Question

Mammals, birds and insects have the ability to produce urine that is hyperosmotic to their bodily fluid; however, insects utilize a more simplistic mechanism. In addition to the final product being the same, there are other stages of urine formation in mammals and insects that is quite similar. Explain

Answer 1

Hyperosmotic uri production in insects seems to be simpler when compared to mammals, this is because

• In mammalian kidney different processes like volume reduction, regulation of individual electrolytes, adjustment of osmotic concentration and pH regulation occur in distinct segments one after the other. But all these processes occur simultaneously in the rectum of the insect, which simplifies the whole process and it is under control of neuropeptide hormones and also the countercurrent multiplier system is a major and complex mechanism that occurs in mammalian kidney, but absent in insects.

The mechanism of urine formation occurs in three steps:

1. Filtration
2. Reabsorption
3. Secretion​​​​​​​

These steps are almost similar in both insects and mammals.But in insects, the malphigian tubules play major role in filtration process whereas in mammals the glomeruli of nephrons is the place for filtration.

The process of secretion in insects is in the following way:​​​​​​​

• ​​​​​​​Potassium ions are actively transported from blood into cavity of tubule and then for maintenance of negative ions enter.These are followed by water by osmosis and other substances like sugars, amino acids, urates by diffusion from blood.
• Whereas in mammals all these processes of secretion into tubules and reabsorption occurs in the proximal & distal convoluted tubules and loop of henle by both passive and active transport mechanisms.
• At the end acidification of urine occurs in both but the nitrogenous wastes produced are urea in mammals while it is uric acid in insects.

To conclude, the steps of urine formation is same in insects and mammals but the sites they are taking place and the mechanisms they involve to accomplish the steps differ in both.