Figure 6

Scanning electron microscopy (SEM) micrographs of PVS tissue isolated from the surface of abdominal organs. (A) SEM micrograph of a whole PVS tissue sample (~4.5 cm) at a low magnification. The primo node (PN), the enlarged, abruptly decreased, and terminal parts of primo vessel (PV) are indicated by “b,” “c,” “*,” and “d,” respectively. The inset illustrates the squared part of the PV at higher magnification. Note longitudinal fibers, circular submicron fibers, and extracellular matrix. (B) The PN and proximal PV marked by “b” are shown at higher magnification. Note the flattened cells scattered (arrow heads), the PV branch curved back to the left (curved arrow), and the other branch underneath running upward and to the right. The inset illustrates the PN–PV transition area marked by a dotted circle at higher magnification. Note also the presence of small cells (~5 µm) on the surface and flat oval cells (~15 µm in length) covering a branch of the PV. (C) A thicker part of the PV marked by “c” in A at higher magnification. Note the presence of three bundles (width: ~100 µm) and small cells on the surface. The inset illustrates the squared area at higher magnification. Note thick amorphous extracellular matrix covering the cell-like structures. (D) A distal part of the right PV marked by “d” at higher magnification. Note several subvessels (width: ~5 µm), submicron fibers crossing the subvessels, and amorphous substances on the surface. The scales for panel A, B, C, and D are 500, 200, 50, and 5 µm and those in the insets of A, B, and C are 2, 5, and 2 µm, respectively. PVS = primo vascular system.