• The corticopapillary osmotic gradient is the osmotic gradient of the renal interstitium
  • It allows the nephrons to adjust the osmolarity of the tubular fluid, and ranges from 300 milliosmoles/liter in the cortex to up to 1200 milliosmoles in the inner medulla
  • Medullary countercurrent multiplication
  • Urea recycling
  • Renal corpuscle
  • Proximal tubule
  • Nephron loop, specify its descending and ascending limbs; recall that the ascending limb is impermeable to water.
  • Distal tubule
  • Collecting duct
  • It is surrounded by the renal interstitium, which comprises tissues and fluids.
  • The corticomedullary junction marks where the cortex becomes the medulla
  • The proximal and distal tubules lie within the cortex, and the nephron loop lies within the medulla.
  • The corticopapillary osmotic gradient (the osmolarity of the interstitium) increases from the cortex to the medulla.
  • Isosmotic tubular fluid enters the descending limb of the nephron loop; its osmolarity is similar to that of blood plasma, 300 milliosmoles/liter.
  • Water is passively reabsorbed in the descending limb;
  • Consequently, by the time it reaches the bend of the nephron loop, the tubular fluid is hyperosmotic, with osmolarity as high as 1200 milliosmoles/liter; this is because water has left the tubular fluid; solutes have not been added to the tubular fluid.
  • The hyperosmotic tubular fluid is “pushed” into the ascending limb by the arrival of new tubular fluid; recall that tubular fluid is constantly flowing through the nephrons.
  • Then, as it passes through the ascending limb, sodium chloride is actively reabsorbed from the tubular fluid, which lowers its osmolarity.
  • Thus, as it exits the nephron loop, the tubular fluid is hypo-osmotic, at approximately 100 milliosmoles/liter. In other words, the nephron loop has created relatively dilute urine.
  • Interstitial fluid of the cortex is isosmotic with blood plasma, at 300 milliosmoles/liter
  • Osmolarity increases incrementally as we move towards the inner medulla, where, like the tubular fluid, its osmolarity can be as high as 1200 milliosmoles/liter.
  • This gradient is created by the continuous reabsorption of water and sodium chloride in the nephron loop:
  • Recall that, because water was reabsorbed in the descending limb, the tubular fluid that enters the ascending limb has a very high solute concentration;
  • Higher tubular fluid solute concentration leads to increased solute reabsorption, which raises the osmolarity of the medullary interstitium.
  • However, as the tubular fluid ascends through the outer medulla and cortex, continuous solute reabsorption reduces its osmolarity.
  • Thus, less solutes are available for transport to the interstitium, so its osmolarity decreases as we move superficially.
  • Urea reabsorption relies on the presence of anti-diuretic hormone (ADH, aka, arginine, vasopressin), thus it is most prominent in water depletion states: when circulating ADH levels are high.
  • ADH increases water permeability, but has no effect on urea transport.
  • As a result of water reabsorption, urea concentration in the tubular fluid increases.
  • Then, in the inner medullary collecting duct, indicate that ADH increases both water permeability and urea transport;
  • The diffusion of urea into the interstitial fluid increases the osmolarity of the inner medulla, which adds to the corticopapillary osmotic gradient.
  • Urea can be secreted into the nephron loop, or, taken up by the vasa recta.
  • The corticopapillary osmotic gradient is the osmotic gradient of the renal interstitium
  • It allows the nephrons to adjust the osmolarity of the tubular fluid, and ranges from 300 milliosmoles/liter in the cortex to up to 1200 milliosmoles in the inner medulla
  • Medullary countercurrent multiplication
  • Urea recycling
  • Renal corpuscle
  • Proximal tubule
  • Nephron loop, specify its descending and ascending limbs; recall that the ascending limb is impermeable to water.
  • Distal tubule
  • Collecting duct
  • It is surrounded by the renal interstitium, which comprises tissues and fluids.
  • The corticomedullary junction marks where the cortex becomes the medulla
  • The proximal and distal tubules lie within the cortex, and the nephron loop lies within the medulla.
  • The corticopapillary osmotic gradient (the osmolarity of the interstitium) increases from the cortex to the medulla.
  • Isosmotic tubular fluid enters the descending limb of the nephron loop; its osmolarity is similar to that of blood plasma, 300 milliosmoles/liter.
  • Water is passively reabsorbed in the descending limb;
  • Consequently, by the time it reaches the bend of the nephron loop, the tubular fluid is hyperosmotic, with osmolarity as high as 1200 milliosmoles/liter; this is because water has left the tubular fluid; solutes have not been added to the tubular fluid.
  • The hyperosmotic tubular fluid is “pushed” into the ascending limb by the arrival of new tubular fluid; recall that tubular fluid is constantly flowing through the nephrons.
  • Then, as it passes through the ascending limb, sodium chloride is actively reabsorbed from the tubular fluid, which lowers its osmolarity.
  • Thus, as it exits the nephron loop, the tubular fluid is hypo-osmotic, at approximately 100 milliosmoles/liter. In other words, the nephron loop has created relatively dilute urine.
  • Interstitial fluid of the cortex is isosmotic with blood plasma, at 300 milliosmoles/liter
  • Osmolarity increases incrementally as we move towards the inner medulla, where, like the tubular fluid, its osmolarity can be as high as 1200 milliosmoles/liter.
  • This gradient is created by the continuous reabsorption of water and sodium chloride in the nephron loop:
  • Recall that, because water was reabsorbed in the descending limb, the tubular fluid that enters the ascending limb has a very high solute concentration;
  • Higher tubular fluid solute concentration leads to increased solute reabsorption, which raises the osmolarity of the medullary interstitium.
  • However, as the tubular fluid ascends through the outer medulla and cortex, continuous solute reabsorption reduces its osmolarity.
  • Thus, less solutes are available for transport to the interstitium, so its osmolarity decreases as we move superficially.
  • Urea reabsorption relies on the presence of anti-diuretic hormone (ADH, aka, arginine, vasopressin), thus it is most prominent in water depletion states: when circulating ADH levels are high.
  • ADH increases water permeability, but has no effect on urea transport.
  • As a result of water reabsorption, urea concentration in the tubular fluid increases.
  • Then, in the inner medullary collecting duct, indicate that ADH increases both water permeability and urea transport;
  • The diffusion of urea into the interstitial fluid increases the osmolarity of the inner medulla, which adds to the corticopapillary osmotic gradient.
  • Urea can be secreted into the nephron loop, or, taken up by the vasa recta.