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70 Cards in this Set

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what class of hormones enhance the effect of glucose on insulin secreion? give some examples
incretins, such as Gluco-insulinotropic peptide (GIP) and proglucagon-derived peptides 1/2 (GLP 1/2)
Where is secretin secreted? what is its function?
from S cells in the duodenum, increases pancreatic HCO3- and H20 secretion, decreases gastric acid secretion
Where is gastrin secreted? what is its function?
G cells of the gastric antrum. stimulates gastric acid and histamine secretion (which also increases gastric acid)
where is CCK secreted? what is its function?
from I cells of the duodenum. inhibits gastric emptying and acid secretion, stimulates pancreatic ENZYME secretion, induces gallbladder contraction, inhibits food intake
Where is GIP secreted, what is its function?
from K cells of the intestine, stimulates insulin secretion (an incretin)
where is peptide YY secreted, what is its function
L cells of the intestine, all effects are inhibitory: gastric emptying and acid secretion, pancreatic secretion, intestinal motility (the ileal brake), food intake
where is motilin secreted, what is its function?
M cells in the proximal intestine, increases contraction of the LES, increases gastric emptying, increases intestinal motility
where is ghrelin secreted, what is its function?
X/A cells in the stomach and intestine - stimulates gastric emptying, increaes appetite, decreases energy expenditure
where is somatostatin secreted? what is its function?
D cells in stomach and duodenum, inhibits gastrin release, favors net absorption, increases smooth muscle tone and decreases pancreatic secretion
where is serotonin secreted? what is its function?
from enterochromaffin cells. opposes somatostatin (inhibits electrolyte and fluid absorption, favors secretion)
describe acinar (initial) salivary fluid
similar to plasma - isotonic
how is saliva modified by ductal cells?
NaCl is absorbed and KHCO3 is secreted, with more NaCl absorbed -> results in hypotonic solution
how does salivary composition change with flow rate?
all transfer except for HCO3- is diminished at high flow rates - high flow rate will have more NaCl and HCO3-, less K+
what is sjorgen syndrome?
autoimmune disease that attacks Cl/HCO3- exchanger in ductal cells in salivary glands - dry mouth, poor dentition
how does pancreatic secretion vary with flow rate
remember that HCO3- is exchanged for Cl- -> at high flow rates HCO3- is higher and Cl- lower
describe acinar (initial) pancreatic secretion content
High in NaCl, low in KHCO3. acinar cells secrete H20, Cl-, and Na+. Remember Na+ is paraccellular while Cl- in transcellular
what is the strongest hormonal control of pancreated HCO3- secretion?
secretin - activates CA -> increases cAMP -> PKA -> phosphorylates CFTR -> more Cl- secretion and exchange for HCO3-
what is the main hormone responsible for pancreatic enzyme secretion? What hormone has an additive effect with it?
CCK - VIP increases its effect
which surface of hepatocytes faces the sinusoidal space?
basolateral
which 2 compounds were given as examples of secondary bile acids?
lithocholic acid and deoxycholic acid
what signals increased canalicular choleresis? ductular secretion
bile acids increase canalicular secretions while secretin increasing ductular secretions
describe neural stimulation of stomach secretions
parasympathetic neurons release ACh which acts on ECL cells to release histamine -> parietal cells -> release HCL. They also directly synapse on parietal cells. GRP releasing neurons synapse on G cells -> release gastrin -> upregulates ECL and parietal cells
describe the process of acid secretion inhibition in the stomach
acid in the duodenum prompts D cells to release somatostatin which both inhibits gastrin and blocks G cells from releasing gastrin
name three stimulatory signals for gastric acid secretion, 2 inhibitory signals
stimulatory - gastrin and ACh (Through Gq), histamine (Gs). Inhibitory - somatostatin and prostaglandins (Gi)
describe the role of GRP
a neurotransmitter released from vagal nerves which causes gastrin release and SM relaxation in the stomach as part of the vasavagal reflex
what is zollinger-ellison syndrome?
overproduction of gastrin, often due to hormonally active tumors causes ulceration of the duodenum
describe the absorption of monosaccharides
glucose and glactose are absorbed by apical SGLT channels, fructose enters through GLUT5. Both diffuse passively through basal GLUT2
what is enterokinase?
membrane bound protease in intestine that activates pancreatic propeptidases
why can people with specific AA transporter defects still absorb some of the deficient amino acid?
short peptides (2 or 3 residues) can be absorbed via HP (proton/peptide) transporters and these can include the lacking AA
describe the absorption of folate
absorbed by specialized folate transporter, then converted intracellularly to TH4 before secretion into interstitium
what is calbindins role in calcium absorption?
buffers intracellular calcium to favor absorption. vitamin D stimulates expression of calbindin
describe iron absorption
Fe2+ binds to transferrin, which then complexes with transferrin receptor, both are endocytosed. Fe2+ can also enter as a heme or through H+/Fe2+ symporter
which nephrons are primarily responsible for dilution and concentration of urine? describe them
juxtamedullary nephrons

long loops of henle which descend to deep medulla and are supplied by vasa recta
where are juxtaglomerular cells located?
on the afferent (incoming) arteriole
what is the equation for renal clearance? what must be true of substances that follow these dynamics
clearance = (urine flow x urine concentration) / plasma concentration

substance must not be synthesized or metabolized in kidneys
which substances are used to measure glomerular filtration rate? what qualities do these meet?
inulin or creatinine

-not synthesized or metabolized
-freely filtered
-not secreted or absorbed
which substance(s) are used to measure renal plasma flow? what qualities do these meet?
para-aminohippuric acid (PAH)

-not synthesized or metabolized
-freely filtered
-doesnt alter RPF
-100% filtered or secreted
what equation calculates GFR?
remember amount filtered = amount excreted

GFR = ([inulin]u x urine flow)/ [inulin]p
what equation calculates RPF? RBF?
RPF:
RPF = ([PAH]u x urine flow)/ [PAH]p

RBF = RPF / (1-hematocrit)
remember RBCs are the main unfilterable constituent in blood
what is the filtration fraction? give examples that will increase or decrease it
GFR/RPF

will increase with renal artery stenosis
will decrease with filtration dysfunction - systemic lupus erythematosus, rhabdomyolysis
what is clearance ratio? give examples for high and low value
ratio to clearance of inulin (fully and only filtered)

high value (great than 1) indicates secretion, ie PAH
low value (less than 1) indicates reabsorption, ie Na+
how large of particles can be filtered in the glomerulus?
anionic proteins up to 20 angstroms and cationic proteins up to 42 angstroms
describe the mechanism of tubuloglomerular feedback during high flow in the distal tubule
increased calcium in MD cells -> adenosine and ATP to JGA cells -> calcium in smooth muscle cells of afferent arteriole -> vasoconstriction

also decreases renin release (this causes vasodilation, but is mostly active in efferent arteriole -> decreases GFR)
what is a typical GRF? Filtration fraction?
180 L/day, 16%
describe changes in transepithelial voltage gradient in the nephron
very early PT lumen is negative, becomes postive due to paracellular absorption of Cl-, favors absorption of Na+

In the distal nephron (DT and collecting duct), the lumen is negative from high amounts of remaining Cl- following lots of cation reabsorption -> favors K+ and H+ secretion
describe the function and location of aquaporins
AQP1 - apical in PT
AQP2 - regulated by ADH in collecting tubule
AQP3/4 - basal in PT
describe how absorptive gradient acts a feedback to counter changes in GFR
increased GFR -> increased filtered load -> capillary blood has lower volume and higher osmolarity -> favors absorption of Na+ and H20 (~constant ratio)
how does the thick ascending limb of the LOH dilute urine?
absorbs electrolytes, mainly NaCl without H20
what is bartter's syndrome?
variety of mutations (can be NKCC2, ClC-Kb or ROMK) in thick ascending limb

malabsorption of sodium in TAL -> polyuria and salt depletion -> hyperaldosteronism and hyopkalemic metabolic acidosis
where in the nephron do thiazide diuretics act?
on NaCl symporter in distal tubule
where are principal cells found? what is their function?
found in late distal tubule / collecting ducts

Absorb Na+, secrete K+
regulate H20 absorption (ADH responsive)
where are intercalated cells found? what is their function?
found in late distal tubule and collecting duct

regulate acid base balance
reabsorb K+ (exhanged with H+)
what is insulins role in K+ regulation?
causes intracellular uptake of K+ (remember most K+ is stored intracellularly)

in diabetes mellitus -> hyperkalemia with low intracellular concentration
how are H+ and K+ regulation related?
H+/K+ exchanger on intercalated cells (and other cells not in kidney)

during acidosis, plasma will hyperkalemia to buffer acidity
where are the main sites of K+ absorption and regulation
mostly absorbed in PT

regulated by SECRETION when elevated in the DT and CD (principal cells)
where in the nephron is Ca2+ excretion regulated?
in the distal tubule - sensitive to PTH

also, local regulation in the TAL via CaSR/NKCC2 regulation
which calcium regulating hormone affects GI absorption of calcium?
calcitriol (vitamin D)
how is the filtered load of calcium measured?
.6 x [plasma Ca2+] x GFR

remember that ~40 percent of plasma calcium is protein bound
name 4 cells types which express CaSR
Distal tubule and TAL cells -> CaSR upregulates NKCC2 channel, increases Ca absorption

Chief cells in parathyroid -> secrete PTH

Proximal tubule cells -> convert vit D -> calcitriol -> increase GI calcium absorption

Parafollicular cells in thyroid -> regulate calcitonin secretion
which hormone inhibits excretion of both calcium and phosphate?
calcitriol
where in the nephron is phosphate transport regulated?
in the proximal tubule, where its absorption is inhibited by PTH

remember that PTH is primarily trying to raise Ca2+, inhibiting Na/Pi symporter increases positive transepithelial electrical gradient for Ca absorption
what factors affect effective circulating blood volume?
blood volume, cardiac output, total peripheral resistance
what hormone opposes the RAA system
ANP
give an example of a loop diuretic. describe their action
furosemide

inhibits the NKCC2 pump, reduces Na+ absorption and lessens the positive epithelial voltage -> mg2+ and ca2+ excretion due to decreased paracellular absorption
give an example of distal tubule duretics. describe their action
thazides

block NaCl symport in the early distal tubule. increases K+ excretion, but decreases Ca2+ excretion
give an example of K+ sparing diuretics
Amelioride

Act in the late distal tubule, block the ENaC channels - increased Na+ excretion. K+ is retained as Na intracellular is reduced, lowing the Na/K pump which drives secretion
what is the normal range for pH? what are the normal values for HCO3- and pCO2
7.38-7.42

HCO3- = 24
pCO2 = 40
what channels are involed in HCO3- absorption?
NHE-3 = apical Na/H exchanger

NBC-1 = basal Na+/HCO3- symporter
how does effective circulating volume affect HCO3- absorption
it will be absorbed more during volume contraction because H+ secretion is tied to Na+ absorption
why does aldosterones action of principal cells cause K+ excretion?
-upregulates basal Na/K pump
-Increased Na absorption makes distal nephron lumen more negative, favors secretion of K+ (and H+ from intercalated cells)