Questions and Answers
What percentage of sodium does the ascending limb of loop of Henle absorb?
25%
What type of cotransport occurs in the ascending loop of Henle?
Na+-K+-2Cl- cotransporter in luminal membrane
Loop diuretics inhibit:
Na+-K+-2Cl- cotransporter in luminal membrane
What is the diluting segment in the ascending loop of Henle?
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Distal tubule reabsorbs sodium via what co-transporter?
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Where do thiazide diuretics inflict their damage?
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What is the role of the loop of Henle?
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What are the different segments of the loop of Henle?
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What is the thin descending limb most permeable to?
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The thin ascending limb of Loop of Henle is permeable to?
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What is the importance of the basolateral membrane channeling sodium out of the cell in the thick ascending loop of Henle?
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What apical membrane cotransporter system is targeted by high-ceiling diuretics?
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What percentage of sodium is reabsorbed by the thick ascending limb of Henle via the paracellular pathway?
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Why is the thick ascending limb considered to be the diluting segment?
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Compare the transfer of NaCl in the thick ascending loop of Henle and the early distal convoluted tubule.
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NaCl is reabsorbed by the thick limb of the loop of Henle via what transport mechanism?
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What is the countercurrent mechanism/system?
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NaCl reabsorption by the thick ascending limb of the loop of Henle results in the generation of a hyperosmotic interstitial fluid in which region of the kidney?
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As the dilute urine passes up through the thick ascending loop of Henle, what hormone functions to concentrate urine?
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What allows water to leave the tubular lumen into the interstitial fluid?
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What percentage of urea is filtered in the glomerulus and reabsorbed by the proximal tubule?
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After the proximal tubule reabsorption, where does urea reabsorption occur again?
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ADH permits urea reabsorption in what region of the kidney?
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What type of transport does urea undergo along the inner medullary collecting duct?
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What percentage does urea contribute to the total inner medullary interstitial fluid osmolality?
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What is the process of passive countercurrent multiplication by the thin ascending limb of the loop of Henle?
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Study Notes
Loop of Henle Overview
- The loop of Henle reabsorbs approximately 25% of filtered NaCl and water, playing a crucial role in urine concentration and dilution.
- It consists of three segments: thin descending limb, thin ascending limb, and thick ascending limb, each with unique transport and permeability characteristics.
Ascending Limb Functions
- The ascending limb absorbs 25% of sodium through the Na+-K+-2Cl- cotransporter located in the luminal membrane.
- It serves as a diluting segment, impermeable to water but capable of reabsorbing NaCl, thereby reducing tubular Na+ concentration and osmolarity.
Diuretics Mechanism
- Loop diuretics, such as furosemide, inhibit the Na+-K+-2Cl- cotransporter in the luminal membrane, significantly increasing urine flow and sodium excretion.
- Thiazide diuretics act on the early distal tubule, impairing sodium reabsorption via the Na+-Cl- co-transporter.
Concentration Gradients
- The thick ascending limb's basolateral membrane channels sodium out, creating a concentration gradient that facilitates sodium entry from the apical membrane.
- A hyperosmotic interstitial fluid is generated in the outer and inner medulla, aided by NaCl reabsorption.
Countercurrent Mechanism
- The countercurrent mechanism enables the production of concentrated urine by facilitating the exchange of solutes and water in opposing directions within the nephron.
- As dilute urine ascends through the thick ascending limb, antidiuretic hormone (ADH) acts to concentrate urine in the late distal tubule and collecting duct.
Urea Reabsorption
- After glomerular filtration, 50% of urea is reabsorbed in the proximal tubule, with additional reabsorption occurring in the inner medulla.
- ADH promotes urear reabsorption in the inner medullary collecting duct through passive diffusion, contributing to the osmotic gradient necessary for water reabsorption.
Role of Urea
- Urea recycling contributes approximately 40% to the total osmolality of the inner medullary interstitial fluid, enhancing the passive countercurrent multiplication process and promoting additional solute reabsorption.
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