Stomach and Duodenum

Why is the first part of the Duodenum on the right side and the fourth part on the left side? If a patient needs a Vagotany, which is more preferred for surgery, anterior trunk or posterior trunk? Stomach The stomach is the most dilated part in the GI tract and has a J-like shape. It's located between the abdominal esophagus and small intestine. Located at the left hypochondrium, epigastric, and umbilical regions of the abdomen. Curvatures The stomach has two curvatures: lesser curvature and greater curvature. The lesser curvature is the point of attachment for the lesser omentum. The greater curvature is the point of attachment for the Gastro-splenic ligament (a ligament between the spleen and stomach) and greater omentum. Greater Omentum Greater omentum consists of three ligaments: Gastrocolic ligament Gastrosplenic ligament Gastrophrenic ligament Gastrophrenic ligament: a ligament between the fundus of stomach and diaphragm. Gastrosplenic ligament: a ligament between the spleen and stomach. Gastrocolic ligament: a ligament between the stomach and transverse mesocolon. Stomach Parts Stomach is divided into four parts: Cardia, Fundus, Body, and Pyloric part. Cardia: The part where the esophagus meets the stomach. Fundus: The largest area of the stomach, above the level of the cardiac orifice. Body: The body of the stomach. Pyloric part: Subdivided into pyloric antrum, pyloric canal, and pyloric sphincter. It is the most distal part of the stomach. Stomach The stomach has two notches: Cardial notch and Angular Incisure. The cardial notch, which is at the superior angle, is created where the esophagus enters the stomach. The angular incisure is the bend on the lesser curvature. The lesser curvature has two parts: a vertical part and a horizontal part. The point between the two parts forms the angular incisure. The stomach is an intraperitoneal structure. At the pyloric part, the circular muscles contract close to each other, forming the pyloric sphincter. Layers of Stomach Similar to other structures in the GI tract, the stomach is made up of four layers: From inner to outer: Mucosa, Submucosa, Muscularis Mucosa, Serosa. The muscular layer of stomach consists of three layers of muscles: longitudinal layer, circular layer, and oblique layer. (Other structures of the GI tract consist of only two layers of muscles: longitudinal and circular; no oblique layer.) Submucosa The submucosa is a layer of nerves and vessels. Gastric Secretion Stomach produces HCl, pepsin, and other digestive enzymes. Gastric secretion is controlled by two mechanisms: neural and hormonal mechanisms. Neural Mechanism The neural mechanism is controlled by the vagus nerve. Parasympathetic stimulation of the vagus nerve stimulates pepsin and acid production. Hormonal Mechanism The hormonal mechanism is controlled by gastrin, a hormone released from the G-cells of the pyloric antrum. Gastrin stimulates the body for production of pepsin and HCl. Relations of the Stomach Anteriorly: Left abdominal wall, left costal margin, left lobe of liver, diaphragm Posteriorly: Lesser sac/bursa omentalis, pancreas, transverse colon, left kidney, left suprarenal gland (adrenal gland), splenic artery, spleen Stomach's Surface Anatomy Stomach's surface curving is located near the costal margin. Yet, at the cardia, there is no anatomical sphincter, the circular muscles join together to form the pyloric sphincter. Gastroesophageal Reflux Normally, due to gravity, diaphragm, and different folds in esophagus and stomach, people with peptic ulcer disease or other reflux disease cannot prevent gastroesophageal reflux. Celiac Trunk & Blood Supply of Stomach Celiac trunk is a branch of abdominal aorta. It supplies the foregut. It arises from the abdominal aorta anteriorly, immediately below the aortic hiatus at the level of T12. It divides into three branches: left gastric, splenic, and common hepatic artery. Splenic Artery Largest branch of celiac trunk Travels to the left side, posterior to the stomach, and enters the hilum of spleen. It travels in the splenorenal ligament and divides into numerous branches in the hilum of spleen (central and peripheral segments). The splenic artery travels on the left side, passing through the inferior border of pancreas, giving numerous branches supplying the pancreas called pancreaticoduodenal arteries. Left Gastro-Enteric Artery The splenic artery gives another branch called left gastro-enteric artery which supplies the greater curvature of the stomach and forms an anastomosis with the right gastro-enteral artery. Short Gastric Arteries Another branch of splenic artery is the short gastric artery which supplies the fundus of the stomach. These arteries course through/in the gastrosplenic ligament. Common Hepatic Artery It is a middle-sized branch of the celiac trunk. It divides into two branches: Gastroduodenal artery & Proper hepatic artery. Proper hepatic artery ascends to the liver through the lesser omentum and terminates as right hepatic & left hepatic artery. The right hepatic artery enters the left lobe of the liver, gives a branch called cystic artery which supplies the gallbladder. Gastroduodenal Artery Another branch of the gastroduodenal artery called Superior pancreaticoduodenal artery which supplies the superior portion of Duodenum. Gastroduodenal artery is also another branch of common hepatic artery, which exits from the same place as supraduodenal artery. It has Blood Supply of Stomach Arteries: Left gastric artery: A branch from celiac trunk Right gastro-omental artery: A branch from splenic artery Left gastro-omental artery: A branch from gastro-duodenal artery Short gastric artery: A branch from splenic artery Right gastric artery has some variations: It could arise from hepatic artery proper (HP) or from gastroduodenal artery. Veins Left gastric vein, right gastric vein, short gastric vein, left gastro-omental vein, right gastro-omental vein drain to portal vein. Nerve Supply of Stomach Sympathetic (T6-T9): Vasomotor, motor to pyloric sphincter, inhibitory to the rest of the gastric muscular layer, chief pathway for pain sensation in the stomach. Parasympathetic: Motor to the muscular wall of the stomach, secretomotor (stimulates production of HCl & pepsin). Vagus Nerves There are two vagal trunks: Anterior vagal trunk & Posterior vagal trunk. Anterior vagal trunk includes mainly the left vagus nerve, and a small portion of right vagus nerve. Posterior vagal trunk is mainly formed by right vagus nerve. Anterior vagal trunk has four branches: Gastric, pyloric, hepatic, celiac branches. Celiac branch goes to celiac ganglion and plexus. Posterior vagal trunk has only two branches: Gastric and celiac branches. Small Intestine Small intestine is the longest part of the gastrointestinal tract. It extends from the pyloric orifice of the stomach to the ileocecal junction. It is a hollow tube of 6m length & 2.5cm width, with a narrowing diameter from the beginning to the end. It consists of three parts: Duodenum, Jejunum, Ileum. Duodenum Duodenum is the first part of the small intestine. It is a C-shaped tube facing upwards, and is adjacent to the pancreas. It is 20-25cm long and about 2.5cm wide. Its lumen is the widest in all the small intestine. It is covered with retroperitoneal structure, except its beginning, which is covered with lesser omentum (precisely by hepatoduodenal ligament), so its an intraperitoneal structure. Duodenum The duodenum is divided into four parts: First part (bulb): 5 cm Second part (descending): 10 cm Third part (horizontal): 8 cm Fourth part (ascending): 5 cm The fourth part is continuous with the jejunum at the duodenojejunal flexure. Duodenojejunal Flexure The duodenojejunal flexure extends from the pyloric orifice of the stomach to the area of the neck of gallbladder, at the right side of L1 vertebra. It passes anterior to: common bile duct, gastroduodenal artery, portal vein, IVC. All these structures are posterior to the first part of the duodenum. Clinical Significance Clinically, the beginning part of the first part of the duodenum is called the bulb or ampulla, and is covered with lesser omentum, specifically by the hepatoduodenal ligament. Transverse Mesocolon The transverse mesocolon passes through anteriorly at the level of descending duodenum. The root of the mesentery passes through the anterior surface of the horizontal/transverse parts of duodenum, through which pass the superior mesenteric vessels (artery, vein). Hepatoduodenal Ligament Hepatoduodenal ligament attaches to the first part of the duodenum and to the liver. Hepatoduodenal ligament of lesser omentum is the only intraperitoneal structure of the duodenum. The rest is retroperitoneal. Duodenum Under the serous or adventitial layer of duodenum, there is a muscular layer of two kinds: circular and longitudinal muscles. The inner surface of the descending or second part of duodenum, there are two duodenal papillae, major and minor. The minor papilla is right above the major papilla. The major papilla is the insertion point of the common bile duct and the minor papilla is the insertion point for accessory pancreatic duct. They are both for bile drainage. Just before entering the duodenum, the common bile duct and main pancreatic duct join together and enter the major papilla. Inside the duodenum, they get surrounded by circular smooth muscles and form a single sphincter called the Oddi sphincter. So, this area is named hepatopancreatic ampulla (covered by circular muscles and Oddi sphincter). Third Part of Duodenum The third or transverse part of duodenum has the superior mesenteric vessels and root of the mesentery passing through it. Its anterior is IVC and descending aorta, passing across its posterior. Fourth Part of Duodenum The fourth part of the duodenum, at the duodenojejunal junction, is connected to the right crus of the diaphragm by a ligament called suspensory ligament of duodenum or Treitz ligament. Some opinions say that it's a band of smooth muscles extending from the diaphragm to the duodenojejunal junction. Lesser Omentum The lesser omentum is divided into two ligaments: hepatogastric ligament, from liver to stomach, and hepatoduodenal ligament, from liver to duodenum. The free border of the lesser omentum is between the lesser curvature of the stomach and the duodenum. It contains hepatic artery, portal vein, common bile duct, lymph glands, lymph vessels, nerves, forming the hepatic hilum. Behind this free edge is the opening into the lesser sac, called epiploic foramen or foramen of Winslow. Blood Supply of the Duodenum The duodenum is supplied with blood by the superior pancreaticoduodenal artery and inferior pancreaticoduodenal artery. Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right side to the spleen on the left side.   Pancreas Pancreas is a retroperitoneal structure except its tail, which enters the hilum of spleen at which, the tail of pancreas is embedded within the splenorenal ligament with splenic vessels. It's the only part of the pancreas that's intraperitoneal. Functions of Pancreas The pancreas serves both endocrine and exocrine gland functions. Endocrine: Pancreatic islets produce insulin and glucagon. Exocrine: Acini produce digestive enzymes for lipids digestion. Relations Anteriorly related to: Stomach Transverse mesocolon Transverse colon Lesser sac Posteriorly related to: IVC Descending aorta Left kidney Left suprarenal (adrenal) gland Portal and splenic veins Bile duct Pancreas The pancreas is divided into several parts: head, uncinate process, neck, body, tail. The head of pancreas lies in the C-shaped curve of the duodenum. Projecting from it is the uncinate process which passes posterior to the superior mesenteric vessels. The neck of pancreas is posterior to the portal vein. The neck of pancreas is important because posterior to it, exists the portal vein draining from splenic vein, superior mesenteric vein and inferior mesenteric vein. Body of pancreas extends from its neck to its tail. Tail of pancreas passes within the layers of the splenorenal ligament. So, it's intraperitoneal. At the superior border of the body, there exists a tuberosity, called omental tuberosity. This tuberosity is important for locating the celiac trunk. Celiac trunk is right above omental tuberosity. At the right side of the head of the pancreas, there are some pancreatic ducts which drain to the second part of the duodenum. Blood Supply of Pancreas Pancreatic branches from splenic artery Superior pancreaticoduodenal artery (from gastroduodenal artery) Inferior pancreaticoduodenal artery (from superior mesenteric artery