41 Questions
Which factor is NOT considered to be important in affecting the likelihood of a xenobiotic being absorbed?
Color of the substance
What is true about the relationship between exposure dose and absorbed dose for substances injected directly into the body?
They are equal
Which route is NOT considered a primary route of exposure for xenobiotics to enter the body?
Olfactory (nose)
If a xenobiotic is categorized as highly toxic via one route and relatively non-toxic via another, what does this indicate?
Toxicity can vary based on the route of exposure
Which is NOT mentioned as a factor that affects absorption of xenobiotics?
Time of day
Why must a substance be absorbed to exert an effect on internal organs?
To cross cellular barriers
What is the main difference between facilitated diffusion and simple diffusion?
Facilitated diffusion involves carrier-mediated transport proteins.
Which process requires cellular energy to move molecules across the membrane?
Active transport
In endocytosis, how does the cell take in substances?
By engulfing them with a section of the cell wall
What is the importance of active transport in the body?
To maintain electrolyte balance
Which type of cells are involved in phagocytosis?
Lung phagocytes
How do toxicants absorbed through the skin enter the blood supply?
By entering lymphatic vessels
Where are lymph capillaries found in the body?
In the lymph nodes
Which type of transport across cell membranes requires cellular energy or assistance?
Active transport
What is the main feature of facilitated diffusion in toxicant movement across cell membranes?
Pores in the membrane needed for passage
Which factor determines the rate of passive transfer across cell membranes?
Difference in concentrations across the membrane
What role does lipid solubility play in the passive transfer of substances across cell membranes?
Promotes diffusion through lipid portions of the membrane
What determines a substance's ability to pass through aqueous pores in cell membranes?
Molecular weight
In toxicant movement across cell membranes, what is true about large water-soluble molecules?
They are impeded by lipid portions of the membrane
For xenobiotics to move within the body, what must they do when passing cell membranes?
Penetrate multiple cell membranes
Which body defense mechanism prevents substances from gaining entry into body tissues?
Cell Membranes
Which factor affects the distribution of toxicants to tissues primarily due to the volume of blood flowing through a specific tissue?
Volume of blood flowing through a specific tissue
What determines the rate of distribution of toxicants to organs or tissues primarily?
Blood flow
What does the volume of distribution (Vd) of a toxicant depend on?
Unbound fraction of the toxicant in plasma
Why can toxicants bound to plasma proteins not cross capillary walls?
Due to their high molecular weight
What are the primary forces responsible for protein-ligand interactions with toxicants in plasma?
Hydrogen bonding and van der Waals forces
Why can a compound with a high degree of plasma protein binding appear less toxic than one with less binding?
Bound compounds are less biologically active
What is NOT a factor that can influence the distribution of toxicants to tissues?
Rapid elimination of the toxicant from the body
Plasma concentration is high and Vd is low for which type of chemical distribution?
No tissue distribution
Protein binding, active transport, and high fat solubility contribute to the selective accumulation of some toxicants where?
At the site of toxicity
Which factor can cause protective accumulation of a toxicant if it accumulates at a site other than the target organ?
Free fraction in plasma increases due to equilibrium
Which factor can lead to decreased toxicity of a compound in obese individuals compared to lean individuals?
Rapid mobilization of fat
What is a common physiological barrier that restricts the entry of toxicants into the central nervous system?
Presence of glial cell processes
What effect might short-term starvation have on experimental animals previously exposed to persistent organochlorine insecticides?
Decreased intoxication symptoms
Why are lead deposits not considered toxic to bone compared to other substances like fluoride and radioactive strontium?
Non-dynamic deposition process
What is a key role of the placental barrier in relation to toxicants?
Slowing down the diffusion from maternal circulation
How does the blood-brain barrier restrict the entry of toxicants into the brain?
Tight junctions between capillary endothelial cells
Why is storage in bone considered dynamic for toxicants?
Continuous exchange between bone surface and extracellular fluid
What can be a consequence of high lipid/water partition coefficient for certain toxicants?
Enhanced concentration in target organs
Which factor contributes to the concentration of many chemicals in the liver and kidney compared to other organs?
Competitive binding of endogenous substances
What role do astrocytes play in relation to the blood-brain barrier's function?
Secrete chemical actors that modulate endothelial permeability
Test your knowledge on the phases of toxic phenomenon exposure and the process of toxicant absorption in the body. Understand how toxicants enter the body, cross cellular barriers, and exert effects on internal organs.
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