AJP - Regulatory, Integrative and Comparative Physiology, Vol 248, Issue 1 93-R98, Copyright © 1985 by American Physiological Society
Postrenal modification of urine in birds
G. L. Anderson and E. J. Braun
The role of the cloaca and lower intestine in the postrenal modification of
urine was studied in conscious normally hydrated desert quail. The birds
were studied for a period of 12 days during which they were in
intake-output balance. It was calculated that of the combined mixture of
urine-feces entering the lower intestine, 47% water, 62% sodium, and 49%
potassium were reabsorbed. If this material is considered as coming from
the ureteral urine, then the composition of the ureteral urine entering the
lower intestine was changed as follows: 77% water, 72% sodium, and 82%
potassium were reabsorbed. For urate, 68% of the total present in ureteral
urine was degraded in the lower intestine. In terms of the filtered load
produced by the kidneys, the lower intestine reabsorbed 1.5% filtered
water, 0.4% filtered sodium, and 46% filtered potassium. The total filtered
loads reabsorbed by the combined efforts of the kidney and lower intestine
were 99.5% water, 99.8% sodium, and 88% potassium. It appears that the
cloaca and lower intestine of birds may serve a similar function to that of
the distal nephron in mammals, making the fine adjustments in water and
sodium reabsorption from the urine.
