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Liver Anatomy


Liver Anatomy
The liver is the largest organ in the body and lies in the upper part of the abdominal cavity just beneath the diaphragm and mostly under cover of the ribs. It fills the right hypochondrium and extends across the epigastrium into the left hypochondrium. The living organ is reddish-brown and very soft and delicate.

The surface marking of the inferior margin of the liver coincides with the right costal margin as far anteriorly as the ninth costal cartilage and inclines across the abdomen to the eighth left costal cartilage. The healthy liver is not often palpable in the living subject, even during deep inspiration when contraction of the diaphragm pushes the liver inferiorly.

The liver has the shape of a wedge, tapering towards the left (Fig. 4.56). Of its five surfaces, the superior, the anterior and the right lateral merge with no distinct borders intervening. However, a sharp inferior margin separates the anterior from the inferior or visceral surface. The latter faces obliquely downwards, backwards and to the left. The posterior surface blends with the visceral and superior surfaces at indistinct borders. Most of the surface of the liver is clothed in peritoneum.

Surface features and relations
Anterior and lateral surfaces
The anterior and lateral surfaces of the liver are smoothly convex to conform to the diaphragm and the anterior abdominal wall (Fig. 4.57). A two-layered fold of peritoneum, the falciform ligament, connects the anterior surface to the abdominal wall and demarcates the right and left lobes of the organ. In the free lower border of this ligament runs the fibrous remnant of the umbilical vein, the round ligament (ligamentum teres) of the liver, passing from the umbilicus to the visceral surface of the liver.

Superior surface
This surface is gently convex on each side of a shallow depression related to the central tendon of the diaphragm. Above the liver, the two layers of the falciform ligament diverge. One layer passes to the right and continues as the superior layer of the coronary ligament (Fig. 4.58); the other extends to the tip of the left lobe where it forms the left triangular ligament. The posterior layer of this ligament, when traced to the right, is continuous with the lesser omentum.
Visceral surface
This surface (Fig. 4.59) is divided into three areas by two vertical features, the gall bladder and the fissure for the round ligament, the upper ends of which are linked by a horizontal cleft. This cleft is the porta hepatis through which pass the branches of the proper hepatic artery and portal vein and the hepatic ducts. The round ligament (ligamentum teres hepatis) ascends along its fissure to reach the portal vein. To the left of the fissure the left lobe of the liver overlies the body of the stomach and lesser omentum. To the right of the fissure is the small rectangular quadrate lobe, which is related to the anterior aspects of the pyloric region of the stomach and the first part of the duodenum. To the right of the quadrate lobe is the gall bladder, embedded in its fossa. An impression to the right of the gall bladder accommodates the upper pole of the right kidney. This surface of the right lobe is also related to the right colic flexure and the descending duodenum.

Posterior surface
This surface is also divided into three areas (Fig. 4.58). Extending upwards from the left end of the porta hepatis is the fissure in which lies the ligamentum venosum, the fibrous remnant of the fetal ductus venosus. The lesser omentum attaches to the liver in the depths of this fissure and around the margins of the porta hepatis (Fig. 4.60). The portion of the liver to the left of the fissure covers the front of the abdominal oesophagus and the fundus of the stomach.
To the right of the fissure lies the caudate lobe, facing into the superior recess of the omental bursa. To the right of this lobe lies the inferior vena cava, which usually grooves the liver deeply. Further to the right is the bare area (Fig. 4.58), where the right lobe of the liver is in direct contact with the diaphragm and the right suprarenal gland with no intervening peritoneum. The bare area is bounded above and below by the two layers of the coronary ligament, which converge laterally to form the right triangular ligament.

Subphrenic and subhepatic spaces
The arrangement of the various peritoneal ligaments around the liver produces several spaces in which fluids may accumulate. Between the liver and the diaphragm are left and right subphrenic spaces (Fig. 4.57), separated from each other by the falciform ligament and the superior layer of the coronary ligament. The subhepatic spaces lie below and behind the liver, adjacent to either the stomach or the right kidney. Abscesses may occur in these spaces following infections elsewhere in the peritoneal cavity.

Biliary apparatus
Ducts
Bile produced by the liver is collected by a system of canaliculi that drain into the right and left hepatic ducts. The two hepatic ducts emerge through the porta hepatis and soon unite to form the common hepatic duct. As this duct descends in the free border of the lesser omentum, it is joined from the right by the cystic duct to form the bile duct (Fig. 4.59).
Initially, the bile duct lies in the free edge of the lesser omentum, to the right of the hepatic artery and in front of the portal vein. It then passes behind the first part of the duodenum with the gas- troduodenal artery and curves to the right behind the head of the pancreas, sometimes grooving the gland (Fig. 4.54). The bile duct pierces the wall of the descending duodenum in company with the main pancreatic duct (Fig. 4.51). Impaction of stones within the bile duct can give rise to jaundice and to biliary colic, a severe intermittent pain in the epigastrium.
Gall bladder
This is a hollow, pear-shaped organ in which bile from the liver is concentrated and stored (Fig. 4.61). It lies against the visceral surface of the liver, often partially buried in its substance, and usually projects beyond the inferior margin to end blindly in a rounded fundus. The fundus normally makes contact with the anterior abdominal wall where the lateral edge (linea semilunaris) of the right rectus abdominis muscle crosses the costal margin (Fig. 4.2). The body of the gall bladder is its widest part and tapers superiorly into the neck, which continues as the cystic duct. This duct, through which bile enters and leaves, runs upwards towards the porta hepatis and then turns downwards to join the common hepatic duct. The undersurface of the gall bladder is covered by peritoneum continuous with that surrounding the liver. The body is usually related to the proximal part of the duodenum and the fundus often makes contact with the transverse colon. Inflammation associated with gallstones can progress to ulceration, allowing stones to pass from the gall bladder into the duodenum or colon.
The arterial supply to the gall bladder is provided by the cystic artery, which usually springs from the right branch of the proper hepatic artery (Fig. 4.59), though its origin is variable. The cystic vein normally drains into the portal vein or its right branch.

Hepatic blood vessels
Blood is conveyed to the liver by the proper hepatic artery and the portal vein, both of which enter via the porta hepatis. Blood is drained by the hepatic veins embedded in the organ, which enter the anterior aspect of the inferior vena cava immediately below the diaphragm (Fig. 4.58). The common hepatic artery, a branch of the coeliac trunk (Fig. 4.62), runs retroperitoneally downwards and to the right to the superior border of the first part of the duodenum (Fig. 4.59). Here, the common hepatic artery gives off the right gastric and gastroduodenal arteries and continues as the proper hepatic artery. The right gastric artery arises above the first part of the duodenum and runs to the left within the lesser omentum, supplying the lesser curvature of the stomach. The larger gastroduodenal artery descends behind the first part of the duodenum alongside the bile duct. Its terminal branches are the superior pancreaticoduodenal artery (Fig. 4.52) and the right gastro-omental artery (Fig. 4.43). The proper hepatic artery ascends in the free border of the lesser omentum on the left of the bile duct and anterior to the portal vein. Near the porta hepatis, it  divides  into  right  and  left  branches to enter  the liver  with corresponding branches of the portal vein. The left branches of the artery and vein are distributed to the left quadrate and most of the caudate lobes. The right branches supply the remainder of the liver. The proper hepatic artery also supplies the gall bladder via the cystic artery (Fig. 4.59). Within the liver are several segments each with its own arterial supply. During liver and gall bladder surgery, the proper hepatic artery can be compressed, within the free border of the lesser omentum, to stem arterial bleeding.