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Questions and Answers
What type of movement requires a carrier protein but does not require energy?
What type of movement requires a carrier protein but does not require energy?
Which ion has a higher concentration in the extracellular fluid compared to the intracellular fluid?
Which ion has a higher concentration in the extracellular fluid compared to the intracellular fluid?
What defines active transport in membrane transport processes?
What defines active transport in membrane transport processes?
Which process involves the cell membrane engulfing a molecule to form a vesicle?
Which process involves the cell membrane engulfing a molecule to form a vesicle?
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What factor does NOT determine the rate of diffusion?
What factor does NOT determine the rate of diffusion?
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What type of transport allows for the passive movement of ions through specific protein channels?
What type of transport allows for the passive movement of ions through specific protein channels?
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How does simple diffusion differ from facilitated diffusion?
How does simple diffusion differ from facilitated diffusion?
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Which statement accurately describes the direction of K+ movement in the body?
Which statement accurately describes the direction of K+ movement in the body?
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What directly influences the rate of diffusion across a membrane?
What directly influences the rate of diffusion across a membrane?
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Which of the following accurately describes primary transport?
Which of the following accurately describes primary transport?
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Which mechanism is described as using energy from a primary transport to drive another transport?
Which mechanism is described as using energy from a primary transport to drive another transport?
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What is the role of the Na/K+ ATPase pump?
What is the role of the Na/K+ ATPase pump?
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Which equation calculates the electrochemical potential energy difference across a membrane?
Which equation calculates the electrochemical potential energy difference across a membrane?
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What does the term 'antiporter' refer to?
What does the term 'antiporter' refer to?
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How is the flux of a solute across the membrane defined according to Fick's Law?
How is the flux of a solute across the membrane defined according to Fick's Law?
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What happens to the driving force for K+ at the peak of an action potential?
What happens to the driving force for K+ at the peak of an action potential?
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What does the lipid-water partition coefficient (Kp) indicate in terms of solute diffusion?
What does the lipid-water partition coefficient (Kp) indicate in terms of solute diffusion?
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What does a higher lipid-water partition coefficient (Kp) indicate about a drug?
What does a higher lipid-water partition coefficient (Kp) indicate about a drug?
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Which factor influences the ionization of weak acids and bases?
Which factor influences the ionization of weak acids and bases?
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What is the function of GLUT transporters in the body?
What is the function of GLUT transporters in the body?
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What does a low lipid-water partition coefficient (Kp) signify about a drug?
What does a low lipid-water partition coefficient (Kp) signify about a drug?
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What is the main characteristic of primary active transport?
What is the main characteristic of primary active transport?
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How does Michaelis-Menten kinetics relate to drug transport?
How does Michaelis-Menten kinetics relate to drug transport?
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What happens to aspirin (acetylsalicylic acid) in terms of ionization in the stomach versus plasma?
What happens to aspirin (acetylsalicylic acid) in terms of ionization in the stomach versus plasma?
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Which of the following sites is NOT a principle site of carrier-mediated transport?
Which of the following sites is NOT a principle site of carrier-mediated transport?
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What type of transport is utilized by intestinal solute carrier proteins?
What type of transport is utilized by intestinal solute carrier proteins?
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Which characteristic allows drugs to permeate the plasma membrane efficiently?
Which characteristic allows drugs to permeate the plasma membrane efficiently?
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How is glucose primarily absorbed in the gut?
How is glucose primarily absorbed in the gut?
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What is the effect of plasma membrane thickness on permeability?
What is the effect of plasma membrane thickness on permeability?
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What is logP used to measure?
What is logP used to measure?
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What is the primary active transport mechanism exemplified by the Na+/K+ ATPase pump?
What is the primary active transport mechanism exemplified by the Na+/K+ ATPase pump?
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What is the primary mechanism by which thiazide diuretics reduce blood pressure?
What is the primary mechanism by which thiazide diuretics reduce blood pressure?
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Which electrolyte imbalance is most likely to occur with the use of thiazide diuretics?
Which electrolyte imbalance is most likely to occur with the use of thiazide diuretics?
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Which condition is a contraindication for the use of thiazide diuretics?
Which condition is a contraindication for the use of thiazide diuretics?
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How do thiazides influence uric acid levels in the body?
How do thiazides influence uric acid levels in the body?
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What paradoxical effect do thiazides have in nephrogenic diabetes insipidus?
What paradoxical effect do thiazides have in nephrogenic diabetes insipidus?
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Which of the following side effects is most commonly associated with thiazide use?
Which of the following side effects is most commonly associated with thiazide use?
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Which substance's secretion is increased due to thiazide-induced diuresis?
Which substance's secretion is increased due to thiazide-induced diuresis?
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What effect do thiazide diuretics have on calcium levels in the bloodstream?
What effect do thiazide diuretics have on calcium levels in the bloodstream?
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What mechanism primarily drives potassium loss in patients taking thiazide diuretics?
What mechanism primarily drives potassium loss in patients taking thiazide diuretics?
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What impact do thiazides have on blood glucose levels over chronic administration?
What impact do thiazides have on blood glucose levels over chronic administration?
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What is the primary action of loop diuretics in the nephron?
What is the primary action of loop diuretics in the nephron?
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Which ion is primarily inhibited from reabsorption by carbonic anhydrase inhibitors?
Which ion is primarily inhibited from reabsorption by carbonic anhydrase inhibitors?
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What mechanism underlies the diuretic effect of carbonic anhydrase inhibitors?
What mechanism underlies the diuretic effect of carbonic anhydrase inhibitors?
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What condition might loop diuretics be used to manage?
What condition might loop diuretics be used to manage?
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How do osmotic diuretics function in the nephron?
How do osmotic diuretics function in the nephron?
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Which of the following statements about thiazides is correct?
Which of the following statements about thiazides is correct?
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What is one of the key functions of the Na+/K+ pump in cells?
What is one of the key functions of the Na+/K+ pump in cells?
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What happens to bicarbonate levels in the plasma during chronic use of carbonic anhydrase inhibitors?
What happens to bicarbonate levels in the plasma during chronic use of carbonic anhydrase inhibitors?
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What happens to the alpha subunit during the Na+/K+ pumping mechanism?
What happens to the alpha subunit during the Na+/K+ pumping mechanism?
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Which of the following correctly describes the reaction cycle of the Na+/K+ pump?
Which of the following correctly describes the reaction cycle of the Na+/K+ pump?
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Which ion's secretion is promoted by the distal convoluted tubule?
Which ion's secretion is promoted by the distal convoluted tubule?
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What is the effect of digoxin on the Na+/K+ ATPase pump?
What is the effect of digoxin on the Na+/K+ ATPase pump?
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How do potassium-sparing diuretics function in the nephron?
How do potassium-sparing diuretics function in the nephron?
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What indicates the effectiveness of furosemide as a loop diuretic?
What indicates the effectiveness of furosemide as a loop diuretic?
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Which mode enables the Na+/K+ pump to act as an ATP synthesis machine under certain conditions?
Which mode enables the Na+/K+ pump to act as an ATP synthesis machine under certain conditions?
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What is the role of the beta subunit in the Na+/K+ ATPase complex?
What is the role of the beta subunit in the Na+/K+ ATPase complex?
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Which part of the nephron is primarily affected by thiazide diuretics?
Which part of the nephron is primarily affected by thiazide diuretics?
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Which of the following correctly describes P-glycoprotein transporters?
Which of the following correctly describes P-glycoprotein transporters?
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What role does the thick ascending limb of the loop of Henle play with respect to urine concentration?
What role does the thick ascending limb of the loop of Henle play with respect to urine concentration?
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What is the primary reason for loop diuretics causing metabolic alkalosis?
What is the primary reason for loop diuretics causing metabolic alkalosis?
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How does secondary active transport typically use the Na+ gradient?
How does secondary active transport typically use the Na+ gradient?
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What distinguishes a symport from an antiport system in secondary active transport?
What distinguishes a symport from an antiport system in secondary active transport?
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What primary role does the collecting duct play regarding urine composition?
What primary role does the collecting duct play regarding urine composition?
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What is the primary role of the small auxiliary protein (gamma subunit) in Na+/K+ ATPase?
What is the primary role of the small auxiliary protein (gamma subunit) in Na+/K+ ATPase?
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Which statement about the Na+/K+ pump's effect on cell swelling is correct?
Which statement about the Na+/K+ pump's effect on cell swelling is correct?
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Which of the following correctly describes the binding properties of the Na+/K+ pump's alpha subunit?
Which of the following correctly describes the binding properties of the Na+/K+ pump's alpha subunit?
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What is a characteristic of cardiac glycosides like digoxin?
What is a characteristic of cardiac glycosides like digoxin?
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Which mode of the Na+/K+ pump is characterized by moving Na+ and K+ simultaneously but in opposite directions?
Which mode of the Na+/K+ pump is characterized by moving Na+ and K+ simultaneously but in opposite directions?
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What is a key consequence of loop diuretics blocking NKCC2?
What is a key consequence of loop diuretics blocking NKCC2?
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Which of the following side effects is associated with loop diuretics?
Which of the following side effects is associated with loop diuretics?
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What primary mechanism drives the movement of potassium into the interstitium in the kidney?
What primary mechanism drives the movement of potassium into the interstitium in the kidney?
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Which condition is treated using thiazide diuretics?
Which condition is treated using thiazide diuretics?
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How do loop diuretics affect calcium and magnesium levels in the body?
How do loop diuretics affect calcium and magnesium levels in the body?
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In which part of the nephron do thiazide diuretics primarily act?
In which part of the nephron do thiazide diuretics primarily act?
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What is a common result of combining loop diuretics with potassium-sparing diuretics?
What is a common result of combining loop diuretics with potassium-sparing diuretics?
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What effect does thiazide diuretics have on calcium?
What effect does thiazide diuretics have on calcium?
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Which of the following is a potential adverse effect of excessive loss of potassium?
Which of the following is a potential adverse effect of excessive loss of potassium?
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What causes dizziness when using loop diuretics?
What causes dizziness when using loop diuretics?
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What is the main function of primary active transport of hydrogen ions in the gastric glands?
What is the main function of primary active transport of hydrogen ions in the gastric glands?
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Which mechanism describes the absorption of sodium ions in the kidneys?
Which mechanism describes the absorption of sodium ions in the kidneys?
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What component specifically counteracts the transport of sodium ions into cells in the Na+/H+ exchanger?
What component specifically counteracts the transport of sodium ions into cells in the Na+/H+ exchanger?
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What is a consequence of excessive calcium levels within cells?
What is a consequence of excessive calcium levels within cells?
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Where is the most potent primary active transport mechanism for H+ found?
Where is the most potent primary active transport mechanism for H+ found?
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Which of the following best describes the relationship between sodium and glucose absorption in the jejunum?
Which of the following best describes the relationship between sodium and glucose absorption in the jejunum?
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What regulates the action of the Na+/H+ exchanger in the jejunum?
What regulates the action of the Na+/H+ exchanger in the jejunum?
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In which part of the nephron does most sodium reabsorption occur?
In which part of the nephron does most sodium reabsorption occur?
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What type of epithelial cell in the renal tubules is responsible for H+ secretion?
What type of epithelial cell in the renal tubules is responsible for H+ secretion?
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What primarily drives the movement of fluid from the glomerular capillaries into the Bowman’s capsule?
What primarily drives the movement of fluid from the glomerular capillaries into the Bowman’s capsule?
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What impact does increased intracellular cAMP have on NaCl absorption?
What impact does increased intracellular cAMP have on NaCl absorption?
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What describes the Na+/Ca2+ counter-transport mechanism?
What describes the Na+/Ca2+ counter-transport mechanism?
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Which type of drug acts specifically on the nephron's loop of Henle?
Which type of drug acts specifically on the nephron's loop of Henle?
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Which mechanism allows sodium to be reabsorbed from the filtrate into the cells of the proximal convoluted tubule?
Which mechanism allows sodium to be reabsorbed from the filtrate into the cells of the proximal convoluted tubule?
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What happens to bicarbonate ions in the proximal convoluted tubule?
What happens to bicarbonate ions in the proximal convoluted tubule?
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Which segment of the nephron is impermeable to water?
Which segment of the nephron is impermeable to water?
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How is chloride reabsorbed in the thick ascending limb of the Loop of Henle?
How is chloride reabsorbed in the thick ascending limb of the Loop of Henle?
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What regulates calcium excretion in the early distal tubule?
What regulates calcium excretion in the early distal tubule?
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What is the main function of the collecting duct?
What is the main function of the collecting duct?
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What effect does aldosterone have on the nephron?
What effect does aldosterone have on the nephron?
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What occurs in the descending limb of the Loop of Henle?
What occurs in the descending limb of the Loop of Henle?
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How does ADH affect the collecting duct?
How does ADH affect the collecting duct?
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Which of the following best describes the osmolarity of tubular fluid leaving the thick ascending limb?
Which of the following best describes the osmolarity of tubular fluid leaving the thick ascending limb?
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What triggers the reabsorption of water in the collecting duct?
What triggers the reabsorption of water in the collecting duct?
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Which effect does a higher concentration of sodium bicarbonate in the filtrate have on chloride concentration?
Which effect does a higher concentration of sodium bicarbonate in the filtrate have on chloride concentration?
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What is primarily secreted by intercalated cells in the collecting duct?
What is primarily secreted by intercalated cells in the collecting duct?
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What effect does hypokalaemia have on the efficacy of digoxin?
What effect does hypokalaemia have on the efficacy of digoxin?
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What is the primary function of aldosterone in the kidneys?
What is the primary function of aldosterone in the kidneys?
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What is a potential side effect of potassium-sparing diuretics?
What is a potential side effect of potassium-sparing diuretics?
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Which diuretics are typically needed to prevent potassium loss?
Which diuretics are typically needed to prevent potassium loss?
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How do Na+ channel inhibitors help in managing potassium levels?
How do Na+ channel inhibitors help in managing potassium levels?
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Which of the following describes a consequence of using ACE inhibitors with potassium-sparing diuretics?
Which of the following describes a consequence of using ACE inhibitors with potassium-sparing diuretics?
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What is the primary action of aldosterone antagonists on Na+/K+ ATPase?
What is the primary action of aldosterone antagonists on Na+/K+ ATPase?
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What are thiazides known to antagonize, reducing their efficacy?
What are thiazides known to antagonize, reducing their efficacy?
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Which mechanism reduces blood Na+ and increases blood K+ when using aldosterone antagonists?
Which mechanism reduces blood Na+ and increases blood K+ when using aldosterone antagonists?
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What is a characteristic of loop diuretics in relation to digoxin?
What is a characteristic of loop diuretics in relation to digoxin?
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Which condition can result from gastrointestinal disturbances caused by spironolactone?
Which condition can result from gastrointestinal disturbances caused by spironolactone?
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What is the primary action of Na+/Ca2+ exchangers during cardiac action potentials?
What is the primary action of Na+/Ca2+ exchangers during cardiac action potentials?
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Which statement best describes Na+ channel inhibitors like amiloride?
Which statement best describes Na+ channel inhibitors like amiloride?
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What type of drug interaction occurs between a drug and a medical condition?
What type of drug interaction occurs between a drug and a medical condition?
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Study Notes
Membrane Transport
- Total body water (70kg): 42L
- Extracellular fluid (3L plasma + 13L interstitial): 16L
- Intracellular fluid: 25L
- Extracellular Na+ (142mM) > intracellular Na+
- Intracellular K+ > extracellular K+ (creates concentration gradient)
Mechanisms of Small Molecule Movement Across Membranes
-
Diffusion: Random movement of molecules. Driven by kinetic energy.
- Simple diffusion: Directly through lipid or aqueous pores. Rate proportional to lipid solubility.
- Facilitated diffusion: Requires carrier protein. Moves molecules down concentration gradients. More efficient for charged ions.
- Active transport: Requires energy (ATP). Moves molecules against concentration gradient.
- Endocytosis (pinocytosis): Membrane invaginates, forming a vesicle around a substance. Brings substance into the cell.
Transport Rates and Factors
- Diffusion rate depends on substance availability, membrane fluidity, and number/size of membrane openings.
- Diffusion rate is directly proportional to lipid solubility.
Primary Active Transport
- Uses ATP hydrolysis directly.
- Carrier proteins differ from facilitated diffusion transporters. Capable of moving substances against electrochemical gradients.
- Example: Na+/K+ ATPase pump (3 Na+ out, 2 K+ in). Maintains gradients for other transport.
Secondary Active Transport
- Energy from a primary transport process (like Na+/K+ pump) drives another transport.
- Examples include:
- Transport systems in renal tubules
- Gastrointestinal tract
- Placenta
- Uptake of some drugs across blood brain barrier
Solute Transport Across Cell Membranes (Passive and Aqueous Diffusion)
- Solute moves down electrical and/or chemical gradient
- Membrane permeability is essential. Either solute is lipophilic or membrane channels are present.
Modelling Equations
- Electrochemical potential difference = chemical potential difference + electrical potential difference. Determines passive and aqueous diffusion.
Nernst Equation
- Net driving force = membrane potential - equilibrium potential.
- At resting potential, K+ driving force is inward. At peak action potential, it's outward.
- Equilibrium potential is the diffusion potential preventing net ion movement. At rest, the driving force of K+ is very large, causing it to exit the cell.
Diffusion of Electrially Neutral Solutes (Fick's Law)
- Jx (flux) = permeability coefficient (Px) * concentration gradient.
- Px = lipid-water partition coefficient (Kp) * diffusion coefficient (D) / membrane thickness (m). The higher the lipid-water partition coefficient (Kp) the easier it is for the solute to dissolve in the membrane.
Lipid-Water Partition Coefficient (logP)
- Measures lipid/water solubility of a drug.
- High logP = high lipid solubility, aiding membrane permeability.
- Low logP = low lipid solubility.
Diffusion of Drugs Across Plasma Membranes
- Weak acids/bases exist as ionized/unionized forms.
- Ionization depends on pH and pKa.
- Unionized form is more permeable to the membrane.
- pH trapping: aspirin ionization (exchanges) at different pHs.
Principle Sites of Carrier-Mediated Transport
- Blood-brain barrier
- Gastrointestinal tract
- Placenta
- Renal tubules
- Biliary tract.
Importance of Transporters
- Intestinal solute carriers are essential for nutrient and vitamin absorption.
- Transporter functions are often subject to saturation kinetics.
Michaelis-Menten Kinetics
- Rate of transport depends on solute concentration and transporter affinity (Km).
- Vmax, max rate for diffusion that transporter can handle.
Glucose Transporters
- Belong to the SLC2 family (solute carriers).
- GLUT2: insulin secretion by pancreatic beta cells.
- GLUT4: insulin-activated.
- GLUT2 and GLUT5: glucose/fructose transport in gut.
- Glucose/galactose absorption (secondary active transport via SGLT1); fructose (facilitated diffusion via GLUT5).
- All exit via GLUT2 (facilitated).
Active Transport
- Moves molecules against gradients.
- Requires energy. Examples include movement of hydrophilic, polar substances across cell membrane and creating and maintaining ion gradients.
- Primary active transport is required to set up conc. gradient for secondary active transport mechanism to function.
Na+/K+ ATPase Pump (Primary Active Transport)
- Crucial for maintaining electrochemical gradients, cell volume.
- 3 Na+ out; 2 K+ in.
- Uses ATP to drive transport and change in protein shape.
- Carrier protein complex, alpha (catalytic) and beta (regulatory) subunits.
- Steps in the transport cycle involve: substrate binding, phosphorylation, conformational change.
Digoxin
- Inhibitor of Na+/K+ ATPase.
- Used to treat arrhythmias
- Elevates intracellular Ca in heart muscle cells increasing contractility. But also potentiates ventricular arrhythmias.
- Narrow therapeutic window, monitor levels.
P-glycoprotein Transporters
- Primary active transport. Pumps drugs out of cells.
- Functions in liver, kidney, placenta, intestines, brain capillaries.
- Role in drug efflux and resistance.
Primary Active Transport of Ca2+
- Maintained at extremely low intracellular concentration (via Ca2+ pumps).
- Cell membrane pumps (Ca2+ out). Intracellular vesicle pumps (e.g., SR in muscles).
Primary Active Transport of H+
- Important in gastric glands (secreting HCl) and renal tubules (excreting H+).
Primary and Secondary Na+ Absorption
- Primary active transport (Na+/K+ pump) creates a Na+ gradient.
- Secondary active transport (e.g., Na+/glucose co-transport) uses this gradient.
- Example of co-transport and counter-transport mechanisms in jejunum, ileum, proximal colon.
Renal Transport Systems (Drugs)
-
Loop diuretics: Inhibit Na+/K+/2Cl- co-transporter (NKCC2) in thick ascending limb of loop of Henle, causing substantial Na+ and water loss.
- Effect: significant increase urine production, decrease Na, Cl, and K reabsorption.
- Side effects: Hyponatremia, hypokalemia, and potentially ototoxicity
-
Thiazide diuretics: Act on Na+/Cl- co-transporter in the distal convoluted tubule.
- Effect: Decreases Na absorption, leading to moderate water loss. May also cause calcium reabsorption.
- Side effects: Dehydration (potential), hyponatremia, hypokalemia, and hypercalcemia.
-
Potassium-sparing diuretics: Reduce Na+ reabsorption and K+ secretion in the distal nephron.
- effect: Mild diuretic effect, main function to prevent K loss by other diuretics, Used when hypokalaemia is a concern.
- Side effects: Hyperkalaemia
Drug Interactions
- Drug interactions involve reactions between two or more drugs.
- Types of interactions include drug-drug interactions and drug-condition interactions.
- Diuretics interfere with the pharmacokinetics of other drugs.
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Description
Explore the various mechanisms of small molecule movement across membranes, including diffusion, facilitated diffusion, and active transport. Understand how concentration gradients and factors like membrane fluidity influence transport rates. This quiz is essential for students studying cell biology or physiology.
