First published online August 23, 2004
Journal of Experimental Biology 207, 3339-3348 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01164
Structural basis for control of secondary vessels in the long-finned eel Anguilla reinhardtii
Peter Vilhelm Skov* and
Michael Brian Bennett
School of Biomedical Sciences, Department of Anatomy and
Developmental Biology, University of Queensland, St Lucia, QLD 4067,
Australia

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Fig. 1. (A) Scanning electron micrograph showing the dense arrangement of
specialised endothelial cells bearing microvilli, which project into the lumen
of the primary segmental artery. Scale bar, 10 µm. (B) High magnification
illustrating the common origin of several microvilli from a single endothelial
cell. Scale bar, 5 µm.
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Fig. 2. Light micrograph of the origin of interarterial anastomoses (iaas)
from a segmental artery. Anastomoses originate as depressions through the
endothelial (E) and medial (M) layer of the primary vessel. Anastomoses follow
a linear perpendicular path to the outer margin of the adventitial (A) layer,
where they coil extensively (*). Note the numerous microvilli
(arrowheads). Scale bar, 10 µm. Lissamine Fast Red, 4 µm section.
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Fig. 3. (A-D) Light micrographs of consecutive sections through a segmental artery
(sg.a.) taken 8 µm apart, showing the connection between interarterial
anastomoses (iaas) and secondary vessels (SV). The vessel path from
the coiled region of iaas (arrowheads in D) is denoted by stippled
arrows in A. Note the numerous nerve bundles (Ne) in association with
secondary vessels. Scale bar, 100 µm. Lissamine Fast Red, 2 µm
section.
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Fig. 4. (A) Light micrograph of lateral collecting vessel, showing a thick
endothelial layer, but no distinct medial layer. The vessel sits within a tube
of dense connective tissue, formed by two opposed crescent-shaped structures.
Numerous blood vessels are readily observed within the `adventitial' layer
(arrowheads). Scale bar, 100 µm. Lissamine Fast Red, 5 µm section. (B)
Transmission electron micrograph of the lateral collecting vessel shows that
the endothelial cell layer (EC) sits on an elastic lamina (EL), and there is
no presence of smooth muscle cells in the vessel. Leukocytes can be seen
migrating through the endothelial layer (arrowheads). Blood vessels are
frequently seen within the adventitial layer of the vessel wall. Scale bar, 20
µm.
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Fig. 5. (A) Transmission electron micrograph of the wall of a primary segmental
artery (sg.a.) showing the structure in a coil from an anastomosis. Here, the
vessel lumen is lined by a single endothelial cell (EC) on a continuous
basement membrane, and is typically only associated with a single smooth
muscle cell (SM). Scale bar, 10 µm. (B) This is also the case for secondary
vessels, which in all aspects have a structure quite similar to that of
primary vessels. Scale bar, 10 µm.
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Fig. 6. 5-HT immunoreactivity of interarterial anastomoses iaas
(*) and a secondary vessel (SV).
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© The Company of Biologists Ltd 2004