Metanephridium (pl. metanephridia) is a type of excretory gland or nephridium found in many types of invertebrates such as arthropods and mollusks.
It 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.
The primary urine produced by filtration of blood (or a similar functioning component) are modified into secondary urine through selective reabsorption by the cells lining the metanephridium.
One thing that a metanephridium can do that protonephridia cannot is to sweep small particulate materials, such as bacteria, into their funnel, and thence eventually out of their body.
A diagram of a metanephridium of an earthworm (modified from Kozloff, 1990).
Although the description of the metanephridium is relatively simple, the physiological reactions occurring in it are anything but simple.
Annelids(Site not responding. Last check: 2007-11-01)
Metanephridium consists of a long, coiled, ciliated tube with a ciliated funnel that opens into coelomic cavity of the body segment immediately anterior to the segment that contains the metanephridium.
Coils of metanephridium are surrounded by a complex network of capillaries that resorb materials selectively from urine, changing its composition as it passes through system.
Respiration usually via the general body surface, the surface area of which is increased by the parapodia.
INVERTEBRATES(Site not responding. Last check: 2007-11-01)
As in most animals with closed circulatory systems, blood vessels are intimately associated with the excretory tubules of the earthworm; a network of capillaries envelops each metanephridium.
At the opposite end of a metanephridium is the nephro-stome, a ciliated funnel that collects coelomic fluid from the body segment just anterior.
(Notice again that the metanephridium, unlike the protonephri-dium of flatworms, is open at both ends.) As the fluid moves along the tubule, the transport epithelium bordering the lumen pumps essential salts out of the tubule, and the salts are reabsorbed into the blood circulating through the surrounding capillaries.
Metanephridium Article, Metanephridium Information(Site not responding. Last check: 2007-11-01)
Metanephridium (pl. metanephridia) is a type of excretory gland or nephridium found in many types ofinvertebrates such as annelids and mollusks.
It typically consists of a ciliated funnel opening into the body cavity or coelom connected to a ductwhich may be variously glandularized, folded or expanded (vesiculate) and which typically opens to the organism's exterior.
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From the nephrostome, fluids move through the collecting tubules and bladder before being eliminated.
As the coelomic fluid passes through the metanephridium, ions and essential molecules are reabsorbed leaving a hypotonic fluid that leaves the earthworm through the nephridiopore.
In addition, select molecules can be secreted into the metanephridia for elimination.
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Glossary of Polychaeta terminology fluid enters the internal end of the more primitive protonephridium through selenocytes fluid enters the internal end of metanephridium though an open, ciliated funnel termed a nephrostome.
Introduction to the Bilateria 1 enters nephrostome of metanephridium, modification continues amino acids, sugars, reabsorbed additional wastes eg uric acid from nucleic acid metabolism, toxins secreted
BIOLOGY 1120 Syllabus(Site not responding. Last check: 2007-11-01)
Discuss the problems that marine, freshwater and terrestrial organisms face in maintaining homeostasis and explain how osmoregulatory adaptations serve as solutions to these problems.
Describe the function and structure of the protonephridium, metanephridium, nephridium, and Malpighian tubules of insects.
Using a diagram, identify and give the function of each structure in the mammalian excretory system.
