Water Reabsorption
- Created by: Tripat
- Created on: 31-10-12 11:08
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- Water Reabsorption
- Reabsorption of Water
- After selective reabsorption in the proximal convoluted tubule about 45 Cm3 is left
- Each minute about 125 cm3of fluid is filtered from the blood and enters the nephron tubules.
- The role of the loop of Henle is to create a low (very negative) water potential in the tissue of the medulla
- This ensures that even more water can be reabsorbed from the fluid in the collecting duct
- The Loop of Henle
- The loop of Henle consists of a descending limb that descends into the medulla and an ascending limb that ascends back out to the cortex
- The arrangement of the loop of Henle allows salts (Na ions and Cl ions) to be transferred from the ascending limb to the descending limb.
- The overall effect is to increase the concentration of salts in the tubule fluid.
- Consequently they diffuse out from the thin walled ascending limb into the surrounding medulla tissue
- This gives the tissue fluid in the medulla a very low (very negative) water potential
- How is this (low water potential) achieved?
- As the fluid in the tubule descends deeper into the medulla its water potential becomes lower (more negative. This is due to two things
- Loss of water by osmosis to the surrounding tissue fluid
- Diffusion of sodium and chloride ions into the tubule from the surrounding tissue fluid
- As the fluid then goes up the ascending limb, Na+ and Cl? ions are actively pumped out so it gets more and more dilute.
- Filtrate passing down the descending limb of the loop of Henle is flowing in the opposite direction to fluid in the ascending limb.
- The fluid is increasingly concentrated as it moves down and increasingly dilute as it moves up. This countercurrent flow (or countercurrent multiplier) allows concentrated urine to be produced.
- As the fluid in the tubule descends deeper into the medulla its water potential becomes lower (more negative. This is due to two things
- The Collecting Duct
- This is important because yet more water is drawn out of the tube (at this point called the collecting duct) when it passes through the medulla again.
- This allows you to make concentrated urine. Any filtrate not reabsorbed - most of the urea, some water and some salt - is drained into the bladder.
- Obviously the amount of water reabsorbed is controlled by the quantity of water in the blood. The less water in the blood, the more that it must be reabsorbed.
- Reabsorption of Water
- Reabsorption of Water
- After selective reabsorption in the proximal convoluted tubule about 45 Cm3 is left
- Each minute about 125 cm3of fluid is filtered from the blood and enters the nephron tubules.
- The role of the loop of Henle is to create a low (very negative) water potential in the tissue of the medulla
- This ensures that even more water can be reabsorbed from the fluid in the collecting duct
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