PHGY 210 Lecture 35: PHGY 210-001 - Lec 35 - Apr 3
Apr 3, 2017
Glossary
Osmolarity: total solute concentration of solution; measure of water concentration in that the
higher the solution osmolarity, the lower the water concentration
Hypoosmotic: having total solute concentration less than that of normal extracellular fluid (300
mOsm)
Isoosmotic: having total solute concentration equal to that of normal extracellular fluid
Hyperosmotic: having total solute concentration greater than that of normal extracellular fluid
Renal regulation of water balance
-water is freely filtered but ~99% is reabsorbed
-majority of water reabsorption (~2/3) occurs in proximal tubule
-but major hormonal control of reabsorption occurs in CD
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Water reabsorption depends on Na reabsorption (proximal tubule)
Water reabsorption depends on Na reabsorption (proximal tubule)
1. Na is reabsorbed from tubular lumen to interstitial fluid across epithelial cells
2. Local osmolarity in lumen decreases, while local osmolarity in interstitium increases
3. This difference in osmolarity causes net diffusion of water from lumen into interstitial fluid
-via tubular cells’ plasma membranes
-via tight junctions
4. From interstitium, water, sodium, and everything else dissolved in interstitial fluid move
together by bulk flow into peritubular capillaries
Maintenance of water balance
-body has to maintain water balance
-when water intake is small, kidney reabsorbs more water (e.g. urine output 0.4 L per day)
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-when water intake is large, kidney reabsorbs less water (e.g. urine output 25 L per day)
-this dynamic regulation takes place in CD and there are two critical components:
1. High osmolarity of medullary interstitium
2. Permeability of CD to water (regulated by vasopressin)
Urine concentration: countercurrent multiplier system
-kidney has ability to concentrate urine up to 1400 mOsm/L
-urinary concentration takes place as tubular fluid flows through medullary collecting ducts
-urinary concentration depends on hyperosmolarity of interstitial fluid
-in presence of vasopressin, water diffuses out of ducts into interstitial fluid in medulla to
be carried away
-how does medullary interstitial fluid become hyperosmotic?
Urine concentration: countercurrent multiplier system
-medullary interstitial fluid becomes hyperosmotic through function of Henle’s loop
Countercurrent multiplier system
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Osmolarity: total solute concentration of solution; measure of water concentration in that the higher the solution osmolarity, the lower the water concentration. Hypoosmotic: having total solute concentration less than that of normal extracellular fluid (300 mosm) Isoosmotic: having total solute concentration equal to that of normal extracellular fluid. Hyperosmotic: having total solute concentration greater than that of normal extracellular fluid. Water is freely filtered but ~99% is reabsorbed. Majority of water reabsorption (~2/3) occurs in proximal tubule. But major hormonal control of reabsorption occurs in cd. Water reabsorption depends on na reabsorption (proximal tubule) Via tight junctions: from interstitium, water, sodium, and everything else dissolved in interstitial fluid move together by bulk flow into peritubular capillaries. When water intake is small, kidney reabsorbs more water (e. g. urine output 0. 4 l per day) When water intake is large, kidney reabsorbs less water (e. g. urine output 25 l per day)
