of pancreatic enzymes
- relax spinchter of Oddi
what does secretin do during the intestinal phase?
2
- release bicarb
- inhibit H+ secretion
