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1. Describe the structure and features of the stomach and its relationships to other viscera within the abdomen.
1. Describe the structure and features of the stomach and its relationships to other viscera within the abdomen.
The stomach receives boluses from the esophagus, stores and chemically digests boluses into chyme, absorbs water and small molecules, and secretes chyme into the duodenum.
Parts and Features
The stomach is an intraperitoneal organ, and is located predominantly in the left upper quadrant (LUQ). It is bounded (left) laterally by the greater curvature and (right) medially by the lesser curvature. The lesser curvature connects to the liver by means of the hepatogastric ligament of the lesser omentum. The greater curvature is associated to various organs by ligaments of the greater omentum, such as:
Gastrophrenic ligament - connects the greater curvature of the stomach to the left hemidiaphragm.
Gastrosplenic ligament - connects the greater curvature of the stomach to the spleen.
Gastrocolic ligament - connects the greater curvature of the stomach to the transverse colon as a long, adipose-rich, four-layered omental apron.
As the widest part of the gastrointestinal tract (GIT), the stomach has three parts:
Body - the body of the stomach is the largest part, and accounts for the greatest volume and the largest portions of the greater and lesser curvatures of the stomach. The body of the stomach receives boluses of food from the abdominal part of the esophagus at the cardiac orifice. The superior-most extent of the body is the cardiac notch, above which is the fundus.
Cardiac region - the cardiac region is the portion of the stomach into which the esophagus empties.
Fundus - the domed part of the stomach above the body. The fundus lies inferior to the left hemidiaphragm.
Pyloric part - the pyloric part is comprised of the (pyloric) antrum and pyloric canal. It extends from the body to the pyloric orifice, which is surrounded by the pyloric sphincter. The pyloric part (and inferior portions of the body) sit anterior to the body of the pancreas.
(Pyloric) Antrum - the antrum is the portion of the pyloric part just proximal to the canal.
Pyloric canal - distinguishing the pyloric canal from the antrum is often challenging. The canal terminates in the pyloric orifice, the opening surrounded by the pyloric sphincter. Relaxation of the pyloric sphincter allow chyme to enter the duodenum.
As an organ, the stomach is capable of expansion to accommodate food and contraction as part of the digestive process. During contraction or relaxation, folds of mucosa may be observed within the lumen of the stomach. These folds are called gastric rugae.
Blood Supply
The stomach is supplied by blood by the celiac trunk (brs. of celiac trunk below, in bold). In particular by the:
Left gastric a. - forms an anastomosis with the right gastric a. to serve the lesser curvature.
Common hepatic a.
Hepatic artery proper (HAP)
Right gastric a. forms an anastomosis with the left gastric a. to serve the lesser curvature.
Gastroduodenal a.
Right gastro-omental a. - forms an anastomosis with the left gastro-omental a. to serve the greater curvature.
Splenic a.
Left gastro-omental a. - forms an anastomosis with the right gastro-omental a. to serve the greater curvature.
Short gastric brs. -supply the greater curvature in the vicinity of the fundus. May anastomose with the left gastric a.
Innervation
The stomach, as part of the foregut, is served by the celiac (autonomic) plexus.
Sympathetics:
The celiac plexus is associated with the celiac ganglia, pre-aortic sympathetic ganglia, in which preganglionic fibers of the greater thoracic splanchnic nn. (T5-9) and some fibers from the 1st lumbar splanchnic nn. synapse. Sympathetic stimulation causes vasoconstriction & inhibits smooth muscle contraction.
General visceral afferent (GVA) fibers that relate to distention, traction, and ischemia (those loosely categorized as visceral ‘pain’) travel with sympathetic fibers. While these are not true pain fibers, the brain will often interpret these signals as difficult to describe, poorly localized, and midline sensations of pain. Referred pain of the stomach is referred to the epigastric region.
Parasympathetics:
Fibers from the vagal trunks also serve the stomach. Parasympathetic stimulation to the stomach causes smooth muscle contraction and mucosal secretion.
Anterior vagal trunk: enters the abdominopelvic cavity via the esophageal hiatus of the diaphragm (~T10), and divides shortly thereafter into hepatic, gastric, and pyloric brs. The hepatic br. serves the liver, gallbladder, and extrahepatic biliary tree. The gastric and pyloric brs. serve the anterior aspects of the stomach.
Posterior vagal trunk: the posterior vagal trunk enters the abdominopelvic cavity via the esophageal hiatus of the diaphragm (~T10), with fibers contributing to the celiac plexus (and plexuses beyond). Many fibers will move through the celiac ganglia, but they do not synapse. Preganglionic parasympathetic fibers of the posterior vagal trunk serve the posterior and distal aspects of the stomach and the remainder of the foregut and midgut.
2. Describe the blood supply of the foregut, specifically the branches of the celiac trunk and their targets.
2. Describe the blood supply of the foregut, specifically the branches of the celiac trunk and their targets.
The celiac trunk is the main supply to the abdominal viscera derived from the foregut. The trunk branches from the abdominal aorta at approximately the level of T12, or just inferior to the aortic hiatus of the diaphragm. The trunk is very short and immediately branches into: L. gastric a., common hepatic a., and splenic a.
The L. gastric a. supplies small portions of the distal esophagus and liver and the lesser curvature of the stomach, where it openly anastomoses with the R. gastric a.
The common hepatic a. divides into the hepatic artery proper (HAP) and gastroduodenal a. in the vicinity of the pylorus of the stomach (pyloroduodenal junction).
The hepatic artery proper (HAP) runs in the hepatoduodenal ligament and has three main branches. The R. gastric a. supplies the lesser curvature of the stomach and anastomoses with the L. gastric a. The other two branches are the R. & L. brs of HAP, which supply the liver parenchyma.
The gastroduodenal a. descends posterior to the duodenum. It has three main branches: anterior & posterior superior pancreaticoduodenal aa. (supply the superoanterior and superoposterior portions of the duodenum and head of pancreas) & R. gastro-omental (-epiploic) a. (supplies greater curvature of stomach; openly anastomoses with L. gastro-omental a.).
The large and tortuous splenic a. runs posterior to the superior portion of the pancreas. There are multiple branches that supply the pancreas, and these will be discussed in a later session. It also has branches that supply the stomach and spleen. These include short gastric aa. (supply the fundus of the stomach), L. gastro-omental (-epiploic) a. (supply the greater curvature of the stomach; anastomose with the R. gastro-omental a.), and splenic brs. (supply the spleen).
Anastomoses:
Lesser curvature of stomach:
R. gastric a. [branch of hepatic artery proper]
L. gastric a. [direct branch of celiac trunk]
Greater curvature of stomach:
R. gastro-omental (-epiploic) a. [branch of gastroduodenal a.]
L. gastro-omental (-epiploic) a. [branch of splenic a.]
Anterior aspects of duodenum & head of pancreas
Anterior superior pancreaticoduodenal a. [branch of gastroduodenal a.]
Anterior brs. of inferior pancreaticoduodenal a. [branch of SMA]
Posterior aspects of duodenum & head of pancreas
Posterior superior pancreaticoduodenal a. [branch of gastroduodenal a.]
Posterior brs. of inferior pancreaticoduodenal a. [branch of SMA]
3. Describe the basic structure of the liver and gallbladder.
3. Describe the basic structure of the liver and gallbladder.
Nestled within the right hypochondriac and epigastric region, the liver is the largest abdominal organ and a dominant intraperitoneal accessory organ of the foregut. The liver has numerous physiological functions including: producing bile for the emulsification of lipids, regulation and storage of blood glucose, conversion of ammonia to urea, filtering of toxic and bioactive substances, storage of iron for hemoglobin, production of cholesterol and proteins, etc.
Lobes and Surfaces
The liver may be described physiologically as eight segments (each having its own branches of the hepatic portal v., arterial br., & bile duct), or anatomically as four lobes.
There are two prominent anatomical lobes of the liver: a larger right lobe and smaller left lobe. There are two accessory lobes (quadrate and caudate) of the liver, and to see them an inferior view (visceral surface) is necessary. The quadrate lobe is more anteriorly positioned, square-shaped, and adjacent to the gallbladder and round ligament of the liver. The caudate lobe is more posteriorly positioned, comma-shaped, and lies between the inferior vena cava and ligamentum venosum.
The liver has four surfaces, each well named by their relative anatomical faces. These include:
Superior surface - faces and contoured by the shape of the diaphragm. Several peritoneal ligaments attach the superior (and posterior) surface of the liver to the diaphragm and anterior abdominal wall. The coronary ligament attaches the superior surface of the liver to the diaphragm. The coronary ligament is flanked laterally and posteriorly by the triangular ligaments, and intersected anteriorly by the falciform ligament. The area between the coronary ligament and triangular ligaments on the posterior surface of the right lobe is known as the bare area, a region devoid of peritoneum, where areolar connective tissue separates the liver from the diaphragm.
Posterior surface - faces the posterior portion of the diaphragm and abdominal wall. The inferior vena cava (IVC) is conveyed through the posterior surface towards the diaphragm (hiatus at T8). Most of the posterior surface, which is especially of the right lobe, is the bare area.
Right surface - faces the portions of the right hemidiaphragm associated with the right costodiaphragmatic recess and inferior lobe of the right lung.
Inferior (visceral) surface - faces the abdominal viscera inferiorly. The most conspicuous features of the visceral surface include the:
Porta hepatis, a transverse region between the quadrate and caudate lobes, conveying the following structures:
Hepatic portal v.,
Branches of the HAP,
Tributaries of the bile duct,
Hepatic nerve plexus, &
Lymphatics.
Recall that the hepatoduodenal ligament is closely associated with the porta hepatis. It contains the following structures referred to as the portal triad: hepatic portal v., hepatic artery proper, and (common) bile duct.
The round ligament of the liver (ligamentum teres hepatis), a remnant of the fetal left umbilical v., which connects the umbilicus to the porta hepatis. The round ligament is associated with the free margin of the falciform ligament.
Ligamentum venosum, a remnant of the fetal ductus venosus (shunt between the umbilical vein and IVC). The fissure for the ligamentum venosum is located between the left lobe and caudate lobe.
Gallbladder, an intraperitoneal storage sac for bile from the liver associated with the inferior surface of the right lobe of the liver. The gallbladder may also be intrahepatic, or buried within the substance of the right lobe. The cystic duct conveys bile between the lumen of the gallbladder and the common hepatic duct at the point where the duct becomes the (common) bile duct.
Blood Supply and Autonomics
The liver is supplied with oxygen-rich blood via right and left branches of the hepatic artery proper, located within the hepatoduodenal ligament. The branches of HAP enter the porta hepatis.
The hepatic portal v., which transports blood from capillaries of the GI tract to the hepatic sinusoids, is also conveyed via the hepatoduodenal ligament and enters the porta hepatis. Blood from both the HAP and hepatic portal v. mixes in the liver sinusoids.
The liver is drained of blood via the hepatic veins into the inferior vena cava. The hepatic vv. are embedded in the substance of the liver, specifically in the groove for the inferior vena cava.
The liver is innervated by the hepatic plexus, which accompanies the HAP to the porta hepatis and on to hepatocytes. The hepatic plexus receives most of its preganglionic parasympathetic fibers from the anterior vagal trunk and also some from the posterior vagal trunk. Postganglionic sympathetic fibers are sourced from the celiac and superior mesenteric plexuses. Parasympathetic stimulation causes vasodilation, whereas sympathetic stimulation causes vasoconstriction. Referred pain from the liver presents to the epigastric and right hypochondriac regions.
4. Diagram the hepatic portal system, differentiate between hepatic portal & hepatic vein (caval) systems, and identify examples of portal-caval anastomoses.
4. Diagram the hepatic portal system, differentiate between hepatic portal & hepatic vein (caval) systems, and identify examples of portal-caval anastomoses.
Portal systems are vessels that link sets of capillary beds. The hepatic portal system is a venous portal system consisting of all veins that drain the gastrointestinal tract (GIT) from the abdominal esophagus to the superior rectum. These veins coalesce into the hepatic portal v. which delivers blood from the capillary beds of the GIT to capillary beds of the hepatic sinusoidal cells. As the hepatic portal system connects capillary beds, it is a separate system from the caval system (those veins which drain into the vena cavae). Blood from the hepatic sinusoidal cells is delivered back into the caval system via hepatic vv. draining into the inferior vena cava.
The hepatic portal v. typically originates as a union of the superior mesenteric v. with the splenic v. in the transpyloric plane (approximately at L1), posterior to the neck of the pancreas. The hepatic portal v. ascends to the liver within the hepatoduodenal ligament with the (common) bile duct and the hepatic a. proper. These three elements are often referred to as the portal triad.
Typically, three (left, middle, & right) hepatic vv. drain blood of the liver to the inferior vena cava. These may be found draining into the portion of the inferior vena cava that passes through the fissure of inferior vena cava of the liver.
Portacaval anastomoses are areas where vessels of the portal venous & systemic venous systems communicate, allowing blood to still drain through one system (typically caval) if there is obstruction/diminished flow/increased pressure in the other (typically portal). These anastomoses are of particular importance in cases of portal hypertension (increased pressure in portal venous system). In more severe cases, an artificial communication (e.g. shunt) may reduce portal hypertension, and larger veins are typically used to allow more flow, such as the splenic v. (portal) and L. renal v. (caval). Modern approaches to shunting typically involve a Transjugular Intrahepatic Portosystemic Shunt (TIPS), in which the shunt is placed between the hepatic portal v. and a hepatic v.
With portal hypertension, the increased flow of blood through caval veins can lead to dilations called varices. Varices resulting from naturally occurring portacaval anastomoses may arise in the following regions:
Esophageal (distal) submucosa
Esophageal brs. of left gastric v. to Esophageal vv. (Azygos)
Peri-umbilical region
Paraumbilical vv. to superficial epigastric vv.
Retroperitoneal vv.
Anorectal submucosa
Superior rectal vv. to Middle & Inferior rectal vv.
5. Describe the biliary tree and explain the movement of bile between the liver and gallbladder to the duodenum.
5. Describe the biliary tree and explain the movement of bile between the liver and gallbladder to the duodenum.
Bile is an emulsifying substance produced by hepatocytes of the liver. Hepatocytes secrete bile into bile canaliculi, which coalesce into increasingly larger ducts which are the proximal portions of the hepatobiliary tree.
Bile is stored and concentrated in the gallbladder, and secreted into the duodenum. Bile contains bilirubin (orange) and biliverdin (green), which impart a brown-green hue.
Intrahepatic ducts conduct bile into either the right or left hepatic ducts, which unite to form the common hepatic duct. The common hepatic duct conducts bile to the cystic duct, where bi-directional flow of bile can fill or drain the gallbladder. The cystic duct joins the common hepatic duct to form the (common) bile duct, which runs in the hepatoduodenal ligament. The (common) bile duct joins with the main pancreatic duct (which is NOT part of the biliary tract - transports pancreatic fluids). Typically, a dilation of the junction of (common) bile duct and pancreatic duct, the hepatopancreatic ampulla, drains into the 2nd part of the duodenum via the major duodenal papilla.
6. Understand the typical branching pattern of the cystic a. and the boundaries of the hepatobiliary triangle.
6. Understand the typical branching pattern of the cystic a. and the boundaries of the hepatobiliary triangle.
The cystic a. typically branches from the right br. of the hepatic a. proper, but it may also arise directly from the left br. of HAP, HAP, gastroduodenal a., another celiac br., or the superior mesenteric a.
The cystic a. is most often located within the hepatobiliary triangle - a triangular area with borders of the common hepatic duct, the cystic duct, and the inferior surface of the right lobe of the liver. The hepatobiliary triangle is frequently confused with the triangle of Calot - a triangular area with borders of the common hepatic duct, the cystic duct, and the cystic a.
7. Describe the location of the spleen and its spatial relationships with surrounding structures.
7. Describe the location of the spleen and its spatial relationships with surrounding structures.
The spleen is an intraperitoneal, encapsulated mass of lymphoid tissue found in the left upper quadrant (LUQ). The parenchyma of the spleen consists of white pulp (immune responses) and red pulp (phagocytosis).
The spleen is anchored to the stomach by the gastrosplenic ligament, to the left kidney by the splenorenal ligament, and to the diaphragm by the phrenicosplenic ligament. The hilum of the spleen faces medially, and in addition to conveying the splenic a. & v., splenic plexus, and lymphatics, also is associated with the tail of the pancreas.
The spleen is spatially related to the following structures:
L. inferior rib cage, particularly 9th and 10th ribs
Diaphragm
Tail of pancreas
L. kidney
Stomach
Transverse colon/L. colic flexure
The spleen is supplied with blood via the large-calibre, tortuous splenic a. The splenic v. drains the spleen of blood, and is a major formative tributary of the hepatic portal vein.
The spleen is innervated by the splenic plexus, which is conducted to the spleen from the celiac plexus. Referred pain from the pulp of the spleen presents to either the left hypochondriac or epigastric regions.
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