関: protonephridium

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/06/15 06:59:24」(JST)

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The nephridium (plural nephridia) is an invertebrate organ which occurs in pairs and performs a function similar to the vertebrate kidney. Nephridia remove metabolic wastes from an animal's body. They are present in many different invertebrate lines. There are two basic types, metanephridia and protonephridia, but there are other types.

Metanephridia

A metanephridium (meta = "after") is a type of excretory gland found in many types of invertebrates such as annelids, arthropods and molluscs. (In molluscs it is known as the Bojanus organ.)

A metanephridium typically consists of a ciliated funnel opening into the body cavity or coelom connected to a duct which may be variously glandularized, folded or expanded (vesiculate) and which typically opens to the organism's exterior. These ciliated tubules pump water carrying surplus ions, metabolic waste, toxins from food, and useless hormones out of the organism by directing them down funnel-shaped bodies called nephrostomes. This waste is passed out of the organism at the nephridiopore. The primary urine produced by filtration of blood (or a similar functioning fluid) is modified into secondary urine through selective reabsorption by the cells lining the metanephridium.

Saccate metanephridia

The saccate metanephridia are excretory glands which function similarly to the metanephridia. They are found in the arthropods. The saccate metanephridia filter the fluid of the hemocoel, as opposed to the metanephridia which filter coelomic fluid. In a saccate metanephridium, there is a ciliated funnel covered with a membrane that helps to filter the hemocoel of heavy particles (such as proteins and carbohydrates) before the fluid even enters the funnel. Inside the funnel, the fluid is further processed through selective reabsorption, and eventually excreted from the nephridiopore. In crustacea, the saccate metanephridia are associated with the antennae and form the antennal gland. In freshwater crustacea, the saccate metanephridia are especially large because they are involved in osmoregulation. They have to remove large amounts of water from the tissues, as the crustacean's tissues are hypertonic to the surrounding water.

Protonephridia

A protonephridium (proto = "first") is a network of dead-end tubules lacking internal openings found in the phyla Platyhelminthes, Nemertea and Rotifera. The ends are called flame cells (if ciliated) or solenocytes (if flagellated); they function in osmoregulation and ionoregulation, respectively. The terminal cells are located at the blind end of the protonephridium. Each cell has one or more cilia and their beating inside the protonephridial tube creates an outward going current and hence a partial pressurization in the blind of the tube. Because of this, pressurization drives waste fluids from the inside of the animal, and they are pulled through small perforations in the terminal cells and into the protonephridium. The perforations in the terminal cell are large enough for small molecules to pass, but larger proteins are retained within the animal. From the bottom of the protonephridium the solutes are led through the tube, formed by the canal cells, and exits the animal from a small opening formed by the nephridiopore. Selective reabsorption of useful molecules by the canal cells occurs as the solutes pass down the tubule. Protonephridia are generally found in basal organisms such as flatworms. Protonephridia likely first arose as a way to cope with a hypotonic environment by removing excess water from the organism (osmoregulation). Their use as excretory and ionoregulatory structures likely arose secondarily.

These are excretory systems in phyla Platyhelminthes and are also called blind tubules. These tubules bear a tuft of cilia or flagellum.An organ of excretion in flatworms: a hollow cup-shaped cell containing a bunch of cilia or flagellum, whose movement draws in waste products and wafts them to the outside through a connecting tubule.

References

External links

http://www.biology.ualberta.ca/courses.hp/zool250/animations/Excretion.swf
Baeumler N., Haszprunar G. & Ruthensteiner B. (2012). "Development of the excretory system in a polyplacophoran mollusc: stages in metanephridial system development". Frontiers in Zoology 9: 23. doi:10.1186/1742-9994-9-23.

English Journal

Development of the excretory system in a polyplacophoran mollusc: stages in metanephridial system development.

Baeumler N1, Haszprunar G, Ruthensteiner B.
Frontiers in zoology.Front Zool.2012 Sep 14;9(1):23. doi: 10.1186/1742-9994-9-23.
BACKGROUND: Two types of excretory systems, protonephridia and metanephridial systems are common among bilaterians. The homology of protonephridia of lophotrochozoan taxa has been widely accepted. In contrast, the homology of metanephridial systems - including coelomic cavities as functional units -
PMID 22973977

Gastrotricha: a marine sister for a freshwater puzzle.

Todaro MA1, Dal Zotto M, Jondelius U, Hochberg R, Hummon WD, Kånneby T, Rocha CE.
PloS one.PLoS One.2012;7(2):e31740. doi: 10.1371/journal.pone.0031740. Epub 2012 Feb 14.
BACKGROUND: Within an evolutionary framework of Gastrotricha Marinellina flagellata and Redudasys fornerise bear special interest, as they are the only Macrodasyida that inhabit freshwater ecosystems. Notwithstanding, these rare animals are poorly known; found only once (Austria and Brazil), they ar
PMID 22348127

A regulatory program for excretory system regeneration in planarians.

Scimone ML1, Srivastava M, Bell GW, Reddien PW.
Development (Cambridge, England).Development.2011 Oct;138(20):4387-98. doi: 10.1242/dev.068098.
Planarians can regenerate any missing body part, requiring mechanisms for the production of organ systems in the adult, including their prominent tubule-based filtration excretory system called protonephridia. Here, we identify a set of genes, Six1/2-2, POU2/3, hunchback, Eya and Sall, that encode t
PMID 21937596

Japanese Journal

輪虫類に於ける核数安定性とその分類学への応用 : I.属Asplanchna

鈴木実
動物学雑誌 67(9), 277-285, 1958-09-15
… 40, Magendruse :10×2, Magen: 41, Protonephridia: 17?, Dotterstock: 23, Protonephridialblase: 16, Fusa:^1) 5 usw. …
NAID 110003362730

輪虫類における雄虫の形態とその季節的消長第4報

鈴木実
動物学雑誌 65(1), 1-6, 1956-01-15
… concerning the number and arrangement of flame bulbs, distribution of the protonephridia and muscles, etc. …
NAID 110003361672