HEPATOBILIARY SYSTEM BY ETIBOR T A 2016 LIVER

HEPATOBILIARY SYSTEM BY ETIBOR, T. A. 2016

LIVER • The liver is the largest gland in the body • After the skin, it is the largest single organ (2 nd largest) • Weighs about 1500 g and accounts for approximately 2. 5% of adult body weight. • In the late fetus, it serves as a hematopoietic organ and about twice as large (5% of body weight). • Position: occupies almost all of the right hypochondrium and epigastrium. It extends into the left hypochondrium, inferior to the diaphragm, which separates it from the pleural and mediastinal cavities • Except for fat, all nutrients absorbed from the GIT are initially conveyed first to the liver by the portal venous system. It stores glycogen and secretes bile • Bile passes from the liver via the biliary ducts. The right and left hepatic ducts join to form the common hepatic duct, which unites with the cystic duct to form the bile duct. • The liver produces bile continuously

SURFACE ANATOMY OF THE LIVER

SURFACES AND RECESSES 1. Diaphragmatic 2. visceral Diaphragmatic Surface is a smooth convex (anterior, superior, and some posterior), WHILE Visceral surface is relatively flat or even concave (posteroinferior), which are separated anteriorly by its sharp inferior border. It bears multiple fissures and impressions from contact with other organs. N. B. : Recall that normally all recesses of the peritoneal cavity are potential spaces only, containing only enough peritoneal fluid to lubricate the adjacent peritoneal membranes.

RECESSES • Subphrenic recesses: a superior extensions of the peritoneal cavity (greater sac) existing between the diaphragm and the anterior and superior aspects of the diaphragmatic surface of the liver. It is separated into right and left recesses by the falciform ligament • Subhepatic space: the portion of the supracolic compartment of the peritoneal cavity immediately inferior to the liver. • Hepatorenal recess (hepatorenal pouch; Morison pouch): the posterosuperior extension of the subhepatic space, lying between the right part of the visceral surface of the liver and the right kidney and suprarenal gland. It is a gravitydependent part of the peritoneal cavity in the supine position; fluid draining from the omental bursa flows into this recess. It communicates anteriorly with the right subphrenic recess.

PERITONEAL REFLECTIONS AND RELATIONSHIPS • The diaphragmatic surface of the liver is covered with visceral peritoneum, except posteriorly in the bare area of the liver; where it lies in direct contact with the diaphragm • Bare area is demarcated by the reflection of peritoneum from the diaphragm as the coronary ligament • The anterior (upper) and posterior (lower) layers of the coronary ligament meet on the right to form the right triangular ligament and diverge toward the left to enclose the triangular bare area • The anterior layer of the coronary ligament is continuous on the left with the right layer of the falciform ligament, and the posterior layer is continuous with the right layer of the lesser omentum • Near the apex of the wedge-shaped liver, the anterior and posterior layers of the left part of the coronary ligament meet to form the left triangular ligament • Relations: The inferior vena cava traverses a deep groove for the vena cava within the bare area of the liver.

PERITONEAL REFLECTIONS AND RELATIONSHIPS • The visceral surface of the liver is covered with peritoneum, except at the fossa for the gallbladder and the porta hepatis; a transverse fissure where the vessels (portal vein, hepatic artery, and lymphatic vessels), the hepatic nerve plexus, and hepatic ducts • Two sagittal fissures, linked centrally by the transverse porta hepatis, form the letter H on the visceral surface • Right sagittal fissure continues with the gallbladder (ant. ) and inferior vena cava(post. ) • Left sagittal fissure contiues with the ligamentum teres (round ligament, ant. ) and ligamentum venosum (post. ) • The ligamentum teres and L. venosum are fibrous remnant of the umbilical vein and ductus venosus respectively

PERITONEAL REFLECTIONS AND RELATIONSHIPS • The lesser omentum, encloses the portal triad (bile duct, hepatic artery, and portal vein) • It passes from the liver to the lesser curvature of the stomach and the first 2 cm of the superior part of the duodenum. • The thick, free edge of the lesser omentum extends between the porta hepatis and the duodenum (the hepatoduodenal ligament) • It encloses the structures that pass through the porta hepatis. • The sheet-like remainder of the lesser omentum, the hepatogastric ligament, extends between the groove for the ligamentum venosum of the liver and the lesser curvature of the stomach.

RELATIONSHIPS OF THE LIVER In addition to the fissures, impressions on (areas of) the visceral surface reflect the liver's relationship to the: • Right side of the anterior aspect of the stomach (the gastric and pyloric areas). • Superior part of the duodenum (the duodenal area). • Lesser omentum (extends into the fissure for the ligamentum venosum). • Gallbladder (fossa for gallbladder). • Right colic flexure and right transverse colon (the colic area). • Right kidney and suprarenal gland (the renal and suprarenal areas).

ANATOMICAL LOBES OF THE LIVER • Externally: 2 topographical (anatomical) lobes and 2 accessory lobes • These superficial lobes are not true lobes as the term is generally used in relation to glands and are only secondarily related to the liver's internal architecture • The essentially midline plane defined by the attachment of the falciform ligament and the left sagittal fissure separates a large right lobe from a much smaller left lobe • On the slanted visceral surface, the right and left sagittal fissures surround and the transverse porta hepatis demarcates two accessory lobes (parts of the anatomic right lobe) • Quadrate lobe (ant. and inf. ) and the Caudate lobe (post. and sup. ) The caudate lobe is so-named not because it is caudal in position (it is not) but because it often gives rise to a tail in the form of an elongated papillary process. • A caudate process extends to the right, between the IVC and the portal hepatis, connecting the caudate and right lobes (Fig. 2. 50 B).

FUNCTIONAL SUBDIVISIONS OF THE LIVER • Although not distinctly demarcated internally, where the parenchyma appears continuous, the liver has functionally independent right and left livers (parts or portal lobes) that are much more equal in size than the anatomical lobes; however, the right liver is still somewhat larger • Each part receives its own primary branch of the hepatic artery and portal vein and is drained by its own hepatic duct. • The caudate lobe may in fact be considered a third liver; its vascularization is independent of the bifurcation of the portal triad (it receives vessels from both bundles) and is drained by one or two small hepatic veins, which enter directly into the IVC distal to the main hepatic veins • The liver can be further subdivided into 4 divisions and then into 8 surgically resectable hepatic segments, each served independently by a secondary or tertiary branch of the portal triad

BLOOD VESSELS OF THE LIVER Dual blood supply (afferent vessels)- a dominant venous source and a lesser arterial one: • Portal vein (75 -80% blood, 40% O 2): carrries all nutrients except lipids. It formed by the superior mesenteric and splenic veins posterior to the neck of the pancreas and ascends anterior to the IVC as part of the portal triad in the hepatoduodenal ligament • Hepatic artery (20 -25% blood): a branch of the celiac trunk • At or close to the porta hepatis, the hepatic artery and portal vein terminate by dividing into right and left branches; these primary branches supply the right and left livers, respectively. Between the divisions are the right, intermediate (middle), and left hepatic veins, which are intersegmental in their distribution and function, draining parts of adjacent segments. • The hepatic veins, formed by the union of collecting veins that in turn drain the central veins of the hepatic parenchyma, open into the IVC just inferior to the diaphragm. The attachment of these veins to the IVC helps hold the liver in position.

LYMPAHTICS AND INNERVATION OF THE LIVER • Superficial lymphatics (fibrous capsule of the liver ‘Glisson capsule’) • Deep lymphatics (accompanying ramification of the portal triad and hepatic vein) • Mostly formed in the perisinusoidal spaces (of Disse) and drains to the deep lymphatics in the surrounding intralobular portal triads. • Superficial (ant. ) and deep lymphatic vessels drain to the hepatic lymph nodes, then to coeliac lymph nodes, then to chyle cistern • Superficial (post. ) drains to the bare area, to phrenic lymph nodes, or join deep lymphatics accompanying the hepatic veins converging on the IVC, into the posterior mediastinal lymph nodes. Efferent vessels from these nodes join the right lymphatic and thoracic ducts.

LYMPAHTICS AND INNERVATION OF THE LIVER A few lymphatic vessels follow different routes: • From the posterior surface of the left lobe toward the esophageal hiatus of the diaphragm to end in the left gastric lymph nodes • From the anterior central diaphragmatic surface along the falciform ligament to the parasternal lymph nodes. • Along the round ligament of the liver to the umbilicus and lymphatics of the anterior abdominal wall. INNERVATION: • Hepatic plexus (largest derivative of the celiac plexus). • Consists: sympathetic fibers from the celiac plexus and parasympathetic fibers from the anterior and posterior vagal trunks • Function: Other than vasoconstriction, their function is unclear.

APPLED ANATOMY OF THE LIVER • • Subphrenic abscess Hepatic lobectomies and segmentectomies Rupture of the liver Aberrant hepatic artery Variations in the relationships of hepatic artery Unusual formation of the portal vein Hepatomegaly Cirrhosis of the liver

BILIARY DUCTS • The biliary ducts convey bile from the liver to the duodenum. Bile emulsifies the fat • Forms in the free edge of the lesser omentum by the union of the cystic duct and the common hepatic duct • Length: varies 5 -15 cm, depending on where the cystic duct joins the common hepatic duct • Form hepatopancreatic ampulla in the duodenal papilla • Contraction of the sphincter of the bile duct makes bile backs up and passes along the cystic duct to the gallbladder for concentration and storage

ARTERIES, VEINS AND LYMPHATICS OF THE BILE DUCT ARTERIES: • Cystic artery: supplying the proximal part of the duct • Right hepatic artery: supplying the middle part of the duct • Posterior superior pancreaticoduodenal artery and gastroduodenal artery: supplying the retroduodenal part of the duct VEINS: • The veins from the proximal part of the bile duct and the hepatic ducts usually enter the liver directly • The posterior superior pancreaticoduodenal vein drains the distal part of the bile duct and empties into the portal vein or one of its tributaries. LYMPAHTICS: • The lymphatic vessels from the bile duct pass to the cystic lymph nodes near the neck of the gallbladder, the node of the omental foramen, and the hepatic lymph nodes. Efferent lymphatic vessels from the bile duct pass to the celiac lymph nodes.

GALL BLADDER • 50 m. L of bile, Pear shaped, 7 -10 cm long, lies in the fossa for the gallbladder on the visceral surface of the liver • The body of the gallbladder lies anterior to the duodenum, and its neck and the cystic duct are immediately superior to the duodenum • Peritoneum completely surrounds the fundus of the gallbladder and binds its body and neck to the liver. The hepatic surface of the gallbladder attaches to the liver by connective tissue of the fibrous capsule of the liver. Parts: • Fundus: the wide end of the organ, projects from the inferior border of the liver and is usually located at the tip of the right 9 th costal cartilage in the MCL • Body: contacts the visceral surface of the liver, the transverse colon, and the superior part of the duodenum. • Neck: narrow and tapered; directed toward the porta hepatis; it makes an S-shaped bend and joins the cystic duct.

CYSTIC DUCT, ARTERY AND VEIN • Cystic duct: 3 -4 cm long, connects the neck of the gallbladder to the common hepatic duct. The mucosa of the neck spirals into the spiral fold (spiral valve). The spiral fold helps keep the cystic duct. The spiral fold also offers additional resistance to sudden dumping of bile when the sphincters are closed • Cystic artery: supplying the gallbladder and cystic duct, commonly arises from the right hepatic artery in the angle between the common hepatic duct and the cystic duct (cystohepatic triangle). Variations occur in the origin and course of the cystic artery • Cystic veins: draining the neck of the gallbladder and cystic duct, enter the liver directly or drain through the portal vein to the liver, after joining the veins draining the hepatic ducts and upper bile duct. The veins from the fundus and body of the gallbladder pass directly into the visceral surface of the liver and drain into the hepatic sinusoids. Because this is drainage from one capillary (sinusoidal) bed to another, it constitutes an addition (parallel) portal system.

LYMPAHTICS AND INNERVATION OF THE GALL BLADDER AND CYSTIC DUCT • LYMPHATICS of the gallbladder is to the hepatic lymph nodes, often through cystic lymph nodes located near the neck of the gallbladder. Efferent lymphatic vessels from these nodes pass to the celiac lymph nodes. • NERVES to the gallbladder and cystic duct pass along the cystic artery from the celiac nerve plexus (sympathetic and visceral afferent [pain] fibers), the vagus nerve (parasympathetic), and the right phrenic nerve (actually somatic afferent fibers). • Parasympathetic stimulation causes contractions of the gallbladder and relaxation of the sphincters at the hepatopancreatic ampulla. However, these responses are generally stimulated by the hormone cholecystokinin (CCK), produced by the duodenal walls (in response to the arrival of a fatty meal) and circulated through the bloodstream.

APPLIED ANATOMY OF BILE DUCT AND GALL BLADDER Infundibulum of the gall bladder (Hartmann pouch) Mobile gall bladder Variations in cystic and hepatic ducts Accessory hepatic ducts Gall stones (cholecytitis) Gall stones in the duodenum (cholecystenteric fistula, can lead to gallstone ileus) • Cholecystectomy • • •

Assignment: Portocaval/ portosystemic anastomosis