Chapter 30: Blood vessels, lymphatic drainage and nerves of the abdomen
Apart from the anterolateral abdominal wall, the abdomen is supplied by branches of the abdominal aorta.
The abdominal aorta begins at the aortic opening in the diaphragm (at about T12) and descends anterior to the vertebral bodies and to the left of the inferior vena cava (figs. 30-1 and 30-4). It ends (at about the L4 vertebra and slightly to the left) by dividing into the right and left common iliac arteries. The celiac plexus and ganglia are anterior to it in the upper abdomen, and the intermesenteric part of the aortic plexus covers its anterior aspect at a lower level. The abdominal aorta may be compressed against the vertebral column by posteriorward pressure on the anterior abdominal wall at the level of L4, especially in children and thin adults.
All of the parietal branches of the abdominal aorta are paired except the median sacral artery, which arises near the bifurcation and descends to the coccygeal body. The inferior phrenic arteries, which frequently arise from the celiac trunk, supply the diaphragm and suprarenal glands. The lumbar arteries are small segmental branches that supply the muscles of the back and provide spinal branches.
Each common iliac artery runs inferiolateral and divides into the external and internal iliac arteries. The external iliac artery descends in the iliac fossa and passes posterior to the inguinal ligament to become the femoral artery. The aortic plexus of nerves is continued along the external iliac and femoral arteries. The external iliac artery gives off the inferior epigastric and deep circumflex iliac arteries. The internal iliac artery is described with the pelvis.
The middle suprarenal, renal, and gonadal arteries are paired. The renal arteries, which give off the inferior suprarenal arteries, divide near or at the hili of the kidneys. The gonadal arteries arise inferior to the renal arteries (the gonads develop near the kidneys) and are either testicular or ovarian in distribution. Each testicular artery, long and slender, descends on the psoas muscle and reaches the deep inguinal ring. It then accompanies the ductus deferens and supplies the spermatic cord and testis. Each ovarian artery descends similarly and then enters the suspensory ligament of the ovary, runs medially in the mesovarium, and supplies the ovary.
The celiac trunk and superior and inferior mesenteric arteries are unpaired. The celiac trunk is the artery to the caudal part of the foregut, i.e., as far as the second part of the duodenum. It arises immediately inferior to the aortic opening of the diaphragm, between the crura, and is embedded in the celiac plexus and ganglia. Commonly it divides into the left gastric, splenic, and common hepatic arteries. The left gastric artery (see fig. 27-4) runs to the left to reach the stomach, where it courses along the lesser curvature and anastomoses with the right gastric artery. The splenic artery (see fig. 27-4) runs tortuously to the left along the upper border of the pancreas. It gives off a number of pancreatic branches and the left gastro-epiploic artery (which courses along the greater curvature between the layers of the greater omentum), short gastric arteries, and splenic branches.
The common hepatic artery (see fig. 27-4) runs to the right along the upper border of the pancreas. On reaching the duodenum, it divides in a variable manner into the hepatic artery proper, the right gastric artery, and the gastroduodenal artery. The hepatic artery proper ascends in the free edge of the lesser omentum to the liver, where it divides into right and left branches, the former of which gives off the highly variable cystic artery. The right gastric artery courses along the lesser curvature and anastomoses with the left gastric artery. The gastroduodenal artery descends posterior to the first part of the duodenum, gives off the posterior superior pancreaticoduodenal artery, and divides into the anterior superior pancreaticoduodenal and right gastro-epiploic arteries. The last-named courses between the layers of the greater omentum and, like its left counterpart, gives rise to gastric and epiploic (omental) branches.
The superior mesenteric artery supplies the midgut, i.e., from the second part of the duodenum to the left part of the transverse colon. It arises from the front of the aorta inferior to the origin of the celiac trunk. It emerges anterior to the uncinate process of the pancreas and the third part of the duodenum (see fig. 27-7) to enter the root of the mesentery and orient itself toward the right iliac fossa. Its branches include the inferior pancreaticoduodenal artery (which divides into anterior and posterior components; see fig. 27-4); the ileocolic, right colic, and middle colic arteries, which contribute to the marginal artery and supply the terminal ileum, cecum, appendix, and much of the colon; and the jejunal and ileal arteries to the small intestine.
The inferior mesenteric artery supplies the hindgut, i.e., from the left part of the transverse colon to the rectum. It arises from the aorta a little superior to its bifurcation and descends to the left on the psoas. It gives off the left colic and sigmoid arteries (see fig. 27-7), which contribute to the marginal artery. On crossing the pelvic inlet, the inferior mesenteric artery becomes the superior rectal artery, which passes between the layers of the sigmoid mesocolon to reach the rectum (see fig. 27-10).
The portal, caval, and vertebral systems require special consideration.
Venous blood from the stomach and intestine is collected by the portal vein and carried to the sinusoids of the liver and thence via the hepatic veins to the inferior vena cava (see fig. 28-5).
The portal vein is formed posterior to the neck of the pancreas, usually by the union of the superior mesenteric and splenic veins (fig. 30-2). The portal vein enters the hepatoduodenal ligament (lesser omentum) and ascends to divide at the porta hepatis into right and left branches.
Because valves are insignificant or absent, portal hypertension from obstruction of the portal vein readily causes enlargement of portal-systemic anastomoses and reversed flow of portal blood into systemic veins. The important anastomoses are as follows:
Inferior Vena Cava (see fig. 29-4).
The inferior vena cava receives the blood from the lower limbs and much of the blood from the back and from the walls and contents of the abdomen and pelvis. It is formed by the union of the two common iliac veins at L5, ascends to the right of the aorta, traverses the central tendon of the diaphragm, and empties into the right atrium. Its usual tributaries are the common iliac, gonadal, renal, suprarenal, inferior phrenic, lumbar, and hepatic veins. In some instances the vena cava crosses anterior to (instead of posterior to) the ureter (pre-ureteric vena cava or postcaval ureter) and may cause ureteric obstruction. Uncommonly, the embryonic left inferior vena cava may persist.
The main systemic channels have widespread valveless connections with the valveless vertebral plexus (see fig. 24-2). These are important in the spread of infections and tumors (e.g., from the prostate to the skeleton). During inspiration, venous return increases, and blood flows up into the vertebral plexus from the abdomen and out of the vertebral plexus into the thorax. The converse occurs during expiration. Unlike the constant direction of flow in the main systemic venous channels, the direction of flow in the vertebral plexus varies according to the respiratory phase. Furthermore, the flow of blood from the abdomen and pelvis into the vertebral plexus is accentuated by any increase in intra-abdominal pressure caused by coughing or straining.
Lumbar lymphatics ascend from the iliac nodes (see fig. 32-7) along the vertebral bodies and join the thoracic duct. Lumbar (aortic) nodes (fig. 30-3) overlie the transverse processes and the aorta. Bilateral connections are common. Nodes are also found scattered along the vessels supplying the abdominal organs.
The thoracic duct begins as either a plexus or a dilatation termed the cisterna chyli, which receives a variable number of collecting trunks. The thoracic duct lies posterior to and on the right side of the aorta adjacent to the vertebral column and the right crus of the diaphragm. It passes through the aortic opening in the diaphragm and ascends in the thorax to the root of the neck, where it empties into the venous system (see figs. 24-4 and 24-5).
Intercostal nerves 7 to 11 supply the abdominal as well as the thoracic wall (see fig. 25-12).
The phrenic nerves, which contain motor, sensory, and sympathetic fibers (see fig. 24-6), pierce the diaphragm and supply it (mostly from the inferior side), as well as giving branches to the peritoneum.
Anterior and posterior vagal trunks from the esophageal plexus supply the anterior and posterior stomach, respectively. Each trunk contains fibers from both right and left vagi. The trunks have hepatic, gastric, and celiac branches. Vagal fibers enter the celiac and superior mesenteric plexuses and are distributed to the derivatives of the foregut and midgut: stomach, liver, pancreas, and intestine as far as the left colic flexure. (The remainder of the large intestine receives parasympathetic fibers from the pelvic splanchnic nerves).
The greater, lesser, and least splanchnic nerves arise from the thoracic part of the sympathetic trunk and carry much of the sympathetic and sensory supply of the abdominal viscera. The nerves pierce the diaphragm and reach the celiac and aorticorenal ganglia (fig. 30-4).
The sympathetic trunks pierce the diaphragm (or pass posterior to the medial arcuate ligaments) and descend on the vertebral column. The right trunk lies posterior to the inferior vena cava, the left one beside the aorta. Each trunk commonly presents three to five lumbar ganglia, each of which is connected by rami communicantes to the ventral rami of the spinal nerves. The trunk and ganglia give rise to several lumbar splanchnic nerves, which join the celiac, intermesenteric, and superior hypogastric plexuses. Both sympathetic trunks continue into the pelvis anterior to the sacrum.
A dense prevertebral plexus is formed in the abdomen by the splanchnic nerves, branches from both vagi, and masses of ganglion cells. The prevertebral plexus, which lies anterior to the aorta, extends along that vessel and its branches (fig. 30-4) and contains preganglionic and postganglionic sympathetic, preganglionic parasympathetic, and sensory fibers. Parts of the plexus are named after their associated arteries. The celiac (or "solar") plexus, situated at the origin of the celiac trunk, contains paired celiac ganglia (fig. 30-5), which distribute branches along the arteries (e.g., to the liver and stomach). Aorticorenal ganglia are found near the origin of the renal arteries. Continuing fibers constitute the aortic plexus, parts of which are named the superior mesenteric, intermesenteric, and inferior mesenteric plexuses. The aortic plexus, which continues as the superior hypogastric plexus, receives many branches from the lumbar splanchnic nerves. Filaments descend from the aortic plexus along the iliac and femoral arteries.
The ventral rami of the lumbar spinal nerves enter the psoas major muscle, where they combine in a variable manner to form the lumbar plexus (figs. 30-6 and 30-7). Within the muscle, the rami are connected to the lumbar sympathetic trunk by rami communicantes. The term "lumbosacral plexus" is used for the lumbar plexus proper (which is formed by L2 to 4) and the sacral plexus (which is formed by L4 to S4). The fourth lumbar nerve bifurcates to go to both the lumbar and sacral plexuses (fig. 30-6). The rami that supply the lower limbs (exclusive of cutaneous branches of T12 and L1) extend from L1 to S3. The lumbar plexus supplies direct branches to the quadratus lumborum and psoas muscles.
The first lumbar nerve resembles an intercostal nerve in giving off a collateral branch, the ilio-inguinal nerve, and then continuing as the iliohypogastric nerve, which has a lateral cutaneous branch (fig. 30-8). The iliohypogastric nerve runs through the muscles of the anterolateral abdominal wall to reach the skin. The ilio-inguinal nerve accompanies the spermatic cord or round ligament through the inguinal canal, emerges from the superficial ring, and becomes cutaneous.
The femoral nerve (L2 to 4) emerges from the lateral side of the psoas major, descends between the psoas and iliacus, and enters the thigh posterior to the inguinal ligament. It supplies the iliacus, quadriceps femoris, pectineus, and sartorius muscles, the skin of the medial side of the thigh and leg, and the hip and knee joints.
The genitofemoral nerve (chiefly L2) divides into 1) a genital branch, which enters the inguinal canal through the deep ring and supplies the cremaster and scrotum (or labium majus), and (2) a femoral branch, which enters the femoral sheath and supplies the skin of the femoral triangle.
The obturator nerve (L2 to 4) emerges from the medial side of the psoas and enters the thigh through the obturator foramen. It supplies the adductor muscles and gracilis, the skin of the medial side of the thigh, and the hip and knee joints. The accessory obturator nerve (L3, 4), when present, enters the thigh deep to the pectineus, which it supplies.
Michels, N. A., Blood Supply and Anatomy of the Upper Abdominal Organs, Lippincott, Philadelphia, 1955. A descriptive atlas of patterns and variations for surgeons.
30-1 Where does the aorta end?
30-2 Which arteries supply (a) the caudal part of the foregut, (b) the midgut, (c) the hindgut?
30-3 Name two important sites of portal-systemic anastomosis.
30-4 Where does the inferior vena cava begin?
30-5 What is the relationship of the inferior vena cava to the right ureter?
30-6 How far distally do vagal fibers extend?
30-7 From which spinal segments is the lumbosacral plexus derived?
30-8 What is the distribution of the iliohypogastric, ilio-inguinal, and genito-femoral nerves?
Figure 30-1 The branches of the aorta are arranged as unpaired visceral, paired visceral, and parietal.
Figure 30-2 The portal vein and its major tributaries.
Figure 30-3 lymphatic pathways and nodes of the posterior abdominal wall. CI, common iliac; EI, external iliac; II, internal iliac; L, lumbar; R, retro-aortic; 5, sacral.
Figure 30-5 Functional components of the celiac ganglia and plexus. Sympathetic fibers are shown as continuous lines, parasympathetic fibers as interrupted lines, and sensory fibers in blue.
Figure 30-8 Comparison of an intercostal nerve (A) with the first lumbar nerve (B). (After Davies.)