Lymph Vessels of the Intestine

The following general behaviours of the intestinal lymph vessels were demonstrated:

Lymph vessels arise from all 3 layers of the intestinal wall. Those of the mucosa form either mucosal or submucosal networks: the lymph vessels arising from these networks usually run a variable distance between the mucous membrane and the fascia, before penetrating the fascia and joining its lymph vessels. The lymph vessels of the musculature and serosa form subserosal networks, though some of the networks also lie in the muscle layer (as has been demonstrated microscopically); the lymph vessels arising from these networks run between the serosa and musculature to the mesenteric border (see below) before entering the mesentery.

A. Lymph Vessels of the Small Intestine

A smaller number of the lymph vessels of the small intestine drain to the duodenal lymph node, the right hepatic lymph nodes, and the right colic lymph nodes, while most drain to the jejunal lymph nodes.

i. Lymph Vessels of the Duodenum (Figure 26: 2)

The lymph vessels from the initial part of the duodenum drain to the duodenal lymph node (Figure 26: a). Those of the middle part of the duodenum drain directly to the right hepatic lymph nodes (Figure 26: b), and those of the terminal part (as far as the flexura tertia) drain to the right jejunal lymph node (Figures 25: 9; 26: l). If there are several nodes in the group, they will drain to either the cranial lymph node or to the 2 cranial lymph nodes. The lymph vessels lie between the two sheets of the mesentery and usually accompany the corresponding veins, though they may, to a lesser extent, also run irregularly between these veins. Most of the lymph vessels draining to the right hepatic lymph nodes run over the ventral side of the pancreas, only occasionally over its dorsal surface (as shown in Figure 26), but some of the lymph vessels also enter the pancreas. Some of the lymph vessels, especially those that enter the pancreas, merge with the lymph vessels of the pancreas. Because the lymph vessels of the duodenum and the pancreas are connected in this way, the lymph vessels of the duodenum can also be filled from the pancreas (see lymph vessels of the pancreas).

ii. Lymph Vessels of the Jejunum

The lymph vessels of the jejunum (Figure 25: b, b’) drain to the jejunal lymph nodes (Figure 25: 6, 6¹, 6²). Specifically, the lymph vessels from the part of the jejunum immediately after the duodenum drain to the right jejunal lymph node, those from the much larger central part of the jejunum (Figure 25: b, b) drain to the left jejunal lymph node (Figure 25: 6¹, 6²), and those from the terminal part of the jejunum (Figure 25: b’, b’) drain to the right jejunal lymph node (Figure 25: 6).

iii. Lymph Vessels of the Ileum

Most of the lymph vessels of the ileum (Figures 25: c, 26: 5) drain to the right jejunal lymph node (Figure 25: 6), though a small number of them instead drain to the right colic lymph node (Figures 25: 5, 26: e). The lymph vessels draining to the right jejunal lymph node run from the ileum directly to the small intestinal mesentery, running within it to drain to the lymph node (as shown in Figure 25). Some of the lymph vessels draining to the right colic lymph node enter the mesocecum (mesentery between the ileum and cecum) and join the lymph vessels of the cecum (see lymph vessels of the cecum below) to drain with them into the right colic lymph node, while others merge to form 1 to 2 vessels which run along the opposite border of the ileum to the lymph node (as shown in Figure 26).

The lymph vessels of the jejunum and ileum lie between the sheets of the mesentery as they run from the intestine to the lymph nodes. Almost all of them run alongside the jejunal veins, but occasionally they lie between two jejunal veins. From the site of puncture injection, most of the lymph vessels initially form extensive, fine subserosal networks, from which small lymph vessels emerge; these vessels run, mostly subserosally, over both surfaces of the intestine to the mesenteric margin. At this location, and in the adjacent mesentery, they merge with neighbouring vessels and form anastomoses and coarse networks with numerous islands, then mostly run alongside mesenteric veins; only a small number runs between the mesenteric veins (Figure 25). A smaller number of the lymph vessels do not run directly towards the mesenteric margin, but instead, they run around the free border of the jejunum or ileum opposite to the mesenteric margin to the opposite surface of the intestinal loop and from there to the mesenteric margin. It is not uncommon for lymph vessels to fill from one puncture site towards both intestinal surfaces.

B. Lymph Vessels of the Large Intestine

Most lymph vessels of the large intestine drain to the colic lymph nodes; only those of the end of the descending colon, the transition of the colon into the rectum, and the rectum itself drain to the medial iliac lymph nodes and hypogastric lymph nodes.

i. Lymph Vessels of the Cecum

The lymph vessels of the cecum (Figure 26: 6) drain to the right colic lymph node (Figure 26: e). Specific cecal lymph nodes could not be found. The small lymph vessels arising from the subserosal networks run over both surfaces of the cecum towards the mesocecum (the mesentery between the ileum and cecum) and run in the mesocecum together with the lymph vessels of the ileum (see above) towards the transition of the ileum to the colon. The lymph vessels cross both surfaces of this transition area, or the distal end of the ileum, and then run in the mesentery directly to the right colic lymph node.

ii. Lymph Vessels of the Colon

The lymph vessels of the colon (Figure 26: 7, 8 and 9) drain to all 3 groups of the colic lymph nodes (Figure 26: e, f, g), the medial iliac lymph nodes (Figure 26: l), and the hypogastric lymph nodes (Figure 26: k). The lymph vessels of the ascending colon (Figure 26: 7), found in the mesocolon, drain directly to the right colic lymph node (Figure 26: e), and the lymph vessels of the transverse colon (Figure 26: 8) run in the mesentery to the middle colic lymph node (Figure 26: f) and drain to it if the lymph node is present – if it is absent, the lymph vessels of the transverse colon drain directly to the right colic lymph node (Figure 26: e). However, even if a middle colic lymph node is present, not all the lymph vessels of the transverse colon drain to it: some bypass the lymph node and drain directly to the right colic lymph node.

The lymph vessels of the descending colon (Figure 26: 9) drain to the middle colic lymph node (Figure 26: f, f), the left colic lymph nodes (Figure 26: g, g), the medial iliac lymph nodes (Figure 26: i), and the hypogastric lymph nodes (Figure 26: k). The lymph vessels from the initial half of the descending colon drain to the middle colic lymph node (Figure 26: f, f), and the lymph vessels from the second half drain to the left colic lymph nodes (Figure 26: g, g). If the middle colic lymph node is absent, then the lymph vessels that would drain to it drain instead to the right colic lymph nodes (Figure 26: e).

The lymph vessels from the terminal part of the descending colon and the transition of the colon into the rectum drain to both the hypogastric lymph nodes (Figure 26: k) and the medial iliac lymph nodes (Figure 26: i). The lymph vessels drain to the lymph nodes on both sides. These lymph vessels run caudally along the rectum to the point where the peritoneum meets the pelvic wall, then outside of this part of the peritoneum and further subperitoneally along the lateral pelvic wall until they reach the aforementioned lymph nodes. Frequently, lymph vessels filled from a puncture site between two drainage areas run towards the lymph node groups of both areas.

Most of the lymph vessels arising from the intestinal subserosal networks, which tend to form elongated meshes (see Figure 26), run directly to the mesenteric border of the colon. However, some of the lymph vessels may also run towards the free border of the colon (i.e. the border opposite to the mesenteric border) to the opposite surface before travelling from this surface to the mesenteric border (also shown in Figure 26). At this border and in the adjacent mesentery, most of the lymph vessels form coarse networks with very large islands, from which, again, individual lymph vessels arise. In the terminal half of the descending colon, these lymph vessels run directly to the left colic lymph nodes, usually accompanied by the corresponding venous branches. In the initial part of the descending colon, these lymph vessels (or the islands formed by them) mostly accompany the left colic vein to the left colic lymph nodes, although a small number also run transversely through the mesentery towards these lymph nodes.

iii. Lymph Vessels of the Rectum

The lymph vessels of the rectum (Figure 26: 10) drain to both the hypogastric lymph nodes (Figure 26: k) and the medial iliac lymph nodes (Figure 26: i). They merge into 4 to 5 vessels and drain to the lymph nodes on both sides, some of them running over the dorsal side of the rectum (Figure 26: p, p).

C. Lymph Vessels of the Anus

The lymph vessels of the anus (Figure 26: m) join those of the rectum (see above) and drain with them to the hypogastric lymph nodes (Figure 26: k) and the medial iliac lymph nodes (Figure 26: i). The lymph vessels also drain to the lymph nodes on both sides.