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MindMap Gallery Chapter 3 Transport and Transformation of Exogenous Chemicals in the Body
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Chapter 3 Transport and Transformation of Exogenous Chemicals in the Body
This is a mind map about Chapter 3: The transport and transformation of exogenous chemicals in the body. Biological transport mainly refers to the absorption, distribution and excretion process of exogenous chemicals in the body. These processes typically occur through biological membranes and include transmembrane transport, absorption, distribution to tissues throughout the body, and final excretion.
Edited at 2024-04-01 01:02:08
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Chapter 3 Transport and Transformation of Exogenous Chemicals in the Body
- Valentine's Day marketing campaign
This Valentine's Day brand marketing handbook provides businesses with five practical models, covering everything from creating offline experiences to driving online engagement. Whether you're a shopping mall, restaurant, or online brand, you'll find a suitable strategy: each model includes clear objectives and industry-specific guidelines, helping brands transform traffic into real sales and lasting emotional connections during this romantic season.
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- Outline
xenobiotics Transport and transformation in the body
absorb
It refers to the process by which exogenous chemicals enter the blood through various channels through the biological membrane of the body.
main method
Absorbed via respiratory tract
Alveolar physiological structure and characteristics
It enters the systemic circulation directly and is distributed throughout the body without being biotransformed by the liver.
mainly through simple diffusion
Effects of pulmonary absorption of gaseous poisons
Gaseous poison concentration: the partial pressure (tension) of the poison in the absorbed air
~Solubility in blood (fat soluble)
Alveolar ventilation and blood flow
The absorption rate of gaseous exogenous chemicals with low blood gas distribution coefficient through the lungs mainly depends on the pulmonary blood flow (equilibration time is about 8-21 minutes)
The pulmonary absorption rate of gaseous exogenous chemicals with high blood gas distribution coefficient mainly depends on the respiratory frequency and depth (the equilibrium time is at least 1 hour)
Effects of pulmonary absorption of aerosol toxicants
Particle size: Usually only particles of 0.5~1μm can be absorbed into the alveoli
Water solubility: Aerosols with high solubility are easy to be absorbed in the upper respiratory tract, while aerosols with low solubility are easy to reach the alveoli and be absorbed.
Gastrointestinal absorption
The gastrointestinal tract is the primary route of absorption of exogenous chemicals
The site of absorption is mainly in the small intestine
Absorption mode: mainly through simple diffusion, but also through filtration, pinocytosis or phagocytosis and active transport
The first-pass effect of the liver: refers to the fact that exogenous chemicals absorbed through the gastrointestinal tract first enter the liver and undergo metabolic transformation in the liver.
Factors affecting absorption
gastrointestinal pH
Certain substances and flora in the gastrointestinal tract
Molecular structure and physical and chemical properties of exogenous chemicals
Peristalsis of the gastrointestinal tract
Absorbed through skin
Bow stage: the process by which exogenous chemicals penetrate the skin epidermis, the stratum corneum (rate-limiting barrier)
Absorption stage: enters the papillary layer and dermis from the stratum corneum, and is absorbed into the bloodstream
Absorption method: simple diffusion
the main factor of influence
Physical and chemical properties: Lipid/water partition coefficient is close to 1, easily absorbed into the blood
Skin integrity: If the skin is damaged and the barrier function of the epidermal stratum corneum is destroyed, exogenous chemicals can directly enter the absorption phase.
Different parts of the human body have different thicknesses of epidermis and stratum corneum, so the penetration speed of exogenous chemicals is different. Scrotum > Abdomen > Forehead > Palms > Soles
other ways
Ocular absorption: local effects precede systemic effects
By intravenous, intraperitoneal, subcutaneous and intramuscular injection
distributed
Toxicological significance of the distribution of exogenous chemicals
Distribution: refers to the process in which exogenous chemicals enter the blood or other body fluids through absorption and are dispersed to various tissue cells throughout the body with the flow of blood or lymph. The initial distribution mainly depends on the perfusion rate of the organ or tissue.
The blood flow and affinity of an organ or tissue for exogenous chemicals are the most critical factors affecting the distribution of exogenous chemicals.
Characteristics of poison distribution: The distribution of exogenous chemicals in the body is unevenly distributed
Redistribution: Over time, distribution is affected by the transmembrane diffusion rate of exogenous chemicals and the affinity of organs and tissues for them.
Main factors affecting distribution
Chemicals bind to plasma proteins
Chemicals combine with other tissue components
Chemical storage deposits in fatty tissue and bones
The influence of various barriers in the body
Accumulation of poisons in tissues
1. Material accumulation 2. Function accumulation
Reservoir: It means that chemical poisons that enter the blood accumulate in certain organs and tissues with high concentrations. If the chemicals do not show obvious toxic effects on these organs and tissues.
main repository in body
plasma protein depot
Liver and kidney storage
adipose tissue storage depot
bone tissue repository
Chemical poisons in the body Storage has a double meaning
Protective against acute poisoning and reduce the amount of chemical poisons in target organs
May become a source of free chemical poisons, potentially harmful
special barrier
blood brain barrier
It refers to a special functional structure composed of capillary endothelial cells and soft brain that gathers astrocytes surrounding capillaries.
The importance of the blood-brain barrier: It ensures the normal exchange of metabolic substances between blood and brain tissue, and the entry of unnecessary tissue substances, thereby maintaining the normal function of the brain.
•Large molecules, low lipid solubility, DP cannot pass •Drugs with central effects must have high lipid solubility •There are also carrier transporters, such as glucose through •Variable: In inflammation, permeability ↑, large doses of penicillin are available
placental barrier
refers to several layers of cellular structures located between the maternal blood circulation system and the embryo
The mechanism by which most exogenous chemicals pass through the placenta is simple diffusion, while nutrients necessary for embryonic development enter the embryo through active transport.
•Teratogens can pass through the placenta and cause embryonic malformations, and some carcinogens can pass through the placenta and cause cancer. •Selectivity of fetal capillary endothelium for drug transport •Lipid solubility and molecular size are the main influencing factors (<MW600 can pass easily; >1000 cannot) •Maternal blood PH=7.44; fetal blood PH=7.30; weakly alkaline drugs are easily dissociated in fetal blood •The placenta has the function of metabolizing (such as oxidizing) drugs •Transport occurs in the same manner as in other cells: simple diffusion •Most drugs can enter the fetus
other barriers
blood-testis barrier blood thymus barrier aqueous barrier
excretion
It is the process of transporting exogenous chemicals and their metabolites outside the body.
Biological half-life: abbreviated as t 1/2, refers to the reduction of exogenous chemicals Half time is the time when the concentration or quantity is reduced by half
main route of excretion
Passed through kidneys and urine
Main excretion mechanism
glomerular filtration
The capillary wall of the glomerulus is different from the general cell membrane and has membrane pores with a size of 7-10nm. Substances in blood components with a molecular weight below 60OODa can be filtered. Large molecular substances such as plasma albumin (molecular weight about 60,000 Da) basically cannot pass through
It is difficult to filter after binding to plasma proteins, so changes in the plasma protein binding rate of exogenous chemicals will cause changes in renal excretion. Negatively charged exogenous chemicals are not easily filtered, while positively charged substances are easily filtered into raw urine.
glomerular simple diffusion
tubular active transport
The renal tubule has an active transport function including organic anions (oat family located in the proximal Two systems of tubule basement membrane) and organic cations (oct family) can move exogenous chemicals to the proximal tubule against the liquid gradient. It is actively transported from capillaries to tubular fluid, which is called renal tubular secretion.
Excreted in the feces along with bile through the liver
Exogenous chemicals enter the bile and are excreted by liver parenchymal cells
Exogenous chemicals enter the small intestine from the bile Finally, there may be two ways to go
Directly excreted from the body
Enterohepatic circulation
It means that some exogenous chemicals form conjugates during the biological transformation process and are excreted in the bile in the form of conjugates; the intestinal flora and glucuronidase present in the intestine can hydrolyze some of the conjugates, causing exogenous The process by which source chemicals are reabsorbed.
Toxicological significance: Decreased excretion rate, prolonged biological half-life, and prolonged duration of toxic effects
Physiological significance: it allows some compounds needed by the body to be reused
Expelled through the respiratory tract along with exhaled air
Its excretion speed is inversely proportional to the blood/gas distribution coefficient, that is, the greater the blood-gas distribution coefficient, the slower the excretion will be.
Opposite of absorption rate
Other excretions
Exogenous chemicals are primarily “excreted” into breast milk by simple diffusion. Milk is rich in fat and usually acidic (pH 6.5~7.0). Fat-soluble substances and weakly alkaline chemicals are easily concentrated in milk (such as morphine, atropine, erythromycin, ethanol), and more than dozens of foreign substances Source chemicals can be excreted in breast milk.
Toxicological significance of milk excretion
Toxic substances are passed from mother to infant through breast milk
Causes contamination of dairy products and transfers contamination to people who consume dairy products
toxicokinetics
Overview
Definition: From the perspective of rate theory, toxicokinetics uses mathematical models to analyze and study the dynamic changes in the quantity of exogenous chemicals during biological transport and transformation.
Toxicokinetics: Study of the body's effects on chemical poisons and the amount of chemical poisons or their active metabolites in target organs
Toxic effect kinetics: Study of the interaction between chemical poisons or their active metabolites and macromolecules in target organs and the resulting local or overall toxic effects
Purpose
Contribute to the design of toxicological studies (e.g. dose and route of exposure);
Explain the mechanism of toxic effects by studying the relationship between exposure and time-dependent target organ dose and toxic effects.
Determination of parameters related to dose, distribution, metabolism and elimination for risk assessment in humans.
time volume curve
•Collect blood samples at different times after exposure to poison, measure the blood poison concentration, and plot the blood poison concentration as the ordinate and time as the abscissa, which is the poison concentration-time curve, referred to as the time-volume curve. •The dynamic process of changes in plasma poison concentration over time can be expressed by the time-quantity relationship
The time-volume curve can quantitatively analyze the dynamic changes of poisons in the body. When the poison ADME process is carried out simultaneously, the quantity curve is actually the algebraic value of the absorption, distribution rate and elimination rate.
The time-dose curve of non-intravenous exposure can be divided into
incubation period
The period of time after exposure to poison and the onset of toxic effects, the absorption and distribution process of poisons
Duration
The time a poison lasts in harmful concentration is related to the absorption and elimination rate of the poison
residual period
Toxins in the body have been reduced to below harmful concentrations but have not yet been completely eliminated from the body. disabled The length of retention period is related to the elimination rate
Classical Toxicology
Basic idea: The blood or plasma concentration of an exogenous chemical maintains a dynamic balance with its tissue concentration, and changes in plasma concentration can reflect changes in tissue concentration.
Basic theory
rate theory
first order rate process
Concept: The rate of change of a poison in the body at a certain moment is proportional to the power of its instantaneous content (constant ratio elimination)
Formula: dc/dt＝-KeC dc/dt: is the rate of change of poison concentration over time Ke: is the rate constant C: is the concentration of poisons in the body
Features: •The elimination rate of a poison at any time is directly proportional to the amount of the poison in the body at that time •Plotting the logarithm of plasma concentration against time yields a straight line •The half-life of the poison is constant and does not change due to the quantity of the poison itself, the route or method of exposure •The concentration of toxicants in plasma and other tissues decreases by a constant fraction per unit time, that is, constant ratio attenuation
zero order rate process
Concept: When the amount of compounds exceeds the transport capacity of the body, their transport speed is independent of their quantity, that is, the transport speed is proportional to the zero power of the number of compounds.
Formula: dc/dt=-Ke • Explain that the rate of change of poisons in the body over time has nothing to do with the concentration of the poison. •Some in vivo processes that require carrier transport or rate-limiting enzyme metabolism of poisons have zero-order rates.
Features: •Plasma concentration versus time as a straight line •The elimination rate of poison at any time is a constant, which is a constant decay. The half-life period has nothing to do with the amount of poison in the body •The poison half-life increases with increasing initial concentration or dose.
nonlinear dynamics
Definition: It refers to a large dose of exogenous chemicals, and certain processes of the chemicals in the body are inconsistent with There are obvious nonlinear characteristics in the requirements of linear speed process.
•When the blood poison concentration is very high, the poison is eliminated slowly, and the change in the blood poison concentration is equivalent to zero order and non-linear. sexual dynamics •When the blood poison concentration is low, it switches to a linear kinetic process
For poisons with nonlinear kinetic characteristics, the increase in blood poison concentration during repeated exposure is related to the dose increase. There is a non-proportional relationship. An increase in dose will cause the steady-state blood poison concentration to increase more than the proportional increase. With increasing dosage, the toxic effect increases.
chamber model
Definition: The body is divided into several parts according to the dynamic characteristics. Each part is called a chamber, which is used to describe the poison. The distribution state of substances in the body, and therefore the relevant parameters and mathematical equations of metabolic kinetics are derived. •Explanation: All those with similar transport and transformation can be regarded as one room.
type
Distribution rate
One room open model
When the poison is absorbed into the blood circulation, it is immediately and evenly distributed to the body fluids and various tissues and organs, and quickly reaches a dynamic state. Balance, considering the entire body as one compartment, is called the one-compartment open model.
Elimination of chemical poisons from the body in a one-compartment model generally complies with first-order dynamics
One-room calculation formula: Ct＝C₀•e⁻ᴷᵗ
Two-room open mold room
When poisons are distributed at different rates in tissues and organs in the body, poisons first enter the central chamber and then slowly enter the peripheral chambers.
The transport between the central chamber and the peripheral chamber is reversible, and the transport rates between the two chambers are equal when reaching dynamic equilibrium.
Two-chamber calculation formula: Ae⁻ᵃᵗ Be- βᵗ
multi-room model
It is composed of a central room and several peripheral rooms connected to each other.
central room
It is mostly composed of blood and tissues and organs with rich blood supply and smooth blood flow, such as extracellular fluid, heart, liver, kidneys, glands, etc.
Perimeter room
Organs with low blood supply, slow blood flow or difficult for chemicals to pass through, such as muscles, fat, bones, and skin at rest.
Whether it is excreted or metabolized from the body
closed model
Chemicals that enter the body and are only transported between compartments and never excreted or metabolized from the body are called closed models.
open model
Poisons that are irreversibly excreted from the body or undergo metabolic processes through various pathways are called open models. Most poisons conform to the open model.
Basic parameters
half period
Refers to the time required for the plasma concentration of exogenous chemicals to decrease by half. It is a parameter indicating the elimination rate of poisons. (Unit:min·hr.d)
A short t₁/₂ indicates that the poison is eliminated quickly and is not easy to accumulate poisoning. t₁/₂＝0.693/Ke
Area under the curve (AUC)
The total area covered under the time-volume curve, or the total area covered under the curve from the appearance of the poison in the plasma to its complete elimination. It is a parameter that reflects the body’s elimination ability.
The unit is: mg·L·h⁻¹ AUC＝C₀/Ke
Expression volume of distribution (Vd)
Refers to the ratio of the amount of poison in the body (D) to the blood poison concentration (C) when the body reaches dynamic equilibrium, indicating the volume of body fluid that the poison should occupy based on the blood poison concentration.
The unit is L or L/Kg Vd＝D(amount of poison in body)/C(blood poison concentration) Vd＝D₀(intravenous poisonous amount/C₀(zero hour poison concentration)
Elimination rate constant (Ke)
Indicates the speed of elimination of poisons in the body, which can be expressed as the percentage of elimination of poisons in the body per unit time (unit: h⁻¹)
A large Ke value indicates a fast elimination rate.
Clearance rate (CL)
It refers to the part of the apparent distribution volume that is removed from the body in a unit time, that is, the amount of toxicants removed from the blood per unit time. The unit is L/h or L/(h·kg).
• Clearance pathways: Renal clearance (CLr) Hepatic clearance (CLh)
Plasma clearance is the sum of renal and hepatic clearance. CL＝Vd·Ke or CL＝D/AUC
Bioavailability (F)
Also called biological validity. Refers to the extent to which poisons are absorbed and utilized by the body.
Oral bioavailability refers to the difference between the AUC of oral exposure and the AUC of the poison after intravenous injection. Ratio, expressed as percentage of oral absorption.
Formula: F=(AUCpₒ/AUCiv)X100%
Biotransformation
Biotransformation and toxicant metabolizing enzymes
Biotransformation, also known as metabolic transformation, refers to the process in which exogenous chemicals undergo a series of chemical changes in the body to form their derivatives and decompose.
The metabolic process of chemical poisons is mainly carried out in the liver, but extrahepatic tissues also have certain metabolic capabilities, such as the kidneys, small intestine, lungs and skin.
The meaning of biotransformation
As the polarity of exogenous chemicals increases, their water solubility will increase, and they will be easily excreted through the kidneys along with urine or mixed with bile into feces.
Metabolic detoxification and metabolic activation
Metabolic detoxification: chemical (toxicity) → intermediate product (low toxicity or no toxicity) → product (no toxicity)
Metabolic activation: chemicals (non-toxic) → activation intermediates (toxic) → products (non-toxic)
ultimate poison
Refers to the chemical form when exogenous chemicals can directly react with endogenous target molecules and cause damage to the body
①Exogenous chemicals themselves are terminal poisons Such as strong acids, strong bases, nicotine, heavy metal ions, hydrogen cyanide, etc.
②Exogenous chemicals themselves are relatively non-toxic, but their toxicity increases after metabolic activation in the body, becoming final poisons.
③Exogenous chemicals stimulate the production of endogenous toxicants through a certain metabolic process. For example, oxygen free radicals explode and lipid peroxides accumulate in large quantities.
Type of final poison: ① Electrophilic agent; ② Free radical; ③ Nucleophilic agent; ④ Redox reaction
Phase I reaction
reaction meaning
Expose or obtain some functional groups on the catalyzed substrate, such as -OH, -COOH, -SH, etc. These groups not only increase the water solubility of the reaction product, but also make it easier to proceed with the phase II reaction.
type
Oxidation
Cytochrome P450 enzyme system (Cyt P450) catalyzes
Catalyzed by flavin plus monooxygenase (FMO)
extracorporeal oxidation
reduction
Nitro and azo reduction
carbonyl reduction reaction
Disulfide, sulfur oxide and N-oxide reduction
Quinone reduction
Dehalogenation reduction
hydrolysis
Hydrolysis of esters
amidase-catalyzed hydrolysis
Reaction catalyzed by epoxide hydratase
Hydrolysis reaction is the main metabolism mode of many organophosphorus pesticides in the body
Phase II reaction (binding reaction)
reaction meaning
Deactivate certain functional groups on foreign chemical molecules and lose their toxicity
Increase its polarity, reduce fat solubility, and accelerate the excretion process from the body
After the poisons entering the central nervous system are biotransformed, if the water solubility is enhanced, it will be difficult for them to be excreted through the blood-brain barrier and blood-brain suction barrier. •Methylation and acetylation reactions often reduce the water solubility of conjugates
Glucuronic acid conjugation
Enzyme: Glucuronosyltransferase (UDPGT)
Cofactor: Uridine diphosphate glucose (UDPGA)
Overall reaction: UDPGA ROH→R—O—GA UDP
sulfuric acid combination
Enzyme: Sulfotransferase (SULT)
Cofactor: Adenosine 3'phosphate-5'phosphate sulfate (PAPS)
Product: sulfate ester (high water solubility)
glutathione binding
Function: Electrophilic agent detoxifies, eliminates free radicals, H2O2, organic hydroperoxides and organic free radicals, etc.
Enzyme: glutathione S-transferase (GST)
Cofactor: Glutathione (GSH) Substrate: electrophile, free radical
methylation reaction
Enzyme: Methyltransferase
Cofactor: S-adenosylmethionine (SAM)
Acetylation
Enzyme: Acetyltransferase (NAT) It can be both metabolic interpretation and metabolic activation.
Cofactor: Acetyl CoA •Substrates: Chemical poisons with aromatic amine or hydrazine groups
Amino acid binding
Enzyme: N-acyltransferase
Cofactors: amino acids •Requires ATP and acetyl-CoA for detoxification process
Influencing factors
Genetic polymorphisms of poison metabolizing enzymes
Gut flora and metagenome
Inhibition and induction of metabolic enzymes
Enzyme induction: Some poisons cause the increase of certain metabolic enzyme systems and their activity.
Inducer: Poison that has an inducing effect
Inhibition and activation of poison metabolizing enzymes
Competitive inhibition: Competitive inhibition occurs between two different enzymes at the active center of the same enzyme
Non-competitive inhibition: •The inhibitor binds reversibly or irreversibly to the active center of the enzyme • Destroy enzyme • Reduce enzyme synthesis • Allosteric effect • Lack of cofactors
Toxicological significance of induction or inhibition of poison metabolizing enzymes
When metabolic enzymes are induced, if the chemical poison is metabolically activated in the body, the toxicity will be enhanced; if the chemical poison is attenuated by metabolic conversion, the toxicity will be reduced. When inhibitors are present, the opposite result is obtained
membrane transport
endocytosis/pinocytosis
Liquid or solid exogenous chemicals are surrounded by protruding biological membranes, and then the surrounded droplets or larger particles are incorporated into the cells to achieve the purpose of transport. The former is called pinocytosis, and the latter is called phagocytosis, collectively called endocytosis
exocytosis
The process by which particulate matter is transported out of cells
Consume energy
special transport
The process in which exogenous chemicals first physically combine with certain substances (carriers) in the body and then pass through the biological membrane.
active transport
The process by which exogenous chemicals move from low concentration to high concentration through biological membranes
Features
Reversible concentration gradient transport consumes a certain amount of metabolic energy
The transfer process requires the participation of carriers
The carrier has a certain capacity; when the concentration of the compound reaches a certain level, the carrier can be saturated and the transport reaches its limit.
Active transport is selective
Competitive inhibition: If two compounds have similar basic structures and require the same transport system
facilitated diffusion
Chemicals that are not easily soluble in lipids use the process of carriers to move from high concentration to low concentration.
Features
Don't waste my energy
Using carrier, saturable
Have some initiative or choice
competitive inhibition
passive transport
simple diffusion
Chemicals diffuse from the higher-concentration side of the biofilm to the lower-concentration side. When the concentrations on both sides reach a dynamic equilibrium, diffusion ends. •The concentration difference on both sides of the membrane is called concentration gradient or concentration difference (source of power)
condition
There is a concentration difference on both sides of the membrane
Exogenous chemicals are fat-soluble
Exogenous chemicals are in a non-dissociated state
The simple diffusion method does not consume energy, does not require a carrier, and is not affected by saturation rate limitation and competitive inhibition.
Features
Smooth shave without consuming energy
Toxins do not react chemically with biofilms
Biofilm is not active and is a simple physical process
Toxicological significance
In general, most exogenous chemicals are biologically transported by simple diffusion
Influencing factors
Concentration gradient difference
Solubility of exogenous chemicals in lipids Lipid-water partition coefficient = concentration in lipid phase/concentration in water phase
Ionization or electrolysis state and pH in body fluids
Protein concentration and protein binding affinity of body fluids on both sides of biofilm
filter
The process of exogenous chemicals penetrating the hydrophilic pores in the biological membrane relies on the osmotic pressure gradient and hydrostatic pressure on both sides of the biological membrane.
Influencing factors and toxicological significance
The molecular weight of a chemical
The 40nm pore can pass >200 molecules
70nm pore can pass >60,000 molecules
Water and some substances that are soluble in water but not soluble in lipids can complete the biological transport process through filtration.