Whats the purpose of the loop of the henle?

Different organisms have different sizes of it why is this so?

The reason for the different sizes have to do with the amount of fluid that the organism needs to retain. The purpose of the loop of Henle or the nephron loop is to exchange ions and water, this is important in maintaining homeostasis.

This is an example of text that I found:

long, U-shaped portion of the tubule that conducts urine within each nephron of the kidney of reptiles, birds, and mammals. The principal function of the loop of Henle appears to be the recovery of water and sodium chloride from the urine. This function allows production of urine that is far more concentrated than blood, limiting the amount of water needed as intake for survival. Many species that live in arid environments such as deserts have highly efficient loops of Henle.

The main function of this structure is to create a concentration gradient in the medulla of the kidney.This process reabsorbs water and creates a concentrated urine for excretion.The descending limb is permeable to water and water flows from LOH into the surrounding intestitial fluid.Hence the urine becomes more concentrated (1200mosmol)as u go down the loop.And the ascending limb is impermeable to water but permeable to salts like NaCl.Hence the salt comes out this time making the urine back hypoosmotic as it enters the DCT.

Desert animals like camels have long LOHs since they need to retain water to survive from dehydration.Hence more water is absorbed.While aquatic animals have short LOHs coz they needn't absorb water.

The main function of the loop of Henle structure is to create a concentration gradient in the medulla of the kidney. By means of a countercurrent multiplier system, which utilizes sodium pumps, it creates an area of high sodium concentration deep in the medulla, near the collecting duct. Water present in the filtrate in the collecting duct flows through aquaporin channels out of the collecting duct, moving passively down its concentration gradient.

There are differences in the sizes of this regarding various species because different species live in more arid environments such as deserts have and need more efficient loops of Henle in order to survive as compared to those in other environment. Different milieu equals different survival.