Membrane Transport Concepts
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Membrane Transport Concepts

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Questions and Answers

Which type of transport requires energy to move drugs across membranes?

  • Active transport (correct)
  • Passive diffusion
  • Filtration
  • Facilitated diffusion

    • The primary factor influencing passive diffusion of a drug is its:

  • Solubility in water
  • Degree of ionization (correct)
  • Presence of carrier proteins
  • Molecular weight

    • What does the term bioavailability refer to?

  • The amount of drug absorbed by the body (correct)
  • The rate at which a drug is eliminated
  • The concentration of the drug in the bloodstream
  • The effectiveness of a drug compared to another

    • According to Henderson-Hasselbalch’s equation, what does a higher pH indicate for a weak acid?

    <p>Increased ionization of the acid</p> Signup and view all the answers

    What is the primary course of drug concentration after administration in relation to the first-pass effect?

    <p>Metabolism by hepatic enzymes before reaching systemic circulation</p> Signup and view all the answers

    Which factor is NOT a major influence on the absorption of a drug?

    <p>Environmental temperature</p> Signup and view all the answers

    Which transport mechanism does NOT involve a concentration gradient?

    <p>Endocytosis</p> Signup and view all the answers

    Which of the following statements about pKa is true?

    <p>pKa values are constant for a drug</p> Signup and view all the answers

    What happens to weak acids in acidic pH environments?

    <p>They become more ionized.</p> Signup and view all the answers

    Which statement is true regarding the effect of pH on drug ionization?

    <p>Weak bases are ionized in acidic pH.</p> Signup and view all the answers

    How is the degree of ionization of a drug affected by pKa and pH?

    <p>When pKa equals pH, 50% of the drug is ionized.</p> Signup and view all the answers

    What is the relationship between pKa and the strength of an acid?

    <p>Stronger acids have lower pKa values.</p> Signup and view all the answers

    What occurs to drug absorption when moving from the stomach to the intestine?

    <p>Many drugs become nonionized when in a basic environment.</p> Signup and view all the answers

    Why is a drug more available for absorption when it is completely unionized?

    <p>Unionized drugs can easily cross cell membranes.</p> Signup and view all the answers

    In which of the following pH environments would a weak base be ionized?

    <p>Acidic pH.</p> Signup and view all the answers

    What is the impact of drug ionization on its absorption in the gastrointestinal tract?

    <p>Unionized drugs generally have higher absorption rates.</p> Signup and view all the answers

    What happens to weak acids in an acidic pH environment?

    <p>They are mostly nonionized.</p> Signup and view all the answers

    Why are acidic drugs ion trapped in a basic pH environment?

    <p>They remain in their ionized state.</p> Signup and view all the answers

    How does the ionization of aspirin affect its absorption in the stomach?

    <p>It crosses the gastric mucosa but is ionized at pH 7.</p> Signup and view all the answers

    What characteristic is true about strong acids and bases at standard pH?

    <p>They remain mostly ionized.</p> Signup and view all the answers

    What is the primary difference between facilitated diffusion and active transport?

    <p>Active transport requires energy while facilitated diffusion does not.</p> Signup and view all the answers

    What occurs when barbiturates reach alkaline urine?

    <p>They become ion trapped and are excreted.</p> Signup and view all the answers

    What does the concept of 'ion trapping' refer to in pharmacology?

    <p>The retention of drugs in the body due to their ionized state in certain pH.</p> Signup and view all the answers

    What limitation is associated with carrier-mediated transport systems?

    <p>Their capacity is limited by the number of available carriers.</p> Signup and view all the answers

    What term is used when formulations are not bioequivalent?

    <p>Bioinequivalent</p> Signup and view all the answers

    Which factor enhances the speed of drug absorption when taken in solution or powder form?

    <p>Particle size</p> Signup and view all the answers

    What is the effect of amorphous drugs compared to crystalline drugs?

    <p>Amorphous drugs dissolve faster</p> Signup and view all the answers

    Which of the following factors can cause reduction in bioavailability due to drug metabolism?

    <p>First pass effect</p> Signup and view all the answers

    What condition can lead to a significant change in drug absorption due to altered gastrointestinal function?

    <p>Gastrointestinal diseases</p> Signup and view all the answers

    How does the presence of food in the gastrointestinal tract affect drug bioavailability?

    <p>It can either increase or decrease absorption</p> Signup and view all the answers

    What type of drug substance tends to dissolve quicker due to the absence of water molecules?

    <p>Anhydrous substances</p> Signup and view all the answers

    Which of the following factors is a pharmacological consideration affecting bioavailability?

    <p>Gastrointestinal diseases</p> Signup and view all the answers

    What defines the central compartment in pharmacokinetics?

    <p>It consists of blood and highly vascular organs.</p> Signup and view all the answers

    Which of the following describes a characteristic of the peripheral compartment?

    <p>It may consist of single or multiple parts.</p> Signup and view all the answers

    What happens during the elimination phase of a one-compartment model?

    <p>Only the central compartment is involved in elimination.</p> Signup and view all the answers

    What is true about the distribution of a drug in a one-compartment model?

    <p>There is no drug distribution across compartments.</p> Signup and view all the answers

    Which drug is known to accumulate in skeletal muscle and organs like the heart?

    <p>Digoxin</p> Signup and view all the answers

    What is a significant function of plasma protein binding for drugs?

    <p>It governs the dynamic equilibrium of drug distribution.</p> Signup and view all the answers

    Which of the following substances is known to form complexes with bone salts?

    <p>Cisplatin</p> Signup and view all the answers

    How are drugs absorbed into the peripheral compartment?

    <p>They pass through tissue membranes from the bloodstream.</p> Signup and view all the answers

    Study Notes

    Membrane Transport

    • Passive Diffusion: Does not require energy; moves from a higher concentration to a lower concentration.
    • Facilitated Diffusion: Does not require energy; moves from a higher concentration to a lower concentration using carrier proteins.
    • Active Transport: Requires energy (ATP); moves from a lower concentration to a higher concentration using carrier proteins.
    • Endocytosis: A process where a cell engulfs material from its surroundings.
    • Filtration: A process where fluids and small molecules are pushed through a membrane.

    Passive Diffusion

    • Key factors affecting passive diffusion:
      • Lipophilicity: A drug's ability to dissolve in fats and oils; more lipophilic drugs cross membranes more easily.
      • Degree of Ionization: The extent to which a drug is ionized; non-ionized drugs are generally more lipophilic and cross membranes easier.
      • pH of surrounding environment: pH affects the degree of ionization of drugs, impacting membrane permeability.
      • pKa: Dissociation constant of a drug; determines the pH at which a drug is 50% ionized and 50% non-ionized.
    • Henderson-Hasselbalch equation: Used to calculate the pH of a solution and predict the degree of ionization of a weak acid or weak base.

    Implications of Passive Diffusion and Ionization

    • Strong acids and bases: Generally stay ionized at standard pH, making it difficult for them to cross cell membranes.
    • Weak acids: Are mostly non-ionized in acidic environments (e.g., stomach) and mostly ionized in basic environments (e.g., intestines).
    • Weak bases: Are mostly non-ionized in basic environments (e.g., intestines) and mostly ionized in acidic environments (e.g., stomach).
    • Ion Trapping: When a drug is trapped on one side of a membrane due to a difference in pH; for example, an acidic drug will be trapped in a basic environment and a basic drug will be trapped in an acidic environment.

    Carrier-Mediated Transport

    • Facilitated Diffusion (Carrier-mediated): No energy required, moves from higher to lower concentration, carrier proteins specific for certain drugs.
    • Active Transport (Carrier-mediated): Requires energy, moves from lower to higher concentration, carrier proteins specific for certain drugs.
    • Competition between drugs: Two drugs can compete for the same carrier protein, potentially leading to reduced absorption or bioavailability.

    Factors Affecting Absorption and Bioavailability

    • Pharmaceutical Factors:

      • Particle Size: Fine particles (e.g., powders) are absorbed faster than larger particles (e.g., tablets, capsules).
      • Crystal Form: Amorphous forms dissolve faster than crystalline forms.
      • Water of Hydration: Anhydrous forms dissolve faster than hydrated forms.
      • Excipients/Additives: These can affect the dissolution rate and absorption of the drug.
      • Degree of Ionization/Lipophilicity: Influence how easily a drug can cross cell membranes.

    • Pharmacological Factors:

      • First-pass Effect/ Presystemic Elimination: Metabolism of a drug in the gut and liver before it reaches systemic circulation.
      • Gastrointestinal Emptying Time: The rate at which the stomach empties into the intestines.
      • Gastrointestinal Diseases: Conditions affecting the gut can impact drug absorption.
      • Presence of Food/ Interactions with Food: Food can affect the absorption of drugs.
      • Pharmacogenetic Factors: Genetic differences in drug metabolism and absorption can influence bioavailability.

    First- Pass Effect

    • The first-pass effect is the metabolism of a drug in the liver before it reaches systemic circulation.
    • It can significantly reduce the bioavailability of drugs.
    • Factors that influence the first-pass effect:
      • Liver function: Liver disease can reduce metabolism and lead to increased bioavailability.
      • Dosage form: The way a drug is administered (e.g., oral, IV) can impact the first-pass effect.

    Distribution

    • Describes how a drug moves from the bloodstream to various tissues and organs.
    • The volume of distribution (Vd) indicates how much drug is distributed throughout the body relative to the plasma concentration.
    • One-Compartment Model: The drug is considered to be equally distributed in the body.
    • Two/Multi-Compartment Model: The drug can be found in different compartments (e.g., central compartment, peripheral compartments) over time.
    • Distribution is often characterized by two phases:
      • α phase: The rapid distribution of the drug into tissues.
      • β phase: The elimination of the drug from the body.

    Distribution: Drug Reservoirs

    • Cellular/Tissue Reservoirs: Some drugs can accumulate in specific tissues, such as muscles, liver, heart, and kidney.
    • Fat: Some lipophilic drugs can accumulate in fat tissues.
    • Bones and Connective Tissues: Certain drugs can form complexes with bone salts, leading to long-term storage.

    Plasma Protein Binding

    • Many drugs bind to plasma proteins, such as albumin.
    • This binding is reversible.
    • Only unbound, free drugs are therapeutically active and can cross cell membranes.
    • Protein binding can affect distribution, metabolism, and elimination.

    Pharmacokinetic Interactions

    • Interactions between drugs can affect the way they are absorbed, distributed, metabolized, and eliminated.
    • Example: Co-administration of two drugs that compete for the same binding site on plasma proteins can alter the free drug concentrations of both drugs.

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    Description

    Explore the mechanisms of membrane transport including passive diffusion, facilitated diffusion, active transport, endocytosis, and filtration. Understand the key factors that influence passive diffusion such as lipophilicity, degree of ionization, and pH. Test your knowledge of these essential biological concepts.

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