Excretion

What are the three processes involved in renal excretion

1. Glomerular filtration

2. Tubular reabsorption

3. Tubular secretion

what is glomerular filtration

a process where xenobiotics are filtered from the blood into the kidney tubule

What is tubular reabsorption

A xenobiotic moves from the kidney tubule back into the blood → reducing its elimination

What is tubular secretion

a xenobiotic is actively/facilitated transported from the blood into the kidney

What is biliary excretion

excretion of xenobiotics or metabolites from the liver into bile, which carries them into the intestine

what is enterohepatic cycling

xenobiotics or metabolites excreted into the intestine through bile can be reabsorbed and returned to the liver

what effect can enterohepatic cycling have on a xenobiotic

It can increase the xenobiotic’s half-life by allowing it to be reabsorbed instead of eliminated

why can enterohepatic cycling increase toxicity

if a xenobiotic produces toxic metabolites, repeated reabsorption can increase exposure and exacerbate liver toxicity

how is ethanol related to pulmonary excretion

about 90% of ethanol is metabolized in the liver, while approx. 2% is excreted in expired air

Why can breathalyzers detect alcohol

Because some ethanol is excreted in expired air, allowing alcohol to be detected in breath

How can lactation eliminate xenobiotics

Lipophilic xenobiotics can be excreted into breast milk

what are the four important types of xenobiotic interactions

1. summation

2. synergism

3. potentiation

4. antagonism

what is summation

the combined effect equals the sum of the individual effects (2+2=4)

What is synergism

the combined effect is greater than the sum of the individual effects (2+2 = 10)

what is potentiation

one xenobiotic has no effect by itself but increases the effect of another (2+0=10)

what is antagonism

the combined effect is less than additive (2+2=1)

at what four stages can xenobiotic interactions occur

1. biotransformation

2. distribution

3. excretion

4. absorption

how can xenobiotics interact during biotransformation

by causing induction or inhibition of Phase I or Phase II enzymes

How can xenobiotics interact during distribution

They can compete for plasma or cellular protein-binding sites

what can happen when a xenobiotic is displaced from a binding protein

the free/unbound fraction increases → producing a greater response

how can xenobiotics interact during excretion

one xenobiotic can inhibit renal excretion of another → decreasing clearance

how can xenobiotics interact during absorption

substances that change GI and pH can alter xenobiotic absorption