Lesson 10 - Abdominal Vasculature, Innervation, Posterior Abdominal Region
In this lesson, we will be covering the blood supply and venous drainage of the abdominal region, abdominal innervation, and details about structures in the posterior abdominal region, which provides a passageway for nerves, arteries, veins, and muscles that extend from the thoracic cavity to the abdominal cavity across the abdominal diaphragm. This lesson builds on lesson #9, which listed the abdominal organs and gave some basic information about their positions in the abdominopelvic cavity. Together, lessons #9 and #10 complete our investigation of the abdomen, and we will be moving to the pelvis and perineum in lesson #11.
Learning Objectives - By the end of this lesson, you should be able to ...
- List each of the arteries that supply parts of the digestive system in the abdominopelvic cavity, and describe their course in the abdomen after branching off the abdominal aorta or related artery
- Describe venous drainage of the abdominal region, including the portacaval system of veins
- Understand how details about embryological development can be used to learn the pattern of blood supply in the abdomen
- Describe the nerves that supply the abdominal wall and viscera
- List and describe muscles, organs, nerves, arteries, and veins running through the posterior abdominal region
Arterial Supply of Abdominal Structures
Blood supply to the abdomen is via branches of the abdominal aorta, which begins at the aortic hiatus of the diaphragm, anterior to vertebra T12, and descends to the left of the midline at vertebra L4, where it splits into the right and left common iliac arteries. The three anterior branches in the abdomen, the celiac trunk, superior mesenteric artery, and inferior mesenteric artery, supply abdominal organs. The celiac trunk supplies derivatives of the embryonic foregut, which include the abdominal esophagus, stomach, and half of the duodenum (up to the descending part), liver, pancreas, gallbladder, and spleen. The superior mesenteric artery supplies derivatives of the embryonic midgut, which include the distal 1/2 of the duodenum, jejunum, ileum, cecum, appendix, ascending colon, and the right 2/3 of the transverse colon. The inferior mesenteric artery supplies derivatives of the embryonic hindgut, which include the left 1/3 of the transverse colon, the descending and sigmoid colons, rectum, and upper part of the anal canal. We will go over branches of each of these arteries in turn below:
- Celiac trunk: As noted above, the celiac trunk supplies blood to structures derived from the embryonic foregut. The celiac trunk has three main branches: the left gastric artery, splenic artery, and common hepatic artery.
- Left gastric artery: ascends from the abdominal aorta to the junction between the stomach and esophagus, and sends esophageal branches upward to the abdominal esophagus, which anastomose with esophageal branches from the thoracic aorta. The left gastric artery turns to the right and runs along the lesser curvature of the stomach in the lesser omentum, supplying both surfaces of the stomach and anastomosing with the right gastric artery, which is a branch off the common hepatic artery (see below).
- Splenic artery: runs along the superior border of the pancreas, sending numerous branches to the spleen, to the neck, body, and tail of the pancreas, and short gastric arteries to supply the fundus of the stomach. It also gives off the left gastro-omental artery, which runs to the right along the greater curvature of the stomach to anastomose with the right gastro-omental artery, which is a branch of the common hepatic artery.
- Common hepatic artery: runs to the right off the abdominal aorta, gives off the right gastric artery, and divides into the hepatic artery proper and the gastroduodenal artery. The hepatic artery proper ascends to the liver in the free edge of the lesser omentum, to the left of the bile duct and anterior to the portal vein, and divides into the right and left hepatic arteries. The right hepatic artery gives off the cystic artery to the gallbladder. The gastroduodenal artery descends from the hepatic artery proper posterior to the superior part of the duodenum, gives off the posterior superior pancreaticoduodenal artery (posterior superior PDA), and splits again at the inferior edge of the superior duodenum into the anterior superior pancreaticoduodenal artery (anterior superior PDA) and the right gastro-omental artery. The right gastro-omental artery runs to the left along the greater curvature of the stomach and anastomoses with the left-gastro-omental artery (a branch of the splenic artery). The anterior and posterior superior PDA supply the head of the pancreas and the duodenum, as their name suggests, and wind up anastomosing with the anterior and posterior branches of the inferior pancreaticoduodenal artery.
- Superior mesenteric artery: arises form the abdominal artery immediately below the celiac trunk anterior to vertebra L1. It is crossed by the splenic vein and the neck of pancreas, and the inferior part of the duodenum runs posterior to it. It gives off left and right branches. On the left, it gives off the inferior pancreaticoduodenal artery and jejunal and ileal arteries. To the right, it gives off the middle colic artery, right colic artery, and ileocolic artery.
- Inferior pancreaticoduodenal artery (PDA): divides immediately into anterior and posterior branches which anastomose with anterior and posterior superior PDA (branches of the common hepatic artery). As its name suggests, it supplies blood to parts of the pancreas and the duodenum.
- Jejunal and ileal arteries: These arteries form a complex network of arcades that supply the jejunum and ileum. Jejunal arteries generally have single arcades, although the number increases distally; whereas ileal arteries typically have multiple arcades. Vasa recta, or "straight arteries," extend from the terminal arcades to supply the walls of the small intestine. Vasa recta are usually long and close together in the jejunum, and short but far apart in the ileum.
- Middle colic artery: first of the three right branches of the superior mesenteric artery. Runs underneath the pancreas, enters the transverse mesocolon, and splits into right and left branches. The right branch anastomoses with the right colic artery and the left branch anastomoses with the left colic artery (a branch of the inferior mesenteric artery).
- Right colic artery: second of the three right branches of the superior mesenteric artery. Passes to the right to supply the ascending colon, then divides into a descending branch which anastomoses with the ileocolic artery and an ascending branch which anastomoses with the middle colic artery.
- Ileocolic artery: third of three branches of the superior mesenteric artery. Passes downward and to the right where it divides into a superior branch which anastomoses with the right colic artery along the ascending colon and an inferior branch which divides into colic, cecal, appendicular, and ileal branches. The colic branch supplies the first part of the ascending colon. The cecal branches supply the two sides of the cecum. The appendicular branch supplies the appendix. The ileal branch supplies the final part of the ileum.
- Inferior mesenteric artery: arises anterior to the body of vertebra L3. Descends anterior to the aorta and passes to the left to branch into the left colic artery, sigmoid arteries, and the superior rectal artery.
- Left colic artery: ascends retroperitoneally and divides into ascending and descending branches. The ascending branch passes anterior to the left kidney, enters the transverse mesocolon, and supplies the upper part of the descending colon and the distal part of the transverse colon, finally anatostomosing with branches of the middle colic artery (a branch of the superior mesenteric artery). The descending branch passes inferiorly, supplies the lower part of the descending colon, and anatostomoses with the first sigmoid artery.
- Sigmoid arteries: two to four branches which descend to the left in the sigmoid mesocolon to supply the lower part of the descending colon and the sigmoid colon. Anastomoses superiorly with branches from the left colic artery and inferiorly with branches from the superior rectal artery.
- Superior rectal artery: descends into the pelvic cavity in the sigmoid mesocolon, crossing the left common iliac vessels. Divides opposite S3 vertebra to send a terminal branch to each side of the rectum inferiorly to the level of the internal anal sphincter, anastomosing with branches of the inferior rectal arteries (from the internal pudendal artery, which we will cover in the next lesson).
Venous Drainage in the Abdomen
Venous drainage of the spleen, pancreas, gallbladder, and the abdominal part of the gastrointestinal tract (except for the inferior part of the rectum) is via the portal system of veins, which delivers blood to the liver before it enters the hepatic veins and eventually the inferior vena cava. The portal vein, which empties directly into the liver, is formed by the union of the splenic vein and the superior mesenteric vein posterior to the neck of the pancreas at the level of vertebra L2.
In order from the liver out, the portal vein receives venous blood from (students in my fall 2020 course should focus on the veins in bold):
- Right and left gastric veins which drain the lesser curvature of the stomach and abdominal esophagus.
- Cystic veins which drain the gallbladder.
- Para-umbilical veins which drain the anterior abdominal wall.
- Splenic vein, with tributaries from short gastric veins from the fundus and left part of the greater curvature of the stomach, the left gastro-omental vein from the greater curvature of the stomach, pancreatic veins from the body and tail of pancreas, and the inferior mesenteric vein, which drains blood from the rectum, sigmoid colon, descending colon, and splenic flexure via named veins that correspond to arteries.
- Superior mesenteric vein, which drains blood from the small intestine, cecum, ascending colon, and transverse colon via named veins corresponding to arteries and the right gastro-omental vein and anterior and posterior superior pancreaticoduodenal veins.
- Sympathetic trunks: In the abdomen, the sympathetic trunks are positioned anterolateral to the lumbar vertebral bodies. There are generally four ganglia in the lumbar region. As noted previously, these ganglia are connected to adjacent spinal nerves via gray rami communicans. There are also connections with white rami communicans at L1-L2 in the abdomen (remember that the sympathetic part of the autonomic division is housed in the CNS between T1 and L2).
- In this course, I have been using the term "subdiaphragmatic ganglia" or "subdiaphragmatic plexus" to refer to the ganglia clustered in the prevertebral region around the abdominal aorta, lumbar vertebrae, and sacrum. This plexus can be broken down further into the celiac plexus around the celiac trunk, root of the superior mesenteric artery, and adrenal glands; an aortic plexus on the anterior and lateral surface of the abdominal aorta from below the superior mesenteric artery to the bifurcation of the aorta into the common iliac arteries; a superior hypogastric plexus between the common iliac arteries; and an inferior hypogastric plexus that runs from the superior hypogastric plexus to where the common iliac arteries split into external and internal iliac arteries.
- Splanchnic nerves: pass from the sympathetic trunk or ganglia to the subdiapgragmatic plexus anterior to the abdominal aorta. Remember, the thoracic, lumbar, and sacral splanchnic nerves carry preganglionic sympathetic fibers from the sympathetic trunk to ganglia in the subdiaphragmatic plexus, whereas pelvic splanchnic nerves carry preganglionic parasympathetic fibers from anterior rami of S2-S4 spinal nerves to an extension of the subdiaphragmatic plexus in the pelvis.
- Thoracic splanchnic nerves: pass from sympathetic ganglia along the sympathetic trunk in the thorax to the celiac plexus. The greater splanchnic nerve arises from T5 to T9 or T10 ganglia and travels to the celiac plexus near the celiac trunk. The lesser splanchnic nerve arises from T9 and T10 (or T10 and T11) thoracic ganglia and travels to the celiac plexus near the aorta and adrenal gland. The least splanchnic nerve arises from the T12 ganglion and travels to the celiac plexus near the adrenal gland.
- Lumbar and sacral splanchnic nerves: 2-4 lumbar splanchnic nerves pass from the lumbar part of the sympathetic trunk to the aortic plexus. Sacral splanchnic nerves pass from the sacral part of the sympathetic trunk and run to the inferior hypogastric plexus in the pelvis.
- Pelvic splanchnic nerves: Remember, these are the only splanchnic nerves that carry parasympathetic fibers - they originate directly from the anterior rami of S2 to S4, and pass to the inferior hypogastric plexus to provide parasympathetic innervation to the distal 1/3 of the transverse colon, the descending colon, and the sigmoid colon.
Posterior Abdominal Region
This region is posterior to the abdominal part of the GI tract, the spleen, and the pancreas, and includes the muscles of the posterior abdominal wall (the quadratus lumborum and iliopsoas muscles), the abdominal aorta and its various branches, the inferior vena cava, and the kidneys, adrenal glands, and ureters.
- Muscles: The two psoas muscles, psoas major and psoas minor, run from lateral surfaces of vertebral bodies and transverse processes to insert onto the the pelvis and femur. Psoas major originates on the lateral surfaces of bodies and intervertebral discs for T12 to L5 vertebra and transverse processes of the lumbar vertebrae, and inserts onto the lesser trochanter of the femur. It is innervated by anterior rami of lumbar spinal nerves and flexes the thigh at the hip joint. Psoas minor originates on the lateral surfaces of T12 to L1 vertebral bodies and intervertebral discs and inserts onto the pectineal line of the pelvic brim and the iliopubic eminence. It is innervated by the anterior ramus of a lumbar spinal nerve, and weakly flexes the lumbar vertebral column. The iliacus muscle originates on the upper 2/3 of the iliac fossa and nearby ligaments and the upper lateral surface of the sacrum, and inserts, along with psoas major, onto the lesser trochanter of the femur. It is innervated by the femoral nerve and flexes the thigh at the hip joint. The iliacus and psoas muscles are often grouped together and called the iliopsoas muscle. Quadratus lumborum runs from the last rib to the iliac crest on both sides of the vertebral column, and attaches to the transverse processes of L1 to L4 vertebrae. These muscles are overlapped on their medial side by the psoas muscles, and the transversus abdominis muscles originate from their lateral border. They are innervated by anterior rami of thoracic and lumbar spinal nerves and largely depress and stabilize rib 12. We covered the last muscle in this region, the diaphragm, in our discussion of the thorax. It is important for our purposes here to note that structures enter and leave the abdomen posterior to its posterior border via the median arcuate ligament or one of the two medial arcuate ligaments or lateral arcuate ligaments. The aorta and thoracic duct pass behind the median arcuate ligament; psoas minor, the sympathetic trunks, and the least splanchnic nerves pass behind the medial arcuate ligament; and psoas major passes behind the lateral arcuate ligament. The greater and lesser splanchnic nerves, hemiazygos veins, esophagus, vagus and phrenic nerves, and inferior vena cava pass through the fibers of the diaphragm directly.
- Viscera: The kidneys, ureters, and adrenal glands are all in the posterior abdominal region. As noted previously, you will undoubtedly learn more about these structures when you take physiology or histology. For now, we will learn a little something about their position, innervation, and blood supply. The adrenal glands sit on top of each kidney, and the anterior surface is covered by the liver on the right side and by intraperitoneal parts of the stomach and the spleen on the left side. The inferior pole of the kidney is associated with the right colic flexure on the right side and the pancreas and left colic flexure on the left side. The ureters come out of the kidneys at the renal pelvis and run to the bladder in the pelvis. We will cover further details about nerves in the lumbar plexus when we cover the pelvis and lower limb.
- Vasculature: The kidneys receive their arterial blood supply via the right and left renal arteries directly off the abdominal aorta lateral to the superior mesenteric artery, and venous drainage via the right and left renal veins which empty into the inferior vena cava at the same level. The renal veins are anterior in relation to the renal arteries (in other words, you have to flip the kidneys over on their posterior side to see the renal arteries). The adrenal glands receive blood from superior suprarenal arteries, branches of the inferior phrenic arteries; middle suprarenal arteries which arise directly from the abdominal aorta; and inferior suprarenal arteries which arise from the right and left renal arteries. The ureters receive blood from branches off the right and left renal arteries, gonadal arteries (testicular arteries in males, ovarian arteries in females), and small branches off the common iliac and internal iliac arteries.
This ends our tour of the abdomen. Next, we turn to the pelvis and perineum and then to the head.
- Human Anatomy Lesson 11
This lesson covers the basic anatomy of the pelvis and perineum, focusing on osteology of the pelvis and the muscles of the pelvic floor.
- Human Anatomy Lesson 12
Lesson #12 covers pelvic organs and the male and female reproductive systems
- Human Anatomy Lesson 13
This lesson covers the superficial tissues of the head, including the muscles of facial expression and the nerves, arteries, veins, and glands.
- Human Anatomy Lesson 14
This lesson covers the skull, which is the bone that surrounds the sensory organs in the head.
- Human Anatomy Lesson 15
This lesson covers the 12 cranial nerves, including their origin, route of passage through the skull base, and the things that they innervate.
- Human Anatomy Lesson 16
This lesson covers the brain and its meninges and vasculature.
- Human Anatomy Lesson 17
This lesson covers the temperomandibular joint and the structures in the temporal and infratemporal fossae.
- Human Anatomy Lesson 18
This lesson covers the anatomy of the orbit, eye, and ear. It is the 18th lesson in a comprehensive undergraduate Human Anatomy course.
© 2015 Robert McCarthy