Invertebrates - Osmotic and Ionic Regulation

Regulation of water and ions in invertebrates is done by neuroendocrine mechanism. It operates at the level of Malpighian tubules and the rectum in insects. A neurosecretory substance termed, diuretic hormone inhibits water resorption from the rectum and also stimulates water uptake by the Malpighian tubules.

In some insects an antidiuretic hormone lowers the rate of water output by the tubules and increases water absorption by the rectum. Another neurosecretory hormone termed Chloride transport stimulating hormone is known to regulate electrolyte balance in insects. It causes a two-to-three fold increase in cyclic AMP levels in the rectal tissues, which in turn activates the chloride pump of the rectal cells, actively transporting chloride ions into the haemocoel.