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Other Terms: Hepar, Foie, Leber, Hígado, Fegato, Atay
The liver is the largest gland and internal organ of the body. It has both endocrine and exocrine secretions, which are formed in the hepatic cells. Its exocrine secretion, bile, is collected after passing through the bile capillaries by the bile ducts. The bile ducts unite to form the hepatic duct. The bile is either carried to the gallbladder by the cystic duct or poured directly into the duodenum by the common bile duct where it emulsifies fats. The endocrine secretionsare concerned with the metabolism of both nitrogenous and carbohydrate materials absorbed from the intestine and carried to the liver by the portal vein. The carbohydrates are stored in the hepatic cells in the form of glycogen which is secreted in the form of sugar directly into the blood stream. Some of the cells lining the blood capillaries of the liver are involved in the destruction of red blood cells. It is situated in the upper and right parts of the abdominal cavity, occupying almost the entire space of the right hypochondriac region, the greater part of the epigastric region, and not uncommonly extending into the left hypochondriac. In the male it weighs 1.4-1.6 kilograms. In the female, it weighs 1.2-1.4 kilograms. Its great transverse measurement is from 20-22.5 centimeters. Near its lateral surface, it measures about 15-17.5 centimeters. Its greatest anteroposterior diameter is on a level with the upper end of the right kidney and is from 10-12.5 centimeters.
The larger portion of the liver lies in the right hypochondriac region. The anterior margin of the right lobe projects about one centimeter below the costal border. During respiration, it can be felt moving upward and downward with the diaphragm, to which it is attached. This border is not as easily recognized as the anterior margin of the left lobe, which extends across the epigastric region, below the xiphoid process and is pushed prominently forward by the stomach when it is distended. The liver ascends as high as the right dome of the diaphragm, which conforms to its upper surface. It extends within two and a half centimeters of the level of the nipple, and to a position opposite the lower end of the body of the sternum. At the side of the spinal column, the liver approaches the surface at the level of the tenth and eleventh thoracic spines, or at the posterior part of the base of the lung. The liver is in relation above with the diaphragm and the anterior abdominal wall. Below it is the stomach, the lesser omentum, the gall-bladder, the right colic flexure of the colon, the right kidney, and the first and second portions of the duodenum. Behind it, is the lower end of the esophagus, the right suprarenal gland, the aorta and inferior vena cava, the crura of the diaphragm, the tenth and eleventh thoracic vertebrae, and the structures just mentioned as being below it. In front of it are the diaphragm and the anterior abdominal wall. The organ is held in place by five ligaments: the ligamentum teres, the falciform, the right and the left triangular, and the coronary. The ligamentum teres consists of the obliterated umbilical vein. The others are reflections of the peritoneum. The structural arrangement of the liver is comparable to clusters of grapes so closely packed together that the mutual pressure would give the fruit a polyhedral form. Each grape represents a liver lobule through the center of which passes a vein called the central or intralobular, vein. The stems which support the grapes represent the sublobular veins into which the central veins empty. The larger stalks formed by the union of many branches represent the hepatic veins which eventually enter the inferior vena cava. The interspaces between the compressed polygonal grapes correspond to the interlobular spaces of the liver, in which are found the branches of the hepatic duct and of the afferent vessels-the portal vein and the hepatic artery. The hepatic artery and porta hepatis vein form a network around each lobule, from which small vessels penetrate the lobule, those from the artery for nourishment, and those from the portal vein to bring work. All of this is done in the short transit of blood from the periphery to the center of the lobule. This arrangement of the liver is simple, readily understood, and when once mastered is the key to a number of important pathologic facts that are otherwise difficult to remember.
The liver possesses three surfaces: superior, inferior, and posterior. A sharp, well-defined margin divides the inferior from the superior in front; the other margins are rounded. The superior surface is attached to the diaphragm and anterior abdominal wall by the falciform ligament. In the free margin of the falciform ligament is the ligamentum teres, which is the remnant of the umbilical vein. The line of attachment of the falciform ligament divides the liver into two parts, the right and left lobes. The right is much larger than the left. The inferior and posterior surfaces are divided into four lobes by fossa: the right, left, quadrate, and caudate lobes. The superior surface comprises a part of both lobes, and, as a whole is convex and fits under the vault of the diaphragm. The diaphragm separates it on the right from the sixth to the tenth ribs and their cartilages, and on the left from the seventh and eight costal cartilages. Its middle part lies posterior to the xiphoid process. Behind this, the diaphragm separates the liver from the lower part of the lungs and pleura, the heart and pericardium and the right costal arches from the seventh to the eleventh inclusive. It is completely covered by peritoneum except along the line of attachment of the falciform ligament. The inferior surface is uneven, concave, directed inferior, posterior, and to the left. It is in relation with the stomach and duodenum, the right colic flexure, and the right kidney and adrenal gland. The surface is almost completely invested by peritoneum. The only parts devoid of peritoneum are where the gallbladder is attached to the liver and at the porta hepatis where the two layers of the lesser omentum are separated from each other by the blood vessels and ducts of the liver. The gastric impression is on the inferior surface of the left lobe. It is molded over the antero-superior surface of the stomach. The under surface of the right lobe is divided into two unequal portions by the impression for the gallbladder. The portion to the left, the smaller of the two, is the quadrate lobe. It is in relation with the pyloric end of the stomach, the superior portion of the duodenum, and the transverse colon. The portion of the under surface of the right lobe to the right of the impression for the gallbladder presents two impressions, one located behind the other, and separated by a ridge. The anterior of these two impressions is the colic impression. It is shallow and is produced by the right colic flexure. The posterior of the impressions is the renal impression. It is deeper and is occupied by the upper part of the right kidney and lower part of the right adrenal gland. Medial to the renal impression is the duodenal impression. Just anterior to the inferior vena cava is a narrow strip of liver tissue, the caudate process. This process connects the right inferior angle of the caudate lobe to the under surface of the right lobe. It forms the upper boundary of the epiploic foramen of the peritoneum. The posterior surface is rounded and broad behind the right lobe, but narrow on the left. Over a large part of its extent, it is not covered by peritoneum. This uncovered portion is about 7.5 centimeters broad at its widest part. It is in direct contact with the diaphragm. It is marked off from the upper surface by the line of reflection of the upper layer of the coronary ligament, and from the under surface by the line of reflection of the lower layer of the coronary ligament. The central part of the posterior surface presents a deep concavity which is molded on the vertebral column and crura of the diaphragm. To the right of this, the inferior vena cava is lodged in its fossa between the uncovered area of the caudate lobe. Close to the right of this impression and immediately above the renal impression is a small triangular depressed area, the suprarenal impression, the greater part of which is devoid of peritoneum. It lodges the right adrenal gland. The left of the inferior vena cava is the caudate lobe, which lies between the fossa for the vena cava and the fossa for the ductus venosus. Its inferior end projects and forms part of the posterior boundary of the porta hepatis. On the right, it is connected with the inferior surface of the right lobe of the liver by the caudate process. Its posterior surface rests upon the diaphragm, being separated from it merely by the upper part of the omental bursa. The anterior border is thin and sharp and marked opposite the attachment of the falciform ligament by the umbilical notch.
The longitudinal fissure is a deep groove that extends from the notch on the anterior margin of the liver to the upper border o the posterior surface of the organ. It separates the right and left lobes. The porta hepatis joins it, at right angles, and divides it into two parts. The anterior part lodges the umbilical vein in the fetus and the ligamentum teres in the adult. It lies between the quadrate lobe and the left lobe of the liver. It is often partially bridge over by a prolongation of the hepatic substance. The posterior part lies between the left lobe and the caudate lobe. It lodges in the fetus, the ductus venosus and in the adult the ligamentum venosum, the obliterated remains of the ductus venosus. The porta hepatis is a short but deep fissure. It extends transversely across the under surface of the left portion of the right lobe, nearer its posterior surface than its anterior border. It joins nearly at right angles with the left sagittal fossa, and separates the quadrate lobe in front from the caudate lobe and process behind. It transmits the portal vein, the hepatic artery and nerves, and the hepatic duct and lymphatics. The hepatic duct is in front and to the right, the hepatic artery to the left, and the portal vein posterior and between the duct and artery.
The right lobe is much larger than the left. The proportion is usually six to one. It occupies the right hypochondriac region. It is separated from the left lobe on its upper surface by the falciform ligament. On its under and posterior surfaces it is separated by the longitudinal fissure. Its left part is separated into the quadrate and caudate lobes. The quadrate lobe is situated on the under surface of the right lobe. It is bound in front by the anterior margin of the liver; behind by the porta hepatis. It is oblong in shape. Its anteroposterior diameter is greater than its transverse. The caudate lobe is situated upon the posterior surface of the right lobe of the liver, opposite the tenth and eleventh thoracic vertebrae. It is bound below by the porta hepatis. It looks backward and is nearly vertical in position. The caudate process is a small elevation of the hepatic substance extending obliquely lateral, from the lower extremity of the caudate lobe to the under surface of the right lobe. It is situated behind the porta hepatis. The left lobe is smaller and more flattened than the right. It is situated in the epigastric and left hypochondriac regions. Its superior surface is slightly convex and is molded onto the diaphragm. Its under surface presents the gastric impression and omental tuberosity.
The liver is connected to the under surface of the diaphragm and to the anterior wall of the abdomen by five ligaments: falciform, coronary, two laterals, and the ligamentum teres. All of these ligaments are peritoneal folds except for the ligamentum teres. The liver is also attached to the stomach by the hepatogastric ligament and to the duodenum by the hepatoduodenal ligament. The falciform ligament is a broad and thin anteroposterior peritoneal fold. Its base is directed inferior and posterior, its apex superior and posterior. It is situated in an anteroposterior plane, but lies obliquely so that one surface faces forward and is in contact with the peritoneum posterior to the right rectus and the diaphragm. It is attached by its left margin to the under surface of the diaphragm, and the posterior surface of the sheath of the right rectus as low down as the umbilicus. By its right margin, it extends from the notch on the anterior margin of the liver, as far back as the posterior surface. It is composed of two layers of peritoneum closely united together. Its base contains between its layers the ligamentum teres and the parumbilical veins. The coronary ligament consists of an upper and a lower layer. The upper layer is formed by the reflection of the peritoneum from the upper margin of the bare area of the liver to the under surface of the diaphragm. It is continuous with the right layer of the falciform ligament. The lower layer is reflected from the lower margin of the bare area on to the right kidney and adrenal gland. It is termed the hepatorenal ligament. The triangular ligaments are two in number, right and left. The right triangular ligament is situated at the right extremity of the bare area, and is a small fold which passes to the diaphragm. The left triangular ligament is a fold that connects the posterior part of the superior surface of the left lobe to the diaphragm. Its anterior layer is continuous with the left layer of the falciform ligament. The ligamentum teres is a fibrous cord resulting from the obliteration of the umbilical vein. It ascends from the umbilicus to the umbilical notch of the liver. It becomes continuous with the ligamentum venosum on the inferior surface of the live in the porta hepatis.
Fixation of the Liver
Several factors contribute to maintain the liver in place. The attachments of the liver to the diaphragm by the coronary and triangular ligaments and the intervening connective tissue of the uncovered area help to hold up the posterior part of the liver. The intimate connection of the inferior vena cava by the connective tissue and hepatic veins also help hold up the posterior part of the liver. Some support is derived from the pressure of the abdominal viscera which completely fills the abdomen whose muscular walls are always in a state of tonic contraction. The superior surface of the liver is perfectly fitted to the under surface of the diaphragm so that atmospheric pressure alone would be enough to hold it against the diaphragm. The latter in turn is held up by the negative pressure in the thorax.
The nerves of the liver arise from the left vagus and sympathetic nerves. They enter at the porta hepatis and accompany the vessels and ducts to the interlobular spaces.
Blood Supply and Venous Drainage
The vessels connected with the liver are: the hepatic artery, the portal vein, and the hepatic veins. The hepatic artery and portal vein are accompanied by numerous nerves. They ascend to the porta hepatis, between the layers of the lesser omentum. The bile duct and the lymphatic vessels descend from the porta hepatis between the layers of the same omentum. The relative positions of the three structures are as follows: the bile duct lies to the right, the hepatic artery to the left, and the portal vein posterior and between the other two. They are enveloped in a loose connective tissue, the fibrous capsule of glisson, which accompanies the vessels in their course through the portal canals in the interior of the organ.