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Questions and Answers
Which statement correctly differentiates active transport from passive diffusion?
Which statement correctly differentiates active transport from passive diffusion?
- Passive diffusion requires protein receptors to facilitate movement.
- Active transport cannot be saturated.
- Both move only down the concentration gradient.
- Active transport requires energy and can move up the concentration gradient. (correct)
What is a key characteristic of transcellular drug absorption?
What is a key characteristic of transcellular drug absorption?
- Drugs pass through the space between cells.
- It requires specific protein receptors for the movement. (correct)
- It can occur regardless of drug size.
- Drugs diffuse only along electrochemical gradients.
Which of the following factors does not affect paracellular absorption?
Which of the following factors does not affect paracellular absorption?
- Presence of lipid bilayer. (correct)
- Size of the drug molecule.
- Size of the pores between cells.
- Concentration gradient of the drug.
Why is Enhanced Permeability and Retention (EPR) critical in drug delivery to tumors?
Why is Enhanced Permeability and Retention (EPR) critical in drug delivery to tumors?
Which of the following statements about facilitated transport is accurate?
Which of the following statements about facilitated transport is accurate?
What is a key characteristic of passive diffusion in drug absorption?
What is a key characteristic of passive diffusion in drug absorption?
Which of the following best describes active transport mechanisms?
Which of the following best describes active transport mechanisms?
What is the primary function of carrier-mediated transport in drug absorption?
What is the primary function of carrier-mediated transport in drug absorption?
In transcellular absorption, what is primarily required for drugs to pass through membranes via active transport?
In transcellular absorption, what is primarily required for drugs to pass through membranes via active transport?
Which statement is true concerning membrane channels in drug transport?
Which statement is true concerning membrane channels in drug transport?
What distinguishes facilitated transport from passive diffusion in drug absorption?
What distinguishes facilitated transport from passive diffusion in drug absorption?
Which factor does NOT affect the rate of drug absorption through passive diffusion?
Which factor does NOT affect the rate of drug absorption through passive diffusion?
Which transport mechanism requires the input of ATP for drug movement?
Which transport mechanism requires the input of ATP for drug movement?
Which mechanism allows substances to pass through the cell membrane by utilizing specific carriers?
Which mechanism allows substances to pass through the cell membrane by utilizing specific carriers?
What is one effect of agents that block transport proteins?
What is one effect of agents that block transport proteins?
Which type of transport is primarily responsible for the movement of substances across the cell membrane without the use of energy?
Which type of transport is primarily responsible for the movement of substances across the cell membrane without the use of energy?
Which mechanism of drug absorption is most likely affected by competitive inhibition?
Which mechanism of drug absorption is most likely affected by competitive inhibition?
In what way does methylphenidate function as a reuptake inhibitor?
In what way does methylphenidate function as a reuptake inhibitor?
Which statement about passive diffusion is true?
Which statement about passive diffusion is true?
Which of the following types of membrane transport would be affected by a change in temperature?
Which of the following types of membrane transport would be affected by a change in temperature?
What is a common effect of drugs that act as reuptake inhibitors like cocaine?
What is a common effect of drugs that act as reuptake inhibitors like cocaine?
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Study Notes
Membrane Transport
- Passive Diffusion: Drug molecules pass through the membrane based on their lipid solubility. Lipid solubility is directly proportional to the lipid/water partition coefficient of the drug.
- Channel Transport: Specific for certain molecules, requiring binding recognition.
- Carrier-mediated transport: Specific for certain molecules, requiring binding recognition.
Transcellular Absorption
- Passive Diffusion: Down the concentration gradient.
- Channel Transport: Down the concentration gradient.
- Carrier-mediated transport: Down the concentration gradient.
Active Transport
- Carrier mediated active transport: Against a concentration gradient or an electrochemical gradient; can become saturated at high concentrations.
- Active Transport: Through transporter proteins; specific, saturable. Examples include Iron transport in the gut, L-DOPA transport across the blood-brain barrier, and anion/cation transport in the kidney.
Paracellular Absorption
- Dependent on the size of the drug (molecular weight less than 200) compared to the size of the cellular pore.
- Non-specific, allowing anything of the appropriate size to pass.
- Passive: down the concentration gradient or electrochemical gradient.
- Does not move through the lipid bilayer.
Nanoparticle Characteristics
- Smaller in size compared to small-molecule drugs.
- Have different physical and chemical properties compared to small-molecule drugs.
Enhanced Permeability and Retention (EPR) Effect
- Key feature of nanocarrier delivery to tumors.
- Utilizes passive mechanisms of EPR – a critical design parameter of nanocarrier delivery.
- Pore size in the endothelial walls determines the entry of nanoparticles into tissues.
Competitive Inhibition
- Membrane passage via transport mechanisms is subject to competitive inhibition by another substance with similar affinity for the same carrier.
Agents Blocking Transport Proteins
- Agents binding to transport proteins prevent re-uptake of neurotransmitters.
- Examples include:
- Methylphenidate (Ritalin) – reuptake inhibitor for dopamine and noradrenaline.
- Cocaine – reuptake inhibitor for dopamine and serotonin.
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