define the counter current mechanism.
define the counter current mechanism.
Counter-Current Mechanisms The mechanisms shown here are traditionally called the 'counter-current multiplier' and the 'counter-current exchanger'. The first takes place in the region of the nephron called Henle's loop; the second occurs in a region of the peritubular capillary bed called the 'vasa recta'. Both are involved in establishing an osmotic gradient throughout this region.
Henle's Loop The portion of the nephron called the 'Henle's loop' is shown in the right half of the illustration. It consists of a descending limbthat has a down arrow in it and an ascending limbwith an up arrow in it. The ascending limb has a thick and a thin segment. The dotsrepresent various solutes that become more concentrated in both limbs toward the bottom of the loop.
The thick walls of the ascending limb indicates that this region is impermeable to water.
Vasa Recta This capillary bed is shown in red at the left of the illustration. It also also consists of a descending limb and an ascending limb identified by the arrows in each. Again, the dots represent various solutes that are more concentrated at the bottom of the loop.
Counter-Currents Counter-currents exist when fluids flow in opposite directions in parallel and adjacent tubes. The two limbs of Henle's loop are a counter-current. The two limbs of the vasa recta are also a counter-current. It is apparent that these two sets of tubes are parallel and adjacent. Not apprent in the mind map is the fact that the descending limb of Henle is also counter-current with the ascending limb of the vasa recta; the same is true of the ascending limb of Henle and the descending vasa recta.
Counter-Current Exchanger Examination of both limbs of the vasa recta shows the concentration of solutes (number of dots) is the same at any horizontal level. However, imagine the fluid flowing through the vasa recta for a short distance then stopping. Now compare the concentration of solutes at any level and they will not be the same. At any level the solute concentration in the descending limb will be less than in the ascending limb! But, because both limbs are freely permeable, sodium chloride will diffuse from the ascending into the descendingwhile water will diffuse from the descending to the ascending...see block arrows. When equilibrium is reached both limbs will, once again, have the same concentration of water and solutes. Water is exchanged for sodium chloride...the counter-current exchange mechanism.
The mechanisms shown here are traditionally called the 'counter-current multiplier' and the 'counter-current exchanger'. The first takes place in the region of the nephron called Henle's loop; the second occurs in a region of the peritubular capillary bed called the 'vasa recta'. Both are involved in establishing an osmotic gradient throughout this region.
Henle's LoopThe portion of the nephron called the 'Henle's loop' is shown in the right half of the illustration. It consists of a descending limbthat has a down arrow in it and an ascending limbwith an up arrow in it. The ascending limb has a thick and a thin segment. The dotsrepresent various solutes that become more concentrated in both limbs toward the bottom of the loop.
The thick walls of the ascending limb indicates that this region is impermeable to water.
Vasa RectaThis capillary bed is shown in red at the left of the illustration. It also also consists of a descending limb and an ascending limb identified by the arrows in each. Again, the dots represent various solutes that are more concentrated at the bottom of the loop.
Counter-CurrentsCounter-currents exist when fluids flow in opposite directions in parallel and adjacent tubes. The two limbs of Henle's loop are a counter-current. The two limbs of the vasa recta are also a counter-current. It is apparent that these two sets of tubes are parallel and adjacent. Not apprent in the mind map is the fact that the descending limb of Henle is also counter-current with the ascending limb of the vasa recta; the same is true of the ascending limb of Henle and the descending vasa recta.
Counter-Current ExchangerExamination of both limbs of the vasa recta shows the concentration of solutes (number of dots) is the same at any horizontal level. However, imagine the fluid flowing through the vasa recta for a short distance then stopping. Now compare the concentration of solutes at any level and they will not be the same. At any level the solute concentration in the descending limb will be less than in the ascending limb! But, because both limbs are freely permeable, sodium chloride will diffuse from the ascending into the descendingwhile water will diffuse from the descending to the ascending...see block arrows. When equilibrium is reached both limbs will, once again, have the same concentration of water and solutes. Water is exchanged for sodium chloride...the counter-current exchange mechanism.
