B5-095 GI Physiology II Flashcards
describe pancreatic morphology
acinar + ductal cells = acinus
multiple acini =lobule
multiple lobules -> main pancreatic duct
how does secretin affect the amount of HCO3-, Cl- and amylase
HCO3-: increase
Cl-: decrease
amylase: decrease
the fall in amylase concentration after secretin reflects
dilution
volume increases
stimulate acinar cell secretion of zymogen granules
5
- VIP
- secretin
- CCK
- ACh
- maybe gastrin?
Ca++ oscillations are a hallmark of stimulation by
2
CCK and ACh
potent stimulators of Cl- secretion
2
CCK and ACh
the movement of […] into the lumen makes transepithelial voltage more negative, driving […} into the lumen via tight junctions
Cl-
Na+
most powerful stimulus for HCO3- secretion
secretin
activates cAMP, stimulates PKA, and phosphorylates CFTR
secretin
activates Gq -> stimulates PLC to release DAG and IP3, releasing Ca++ from stores
ACh
the lumen negative voltage pulls Na+ and water into the lumen via
tight junctions
zymogens secreted by pancreas
5
- trypsinogen
- chymotrypsinogen
- proelastase
- Procarboxypeptidase A
- Procarboxypeptidase B
activates trypsinogen to trypsin
enterokinase
and trypisin can too
activates a majority of the zymogens in a sequential fashion
trypsin
stimulant of cephalic pancreatic secretion
sight
smell taste
mastication
regulatory pathway of the cephalic phase of pancreatic secretion
vagal pathways
the cephalic phase of pancreatic secretion is responsible for […]% of secretions
25
stimulant for the gastric phase of pancreatic secretion
distension
gastrin?
regulatory pathway for the gastric phase of pancreatic secretion
vagal-cholinergic
the gastric phase of pancreatic secretion is responsible for […]% of secretion
10-20
stimulant of the intestinal phase of pancreatic secretion
amino acids
fatty acids
H+
regulatory pathway of the intestinal phase of pancreatic secretion
CCK
secretin
enteropancreatic reflexes
the intestinal phase of pancreatic secretion is responsible for […]% of secretions
50-80
protein and lipid products simulate I cells to secrete
CCK
stimulates vagus nerve to release ACh
H+ stimulates S cells in duodenum to secrete
secretin
stimulates HCO3- secretion
how does this mechanism protect the pancreas from autodigestion?
packaging of many digestive proteins as zymogens
percursor proteins lack enzymatic activity
how does this mechanism protect the pancreas from autodigestion?
selective sorting of secretory proteins and storage in zymogen granules
restricts the interaction of secretory proteins with other cellular compartments
how does this mechanism protect the pancreas from autodigestion?
protease inhibitors in the zymogen granule
block the action of prematurely activated enzymes
how does this mechanism protect the pancreas from autodigestion?
condensation of secretory proteins at low pH
limits the activity of active enzymes
how does this mechanism protect the pancreas from autodigestion?
non digestive proteases
degrade active enzymes
morphology of salivary glands
acinar cells line acinus
intercalated cells line acinar duct
striated cells line striated duct
parasympathetic autonomic control of salivation is regulated by
ACh
sympathetic autonomic control of salivation is regulated by
norepinephrine
what two components of saliva contribute to lubrication and antimicrobial properties?
proline-rich proteins
mucin glycoproteins
enzymes present in saliva
4
- a amylase
- lipase
- ribonuclease
- kallikrein
how does the electrolyte composition of saliva change with stimulation?
Na:
K:
Cl:
Total CO2:
Na: increases
K: decreases
Cl: increases
bicarb: increases
basically creates a more basic environment
does the large inestine have villi?
no
does the large intestine provide nutrient absorption?
no
does the small or large intestine have active K+ secretion?
large
does the small or large intestine have active Na+ absorption?
both small and large
- long lived
- antimicrobial
- secrete defensins, lysozyme, TNFa
paneth cells
anti-helminth cells
tuft cells
use chemoreceptors
maintain mucosal barrier of intestinal epithelium
goblet cell
deliver luminal antigens to APCs
goblet cells
secrete cytokine and chemokines to stimulate TH2 response, promotes tissue restoration
goblet cells
overall, how much fluid is excreted in feces?
100 mL
describe the fluid balance in GI tract
in: 8.5 L/day
oral: 2 L
secreted: 6.5 L
reabsorbed: 8.4 L
only about 100mL lost through feces/day
what bacterial endotoxins utilize the cAMP second messenger pathway?
2
cholera
E. coli
what bacterial endotoxins utilize the cGMP second messenger pathway?
2
E. coli
Yersinia
what bacterial endotoxins utilize the Ca++ second messenger pathway?
C. diff
what hormones/neurotransmitters utilize the cAMP second messenger pathway?
VIP
what hormones/neurotransmitters utilize the cGMP second messenger pathway?
1
guanylin
what hormones/neurotransmitters utilize the Ca++ second messenger pathway?
3
ACh
bradykinin
serotonin
what immune cell products utilize the cAMP second messenger pathway?
2
histamine
prostaglandins
what laxatives utilize the Ca++ second messenger pathway?
1
bile acids
primary mechanism for postprandial Na+ absorption
nutrient couple Na+ absorption in jejunum and ileum
electroneutral Na-H exchange at the apical membrane is stimulated by
high pH of HCO3- rich luminal contents
primary mechanism for interdigestive Na absorption
Na-H and Cl-HCO3 exchange coupled by intracellular pH
results in electroneutral NaCl absorption
in electrogenic Na absorption, the apical step of Na movement occurs via
ENaC channels
Na/Glucose or Na/Amino acid cotransporters occurs where in GI tract?
high Na absorption at jejunum
low Na absorption at ileum
primary mechanism of post prandial Na absorption
Na-H exchanger occurs where in GI tract?
moderate Na absorption at duodenum
high Na absorption at jejunum
parallel Na-H and Cl-HCO3 exchangers occur where in GI tract?
moderate absorption at ileum and proximal colon
primary mechanism for interdigestive Na absorption
epithelial Na channels occur where in GI tract?
high Na absorption in distal colon
ENaC channels
passive Cl- absorption occurs where in GI tract
high Cl- absorption in jejunum
low Cl- absorption in ileum
high Cl- absorption in distal colon
Cl-HCO3 exchanger occurs where in GI tract?
moderate Cl- absorption in ileum
high Cl-absorption in proximal colon
moderate Cl- absorption in distal colon
parallel Na-H and Cl-HCO3 exchangers occur where in digestive system?
moderate Cl- absorption in ileum and proximal colon
through interdigestive period
passive K+ absorption occurs where in GI tract?
low K+ transport in jejunum and ileum
via solvent drag
in the small intestine, K+ absorption occurs via
solvent drag
active K+ secretion occurs in what parts of the GI tract?
low K+ transport in proximal colon
high K+ transport in distal colon
throughout the colon, passive K+ secretion occurs via
tight junctions
driven by negative transepithelial voltage
active K+ secretion occurs where in the GI tract?
moderate K+ transport in proximal colon
very low K+ transport in distal colon
throughout the colon, active K+ secretion is
transcellular
active K+ absorption occurs where in the GI tract?
low K+ transport in distal colon
in the distal colon, active K+ absorption is
transcellular
products macrophages produce that affect intestinal ion transport
2
prostaglandins
O2 radicals
products mast cells produce that affect intestinal ion transport
1
histamine
products neutrophils produce that affect intestinal ion transport
2
eicosanoids
platelet-activating factor
products fibroblasts produce that affect intestinal ion transport
2
eicosanoids
bradykinin
mast cell activation causes histamine release to stimulate the release of […] into the lumen
Cl-
activation of the immune response in the GI tract produces numerous and redundant pathways to increase […] secretion
Cl-
anytime Cl- is moved into the lumen, we’re moving […] and […] into the lumen
water and sodium
mast cells release histamine, which can activate the […] to produce cramping with diarrhea
enteric neurons
directly activates epithelial secretion of Cl- by the ENS
ACh
indirectly increases Cl- secretion following release from Mast Cells via PGE2 release
IL-2
what toxin increases Ca++/CAMK activity?
C. diff
secrete CCK in response of dietary fat and protein
I cells
secretes somatostatin to inhibit gastic acid release
D cells
have specific chemoreceptors to
“taste” helmiths
tuft cells
what cells are important in the feedback to stop eating?
I cells and L cells
located in the duodenum and jejunum, allowing for quicker feedback to stop feeding
I cells
slow gastric empyting which may be perceived as a feeling of fullness
macromolecules
protein and lipids
activates Cl- secretion in acinar cells, resulting in increased NaCl and water transport to lumen
gastrin
activates chloride secretion in salivary glands
ACh
activate Cl- secretion in pancreas
2
CCK and secretin
released out of basolateral surface of I cells following stimulation of fat entry into duodenum
CCK
sends signals via the vagus to the CNS and then to the pancreas to increase acinar secretions
CCK
causes slowing of gastric emptying
CCK
causes contraction of the gallbladder
CCK
produced by I cells
CCK
