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STUDENT’S DISCUSSION GUIDE VENOUS DRAINAGE OF THE GASTROINTESTINAL TRACT ; BILE DUCTS OF THE LIVER Contributors: dr. H. Andi Ansharullah, DAAK dr. Arliek Rio Julia, MS Safrina, Msi. Med MEDICAL FACULTY UNIVERSITY OF BRAWIJAYA 2010 VENOUS DRAINAGE OF THE GASTROINTESTINAL TRACT The venous blood from the greater part of the gastrointestinal tract and its accessory organs drains to the liver by the portal venous system. The proximal tributaries drain directly into the portal vein, but the veins forming the distal tributaries correspond to the branches of the celiac artery and the superior and inferior mesenteric arteries.
Portal vein This important vein (fig. 2)drains blood from the abdominal part of the gastrointestinal tract from the lower third of the esophagus to halfway down the anal canal; it also drains blood from the spleen, pancreas, and the gallbladder. The portal vein enters the liver and breaks up into sinusoids, from which blood passes into the hepatic veins that join the inferior vena cava. The portal vein is about 2 inches (5 cm) long and is formed behind the neck of pancreas by the union of the superior mesenteric artery and splenic veins.
It ascends to the right, behind the first part of the duodenum, and enters the lesser omentum. It then runs upward in front of the opening into the lesser sac to the porta hepatis, where it divides into left and right terminal branches. The portal circulation begins as a capillary plexus in the organs it drains and ends by emptying it blood into the sinusoids within the liver. Figure 1 Tributaries of the portal vein. Tributaries of the Portal Vein. The tributaries of the portal vein are the splenic vein, superior mesenteric vein, left gastric vein, right gastric vein, and cystic veins. . Spenic vein. This vein leaves the hilum of the spleen and passes to the right in the splenicorenal ligament lying below the splenic artery. It unites with the superior mesenteric vein behind the neck of the pancreas to form the portal vein (fig. 1). It receives the short gastric, left gastroepiploic, inferior mesenteric, and pancreatic veins. 2. Inferior mesenteric vein. The vein ascends on the posterior abdominal wall and joins the splenic vein behind the body of the pancreas (fig 1). It receives the superior rectal veins, the sigmoid veins, and the left colic vein. . Superior mesenteric vein. This vein ascends in the root of mesentery of the small intestine on the right side of the artery. It passes in front of the third part of duodenum and joins the splenic vein behind the neck of pancreas (fig. 1). It receives the jejuna, ileal, ileoclic, right colic, middle colic, inferior pancreaticoduodenal, and right gastroepiploic veins. 4. Left gastric vein. This vein drains the left portion of the lesser curvature of the stomach and the distal part of the esophagus. It opens directly into the portal vein (fig. ) 5. Right gastric vein. This vein drains the right portion of the lesser curvature of the stomach and drains directly into the portal vein (fig. 1) 6. Cystic veins. These veins either drain the gallbladder directly into the liver or join the portal vein (fig. 1) Figure 2 Portal systemic anastomoses: A, berween esophageal veins; B, between rectal veins; C, between the paraumbilical veins and small epigastric veins of the anterior abdominal wall; D, between colic veins and the retroperitoneal veins Portal-systemic anastomoses
Under normal conditions the portal venous blood traverses the liver and drains into the inferior vena cava of the systemic venous circulation by way of hepatic veins. This is the direct route. However, other, smaller communications exist between the portal and systemic systems, and they become important when the direct route becomes blocked (fig. 2) These communications are as follows: 1. At the lower third of the esophagus, the esophageal branches of the left gastric vein (portal tributary) anastomose with the esophageal veins draining the middle third of the esophagus into the azygos veins (systemic tributary) 2.
Halfway down the anal canal, the superior rectal veins (portal tributary) draining the upper half of the anal canal anastomose with the middle and inferior rectal veins (systemic tributaries), which are tributaries of the internal iliac and internal pudendal veins, respectively. 3. The paraumbilical veins connect the left branch of the portal vein with the superficial veins of the anterior abdominal wall (systemic tributaries). The paraumbilical veins travel in the falciform ligament and accompany the ligamentum teres. 4.
The veins of the ascending colon, descending colon, duodenum, pancreas, and liver (portal tributary) anastomose with the renal, lumbal, and phrenic veins (systemic tributaries). References: Moore, Keith L. , Dalley, A. F. 2006. Clinically Oriented Anatomy. 5th ed. Lippincott Williams ; Wilkins. Moore, Keith L. , Agur, A. M. R. 2007. Essential Clinical Anatomy. 3rd ed. Lippincott Williams ; Wilkins. Snell, Richard S. 2000. Clinical Anatomy for Medical Students. 6th ed. Lippincott Williams ; Wilkins. Student Assignment: 1.
Explain what the portal system is. 2. Describe the structures that contribute in the formation of the system. 3. Explain what the portal-systemic anastomosis is. 4. Mention some of the clinical aspects of the blockade of the portal vein. 5. Answer 1. Vena porta is the final common pathway for the transport of the venous blood from the spleen, pancreas, gallbladder, and the abdominal part of the gastrointestinal tract. It is formed by the union of splenic vein and the superior mesenteric vein. 2. Tributaries to the portal vein contributing n the formation of portal system include: a. Left and right gastric veins, draining the gastric lesser curvature and the abdominal part of the esophagus b. Cystic veins from the gallbladder c. Paraumbilical veins, which are associated with the obliterated umbilical vein and connect to veins on the anterior abdominal wall. 3. Portal-systemic anastomosis is an overlap between veins of the portal and caval systems in some region, mainly: d. Around the inferior end of the esophagus e. Around the inferior part of the rectum f.
Small veins that accompany the degenerated umbilical vein (ligamentum teres hepatis) form a connection between the portal system and the paraumbilical regions of the abdominal wall, which drains into the systemic veins. 4. Blockade of the hepatic portal vein or vascular channels in the liver can affect the pattern of venous return from the abdominal parts of gastrointestinal system. Vessels that interconnect the portal and caval systems can become greatly enlarged and tortuous, allowing blood in tributaries of the portal system to bypass the liver, enter the caval system, and therby return to the heart.
Portal hypertension can result in esophageal varices and hemorrhoids at the esophageal and rectal ends of the gastrointestinal system, respectively, and in the so-called caput medusa in which systemic vessels that radiate from paraumbilical veins enlarged and become visible an the abdominal wall. 5. BILE DUCTS OF THE LIVER Bile is secreted by the liver cells, stored, and concentrated in the gallbladder; later it is delivered to the duodenum. The bile ducts of the liver consist of the right and hepatic ducts, the common hepatic duct, the bile duct, the gallbladder, and the cystic duct.
The smallest interlobular tributaries of the bile ducts are situated in the portal canals of the liver; they receive the bile canaliculi. The interlobular ducts join one another to form progressively larger ducts, and eventually, at the porta hepatis, form the right and left bile ducts. The right hepatic duct drains th right lobe of the liver and the left duct drains the left lobe, caudate lobe, and quadrate lobe. Hepatic ducts (Ductus hepaticus dexter et sinister) The right and left hepatic ducts are situated in the portal canals of the liver in the porta hepatis (fig. ). After a short course, the hepatic ducts unite to form the common hepatic duct (fig. 4). The common hepatic duct is about 1 ? inches (4 cm) long and descends within the free margin of the lesser omentum. It is joined on the right side by the cystic duct from the gallbladder to form the bile duct (fig. 4) Figure 3 Figure 4 Bile Duct (Ductus choledochus; Ductus bilaris) The bile duct (common bile duct) is about 3 inches (8 cm) long. In the first part of its course, it lies in the right free margin of the lesser omentum in front of the opening into the lesser sac.
Here it lies in front of the right margin of the portal vein and on the right of the hepatic artery. In the second part of its course, it is situated behind the first part of the duodenum to the right of the gastroduodenal artery. In the third part of its course, it lies in a groove on the posterior surface of the head of the pancreas . Here, the bile duct comes into contact with the main hepatic duct. The bile duct ends below by piercing the medial wall of the second part of the duodenum about the halfway down its length (5. 7). The main pancreatic duct usually joins it, and together they open into a small ampulla in the duonenal wall, called the ampulla of Vater. The ampulla opens into the lumen of the duodenum by means of the small papilla, the major duodenal papilla (fig. 4). The terminal part of both ducts and the ampulla are surrounded by circular muscle, known as the sphincter of Oddi (fig. 4). Occasionally, the bile and the pancreatic duct open separately into the duodenum. Gallbladder (Vesica fellea; Vesica biliaris) Location and description
The gallbladder is a pear shaped sac lying on the undersurface of the liver. It has a capacity of about 30 to 50 mL and stores bile, which it concentrates by absorbing water. For the descriptive purposes, the gallbladder is divided into fundus, body, and neck. The fundus is rounded and usually projects below the inferior margin of the liver, where it comes into contact with the anterior abdominal wall at the level of tip of the ninth right costal cartilage. The body lies in contact with the visceral surface of the liver and is directed upward, backward, and to the left.
The neck become continuous with the cystic duct, which turns into the lesser omentum to join the right side of the common hepatic duct, to form the bile duct (fig. 3 and 4) The peritoneum completely surrounds the fundus of the gallbladder and binds the body and neck to the visceral surface of the liver. Relations * Anteriorly: the anterior abdominal wall and the inferior surface of the liver * Posteriorly: the transverse colon and the first and second parts of the duodenum Function The gallbladder serves as a reservoir for bile.
It has the ability to concentrate the bile, ant to aid this process the mucous membrane is thrown into permanent folds that unite with each other, giving the surface of a honeycombed appearance. The columnar cells lining the surface also have numerous microvilli on their free surface. Bile is delivered to the duodenum as a result of contraction and partial emptying of the gallbladder. The entrance of fatty foods into the duodenum initiates this mechanism. The fat causes release of the hormone cholecystokinin from the mucous membrane of the duodenum; the hormone then enters the blood, causing the gallbladder to contract.
At the same time the smooth muscle around the distal end of the duct and the ampulla is relaxed, thus allowing the passage of concentrated bile into the duodenum. The bile salts in the bile are important in emulsifying the fat in the intestine and in assisting with its digestion and absorption. Blood supply Arteries. Cystic artery, a branch of the right hepatic artery Veins. The cystic veins drains directly into the portal vein. Several very small arteries and veins also run between the liver and the gallbladder. Lymph drainage
The lymph drains into a cystic lymph node situated near the neck of gallbladder. From here the lymph vessels pass to the hepatic nodes along the course of the hepatic artery and then to the celiac nodes. Nerve supply Sympathetic and parasympathetic vagal fibers from the celiac plexus. The gallbladder contracts in response to the hormone cholecystokinin, which is produced by the mucous membrane of the duodenum, on the arrival of fatty food from stomach. Cystic duct (Ductus cysticus) The cystic duct is about 1 ? inches (3. cm) long and connects the neck of the gallbladder to the common hepatic duct to form the bile duct (fig. 3). It usually is somewhat S shaped and descends for a variable distance in the right free margin of the lesser omentum The mucous membrane of the cystic duct is raised to form a spiral fold that is continuous with a similar fold in the neck of the gallbladder. The fold is commonly known as the “spiral valve”. The function of the spiral valve is to keep the lumen constantly open. References: Moore, Keith L. , Dalley, A. F. 2006. Clinically Oriented Anatomy. th ed. Lippincott Williams ; Wilkins. Moore, Keith L. , Agur, A. M. R. 2007. Essential Clinical Anatomy. 3rd ed. Lippincott Williams ; Wilkins. Snell, Richard S. 2000. Clinical Anatomy for Medical Students. 6th ed. Lippincott Williams ; Wilkins. Student assignment: 1. Describe the course of the biliary tract from the liver to the duodenum. 2. Describe the location of the gallbladder and its relation to its surrounding structures. 3. Explain the function of the gallbladder. 4. Explain the function of the spiral valve of the cystic duct.