A-Level Biology OCR A
Fluid Water Limb Sodium Chloride Gradient Loop Tissue
The descending limb of the Loop of Henle allows water to exit, concentrating the filtrate, while the ascending limb actively transports ions out, making the filtrate dilute. The ascending limb is impermeable to water, leading to a buildup of solutes in the medulla.
In the loop of Henle, the descending limb is permeable to water, making the filtrate hypertonic as it descends. The ascending limb actively pumps out ions, making the filtrate hypotonic as it ascends, while remaining impermeable to water. This process creates a high solute concentration in the medulla.
| Front |
Explain how the reabsorption of water occurs in the loop of Henle. |
| Back |
Loop of Henle:- Descending limb is impermeable to sodium and chloride ions, lower part is permeable to water, upper part isn't
- Filtrate is initially isotonic, as it travels down the limb, water passes out of the loop into the tissue fluid by osmosis down concentration gradient and then into the capillaries
- As fluid reaches apex it is very concentrated and hypertonic
- First section of ascending limb is permeable to sodium and chloride ions - they move out of concentrated solution by diffusion down conc gradient
- Second section of ascending limb - sodium and chloride ions are actively pumped out into tissue fluid against concentrationg gradient
- High sodium and chloride conc produced in medulla tissue, however ascending limb is impermeable to water so water does not follow ions down concentration gradient
- Renal fluid becomes increasingly dilute & eventually hypotonic with blood while tissue fluid becomes more concentrated
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A-Level Biology OCR A