The lymph vessels of the stomach (Figure 26: 1) of the dog all eventually drain to the hepatic lymph nodes, most of them to the left hepatic lymph node (Figure 26: c), and a small number to the right hepatic lymph nodes (Figure 26: b). Some of the lymph vessels that drain to the left hepatic lymph node drain through the splenic lymph nodes (Figure 26: d, d’) and the gastric lymph node (Figure 26: o), and some of the vessels that drain to the right hepatic lymph nodes drain through the duodenal lymph node (Figure 26: a). The detailed behaviours are described below.
a. lymph vessels of THe stomach (excluding the pyloric region)
The lymph vessels of the larger part of the stomach on the left side (excluding the pylorus) drain to the splenic lymph nodes, the left hepatic lymph node, and the duodenal lymph node, and, as shown in Figure 26, take one of the 3 following paths:
i. The lymph vessels of the left part of the greater curvature and from the stomach walls on each side of this part of the greater curvature run towards the splenic vein by following the splenic vein branches. From here, they run in either the gastrosplenic ligament or the omentum and then drain into the splenic lymph nodes (Figure 26: d, d’), which lie next to the splenic vein. Not all the lymph vessels drain into the splenic lymph nodes, however: some bypass these lymph nodes and join their efferent vessels, accompanying the gastrosplenic vein to drain to the left hepatic lymph node (Figure 26: c).
ii. The lymph vessels of the ventral part of the greater curvature and the adjacent parts of the lateral walls merge to form 2 to 3 vessels which run to the large curvature and from there towards the right in the omentum together with the gastroepiploic vein, and join the lymph vessels from the pylorus (see below) to drain to the duodenal lymph node (Figure 26: a).
iii. Lymph vessels of both lateral walls of the stomach adjacent to the lesser curvature and the lesser curvature itself travel, together with the cranial and caudal branches of the left gastric vein, towards the lesser curvature before accompanying the left gastric vein to the gastrosplenic vein, and then joining the lymph vessels accompanying the splenic vein (see above) to drain with them to the left hepatic lymph node (Figure 26: c). If a gastric lymph node (Figure 26: o) is present, then some of these lymph vessels, from both stomach walls, first drain to it. The efferent vessels of the gastric lymph node then join the other lymph vessels. Even if a gastric lymph node is present, not all lymph vessels drain to it – some bypass the lymph node entirely.
b. lymph vessels of the pyloric region of the stomach
The lymph vessels of the pyloric region of the stomach behave as follows:
i. The lymph vessels of the lateral walls and dorsal margin of the pylorus join the lymph vessels accompanying the left gastric vein from the lesser curvature and drain with them to the left hepatic lymph node (Figure 26: c). If a gastric lymph node is present (Figure 26: o), some of the vessels usually first drain to it.
ii. The lymph vessels of the lateral walls adjacent to the ventral border of the pylorus and from the ventral border itself, however, run towards the right gastroepiploic vein and travel with it along the pylorus and the initial part of the duodenum, towards the right, until they reach the duodenal lymph node (Figure 26: a), though they may also bypass this lymph node and drain to a right hepatic lymph node.
The lymph vessels of the areas between the above sections A and B, between A(i) and A(ii), and between B(i) and B(ii), usually drain in both directions.
The lymph vessels of the stomach wall form extensive submucosal and subserous networks, both of which are interconnected. The subserous networks often extend into the musculature, i.e. they are covered by the musculature when viewed from the outside the stomach (this has also been demonstrated by microscopic examination). The lymph vessels arising from the subserous networks usually travel for a short distance before entering the serosa and continuing in the serosa for long distances, again forming very coarse networks. This results in 3 interconnected networks: one serous, one subserous, and one submucosal, all lying one above the other, though the serous and subserous networks often cannot be clearly separated from each other. The serous and subserous lymph vessels may also re-enter the muscles, or at least be covered by parts of the muscle layer. The terminal lymph vessels develop from the serous network. The lymph vessels arising from the submucosal networks frequently continue for a considerable distance in the submucosa before penetrating the musculature.
The lymph vessels of the mucosa form the submucosal networks, from which the subserosal and serosal networks then fill. Some of the lymph vessels of the musculature open into the submucosal networks, some into the subserosal networks – the lymph vessels of the serosa open to a smaller extent into the subserosal networks. More commonly, these lymph vessels directly form serosal networks.