The<unk> , viewed from above, showing the left and right lobes separated by the falciform ligament The<unk>  is a reddish-brown, wedge-shaped organ with two lobes of unequal size and shape. A human<unk>  normally weighs approximately and has a width of about . There is considerable size variation between individuals, with the standard reference range for men being and for women . It is both the heaviest internal organ and the largest gland in the human body. Located in the right upper quadrant of the abdominal cavity, it rests just below the diaphragm, to the right of the stomach and overlies the gallbladder. The<unk>  is connected to two large blood vessels: the hepatic artery and the portal vein. The hepatic artery carries oxygen-rich blood from the aorta via the celiac trunk, whereas the portal vein carries blood rich in digested nutrients from the entire gastrointestinal tract and also from the spleen and pancreas. These blood vessels subdivide into small capillaries known as<unk>  sinusoids, which then lead to lobules. Lobules are the functional units of the<unk> . Each lobule is made up of millions of hepatic cells (hepatocytes), which are the basic metabolic cells. The lobules are held together by a fine, dense, irregular, fibroelastic connective tissue layer extending from the fibrous capsule covering the entire<unk>  known as Glisson's capsule. This extends into the structure of the<unk>  by accompanying the blood vessels, ducts, and nerves at the hepatic hilum. The whole surface of the<unk> , except for the bare area, is covered in a serous coat derived from the peritoneum, and this firmly adheres to the inner Glisson's capsule. Gross anatomy Terminology related to the<unk>  often starts in hepat- from ἡπατο-, from the Greek word for<unk> . Lobes The<unk> , viewed from below, surface showing four lobes and the impressions The<unk>  is grossly divided into two parts when viewed from above – a right and a left lobe - and four parts when viewed from below (left, right, caudate, and quadrate lobes). The falciform ligament makes a superficial division of the<unk>  into a left and right lobe. From below, the two additional lobes are located between the right and left lobes, one in front of the other. A line can be imagined running from the left of the vena cava and all the way forward to divide the<unk>  and gallbladder into two halves. This line is called Cantlie's line. Other anatomical landmarks include the ligamentum venosum and the round ligament of the<unk> , which further divide the left side of the<unk>  in two sections. An important anatomical landmark, the porta hepatis, divides this left portion into four segments, which can be numbered starting at the caudate lobe as I in an anticlockwise manner. From this parietal view, seven segments can be seen, because the eighth segment is only visible in the visceral view. Surfaces On the diaphragmatic surface, apart from a triangular bare area where it connects to the diaphragm, the<unk>  is covered by a thin, double-layered membrane, the peritoneum, that helps to reduce friction against other organs. This surface covers the convex shape of the two lobes where it accommodates the shape of the diaphragm. The peritoneum folds back on itself to form the falciform ligament and the right and left triangular ligaments. These peritoneal ligaments are not related to the anatomic ligaments in joints, and the right and left triangular ligaments have no known functional importance, though they serve as surface landmarks. The falciform ligament functions to attach the<unk>  to the posterior portion of the anterior body wall. The visceral surface or inferior surface is uneven and concave. It is covered in peritoneum apart from where it attaches the gallbladder and the porta hepatis. The fossa of gall bladder lies to the right of the quadrate lobe, occupied by the gallbladder with its cystic duct<unk> ose to the right end of porta hepatis. Impressions Impressions of the<unk>  Several impressions on the surface of the<unk>  accommodate the various adjacent structures and organs. Underneath the right lobe and to the right of the gallbladder fossa are two impressions, one behind the other and separated by a ridge. The one in front is a shallow colic impression, formed by the hepatic flexure and the one behind is a deeper renal impression accommodating part of the right kidney and part of the suprarenal gland. The suprarenal impression is a small, triangular, depressed area on the<unk> . It is located<unk> ose to the right of the fossa, between the bare area and the caudate lobe, and immediately above the renal impression. The greater part of the suprarenal impression is devoid of peritoneum and it lodges the right suprarenal gland. Medial to the renal impression is a third and slightly marked impression, lying between it and the neck of the gall bladder. This is caused by the descending portion of the duodenum, and is known as the duodenal impression. The inferior surface of the left lobe of the<unk>  presents behind and to the left of the gastric impression. This is moulded over the upper front surface of the stomach, and to the right of this is a rounded eminence, the tuber omentale, which fits into the concavity of the lesser curvature of the stomach and lies in front of the anterior layer of the lesser omentum. Microscopic anatomy Cells, ducts, and blood vessels Microscopically, each<unk>  lobe is seen to be made up of hepatic lobules. The lobules are roughly hexagonal, and consist of plates of hepatocytes, and sinusoids radiating from a central vein towards an imaginary perimeter of interlobular portal triads. The central vein joins to the hepatic vein to carry blood out from the<unk> . A distinctive component of a lobule is the portal triad, which can be found running along each of the lobule's corners. The portal triad, consists of the hepatic artery, the portal vein, and the common bile duct. The triad may be seen on a<unk>  ultrasound, as a Mickey Mouse sign with the portal vein as the head, and the hepatic artery, and the common bile duct as the ears. Histology, the study of microscopic anatomy, shows two major types of<unk>  cell: parenchymal cells and nonparenchymal cells. About 70–85% of the<unk>  volume is occupied by parenchymal hepatocytes. Nonparenchymal cells constitute 40% of the total number of<unk>  cells but only 6.5% of its volume. The<unk>  sinusoids are lined with two types of cell, sinusoidal endothelial cells, and phagocytic Kupffer cells. Hepatic stellate cells are nonparenchymal cells found in the perisinusoidal space, between a sinusoid and a hepatocyte. Additionally, intrahepatic lymphocytes are often present in the sinusoidal lumen. 2423 Microscopic Anatomy of<unk> .Microscopic anatomy of the<unk>  2104 Three Major Capillary Types.Types of capillaries–sinusoid on right 3D Medical Animation<unk>  parts.alt=3D Medical Animation Still Shot Depicting parts of<unk>  Functional anatomy Hilum of the<unk> , circled in yellow The central area or hepatic hilum, includes the opening known as the porta hepatis which carries the common bile duct and common hepatic artery, and the opening for the portal vein. The duct, vein, and artery divide into left and right branches, and the areas of the<unk>  supplied by these branches constitute the functional left and right lobes. The functional lobes are separated by the imaginary plane, Cantlie's line, joining the gallbladder fossa to the inferior vena cava. The plane separates the<unk>  into the true right and left lobes. The middle hepatic vein also demarcates the true right and left lobes. The right lobe is further divided into an anterior and posterior segment by the right hepatic vein. The left lobe is divided into the medial and lateral segments by the left hepatic vein. The hilum of the<unk>  is described in terms of three plates that contain the bile ducts and blood vessels. The contents of the whole plate system are surrounded by a sheath. The three plates are the hilar plate, the cystic plate and the umbilical plate and the plate system is the site of the many anatomical variations to be found in the<unk> . Couinaud<unk> assification system Shape of human<unk>  in animation, with eight Couinaud segments labelled In the widely used Couinaud system, the functional lobes are further divided into a total of eight subsegments based on a transverse plane through the bifurcation of the main portal vein. The caudate lobe is a separate structure that receives blood flow from both the right- and left-sided vascular branches. The Couinaud<unk> assification divides the<unk>  into eight functionally independent<unk>  segments. Each segment has its own vascular inflow, outflow and biliary drainage. In the centre of each segment are branches of the portal vein, hepatic artery, and bile duct. In the periphery of each segment is vascular outflow through the hepatic veins. The<unk> assification system uses the vascular supply in the<unk>  to separate the functional units (numbered I to VIII) with unit 1, the caudate lobe, receiving
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Kidney
Lung
Heart
Brain
Central nervous system
Breast
Peripheral nervous system