Malphigian tubules

The Malpighian tubule system is a type of excretory and osmoregulatory system found in some insects, myriapods, arachnids, and tardigrades.

The system consists of branching tubules extending from the alimentary canal that absorbs solutes, water, and wastes from the surrounding hemolymph. The wastes then are released from the organism in the form of solid nitrogenous compounds as calcium oxalate. The system is named after Marcello Malpighi, a seventeenth-century anatomist.

It is unclear as to whether the Malpighian tubules of arachnids and those of the Uniramia are homologous or the result of convergent evolution.

Malpighian tubules are slender tubes normally found in the posterior regions of arthropod alimentary canals. Each tubule consists of a single layer of cells that is closed off at the distal end with the proximal end joining the alimentary canal at the junction between the midgut and hindgut. Most tubules are normally highly convoluted. The number of tubules varies between species although most occur in multiples of two. Tubules are usually bathed in hemolymph and are in proximity to fat body tissue. They contain actin for structural support and microvilli for propulsion of substances along the tubules. Malpighian tubules in most insects also contain accessory musculature associated with the tubules which may function to mix the contents of the tubules or expose the tubules to more hemolymph. The insect orders, Thysanura, Dermaptera and Thysanoptera do not possess these muscles and Collembola and Hemiptera:Aphididae completely lack a Malpighian tubule system.

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