Malpighian tubule system

The Malpighian tubules (after Marcello Malpighi ) can thus be regarded as the kidneys and other insects of terrestrial arthropods ( arthropods ) and as a powerful excretory organs.

It is Blindausstülpungen of the midgut ( in arachnids ) or the rectum ( at Tracheentieren ). Therefore, the Malpighian tubules in the arachnids of endodermal origin, at the Tracheentieren ectodermal origin. In the evolution of the Malpighian tubules is a convergent evolution, which can be seen also on the different ontogenetic origin. The gut and the Malpighian tubules are separated by a membrane peritrophische.

Epithelial cells actively transport potassium and sodium ions from the hemolymph of the body cavity in the Malpighian tubules. On the potassium transport a water import is coupled. Due to the electrochemical gradient constructed uric acid can be transported in the blood vessels, despite difference in concentration. Since uric acid is insoluble in water, it is in the blood vessels present in crystalline form, which provides a water savings. Passive also amino acids, sugars, urea and other salt ions are released. The pH lies in the Malpighian tubules at about 6.8 to 7.5. Salt ions are formed from the iso-osmotic urine in the rectum and the rectum actively pumped into the hemolymph of the body cavity, where water passively nachströmt again. The pH is at 3.5 to 4.5 in the rectum. Such as amino acids and sugars are here and recovered in the rectum. Intra- gastric water cycle contributes greatly to the success of insects as terrestrial species, since it allows to save a majority of water. The regulation of water and ion balance ( osmoregulation ) is performed on the system described.

A big difference to mammalian kidneys, Proto and Metanephridien is that the outfeed of the substances not by means of ultrafiltration, but by (secondary) takes place active transport processes and filtration does not matter.

The Malpighian tubules are formed within the phylogeny of arthropods at least twice: In the Arachnida as a protrusion of the endodermal midgut and at the Antennata as protrusion of the ectodermal rectum.