Absorption, distribution and excretion of toxicants

Question 1

Biotransformation is vital in removing toxins from the circulation. All of the following statements regarding biotransformation are true except:

a. Many toxins must be biotransformed into a more lipid-soluble form before they can be excreted from the body
b. The liver is the most active organ in the biotransformation of toxins
c. Water solubility is required in order for many toxins to be excreted by the kidney
d. The kidney plays a major role in eliminating toxicants from the body.

e the lungs play a minor role in ridding the body of certain types of toxins

Answer 1

A. Many toxins must be biotransformed into a more lipid-soluble form before they can be excreted from the body

Question 2

Which of the following statements about active transport across cell membranes is FALSE?

a. Unlike simple or facilitated diffusion, active transport pumps chemicals against an electrochemical or concentration gradient
b. Unlike Simple diffusion, there is a rate at which active transport becomes saturated and cannot move chemicals any faster.
c. Active transport requires the expenditure of ATP in order to move chemicals against electrochemical or concentration gradients
d. Active transport exhibits a high level of specificity for the compounds that are being moved.
e. Metabolic inhibitors do not affect the ability to perform active transport

Answer 2

E. Metabolic inhibitors do not affect the ability to perform active transport

Question 3

Which of the following might increase the toxicity of a toxin administered orally?

a. increased activity of the mdr transporter (p-glycoprotein).
b. increased biotransformation of the toxin by gastrointestinal cells.
c. increased excretion of the toxin by the liver into bile.
d. increased dilution of the toxin dose
e. increased intestinal motility

Answer 3

B. increased biotransformation of the toxin by gastrointestinal cells.

Question 4

Which of the following most correctly describes the first-pass effect?

a. The body is most sensitive to a toxin the first time that it passes through the circulation
b. Orally administered toxins are partially removed by the GI tract before they reach the systemic circulation.
c. It only results from increased absorption of toxin by GI cells.
d. It is often referred to as “post systemic elimination”.
e. A majority of the toxin is excreted after the first time the blood is filtered by the kidneys.

Answer 4

C. It only results from increased absorption of toxin by GI cells.

Question 5

Which of the following is an important mechanism of removing particulate matter from the alveoli?

a. coughing
b. sneezing
c. blowing one’s nose
d. absorption into the bloodstream, followed by excretion via the kidneys.
e. swallowing.

Answer 5

E. swallowing

Question 6

For a toxin to be absorbed through the skin, it must pass through multiple layers in order to reach the systemic circulation. Which of the following layers is the most important in slowing the rate of toxin absorption through the skin?

a. stratum granulosum
b. stratum spinosum
c. stratum corneum
d. stratum basale
e. dermis

Answer 6

c. stratum corneum

Question 7

A toxin is selectively toxic to the lungs. which of the following modes of toxin delivery would most likely cause the LEAST damage to the lungs?

a. IV
b. IM
c. intraperitoneal
d. SQ
e. inhalation

Answer 7

c. intraperitoneal

Question 8

Which of the following is NOT an important site of toxicant storage in the body?

a. adipose tissue
b. bone
c. plasma proteins
d. muscle
e. liver

Answer 8

D. muscle

Question 9

Which of the following regarding the blood-brain barrier is TRUE?

a. The brains of adults and newborns are equally susceptible to harmful blood-borne chemicals.
b. The degree of lipid solubility is a primary determinant in whether or not a substance can cross the blood-brain barrier.
c. Astrocytes play a role in increasing the permeability of the blood-brain barrier.
d. Active transport processes increase the concentration of xenobiotics in the brain.
e. The capillary endothelial cells of the CNS possess large fenestrations in their basement membranes

Answer 9

b. The degree of lipid solubility is a primary determinant in whether or not a substance can cross the blood-brain barrier.

Question 10

Which of the following will result in DECREASED excretion of toxic compounds by the kidneys?

a. a toxic compound with a molecular weight of 25,000 Da.
b. increased activity of the multidrug-resistance (mdr) protein.
c. increased activity of the multiresistant drug protein (mrp)
d. increased activity of the organic cation transporter.
e. increased hydrophilicity of the toxic compound

Answer 10

d. increased activity of the organic cation transporter.