420
JOHAN B. STEEN
the resorbent part, then forms one or more retia and next the capillary
network of the secretory bladder is formed. Whereas the arterial supply
to the two parts of the bladder comes from one single source, the venous
drainage is separate. The blood from the secretory part flows back
through the gas gland vein to the hepatic portal vein. Thus it passes
the liver before entering the sinus venosus of the heart. The blood from
the reabsorbent bladder, on the other hand, runs directly to the sinus
venosus through a pneumatic duct vein.
In some physoclists, the arterial supply emanates from two sources
(Fig. 4B). The secretory part receives blood from the coeliac artery,
while the resorbent part is supplied from intercostal arteries.
It is important to note that all the blood to and from the secretory
tissue passes through a rete, while that to the reabsorbent area does
not.
C. The Rete Mirabile
Nowhere in biology is the countercurrent principle realized more
perfectly than in the rete mirabile of the swim bladder. It is well developed in most physoclists, while in many physostomes it is only weakly
developed. The herring is one of the rare species that has a bladder
but no rete ( FahlCn, 1967).
Usually the rete consists of one or more distinctly discernible bundles
of capillaries (Figs. 1 and 3 ) . The relationship between the bundle and
the epithelium of the bladder varies. In all euphysoclist bladders the
rete and the secretory epithelium have positions resembling the stem
and hat of a mushroom (Marshall, 1962). In these cases (Fig. 2b) the
rete is termed unipolar since the retial capillaries continue directly into
the secretory epithelium without first running together in larger vessels.
The whole structure may properly be called “the gas gland.” In the
bladder of all stomiatoids and in the eel, Anguilla, the retia are bipolar
(Fig. 2a), that is, with its capillaries distinct from the epithelial ones.
In these cases the term gas gland is less meaningful since neither the
rete nor the epithelium alone has “glandular” capacity. If used, the
gland term should include both structures.
In the case of a bipolar rete there are two capillary beds in parallel.
This makes the vascular nomenclature somewhat complex. Steen ( 1 9 6 3 ~ )
put “pre rete” or “post rete” in front of the artery or vein to distinguish
between vessels before and after they had passed the rete ( Fig. 5 ) .
From a functional point of view the most important aspect of this
structure is that the arterial blood to the bladder and the venous blood
JOHAN B. STEEN
the resorbent part, then forms one or more retia and next the capillary
network of the secretory bladder is formed. Whereas the arterial supply
to the two parts of the bladder comes from one single source, the venous
drainage is separate. The blood from the secretory part flows back
through the gas gland vein to the hepatic portal vein. Thus it passes
the liver before entering the sinus venosus of the heart. The blood from
the reabsorbent bladder, on the other hand, runs directly to the sinus
venosus through a pneumatic duct vein.
In some physoclists, the arterial supply emanates from two sources
(Fig. 4B). The secretory part receives blood from the coeliac artery,
while the resorbent part is supplied from intercostal arteries.
It is important to note that all the blood to and from the secretory
tissue passes through a rete, while that to the reabsorbent area does
not.
C. The Rete Mirabile
Nowhere in biology is the countercurrent principle realized more
perfectly than in the rete mirabile of the swim bladder. It is well developed in most physoclists, while in many physostomes it is only weakly
developed. The herring is one of the rare species that has a bladder
but no rete ( FahlCn, 1967).
Usually the rete consists of one or more distinctly discernible bundles
of capillaries (Figs. 1 and 3 ) . The relationship between the bundle and
the epithelium of the bladder varies. In all euphysoclist bladders the
rete and the secretory epithelium have positions resembling the stem
and hat of a mushroom (Marshall, 1962). In these cases (Fig. 2b) the
rete is termed unipolar since the retial capillaries continue directly into
the secretory epithelium without first running together in larger vessels.
The whole structure may properly be called “the gas gland.” In the
bladder of all stomiatoids and in the eel, Anguilla, the retia are bipolar
(Fig. 2a), that is, with its capillaries distinct from the epithelial ones.
In these cases the term gas gland is less meaningful since neither the
rete nor the epithelium alone has “glandular” capacity. If used, the
gland term should include both structures.
In the case of a bipolar rete there are two capillary beds in parallel.
This makes the vascular nomenclature somewhat complex. Steen ( 1 9 6 3 ~ )
put “pre rete” or “post rete” in front of the artery or vein to distinguish
between vessels before and after they had passed the rete ( Fig. 5 ) .
From a functional point of view the most important aspect of this
structure is that the arterial blood to the bladder and the venous blood