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Water Limb Potential Ascending Interstitial Fluid Osmosis Moves

Front What happens in the loop of Henle?
Back - Na+ actively transported out of ascending limb by cells in the walls
- using ATP produced by many mitochondria 
- reduces water potential in interstitial fluid

- walls of ascending limb are impermeable
- so water does not move out by osmosis

- wall of descending limb is permeable
- so water moves out through aquaporins by osmosis into interstitial fluid
- sodium ions move in by facilitated diffusion
- water potential of filtrate decreases as it moves down the descending limb
- most negative water potential at base of loop of Henle

- at base of ascending limb, Na+ moves by facilitated diffusion into interstitial fluid
- Na+ actively transported into interstitial fluid higher up ascending limb
- water potential of filtrate increases as it moves up the ascending limb

- collecting duct walls are permeable
- so water moves into blood capillaries by osmosis via aquaporins
- water potential in collecting duct decreases

- counter-current multiplier 
- ensures that water potential gradient is present all the way down the medulla
- for water reabsorption by osmosis

Tags: homeostasis

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