Answer:
Mammals have the
ability to produce concentrated urine. The loop of Henie and vasa recta play a
significant role in it, which can be discussed as follows The proximity between
the Henle's loop and vasa recta, as well as the counter current (formed due to
the flow of filtrate in two limb's of Henle's loop in opposite direction) help in
maintaining an increasing osmolarity towards the inner medullary interstitium,
i'e., from 300 in
the cortex to about 1200 in
the inner medulla.
(ii)This
gradient is caused mainly due to NaCI and urea. NaCI is transported by the ascending
limb of Henle's loop, which is exchanged with the descending limb of vasa recta.
(iii) NaCI
is returned to the interstitium by the ascending portion of vasa recta.
(iv) Similarly,
a small amount of urea enters the thin segment of the .ascending limb of Henle's
loop, which is transported back to the interstitium by the collecting tubule.
(v) This
special arrangement of Henle's loop, and vasa recta, is called the' counter
current mechanism.
(vi) The
counter current exchange reduces the rate of dissipation. This/in turn reduces
the rate at which the current must pump to
maintain any given gradient.
(vii) Presence
of such interstitial gradient helps in an easy passage of water from the
collecting tubule thereby concentrating the filtrate (urine).
(viii) Human kidneys
can produce urine nearly four times concentrated, than the initial filtrate formed.
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