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Water Balance (A Hypertonic Medullary Interstitium Is Needed To Form…
Water Balance
- A Hypertonic Medullary Interstitium Is Needed To Form Concentrated Urine.
- Concentrated urine factor ;- (1) generation of a hypertonic medullary interstitium.;- (2) enhanced water permeability in CD in the presence of ADH.
- Hypertonic of medullary interstitium is produced and maintained by ;- (1) reabsorption of osmolarity active substances by tubules in medulla.;-(2) the removal of water from the medullary interstitium by vasa recta.
- The Kidney Maintains Water Balance
- Maintain water content & plasma tonicity.
- Dog produce concentrated urine 7-8 times concentrated than plasma osmolarity.
- Dog produce hypotonic urine 1/3 of the plasma osmolarity.
- The Proximal Tubule Reabsorbs More Than 60% Of Filtered Water
- Reabsorbs solute by active and passive transport.
- Active transport drive by basolateral Na+/K+ ATPase → secondary active transport and passive paracellular transport.
- PCT brush border ,rapid reabsorption ,↑ permeable to water.
- Abudant aquaporin-1 and aquaporin-7 in the membrane.
- ↑ oncotic pressure & ↓ hydrostatic peritubular capillary → favor solute uptake.
- Water reabsorbed nearly isotonic with salt.
- The Kidney Can Produce Either Concentrated Or Dilute Urine.
- (1) Generation of a hypertonic medullary interstitium → concentrated urine.
- (2) Dilution of tubule fluid by the TAL and DCT → dilute urine.
- (3) Variability in water permeability of CD in response to antidiuretic hormone ADH & vasopressin → determine the final urine concentration.
- The Juxtamedullary Nephros Extend Deep Into The Inner Medulla.
- Mammalian kidney have superficial and juxtamedullary nephrons
- Superficial nephron = short Henle’s loop, extend from inner to outer medulla.
- Juxtamedullary nephron = long Henle’s loop,deep into inner medulla, concentrate urine at higher level > plasma osmolarity .
- Avian,= reptilian -type nephron → near surface cortex → no loop of Henle.;- mammalian -type nephron → excrete urine hypertonic to plasma.
- The Solute Reabsorption By The Medullary Thick Ascending Limb And Collecting Duct Generates And Maintains Medullary Hypertonicity.
- TAL- reabsorb NaCl without water, impermeable to water.
- ↑ interstitial fluid osmolarity → medullary interstitial hypertonicity and osmotic gradient.
- Inner medullary CD reabsorbs urea, while cortical and outer medulla CD does not.
- Terminal inner medullary collecting duct (IMCD)- highly permeable to urea through carrier-mediated urea transport.
- Urea conserved in IMCD in medulla, reabsorption into interstitium by ADH,when body demand for water conservation.
- ↑[urea] uptake, ↑ osmotic gradient for water uptake.
- Thin limb of Henle’s loop permeable to urea.