Anatomy Large Vessels, Lymphatics & Nerves of the GI tract Spring 2024 PDF

WE MAKE DOCTORS LARGE VESSELS, LYMPHATICS AND NERVES OF THE GASTROINTESTINAL TRACT Block 3 Spring 2024 Author: Miguel Alejandro Dávalos Benítez, MD. Objectives • Understand the anatomy of large vessels within the gastrointestinal tract, including key arteries and veins. • Explore the lymphatic...

WE MAKE DOCTORS LARGE VESSELS, LYMPHATICS AND NERVES OF THE GASTROINTESTINAL TRACT Block 3 Spring 2024 Author: Miguel Alejandro Dávalos Benítez, MD. Objectives • Understand the anatomy of large vessels within the gastrointestinal tract, including key arteries and veins. • Explore the lymphatic system associated with the gastrointestinal organs and its role in immune function. • Examine the innervation of the gastrointestinal tract, focusing on major nerves and their functions. ARTERIAL SUPPLY Abdominal Aorta Begins at the aortic hiatus of the diaphragm, anterior to the lower border of vertebra T12 The terminal branches of the abdominal aorta are the two common iliac arteries. Descends through the abdomen, anterior to the vertebral bodies, and by the time it ends at the level of vertebra L4 it is slightly to the left of midline. • Anterior, lateral, and posterior branches • The three anterior branches supply the gastrointestinal viscera: the celiac trunk, the superior mesenteric, inferior mesenteric arteries Celiac Trunk • Anterior branch of the abdominal aorta supplying the foregut. • It arises from the abdominal aorta immediately below the aortic hiatus of the diaphragm anterior to the upper part of vertebra LI. • It immediately divides into the: • Left gastric • Splenic • Common hepatic arteries. LEFT GASTRIC ARTERY • The smallest branch of the celiac trunk. • Esophageal branches upward to the abdominal part of the esophagus. • Descends along the lesser curvature of the stomach and It supplies both surfaces in this area. SPLENIC ARTERY • Largest branch of the celiac trunk. • It travels in the splenorenal ligament and divides into numerous branches, which enter the hilum of the spleen. • It gives off numerous small branches to supply the neck, body, and tail of the pancreas. • Approaching the spleen, the splenic artery gives off short gastric arteries, supply the fundus of the stomach • It also gives the left gastro-omental artery, which runs to the right along the greater curvature of the stomach. COMMON HEPATIC ARTERY • Is a medium-sized branch of the celiac trunk that runs to the right • Divides in two branches: • The hepatic artery proper: • Right and left hepatic arteries near the porta hepatis. • The gastroduodenal artery: • Supraduodenal artery and the posterior superior pancreaticoduodenal artery. • Terminal branches: right gastro-omental artery and the anterior superior pancreaticoduodenal artery. Gastroduodenal artery Superior Mesenteric Artery • Anterior branch of the abdominal aorta supplying the midgut. • It arises from the abdominal aorta immediately below the celiac artery, anterior to the lower part of vertebra LI. INFERIOR PANCREATICODUODENAL ARTERY • The first Branch of the superior mesenteric artery • It divides immediately into anterior and posterior branches. • Supplies the head and uncinate process of the pancreas and the duodenum. JEJUNAL AND ILEAL ARTERIES • There are a large number of jejunal and ileal arteries supplying the jejunum and most of the ileum. • The number of arterial arcades increases distally along the gut. • Extending from the terminal arcade are vasa recta (straight arteries), which provide the final direct vascular supply to the walls of the small intestine. MIDDLE COLIC ARTERY • The first of the three branches from the right side of the main trunk of the superior mesenteric artery. • The middle colic artery enters the transverse mesocolon and divides into right and left branches. RIGHT COLIC ARTERY • Is the second of the three branches from the right side of the main trunk of the superior mesenteric artery • It is an inconsistent branch, and passes to the right in a retroperitoneal position to supply the ascending colon. • Nearing the colon, it divides into a descending branch, which anastomoses with the ileocolic artery, and an ascending branch, which anastomoses with the middle colic artery. ILEOCOLIC ARTERY • The final branch arising from the right side of the superior mesenteric artery. • Passes downward and to the right toward the right iliac fossa where it divides into: • Superior branch. • Inferior branch continues toward the ileocolic junction, dividing into: • Colic, cecal, appendicular, and ileal branches. Inferior Mesenteric Artery • It is the smallest of the three anterior branches of the abdominal aorta and arises anterior to the body of vertebra L3. LEFT COLIC ARTERY • The first branch of the inferior mesenteric artery. • Divided into: • Ascending: supplying the upper part of the descending colon and the distal part of the transverse colon. • Descending: supplying the lower part of the descending colon. SIGMOID ARTERIES • Consist of two to four branches. • Supply the lowest part of the descending colon and the sigmoid colon. SUPERIOR RECTAL ARTERY • The terminal branch of the inferior mesenteric artery. • In vertebra SIII, the superior rectal artery divides in: • Two terminal branches that descend on each side of the rectum, dividing into smaller branches in the wall of the rectum. VENOUS DRAINAGE VENOUS DRAINAGE • Venous drainage of the spleen, pancreas, gallbladder, and abdominal part of the gastrointestinal tract, except for the inferior part of the rectum, is through the portal system of veins, which deliver blood from these structures to the liver. PORTAL VEIN It is formed by the union of the splenic vein and the superior mesenteric vein. On approaching the liver, the portal vein divides into right and left branches. Portal Vein Tributaries: • Right and left gastric veins: draining the lesser curvature of the stomach and abdominal esophagus. • Cystic veins: from the gallbladder. • Para-umbilical veins: associated with the obliterated umbilical vein. SPLENIC VEIN • Numerous smaller vessels leaving the hilum of the spleen. • Posterior to the neck of the pancreas, the splenic vein joins the superior mesenteric vein to form the portal vein. SPLENIC VEIN • Tributaries: • Short gastric veins from the fundus and left part of the greater curvature of the stomach. • Left gastro-omental vein from the greater curvature of the stomach. • Pancreatic veins draining the body and tail of the pancreas. • Inferior mesenteric vein (sometimes). SUPERIOR MESENTERIC VEIN • Drains blood from the small intestine, cecum, ascending colon, and transverse colon. • Accompanies each branch of the superior mesenteric artery (jejunal, ileal, ileocolic, right colic, and middle colic veins). • Additional tributaries: • Right gastro-omental vein. • Anterior and posterior inferior pancreatico-duodenal veins. INFERIOR MESENTERIC VEIN • Drains blood from the rectum, sigmoid colon, descending colon, and splenic flexure. • The inferior mesenteric vein passes posterior to the body of the pancreas and usually joins the splenic vein. LYMPHATICS LYMPHATICS • Is through vessels and nodes that eventually end in large collections of pre-aortic lymph nodes. • These collections are therefore referred to as the celiac, superior mesenteric, and inferior mesenteric groups. INNERVATION CLASSIFICATION • Innervated by: • Extrinsic innervation: involves receiving motor impulses from, and sending sensory information to, the central nervous system. • Intrinsic innervation: involves the regulation of digestive tract activities by a generally self-sufficient network of sensory and motor neurons (the enteric nervous system). ❖ The enteric nervous system consists of motor and sensory neurons in two interconnected plexuses in the walls of the gastrointestinal tract. ❖ These neurons control the coordinated contraction and relaxation of intestinal smooth muscle and regulate gastric secretion and blood flow SYMPATHETIC TRUNKS • Are two parallel nerve cords extending on either side of the vertebral column from the base of the skull to the coccyx. • The two sympathetic trunks come together anterior to the coccyx to form the ganglion impar. SPLANCHNIC NERVES Two different types: • The thoracic, lumbar, and sacral splanchnic nerves: Carry preganglionic sympathetic fibers from the sympathetic trunk to ganglia in the prevertebral plexus. • The pelvic splanchnic nerves: Carry preganglionic parasympathetic fibers from anterior rami of S2, S3, and S4 spinal nerves to an extension of the prevertebral plexus in the pelvis. THORACIC SPLANCHNIC NERVES Three thoracic splanchnic nerves: • Greater splanchnic nerve: Arise from the fifth to the ninth (or tenth) thoracic ganglia celiac ganglion in the abdomen. • Lesser splanchnic nerve: Arise from the ninth and tenth thoracic ganglia. • Least splanchnic nerve: Twelfth thoracic ganglion and travels to the renal plexus. LUMBAR AND SACRAL SPLANCHNIC NERVES • Two to four lumbar splanchnic nerves. • Pass from the sacral part of the sympathetic trunk or associated ganglia and enter the inferior hypogastric plexus. PELVIC SPLANCHNIC NERVES The only splanchnic nerves that carry parasympathetic fibers. They originate directly from the anterior rami of S2 to S4. This provides the pathway for innervation of the distal one-third of the transverse colon, the descending colon, and the sigmoid colon by preganglionic parasympathetic fibers. ABDOMINAL PREVERTEBRAL PLEXUS • Collection of nerve fibers that surrounds the abdominal aorta and is continuous onto its major branches. • Scattered throughout the length of the abdominal prevertebral plexus are cell bodies of postganglionic sympathetic fibers. • Some of these cell bodies are organized into distinct ganglia. ABDOMINAL PREVERTEBRAL PLEXUS • Three major divisions: • Celiac: include two celiac ganglia, a single superior mesenteric ganglion, and two aorticorenal ganglia. • Aortic: The major ganglion in this plexus is the inferior mesenteric ganglion at the root of the inferior mesenteric artery. • Superior hypogastric plexuses: Contains numerous small ganglia. PARASYMPATHETIC INNERVATION • Abdominal part of the gastrointestinal tract and of the spleen, pancreas, gallbladder, and liver is from two sources: • The vagus nerves (X). • The pelvic splanchnic nerves. VAGUS NERVE • Provide parasympathetic innervation to the foregut and midgut. • After entering the abdomen as the anterior and posterior vagal trunks, they send branches to the abdominal prevertebral plexus. PELVIC SPLANCHNIC NERVES • Provide parasympathetic innervation to the hindgut. SUGGESTED READINGS • Drake, R. L., Vogl, W., Mitchell, A. W. M., & Gray, H. (2019). Gray's anatomy for students. (4th edition) Philadelphia: Elsevier/Churchill Livingstone. Pages 343 – 365. Chapter 4.