Question

The longest loop of Henle is found in
A) Kangaroo rat
B) Opossum
C) Rhesus monkey
D) Porcupine

Answer 1

It is present in animals living in arid and semiarid areas, especially on sand or soft soils.This helps the animals live for long periods of time on minimal amounts of water.

Complete Answer:
The Loop of Henle is a long U-shaped tubule that conducts urine in each nephron of the kidney. The main function of the loop is to recover water and sodium chloride from urine. It is present in reptiles, birds and mammals. Henle’s loop is a juxtamedullary nephron because it goes deep down into the medulla of the kidney.
Loop of Henle can be divided into 4 parts:-

Thin descending limb- Highly permeable to water and less permeable to ions and urea.
Thin ascending limb- impermeable to water and permeable to ions.
Ascending limb – Sodium, potassium and chloride ions are reabsorbed from the urine by secondary active transport by a Na-K-Cl transport.
Cortical thick ascending limb- Drains urine into the distal convoluted tubule.
This function of nephron produces a highly concentrated urine, limiting the amount of water intake, needed for survival. Many species of deserts have highly efficient loops of Henle. They do not readily find water, so they excrete very less amount of water and highly concentrated urine.
Kangaroo rats are small, nocturnal rodents which are found in the dry area of North and Central America. They mostly eat dry food and do not take in liquid water by drinking.

The kangaroo rat's kidneys are well-organized and produce only small quantities of urine, which is highly concentrated. They are said to have very long loops of Henle. These long loops of Henle allows the water to be reabsorbed efficiently. This is because, the increase in concentration of ions deep in the medulla is effectively proportional to the length of the loops of Henle.

Hence the correct answer is option A, ‘Kangaroo rat’.

Note: The main function of the Loop of Henle is conservation of water by the countercurrent mechanism.They spend the majority of the time in their cool humid burrows where they retain as much water as possible by effectively recycling water which would else be lost while breathing.