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| Liver marked as red organ |
Features
The liver is A large and solid gland situated in the right upper quadrant of the abdominal cavity. In the living subject, the liver is reddish brown in colour, soft in consistency, and very friable. It weighs about 1600 g in males and about 1300 g in females.
Location
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| Location of liver |
The liver occupies the whole of the right hypo- chondrium, the greater part of the epigastrium, and extends into the left hypochondrium reaching up to the left lateral line. From the above it will be obvious that most of the liver is covered by ribs and costal cartilages, except in the upper part of the epigastrium where it is in contact with the anterior abdominal wall. The liver is the largest gland in the body. It secretes bile and performs various other metabolic functions. The liver is also called the 'hepar' from which we have the adjective 'hepatic' applied to many structures connected with the organ.
EXTERNAL FEATURES
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| Liver seen from the front |
The liver is wedge-shaped. It resembles a four-sided nyramid laid on one side.
Five Surfaces
It has five surfaces. These are:
1 Anterior,
2Posterior,
3 Superior,
4 Inferior, and
5 Right.
Out of these the inferior surface is well defined because it is demarcated, anteriorly, by a sharp inferior border. The other suffaces are more or less continuous with each other and are imperfectly separated from one another by ill-defined, rounded borders.
One Prominent Border
The inferior border is sharp anteriorly where it separates the anterior surface from the inferior surface. It is somewhat rounded laterally where it separates the right surface from the inferior surface. The sharp anterior part is marked by:
a. An interlobar notch or the notch for the ligamentum teres
b. A cystic notch for the fundus of the gallbladder.
In the epigastrium, the inferior border extends from the left 8th costal cartilage to the right 9th costal cartilage.
Two Lobes
The liver is divided into right and left lobes by the attachment of the falciform ligament anteriorly and superiorly; by the fissure for the ligamentum teres inferiorly; and by the fissure for the ligamentum venosum posteriorly.
The right lobe is much larger than the left lobe, and forms five sixth of the liver. It contributes to all the five surfaces of the liver, and presents the caudate and quadrate lobes
The caudate lobe is situated on the posterior surface. It is bounded on the right by the groove for the inferior vena cava, on the left by the fissure for the ligamentum venosum, and inferiorly by the porta hepatis. Above it is continuous with the superior surface. Below and to the right, just behind the porta hepatis, it is connected to the right lobe of the liver by the caudate process. Below and to the left it presents a small rounded elevation called the papillary process.
The quadrate lobe is situated on the inferior surface, and is rectangular in shape. It is bounded anteriorly by the inferior border, posteriorly by the porta hepatis, on the right by the fossa for the gallbladder, and on the left by the fissure for the ligamentum teres.
The porta hepatis is a deep, transverse fissure about 5 cm long, situated on the infernor surface of the right tobe of the tiver, In res between the caudate lobe above and the quadrate lobe below and in front. The portal pein, the hepatic artery and the hepatic plexus of nertes enter the liver through the porta hepatis, while the right and left hepatic ducts and a few lymphatics leave it.The relations within, the porta hepatis are from behind forwards are the portal vein, the hepatic artery and the hepatic ducts. The lips of the porta hepatis provide attachment to the lesser omentum. The left lobe of the liver is much smaller than the right lobe and forms only one-sixth of the liver. It is flattened from above downwards. Near the fissure for the ligamentum venosum, its inferior surface presents a rounded elevation, called the omental tuberosity or tuler omentale.
Relations
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| Relations of the inferior surface of the liver |
Peritoneal Relations
Most of the liver is covered by peritoneum. The areas not covered by peritoneum are as follows.
1 A triangular bare area, on the posterior surface of the right lobe, limited by the superior and inferior layers of the coronary ligament and by the right triangular ligament.
2 The groove for the inferior vena cava, on the posterior surface of the right lobe of the liver, between the caudate lobe and the bare area.
3 The fossa for the gallbladder which lies on the inferior surface of the right lobe to the right of the quadrate lobe.
4 The area of attachment of lesser omentum and the fissure for attachment of ligamentum venOsum.
Visceral Relations
Anterior surface
The anterior surface is triangular and slightly convex: It is related to the xiphoid process and to the anterior abdominal wall in the median plane, and to diaphragm on each side. The diaphragm separates this surface from the pleura above the level of a line drawn from the xiphisternal joint to the 10th rib in the midaxillary line; and from the lung above the level of a line from the same joint to the 8th rib. The falciform ligament is attached to this surface a little to the right of the median plane.
Posterior surface
The posterior surface is triangular. Its middle shows a deep concavity for the vertebtal column. Other relations are as follows.
1 The bare area is related to the diaphragm; and to the right suprarenal gland near the lower end of the groove for the inferior vena cava.
2 The groove for the inferior vena cava lodges the upper part of the vessel, and its floor is pierced by the hepatic veins.
3 The caudate lobe lies in the superior recess of the lesser sac. It is related to the crura of the diaphragm above the aortic opening, to the right inferior phrenic artery, and to the coeliac trunk.
4 The fissure for the ligamentum venosum is very deep and extends to the front of the caudate lobe. It contains two layers of the lesser omentum. The ligamentum venosum lies on its floor. The ligamentum venosum is a remnant of the ductus venosus of foetal life; it is connected below to the left branch of the portal vein, and above to the inferior vena cava.
5 The posterior surface of the left lobe is marked by the oesophageal impression.
Superior surface
The superior surface is quadrilateral and shows a concavity in the middle. This is the cardiac impression On each side of the impression, the surface is convex to fit the dome of the diaphragm. The diaphragm separates this surface from the pericardium and the heart in the middle; and from pleura and lung on each side.
Inferior surface
The inferior surface is quadrilateral and is directed downwards, backwards and to the left. It is marked by impressions for neighbouring viscera as follows.
1 On the inferior surface of the left lobe there is a large concave gasTIC impression. The left lobe also bears a raised area that comes in contact with the lesser omentum: it is called the tuber omentale.
2 The fissure for the ligamentum teres passes from the inferior border to the left end of the porta hepatis. The ligamentum teres represents the obliterated left umbilical vein.
3 The quadrate lobe is related to the lesser omentum, the pylorus, and the first part of the duodenum. When the stomach is empty the quadrate lobe is related to the first part of the duodenum and to a part of the transverse colon. 4 The fossa for the gallbladder lies to the right of the quadrate lobe.
5 To the right of this fossa the inferior surface of the right lobe bears the colic impression for the hepatic flexure of the colon, the renal impression for the right kidney, and the duodenal impression for the second part of the duodenum.
Right surface
The right surface is quadrilateral and convex. It is related to the diaphragm opposite the 7th to 11th ribs in the midaxillary line. It is separated by the diaphragm from the pleura up to the 10th rib, and from the lung up to the 8th rib. Thus, the upper one-third of the urface is related to the diaphragm, the pleura and the lung, the middle one-third, to the diaphragm and the Costodiaphragmatic he-third to the diaphragm alone recess of the pleura ; and the lower The liver receives 20% of its blood supply through the hepatic artery, and 80% through the portal vein. Before entering the liver, both the hepatic artery and the portal vein divide into right and left branches. Within the liver, they redivide to form segmental vessels which further divide to form interlobular vessels which run in the portal canals. Further ramifications of the interlobular branches open into the hepatic sinusoids. Thus the hepatic arterial blood mixes with the portal venous blood in the sinusoids. There are no anastomoses between adjoining hepatic arterial territories and hence each branch is an end artery.
Venous Drainage
Hepatic sinusoids drain into interlobular veins, which join to form sublobular veins. These in turn unite to form the hepatic veins which drain directly into the inferior vena cava. These veins provide great support to the liver, besides the intra-abdominal pressure. The hepatic veins are arranged in two groups: upper and lower. The upper group consists of three large veins: right, left and middle, which emerge through the upper part of the groove for the inferior vena cava, and directly into the vena cava. These veins keep the liver suspended. The lower group consists of a variable number of small veins from the right lobe and the caudate lobe which emerge through the lower part of the caval Microscopically, the tributaries of hepatic veins, ie central veins are seen as separate channels from those of the portal radicles . open groove pue open into the vena cava.
Lymphatic Drainage
The superficial lymphatics of the liver run on the surface of the organ beneath the peritoneum, and terminate in caval, hepatic, paracardial and coeliac lymph nodes. Some vessels from the coronary ligament may directly join the thoracic duct. The deep lymphatics end partly in the nodes around the end of the inferior vena cava, and partly in the hepatic nodes.
Nerve Supply
The liver receives its nerve supply from the hepatic plexus which contains both sympathetic and parasympathetic or vagal fibres. Nerves also reach the liver through its various peritoneal ligaments.
HEPATIC SEGMENTS
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| The segments of liver |
On the basis of the intrahepatic distribution of the hepatic artery, the portal vein and the biliary ducts, the liver can be divided into the right and left functional lobes. These do not correspond to the anatomical lobes ated by a plane passing on the anterosuperior surface along a line joining the cystic notch to the groove for the inferior vena cava. On the inferior surface, the plane passes through the fossa for the gallbladder; and on the posterior surface it passes through the middle of the of the liver. The physiological lobes are sepa caudate lobe. The right lobe is subdivided into anterior and posterior segments, and the left lobe into medial and lateral segments. Thus there are four segments in the liver.
a. Right anterior (V and VIII),
b. Right posterior (VI and VII),
c. Left lateral (II and III) and
d. Left medial (I and IV).
The hepatic segments are of surgical importance The hepatic veins tend to be intersegmental in their course
FUNCTIONS
Liver is an indispensable gland of the body.
1. Metabolism of carbohydrates, fats and
2. Synthesis of bile and prothrombin
3.Excretion of drugs, toxins, poisons, cholesterol, bile pigments and heavy metals
4.Protective by conjugation, destruction, phagocytosis, antibody formation and excretion
5. Storage of glycogen, iron, fat , vitamin A and D.
HISTOLOGY
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| Histology of liver |
Liver is covered by Glisson's capsule. In the are hexagonal lobules with portal radicles at 3-5 corners. Each radicle contains bile ductule, branch each of portal vein and hepatic artery. Central vein lies in the centre and all around the central vein are the hepatocytes in form of laminae. On one side of the lamina is the sinusoid and on the other side is a bıle canaliculus. Portal lobule seen in human is triangular in shape with three central veins at the sides and portal tract in the centre. The liver acinus is defined as the liver parenchyma around a preterminal branch of hepatic arteriole between two adjacent central veins. The liver acinus is the functional unit of liver. Blood reaches the acinus via branches of portal vein and hepatic artery to open into the sinusoids to reach the central vein On the other hand, the flow of bile is along bile canaliculi, bile ductules and the interlobular bile ducts Hepatocytes in zone I close to preterminal branch are better supplied by oxygen, nutrients and toxins The liver cells in zone III close to central veins are relatively hypoxic while cells in zone II are intermediate in oxygen supply.Histology of the liver can be studied by liver biopsy which is done from right lateral surface.
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