Nephridium

This article or the following section is not adequately provided with supporting documents ( e.g. individual evidence ). Information without sufficient evidence could be removed soon. Please help Wikipedia by researching the information and including good evidence.

As Nephridium (from ancient Greek νεφρός nephros , German , kidney ' ) refers to an animal organ for excretion of toxic degradation products.

Types of nephridia

Protonephridia

Protonephridia are the simplest excretory organs and occur mainly in animals without a secondary body cavity . You are e.g. B. typical of flatworms (platelets) and larvae of molluscs .

Multiply branched tubes each start blindly with a trap flagellum cell , also called a cyrtocyte or terminal cell . Here a "lash flame" (a constantly beating cilia bundle) of the terminal cell creates a flow of the liquid into the tube system. This creates a negative pressure and the tissue fluid is filtered through the fish trap rods formed by the podocytes on the cyrtocyte ( ultrafiltration ). These podocytes of the terminal cell and those of the adjacent canal cell form numerous, interlocking feet that are only separated by fine spaces. They are covered by a basement membrane and thus represent a filter barrier for the liquid. When they pass, a filtrate is created “within” the protonephridium, which is called primary urine and contains all the substances present in the blood, except for cells and larger proteins.

In the tubule following the cyrtocyte, the tubule , those parts of the primary urine that the organism can use (smaller proteins, saccharides, amino acids, ions) are reabsorbed again. The secondary urine formed in this way then mainly contains substances harmful to the organism and is excreted via the nephridial pores that open outwards.

Fish trap cell and canal cell probably arise independently of one another in ontogenesis and approach one another in further development. In the process, the little feet formed by the two cells slide into one another, and the tubular channel surrounded by the cells is created.

Metanephridia

Metanephridia are characteristic of the annelid worms (Annelida) and presumably also exist in the worms (Nemertini). They are also found in many molluscs (Mollusca) and crustaceans (Crustacea) (here they are called maxillary or antennae nephridia).

Metanephridia are channels that are connected to the coelom by an eyelash funnel (nephrostome) and then lead to the outside. The ultrafiltration takes place first on the basement membrane of the blood vessels by podocytes (see above), which are located on the coelomepithelium near the eyelash funnel. The driving force here is blood pressure. As in the case of protonephridia, the still usable parts in the tubule are withdrawn from the resulting filtrate (primary urine) and reabsorbed, so that the secondary urine can then flow out through a closable nephridial pore.

A further development of a Metanephridiums is the nephron , the anatomical and functional unit of Vertebrate - kidney .

Malpighian vessels

Malpighian vessels are typical of many arthropods (otherwise metanephridia) such as arachnids (Arachnida), millipedes (Myriapoda) and insects (Insecta).