The archinephros, or holonephros, is a primitive kidney that has been retained by the larvae of
hagfish and some
caecilians
Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics o ...
.
A recent author has referred to this structure as "the hypothetical primitive kidney of ancestral vertebrates". In the earliest vertebrates, this structure potentially extended the entire length of the body and consisted of paired segmental structures which drained via a pair of archinephrenic ducts into the
cloaca
In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
.
The entire structure arises from the nephric ridge,
which in
higher animal embryos
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sper ...
gives rise to nephrotomes and the pronephroi at around 4 weeks gestation in humans.
The pronephroi are supplanted by mesonephroi and finally by definitive kidneys, the metanephroi, by around 5 weeks gestation.
The archinephros is nonfunctional in humans and other
mammals.
The three types of mature
vertebrate kidneys develop from the archinephros: the
pronephros from the front section, the
mesonephros from the mid-section and the
metanephros Kidney development, or nephrogenesis, describes the embryologic origins of the kidney, a major organ in the urinary system. This article covers a 3 part developmental process that is observed in most reptiles, birds and mammals, including humans. N ...
from the rear section.
References
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Anatomy
Developmental biology