OBL HOME | OBL REFERENCES | |||||||||||||
LIVER, GALL BLADDER
|
||||||||||||||
LIVER Where the stomach meets the small intestine
in tunicates, there are a number of tubules collectively called the pyloric
gland which empty through a duct into the intestine. The cells resemble vertebrate liver cells (especially
those of the most primitive fish, the hagfish) and function in the storage
of glycogen and the removal of foreign substances from the blood, as in
vertebrate livers (Burighel, from Harrison,
1997, p. 257). In all chordates, the veins which reach this structure
from the intestines are portal veins (Stach,
2000). In lancelets, the brownish-green hepatic sacculations (also called the hepatic cecum)
are the primary source of digestive enzymes, releasing protease, amylase,
and lipase. (Ruppert, from Harrison, 1997, p. 444-5). Amphioxus
possesses a hepatic portal system in which blood from intestines brought
to a capillary network in liver before the hepatic vein returns it to
general circulation. The same pattern
of circulation exists in vertebrates (Willey, 54). |
||||||||||||||
AMPHIOXUS |
![]() |
|||||||||||||
![]() |
||||||||||||||
In hagfish, the liver no longer functions
in enzyme production and food absorption as in Amphioxus (Romer, p. 390). Gnathostome livers
increase in size and are lobed (Weichert,
1970, p. 194). |
||||||||||||||
HAGFISH |
||||||||||||||
HAGFISH |
||||||||||||||
LAMPREY |
![]() |
|||||||||||||
SHARK |
![]() |
|||||||||||||
GAR |
![]() |
|||||||||||||
BOWFIN |
PERCH |
|||||||||||||
LUNGFISH |
||||||||||||||
FROG |
SALAMANDER |
|||||||||||||
TURTLE |
||||||||||||||
OPOSSUM |
||||||||||||||
CAT |
![]() |
|||||||||||||
SHEEP |
PIG |
|||||||||||||
MONKEY |
HUMAN MODEL |
|||||||||||||
GALL BLADDER In most vertebrates, the bile produced in
the liver can be concentrated and stored in the gall bladder. The cystic duct from the gall
bladder and the hepatic duct from the liver fuse to empty into the common
bile duct which, in turn, empties into the small intestine. Jawless fish possess both a liver and gall bladder
although the liver is small. Lamprey
gall bladders and bile ducts degenerate in adults (Weichert,
1970, p. 194). A few species of
shark, many birds, and a number of mammals (some artiodactyls, rodents,
whales, seals, and perissodactyls) lack gall
bladders (Weichert,
1970, p. 194). Although pigeons
lack a gall bladder, it can be present during embryonic development (Weichert, 1970, p. 194). |
||||||||||||||
HAGFISH |
![]() |
|||||||||||||
LAMPREY |
||||||||||||||
SHARK |
![]() |
|||||||||||||
BOWFIN |
PERCH |
|||||||||||||
LUNGFISH |
||||||||||||||
FROG |
![]() |
|||||||||||||
SALAMANDER![]() |
||||||||||||||
ALLIGATOR |
CHICKEN![]() |
|||||||||||||
OPOSSUM |
||||||||||||||
SHEEP |
GOAT |
|||||||||||||
PIG |
||||||||||||||
CAT |
![]() |
|||||||||||||
MONKEY |
![]() |
|||||||||||||
HUMAN MODEL |
||||||||||||||