The Loop of Henle functions as a counter-current multiplier, using active transport of Na+ in the ascending limb to create a water potential gradient in the medulla, facilitating water reabsorption from the descending limb and collecting duct by osmosis.
- 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
| 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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