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Questions and Answers
What is a primary effect of detoxification processes described in biotransformation?
What is a primary effect of detoxification processes described in biotransformation?
What does the process of activation in biotransformation typically involve?
What does the process of activation in biotransformation typically involve?
Which phase of biotransformation involves the incorporation of methyl or ethyl groups to metals?
Which phase of biotransformation involves the incorporation of methyl or ethyl groups to metals?
What is a common outcome of biotransformation in terms of contaminant retention?
What is a common outcome of biotransformation in terms of contaminant retention?
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Which of the following best describes competitive inhibition in enzymatic catalysis?
Which of the following best describes competitive inhibition in enzymatic catalysis?
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How does bioavailability change with increasing log Kow?
How does bioavailability change with increasing log Kow?
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What defines a substance as persistent in soil?
What defines a substance as persistent in soil?
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Why do predators have higher contaminant concentrations than their prey?
Why do predators have higher contaminant concentrations than their prey?
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Which of the following describes biomagnification?
Which of the following describes biomagnification?
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What technique is used to assess contamination within different trophic levels?
What technique is used to assess contamination within different trophic levels?
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What is the best indicator for defining trophic position?
What is the best indicator for defining trophic position?
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What does the term 'bioconcentration' refer to?
What does the term 'bioconcentration' refer to?
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How is assimilation efficiency measured using the twin-tracer technique?
How is assimilation efficiency measured using the twin-tracer technique?
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What does the Freundlich Equation primarily describe?
What does the Freundlich Equation primarily describe?
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Which of the following factors does NOT influence facilitated diffusion?
Which of the following factors does NOT influence facilitated diffusion?
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In the Langmuir Equation, what does the constant 'k' represent?
In the Langmuir Equation, what does the constant 'k' represent?
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What denotes a Zero Order Reaction in the context of reaction order?
What denotes a Zero Order Reaction in the context of reaction order?
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Which process is responsible for changing hydrophobic substances to hydrophilic to facilitate elimination from the body?
Which process is responsible for changing hydrophobic substances to hydrophilic to facilitate elimination from the body?
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Which scenario is characteristic of active transport?
Which scenario is characteristic of active transport?
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What type of kinetic behavior is displayed above the threshold concentration in Michaelis-Menten kinetics?
What type of kinetic behavior is displayed above the threshold concentration in Michaelis-Menten kinetics?
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Which of the following is a potential mechanism for the transport of charged ions across a cell membrane?
Which of the following is a potential mechanism for the transport of charged ions across a cell membrane?
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Which principle does the Langmuir Equation NOT assume?
Which principle does the Langmuir Equation NOT assume?
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What characterizes adsorption isotherms?
What characterizes adsorption isotherms?
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What is the primary role of metallothioneins in the body?
What is the primary role of metallothioneins in the body?
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What is the purpose of Phase I reactions in metabolism?
What is the purpose of Phase I reactions in metabolism?
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What is a key feature of zero-order kinetics?
What is a key feature of zero-order kinetics?
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Which route is the main pathway for elimination in aquatic animals?
Which route is the main pathway for elimination in aquatic animals?
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What occurs during enterohepatic circulation?
What occurs during enterohepatic circulation?
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What does 'growth dilution' refer to in the context of elimination mechanisms?
What does 'growth dilution' refer to in the context of elimination mechanisms?
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Which statement about first-order kinetics is true?
Which statement about first-order kinetics is true?
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Which of the following is a method animals utilize for eliminating contaminants?
Which of the following is a method animals utilize for eliminating contaminants?
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What is the main goal of pharmacokinetic (PK) models in exposure assessment?
What is the main goal of pharmacokinetic (PK) models in exposure assessment?
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What is the primary mechanism of clearance in pharmacokinetics?
What is the primary mechanism of clearance in pharmacokinetics?
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What is the biological half-life (t½) defined as?
What is the biological half-life (t½) defined as?
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What does the equation Ct = Coe^-kt represent?
What does the equation Ct = Coe^-kt represent?
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In a two-compartment model, what does the effective half-life (keff) depend on?
In a two-compartment model, what does the effective half-life (keff) depend on?
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What is the purpose of the apparent volume of distribution (Vd)?
What is the purpose of the apparent volume of distribution (Vd)?
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How is the bioaccumulation factor (BAF) best described?
How is the bioaccumulation factor (BAF) best described?
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What does the bioconcentration factor (BCF) indicate?
What does the bioconcentration factor (BCF) indicate?
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In pharmacokinetics, what does 'ADD' represent in the non-steady-state PK model?
In pharmacokinetics, what does 'ADD' represent in the non-steady-state PK model?
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Which equation models the rate of change of concentration for bioaccumulation?
Which equation models the rate of change of concentration for bioaccumulation?
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Study Notes
Elimination from Initial Concentration
- The elimination rate of a substance from a compartment is proportional to the amount of the substance present.
- Half-life (t½) is the time it takes for the concentration of a substance in a compartment to decrease by 50%.
- Mean residence time is the average time a particle spends in a compartment and is related to the half-life.
Non-Steady-State PK Model
- This model describes the concentration of a substance in a compartment over time, considering both elimination and continuous input.
- The model incorporates the initial concentration (C(0)), average daily dose (ADD), elimination constant (k), and volume of distribution (V).
Modeling Elimination
- Two-compartment model: The substance is distributed between two compartments, each with its own elimination rate.
- Second-order elimination: The elimination rate is not constant, but instead depends on the concentration of the substance.
- Effective half-life (keff): The slower elimination mechanism in a multi-compartment model controls the overall elimination rate.
Multiple Compartment Model
- Clearance-volume based models: These models use the apparent volume of distribution (Vd) to determine the dose within an organism.
- Physiologically based pharmacokinetics (PBPK): This model incorporates physiological and anatomical features to describe the kinetics of a substance.
Bioaccumulation
- Bioaccumulation is the net concentration of a substance within an organism after uptake, biotransformation, and elimination.
- Bioconcentration factor (BCF): This is the ratio of the concentration of a substance in a tissue to the concentration in water.
- Bioaccumulation factor (BAF): This is the ratio of the concentration of a substance in an organism to its concentration in the environment.
- Bioaccumulation factor from sediment (BSAF): This is the ratio of the concentration of a substance in an organism to its concentration in sediment.
Interactions with Organism Surface
- Before uptake, a substance can interact with the organism's surface, influencing its bioavailability.
Adsorption
- Adsorption is the process of a substance attaching to a surface.
- Freundlich and Langmuir Isotherm Equations: These equations model the adsorption of substances onto surfaces, considering factors like concentration and saturation.
Adsorption Isotherms
- Freundlich Equation: This equation describes the concentration of a substance adsorbed on a surface based on the concentration in solution.
- Langmuir Equation: This equation describes adsorption on planar surfaces with a fixed number of identical sites, considering factors like bonding strength and maximum adsorption.
Across the Cell Membrane
- Diffusion: This is the movement of a substance down its concentration gradient.
- Active transport: This is the movement of a substance against its concentration gradient, requiring energy.
- Facilitated diffusion: This is the movement of a substance down its concentration gradient through a carrier protein, without energy.
- Endocytosis: This is the process of bringing a substance into the cell by engulfing it in a membrane- bound vesicle.
Reaction Order - Kinetics of Uptake & Elimination
- Zero-order reaction: The rate of elimination is constant regardless of the concentration.
- First-order reaction: The rate of elimination is proportional to the concentration.
- Michaelis-Menten Kinetics: This describes enzyme-mediated processes with a threshold concentration, exhibiting zero-order kinetics above and first-order kinetics below the threshold.
Biotransformation
- Biotransformation is the process of changing a substance within the body to facilitate elimination.
- Detoxification: This process transforms substances into less toxic or more hydrophilic forms for easier elimination.
- Activation: This process transforms substances into more toxic forms.
Mechanisms of Biotransformation & Detoxification
- Metals and Metalloids: These can undergo biomethylation, biomineralization, or binding to metallothioneins.
- Organic compounds: These can be eliminated rapidly or undergo Phase I and Phase II metabolism to become more hydrophilic.
Elimination Mechanisms
- Depuration: The release of a contaminant into the environment.
- Clearance: The rate of contaminant movement between compartments.
- Growth dilution: As organisms grow, the concentration of a contaminant decreases due to dilution.
Plants and Animals
- Plants: They eliminate contaminants through leaf dropping, leaching, evaporation, root exudation, and herbivore grazing.
- Animals: They eliminate contaminants through gills, exhalation, bile secretion, intestinal mucosa, molting, kidney excretion, and egg deposition.
Modeling Elimination
- First-order kinetics: The most common model for elimination.
- Zero-order kinetics: Less common than first-order kinetics.
- Saturation kinetics: Also less common, occur at high contaminant concentrations when elimination pathways become saturated.
- Compartment models: These model the movement of a contaminant between different body compartments.
Pharmacokinetic Models
- Pharmacokinetic (PK) models: These models evaluate the internal dose of a compound.
- Simple models: One-compartment, first-order models.
- Complex models: Multi-compartment, physiologically-based pharmacokinetic models.
Bioconcentration Factor
- This is the concentration of a substance in an organism or sediment compared to its concentration in water.
Persistency of Chemicals in Soil
- Chemicals are classified based on their persistence in soil, with categories including persistent, moderately persistent, and non-persistent.
Why Concentrations are Higher in Predators
- Predators accumulate more contaminants due to their larger size and higher trophic level, leading to a dilution effect in prey.
- Biomagnification: This occurs when the concentration of a substance increases as it moves up the food chain.
Trophic Transfer
-
Twin-tracer technique: This technique uses radioisotopes to measure the assimilation efficiency of a contaminant.
- Trophic position: This refers to an organism's position in the food chain, often determined using stable nitrogen isotope analysis.
Quantifying Bioaccumulation from Food
- Assimilation from food: This evaluates the transfer of a contaminant between trophic levels.
- Assimilation efficiency: This quantifies the bioavailability of a contaminant from food.
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Description
Explore the principles of drug elimination from initial concentration in pharmacokinetics. This quiz covers half-life, mean residence time, and both one and two-compartment models. Test your understanding of non-steady-state pharmacokinetic models and key concepts in drug concentration over time.
