plasma clearance
the volume of plasma from which a substance is completely removed per unit time
clearance rate calculation
clearance rate (ml/min)= ((urine conc. quantity/ml)(urine flow rate ml/min)) / (plasma conc. quantity /ml)
what are the 3 variation types of plasma clearance experienced by a substance?
- substances that are filtered, not reabsorbed
- substances that are filtered and reabsorbed
- substances that are filtered and secreted, not reabsorbed
plasma clearance: filtered, not reabsorbed
- eg, insulin
- its plasma clearance is used to estimate glomerular filtration rate
plasma clearance: filtered and reabsorbed
plasma clearance must be less than glomerular filtration rate
plasma clearance: filtered, secreted , and not reabsorbed
plasma clearance will be greater than glomerular filtration rate
what does the vertical osmotic gradient in the interstitial fluid of medulla do?
the ability to concentrate urine
what is the osmolarity in the cortex vs the medulla
in cortex it is lower than in the medulla (300mOsm/L -> 1200mOsm/L)
cortical nephron structure
loop of henle only dips slightly into medulla
juxtamedullary nephron structure
- loop of henle dips all the way down into renal pelvis
- vasa recta also goes all the way to renal pelvis
- flow of loop of henle and vasa recta goes in opposite directions
– countercurrent flow
step 1 in establishing osmotic gradient in medulla
- when fluid leaves bowmans capsule and enters proximal tubule there’s a string drive for osmotic reabsorption of water
– secondary to active reabsorption of of Na+
step 2 in establishing osmotic gradient in medulla
- by end of proximal tubule (due to Na+ reabsorption), 65% of filtrate volume has been reabsorbed
- at this point, osmolarity of tubular fluid is 300mOsm/L (or isotonic to other bodily fluids)
step 3 in establishing osmotic gradient in medulla
- in loop of henle an additional 15% of filtered water will be reabsorbed
– during establishment and maintenance of vert. osmotic gradient
ascending limb of loop of henle relationship to water and Na+
- impermeable to water
- absorbs Na+
– in this case water doesn’t follow Na+
descending limb of loop of henle relationship to water and Na+
- highly permeable to water
- do not reabsorb Na+
what is osmolarity of entering and leaving the distal tubule?
entering= 4x normal body fluids
leaving= 1/3 normal body fluids
7 steps of countercurrent multiplication in loop of henle
1) 200 mOsm/L gradient is first established between interstitial fluid and the ascending limb
2) fluid flows forward several frames
3) ascednign and descending limbs reestablish the 200 mOsm/L gradient
4) fluid flows several frames again
5) 200mOsm/L gradient established again to each horizontal level
6) vertical osmotic gradient is established and maintained in an ongoing fashion
7) gradient remains constant due to constant flow
2 main purposes of countercurrent multiplication
1) established vert. osmotic gradient in the medullary interstitial fluid
- allows collecting ducts to form more conc. and more dilute urine than normal bodily fluids
2) allows for overall volume of urine to be reduced
- allows the body to conserve salt and water
how vasopressin controls water reabsorption
1) released from post. pituitary in response to water deficit when ECF is hypertonic
2) once released, it travels to kidneys acting on distal tubular cells to increase aquaporin molecules in luminal membrane
- increases water reabsorption in epithelial cells
3) once inside epithelial cells, water passively moves into intersitial fluid and plasma
vasopressin action on proximal tubule or loop of henle
NONE
- can only increase water reabsorption in distal and collecting tubules
how can vasopressin regulate water reabsorption when theres a deficit of water?
- increase release of vasopressin
- increases number of aquaporin channels in distal and collecting tubules
- under max influence, osmolarity of tubular fluid at end of collecting duct can be up to 1200mOsm/L (isotonic to interstitial fluid)
– max conc. of urine
how can vasopressin regulate water reabsorption when theres a excess of water?
- vasopressin release is completely supressed
- prevents insertion of aquaporins in luminal membrane of distal and collecting tubules so no water is reabsorbed
what is the vasa recta closely associated with
- descending and ascending loops of henle
– in part due to the hairpin shape allowing it to dive into medulla
vasa recta
- blood supply to renal medulla
- supports countercurrent multiplier mechanism
- highly permeable to NaCl and H2O
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Module 4: Section 136
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Module 4: Section 228
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Module 4: Section 330
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Module 4: Section 454
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Module 4: Section 516
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Module 4: Section 637
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Module 5: Section 115
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Module 5: Section 223
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Module 5: Section 321
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Module 5: Section 427
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Module 6: Section 146
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Module 6: Section 229
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Module 6: Section 351
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Module 6: Section 450
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Module 6: Section 629
