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.
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.
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.
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.
