Chapter 5: Absorption and Distribution

Question 1

What is the disposition of a toxicant? and what does each mean?

Answer 1

absorption (how it gets in the body), distribution (where it goes in the body), biotransformation (what the body does with it) and elimination (how it leaves the body).

Question 2

What does it mean for a toxin to have a local/systemic effect?

Answer 2

local - in a specific tissue
systemic - throughout the organism

Question 3

What is transcellular diffusion?

Answer 3

Diffusion of toxicants through cells (must pass through cellular membranes). Often occurs if the cells are packed tightly with little space between them.

Question 4

What is paracellular diffusion?

Answer 4

Diffusion of toxicants in between cells.

Question 5

What are ATP-binding cassette (ABC) transporters?

Answer 5

a superfamily of genes for active transport.

Question 6

How is ATP produced most efficiently?

Answer 6

Aerobic metabolism (via oxidative phosphorylation that occurs in the mitochondria).

Question 7

What is receptor-mediated endocytosis?

Answer 7

cells have receptors that recognize certain proteins and form a vesicle, which contains the protein

Question 8

What are the main sites of absorption?

Answer 8

1. GI tract
2. Lungs
3. Skin

Question 9

What does enteral administration mean?

Answer 9

All routes involving the alimentary canal (i.e sublingual, oral, rectal)

Question 10

What does the parenteral administration mean?

Answer 10

All other routes (i.e injection)

Question 11

Deposition of aerosols depends on the size:
≥5μm deposited where?
~2.5μm deposited where?
≤1μm deposited where?

Answer 11

≥5μm deposited in the nasopharyngeal region (may end up being swallowed)
~2.5μm deposited in lungs being swallowed (may end up being swallowed)
≤1μm may absorb through alveoli and enter the blood

Question 12

The _____ is the rate-determining barrier. It is thicker on what parts of the body?

Answer 12

hydrated stratum corner. thicker on palms and soles.

Question 13

Absorption through the skin can increase by:

Answer 13

Damage to the stratum corneum.
Increased hydration.
Increased blood flow (↑BF = ↑ chance of toxin to enter)
Size of toxicant (small ones have increased absorption).

Question 14

What is the abundant protein in the blood? and what is it’s normal function?

Answer 14

Albumin. Normal function is to transport fats hormones and other hydrophobic compounds.

Question 15

Why does the concentration of toxins increase when loosing weight?

Answer 15

As you are loosing weight, you start breaking down the fat that was stored in the adipose tissues, thus realizing the toxins

Question 16

How can the BBB keep out toxins out of the brain?

Answer 16

1. The capillaries in the brain have few pores, which can limit diffusion.
2. The capillary endothelial cells have MDR transporters that can send unwanted compounds back into the bloodstream.
3. Paracellular diffusion limited (transcellular can be more regulated).

Question 17

What kind of molecules can readily pass through the BBB?

Answer 17

Very hydrophobic non-ionic chemicals can readily pass through the BBB.