42 Questions
Which factor is considered one of the most important for the likelihood of a xenobiotic being absorbed?
Route of exposure
What is necessary for a substance to exert an effect on internal organs?
Absorption into the body
Which of the following is NOT a primary route of exposure for xenobiotics according to the text?
Intramuscular
What is the absorbed dose in relation to the exposure dose for substances injected or implanted directly into the body?
The same
Local toxicity, such as irritation, may occur even if a substance has not been:
Absorbed
Why are xenobiotics often ranked for hazard according to the route of exposure?
Due to route-specific differences in absorption
Which mechanism of transport requires cellular energy from ATP?
Active Transport
What is a key difference between facilitated diffusion and simple diffusion?
Facilitated diffusion is carrier-mediated
In endocytosis, what happens to the substance and section of the cell membrane after engulfment?
They move into the interior of the cell
Which system is involved in draining excess fluid from tissues and is part of the circulatory system?
Lymphatic System
Why can some large molecules and particles not enter cells via passive or active mechanisms?
They are too large to dissolve in the lipid layer
Which type of cells benefit greatly from phagocytosis as a process of engulfing particles?
Liver cells
What substances are actively transported into the liver, kidney, and central nervous system?
Xenobiotics
What is an essential function of active transport within the body?
Maintenance of electrolyte and nutrient balance
Which factor determines the rate of passive transfer of xenobiotics across cell membranes?
The difference in concentrations of the substance on opposite sides of the membrane
What is the main characteristic of the phosphate head of a phospholipid molecule in cell membranes?
Hydrophilic
What is the term used to describe the movement of toxicants across a membrane barrier without requiring cellular energy?
Passive transfer
What type of molecules can readily diffuse through the phospholipid membrane due to their properties?
Substances with high lipid solubility
Which specialized transport mechanism requires the substance to be engulfed by the cell?
Endocytosis
What property of chemical substances affects their ability for passive transfer across cell membranes?
Degree of ionization
Which type of molecules can pass across a membrane through aqueous pores?
$H_2O$ molecules
What is the primary way that xenobiotics cross cell membranes?
$O_2$ passive transfer
Which type of molecules usually cannot make it through small pores in cell membranes?
$C_{1000}$ molecules
What determines a toxicant's initial absorptive behavior and likelihood of distribution to tissues?
The affinity of a xenobiotic to various tissues
Why is the disposition of a toxicant dependent on its volume of distribution (Vd)?
Because Vd is the volume in which the toxicant needs to be uniformly dissolved to produce observed blood concentration
What can cause a chemical to have a high plasma concentration and low Vd?
Restricted distribution due to inability to cross cell membranes
Why is binding of a toxicant to plasma proteins important in toxicology?
It influences toxicity by affecting the amount of unbound toxicant
Which factor does NOT influence the distribution of a toxicant to tissues?
The speed of diffusion from tissues into the capillary bed
Why may a compound with high plasma protein binding show less toxicity?
Because toxicity is typically related to the unbound fraction of the compound
Which body compartment has a low plasma concentration if a chemical distributes throughout both compartments?
Extracellular water (interstitial water)
What primarily determines the rate of distribution of a toxicant to organs or tissues?
Blood flow and diffusion from capillary beds into cells
Why do some toxicants selectively accumulate in certain body parts?
As a result of binding to plasma proteins
Why might accumulation at a site other than the target organ be viewed as protective?
As it decreases plasma levels and reduces concentration at the target site
What determines if a chemical readily crosses cell membranes for distribution?
Physical and chemical characteristics
What is the main reason why some toxicants do not readily enter the central nervous system?
Tightly joined capillary endothelial cells
Which organ is mentioned to have a high capacity for binding a multitude of chemicals?
Liver
What is a characteristic of the skeletal uptake of xenobiotics?
Deposition of toxicants in bone is dynamic
How does storage in fat impact the toxicity of highly lipophilic toxicants?
Lowers toxicity in lean individuals
Which barrier protects the developing fetus from toxicants absorbed in maternal circulation?
Placental barrier
Which organs are likely to concentrate more toxicants than all other organs combined?
Liver and Kidney
What physiological feature limits the movement of water-insoluble compounds through paracellular transport in the central nervous system?
High protein concentration in interstitial fluid
Why is bone noted as a storage depot for xenobiotics?
Exchange occurs between bone surface and extracellular fluid
Learn about the phases of toxic phenomenon exposure and how toxicants are absorbed into the body. Explore the variability of absorption based on specific chemicals and routes of exposure.
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