Question

Hypertonic urine formation is a characteristic of kidneys of
A. Fishes and amphibians
B. Amphibians and reptiles
C. Reptiles and fishes
D. Birds and mammals

Answer 1

Hint: Urine which has higher osmotic pressure than that of a specified, generally physiological solution with which it is compared (opposite to hypotonic and isotonic). Most of the marine animals produce hypotonic urine.

Complete answer:
Hypertonic solution is that solution in which water moves out by osmosis. So hypertonic urine is that urine in which water moves out from the urine. Since water moves out of the urine, so urine is concentrated and is called hypertonic urine. We mammals produce hypertonic urine to avoid loss of water. The ability of the kidney to produce urine that is hypertonic to the blood plasma is due to the loop of henle.
> Fishes: Hypotonic urine is present. Marine organisms excrete ammonia directly into water and are called ammonotelic.
> Amphibians: Land animals mainly amphibian’s convert ammonia into urea. Hypotonic urine is present
> Reptiles: Uricotelism is the excretion of excess nitrogen in the form of uric acid. Animals include insects, birds, and most reptiles.
Hypertonic urine formation is a characteristic of the kidneys of birds and mammals because of the following phenomenon. The flow of filtrate in the two limbs of Henley’s loop is in opposite directions and thus forms a counter current. The flow of blood through the limbs of vasa recta is also in a countercurrent pattern. The proximity between the Henley’s loop and vasa recta, as well as the formation of hypertonic urine.

So the correct answer is option D.

Note: Excretion of excess water leads to a formation of hypotonic urine, excretion of excess solutes results in a formation of hypertonic urine. Hypertonic urine is highly concentrated urine. Isotonic solution the extracellular fluid has the same osmolarity as the cell and there will be no net movement of water into or out of the cell.