1 excretion Flashcards

1
Q

what is the outline of excretion?

A

-renal excretion (kidneys)
-biliary excretion (liver and fecal)
-pulmonary excretion (lungs)
-other routes of excretion

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2
Q

renal excretion is the most important xenobiotic ___________ in vertebrate animals

A

ELIMINATION PATHWAY

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3
Q

what are the 3 processes involved in changing blood level (clearance) of a xenobiotic?

A

-glomerular filtration
-tubular reabsorption
-tubular secretion

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4
Q

what is the graph of tubular secretion in kidney tubules?

A

kidneys filter about 180L a day (filter plasma 60 times a day)
-facilitated diffusion transporters (OATs and OCTs)
-active transporters (BCRP, MRP, MDR) to move against conc gradient, pump to more conc area
-both have certain affinities for certain xenobiotics that can differ from eachother

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5
Q

what is extrarenal excretion?

A
  1. biliary excretion
  2. pulmonary excretion
  3. lactation
  4. minor routes of excretion
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6
Q

what is biliary excretion?

A

-important for “larger” xeno molecules (MW >300g/mol)
-similar to kidney, facilitated transport (OAT AND OCT) and active transport (MDR, MRP, BCRP) proteins are involved
-hepatocyte=liver cells
-hepatocyte makes xenobiotic (not all) become more water soluble (phase 1 and phase 2 occurs)

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7
Q

what are the options of what xenos can do in hepatocyte?

A

-can never even make it to liver and get excreted into feces
-can be bioactivated by something in the hepatocyte and become much more toxic
-can be metabolized and detoxified in the hepatocyte and pumped in biliary duct and excreted

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8
Q

what is enterohepatic cycling?

A

-xenos or xeno metabolites excreted in the bile into the intestine can be reabsorbed and distributed back to the liver (why its called cycling)
-this can increase the half-life of a xeno, and in the case of xenos producing toxic metabolites, exacerbate toxicity to the liver

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9
Q

what is pulmonary excretion (exhalation)?

A

-important for volatile and gaseous xenos (ammonia gas)
-ex: ethanol is 90% metabolized in liver but approximately 2% is excreted in the expired air; basis for breathalyzer test

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10
Q

what is lactation?

A

-can be a significant route of elimination for lipophilic xenos, ranging from 0.1 to 2% of maternal dose
-important consideration for neonatal exposure
-important consideration for food products (ex: milk and cheese)

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11
Q

what are the minor routes of excretion?

A

-saliva
-sweat
-hair and nails

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12
Q

what is the spiderweb of linking ADME to toxic effects?

A
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13
Q

what are xenobiotic interactions?

A

-the coadministration of two or more xenos is often associated with altered excretion of one (or more) of the xenos

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14
Q

what are some important terms of xenobiotic interactions?

A

-summation (additivity)
-synergism
-potentiation
-antagonism

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15
Q

what is summation (additivity)?

A

-theoretical example: if the effect of xeno A is 2 and the effect of xeno B is 2, then coadministration of both xenos produces a combined (additive) effect of 2+2=4 (ie: there is no interaction and the effects are additive)
-this is most common, but there are exceptions

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16
Q

what is synergism?

A

-the effects of 2 xenos in combination exceeds the sum of their individual effects (2+2=10)

17
Q

what is potentiation?

A

-a xeno with no effect intensifies (potentiates) the effect of a second xeno (2+0=10)

18
Q

what is antagonism?

A

-the effect of 2 xenos in combination is less than additive (2+2=1)

19
Q

what are the mechanisms of xenobiotic interactions?

A

-interaction during biotransformation
-interactions during distribution
-interactions during excretion
-interactions during absorption

20
Q

what are the interactions during biotransformation?

A

-recall: induction or inhibition of phase 1 and phase 2 enzymes

21
Q

what are the interactions during distribution?

A

-recall: plasma and cellular binding proteins
-competition for binding sites can result in displacement of a xenobiotic, causing increased free (unbound) fraction and greater response

22
Q

what are the interactions during excretion?

A

-decreased clearance due to inhibition of renal excretion; usually competition for renal facilitated transport or active transport proteins

23
Q

what are the interactions during absorption?

A

-substances affecting pH of GI tract can alter absorption (recall pKa stuff)