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160 Cards in this Set

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  • Back
function of ICC
interstitial cells of cajal: pacemaker cells
GI smooth muscle resting potential?
between -40 to -80 mV
background oscillations in resting membrane potential are called
slow waves or BER (basic electrical rhythm)
what modulates the amplitude of slow waves?
nerves and hormones
PANS affect on slow wave amplitude?
increases
SANS affect on slow wave amplitude?
decreases
what controls the inherent excitability of pacemaker cells?
tonic inhibition from inhibitory motor neurons
what is the function of the cephalic phase of digestion?
to prepare the GI to receive food
Results of PANS stimulation during cephalic phase?
increased salivation, gastric acid, pepsinogen, gastrin, pancreatic juice, bile
functions of saliva
Digestion: alpha-amylase, mucin to soften and lubricate food; protection: alkaline pH to neutralize acid, IgA, lysozyme, lactoferrin
function of lactoferrin:
binds iron and acts as a bacteriostat
salivary glands consist of these two cell types:
acinar cells: secrete saliva into acini; Duct cells: line salivary duct and secrete stuff to modify saliva composition
two types of salivary acinar cells
mucous and serous
mucus acinar cells secrete:
mucin glycoproteins
serous acinar cells secrete:
alpha amylase, water, K, Cl, Na, HCO3
Innervation of salivary secretion
PANS --> Ach --> M3 receptor on acinar and duct cells; SANS --> NE --> alpha and beta --> stims salivation
Which cells are the primary H+ secreters?
Parietal cells
what is the alkaline tide?
secretion of HCO3- into bloodstream by parietal cells as by product of acid secretion
three direct stimulants of gastric acid secretion
Ach, Gastrin, Histamine
which neurons release Ach in enteric system?
vagal post ganglionic and enteric neurons
what does Ach bind in the enteric system?
M3 receptor
Which cells secrete gastrin?
G cells
What does gastrin bind?
CCKb
through which pathway do gastrin and Ach act?
PLC to IP3 and DAG leading to increased intracellular Ca2+
which cells secrete histamine?
ECL and mast cells
through which pathway does histamine act?
adenylyl cyclase leading to increased cAMP and then PKA
how do Ca and cAMP increase acid secretion?
stimulate K+ channels on apical membrane, promote K+ efflux, hyperpolarizes the cell, promotes Cl- secretion into lumen; also increase insertion of Cl- chans and H+/K+ ATPase in apical membrane
Pathophys of Zollinger-Ellizon Syndrome?
gastrin producing tumor leading to excess production of gastric acid
how does indirect gastrin stimulation work?
gastrin and Ach induce ECL to release more histamine
What does somatostatin do?
reduces acid secretion
How does somatostatin function?
directly: reduces intracellular cAMP in parietal cells via receptors, indirectly by inhibiting gastrin and histamine secretion
which D cells have direct contact with the lumen?
those in the antrum
what stimulates somatostatin secretion?
protons in the antrum
What inhibits somatostatin secretion?
Ach
describe stimulation in cephalic phase
neural Ach directly activates parietal cells, indirectly activates ECL cells, antral vagal stim induces release of GRP, Ach inhibits somatostatin release
describe stimulation in gastric phase
distention triggers vagovagal response and release of Ach, partially digested prots in antrum stim release of gastrin
which cells secrete pepsinogen?
chief cells
what stimulates mucus secretion?
vagal Ach and mucosal irritation
what is intrinsic factor used for?
vital for B12 absorption
describe process of B12 absorption
B12 binds haptocorrin in stomach, duodenal proteases digest haptocorrin, B12 binds intrinsic factor and absorbed in ileum via receptors
name two mediators which inhibit stomach contraction
VIP and NO
what stimulates Secretin release?
acid
what does secretin do?
inhibits antral contractions and stimulates contraction of pyloric sphincter
what induces CCK release?
fat
what does CCK do?
stims vagovagal response to decrease gastric emptying, stimulates prot secretion from acinar cells
function of Sphincter of Oddi?
at junction between common bile duct at entrance into duodenum
list pancreatic digestive enzymes (4)
alpha amylase, lipases, proteases, nucleases
List pancreatic lipases (4)
pancreatic lipase, procolipase, phospholipase A2, carboxyl ester hydrolase
List pancreatic proteases (5)
trypsin, chymotrypsin, carboxypeptidase A and B, elastase
which enzyme activates trypsinogen?
enterokinase
what is CCK
hormone from small intestine
which acinar receptors does CCK bind to?
CCK-A
Which hormones affect Acinar cells?
CCK, Ach, VIP, Secretin
What does Ach do to acinar cells?
binds M3, stimulates protein secretion
what is the mechanism of CCK and Ach in acinar cells?
via IP3 to increase Ca2+
which cells make secretin?
intestinal endocrine cells
which cells make VIP?
pancreatic neurons
what is the mechanism of Secretin and VIP?
increase intracellular cAMP
which hormones regulate duct cell secretion?
Secretin and Ach stimulate it
what stimulates CCK release?
fatty acids and 8+ carbon monoglycerides, peptides and amino acids to a lesser extent
functions of CCK (5)
stim of pancreatic enzyme secretion, stim of gall bladder contraction, relaxation of Oddi, inhibits gastric emptying by pylorus constriction, appetite suppression
most important function of secretin?
increase bicarbonate secretion
where are S cells found most?
duodenum and proximal jejunum
what is the composition of bile?
bile acids, phospholipids, cholesterol, bilirubin pigments, inorganic ions
whats the key acid for bile acid synthesis?
7alpha-hydroxylase
describe bile synthesis negative feedback?
reabsorbed bile acids inhibit 7a-hydroxylase, reducing the use of cholesterol for new bile acids
whats the starting substance for bile acids?
cholesterol
MMC associated with cycling levels of which peptide hormone?
motilin
diff between MMC and Phasic contractions?
MMC: infrequent, long, entire intestine; Phasic: more freq, short, local
two types of intestinal contraction
segmented contractions and peristalsis
two excitatory neurotransmitters that activate circular muscle to contract
Ach on muscarinic receptors and substance P on neurokinin receptors
two inhibitory neurotransmitters that act on circular muscle
VIP and NO
two forms of dietary starch:
amylase (linear glucose polymer), amylopectin (large branched glucose polymer)
sucrose is?
glu-fru
lactose is?
glu-gal
maltose is?
glu-glu
dietary fiber composed of?
cellulose and pectin
two stages of dietary carb digestion
alpha amylase cleaving interior 1,4 linkages, then cell surface oligosaccharidases
name groups of oligosaccharidases
lactase and alpha-glucosidases
what are the end products of disaccharide digestion?
glucose, galactose, fructose
Glucose and galactose enter apical membrane via?
cotransport w/ Na through SGLT1
fructose enters apical membrane via?
facilitated diffusion through GLUT5
monosaccharides leave cell on basolateral side via?
GLUT2, Na+ independent
what is responsible for peptide digestion in the stomach?
pepsin and acid
where does most peptide digestion occur?
duodenum and jejunum by pancreatic proteases
how are peptides absorbed?
di/tri peptides absorbed by H+/oligopeptide cotransporter PepT1
what generates the proton gradient for PepT1?
Na/H transporter
how are amino acids absorbed?
via Na+/amino acid cotransport
which enzymes responsible for early fat digestion?
lingual lipase from saliva and gastric lipase from chief cells
what do lingial and gastric lipases do?
release fatty acids from triglyc, leaving diglyc
where does most lipid digestion occur?
duodenum and jejunum by pancreatic lipase
pancreatic lipase requires this for full activity
alkaline pH and colipase
fatty acids absorption enhanced by?
acidic pH: get protonated (neutral now) and diffuse into cell
what do fatty acid binding proteins do?
bind and transport newly absorbed fatty acid to ER
where are most water soluble vitamins absorbed?
jejunum
where are B12 and vit. C absorbed?
Ileum
describe B12 absorption
binds R proteins in saliva and gastric fluid, R cleaved in duodenum, B12 binds intrinsic factor, binds receptors in ileum, shows up in blood bound to transcobalmin II
what are the fat soluble vitamins?
A, D, E, K
which of the fat soluble vitamins require energy for absorption?
K, needs transporter
Describe Vitamin A absorption
absorbed as beta carotene, cleaved into 2 retinol molecules, transported in blood via retinol binding proteins
describe mass peristaltic movements
strong prolonged contractions that occur 3-4 times a day
what is colonocolonic reflex?
contraction of one part of colon leads to relaxation in other parts
what mediates colonocolonic reflex?
enteric reflexes and sympathetic nerves
what is the gastrocolic reflex?
when food enters stomach, colon motility increases
what modulates gastrocolic reflex?
gastrin and CCK
what is Hirschsprung's disease?
absence of enteric neurons from parts of colon due to failure of neural crest cell migration, lose colonocolonic reflex
what does Hirschsprung's disease cause?
constipation and megacolon
how to treat hirschsprung's disease?
surgical excision of affected colon
mechanisms of water transport across intestinal cells
paracellular and transcellular via aquaporins
list 4 mechanisms of Na+ absorption
cotransport w/ organics, Na+/H+ antiporter, help of Cl-/HCO3- transporter, and ENaC
mechanism of potassium transport?
paracellular and transcellular via aquaporins
mechanism of intestinal secretion
water secretion dependent on Cl-, from Na+/K+/2Cl- on basolat and CFTR on apical
mechanisms of transport regulation
hormonal: corticosteroids, mineralicorticoids, angiotensin, epinephrine stimulate absorption; neuronal: VIP and Ach stim secretion; immune: mast cells release histamine which stims secretion
liver receives blood from these two sources:
portal vein and hepatic artery
percentage of liver blood flow from portal vein and hepatic artery
portal vein: 70%, hepatic artery: 30%
what is hepatic arterial buffer response?
balance between blood from from hepatic artery and portal vein to maintain constant flow
what mediates arterial buffer response?
adenosine
portal hypertension accurs beyond what blood pressure?
>5 mm Hg within the liver
what is budd-chiari syndrome?
thrombotic occlusion of the hepatic veins at their opening into the IVC
mediator of vasoconstriction in the liver
endothelins
mediator of vasodilation in the liver
NO
functions of liver?
synth of plasma proteins, blood protection/clearance, bile, solubilization/transport/storage, energy generation/substrate conversion
which plasma proteins does the liver produce?
albumin, vitakim K dependent clotting factors, substrate binding proteins, hormones (angiotensinogen, IGF-1)
protective functions of liver
phagocytic/endocytic effects of kupffer cells, ammonia metabolism, glutathione synthesis, drug detox
role ammonia metabilism in liver
convert toxic ammonia (product of protein metabolism) into urea for excretion
what is glutathione?
major cytoplasmic reducing agent, crucial for preventing oxidative damage to proteins
function of Phase I drug detox reactions
redox rxns, add oxygen containing group to drug
function of Phase II drug detox reactions
covalent attachment t owater soluble carrier molecule (glucuronic acid or glutathione)
which enzyme is responsible for phase I reactions?
Cyp450
what are Phase III drug detox reactions?
energy dependent pathways for excretion of drugs
downside of phase I rxns?
generally convert substances into more toxic intermediates
which hormone controls gallbladder secretions?
CCK
bile acids synthesized by liver are called?
primary bile acids
two major primary bile acids are:
cholic acid and chenodeoxycholic acid
what are secondary bile acids?
primary bile acids which have been metabolized by bacteria
two major secondary bile acids?
deoxycholic acid and lithocholic acid
what prevents bile acids from destroying hepatocyte cell membrane?
cytosolic bile acids bound to bile-acid binding proteins
what is the key phospholipid in bile?
lecithins
what happens to porphyrin from hemoglobin?
converted to bilirubin
what is indirect bilirubin?
bilirubin bound to albumin
what is direct bilirubin?
bilirubin after it has been conjugated to two glucuronic acids, water soluble
what excretes phospholipids?
MDR2
where is transferrin synthesized?
liver
role of liver and vitamins?
serves as storage site and actively participates in metabolism
where is Vitamin A stored?
liver
describe vitamin A metabolism
absorbed, esterified to retinyl esters into chylomicrons, metabolized to retinol, bound to Retinol Binding Protein, transferred to stellate cell, stored in lipid droplets
describe vitamin D metabolism
VitD synth from preVitamin D in skin or absorbed in intestine, hydroxylated, hydroxylated again in kidney to 1,25 dihydroxy vitamin D
what does vitamin E do?
potent antioxidant, protects membrane structures against free radicals and lipid peroxidation
describe vitamin E metabolism
some trnasferred to HDL and LDL, some to liver, packaged into VLDL for distribution
role of liver in B12 absorption?
produces transcobalamin II, plasma protein, which binds B12 and takes it to liver
understand Zonal Gradients
outer zone (1): most oxygenated, high glucose, inner zone (3) least oxygenated
what does Zone I do?
oxidative metab olism, beta oxidation, gluconeogenesis, amino acid metabolism, cholesterol synth, bile formation
what does Zone III do?
xenobiotic metabilism, glycolysis, liponeogensis, glucose utilization
how to control liver function?
via substrates, hormones, receptors, gene expression changes
acetominophen intermediate after Phase I?
NAPQI - very toxic
how is liver function controlled by substrates?
glucose enters via GLUT2, phosphorylated: prevents glucose from leaving cell and maintains gradient
effects of glucagon and epinephrine on liver?
stimulate glycogen breakdown into glucose
describe apotransferrin receptor function in liver
in normal pH low affinity for apotransferrin but high affinity for transferrin, in low vesicle pH, increased affinity for apotransferrin and low affinity for transferrin…this induces iron release
what is apotransferrin?
transferrin without iron bound
hormones critical for hepatocyte regeneration?
EGF, TGF-a, HGF