8: Liver

Liver: anatomy, microscopic structure, and cell types

Maria Westerhoff and Laura Lamps

University of Michigan, Ann Arbor, MI, USA


Embryologically, the primordial liver first appears toward the end of gestational week 3. It derives from an outpouching of the foregut called the “hepatic diverticulum.” This diverticulum has cranial and caudal buds; the cranial portion grows into the septum transversum and becomes the right and left liver lobes as well as the intrahepatic bile duct structures. The caudal aspect becomes the gallbladder and cystic duct. The stalk of the diverticulum connecting the developing liver and foregut narrows, forming the extrahepatic biliary system (Figure 8.1). The endodermal cells of the diverticulum that form the hepatic parenchyma and the intrahepatic duct structures are called “hepatoblasts.”

The vascular network is originally derived from both the vitelline and umbilical veins. The hepatoblast cords enmesh the vessels, forming the hepatic sinusoids. By week 5, most of the major vessels are identifiable, including the right and left umbilical veins, the transverse portal sinus, and the ductus venosus (Figure 8.2). The portal vein develops from the vitelline veins and then subdivides into the right and left branches (Figure 8.3).

The bile canaliculi are first seen as intercellular spaces between hepatoblasts at gestational week 6. They eventually become linked to the extrahepatic biliary system via the intrahepatic bile ducts. Intrahepatic bile ducts develop from the “ductal plate,” primitive duct structures formed by a layer of hepatoblasts that surround the portal tracts (Figure 8.4).

Of note, extramedullary hematopoiesis is prominent in the liver during fetal development; the red blood cell precursors are present mostly in the parenchyma (Figure 8.5) while myeloid and megakaryocytic precursors are particularly more evident within the portal tracts.

Hemosiderin is usually visible in early stages and becomes most marked as intrahepatic hematopoiesis decreases. Hemosiderin then gradually decreases but may still be seen at birth in the periportal hepatocytes. The Kupffer cells appear by the third gestational month.

Gross anatomy

The weight of the adult liver varies from 1200 to 1800 g, depending on the overall body size. The liver has four anatomical lobes: right, left, caudate, and quadrate (Figures 8.6 and 8.7). Functionally, the liver is divided based on the branching pattern of the portal structures (portal vein, hepatic, artery, and bile duct). This creates a total of eight functional segments, each demarcated by their own vascular and biliary drainage (see Figure 8.2).

The portal vein is formed by the convergence of the superior mesenteric and splenic veins. The hepatic vein is composed of three major tributaries (right, middle, and left), while the hepatic artery ascends along the hepatoduodenal ligament and eventually divides into the right and left main branches. The biliary drainage of the right lobe is derived from anterior and posterior segmental duct branches that merge to form the right hepatic duct. Lateral and medial segmental branches merge to form the left hepatic duct, which drains the left lobe. The intrahepatic components of these vessels and ducts follow along the varous hepatic segments (Figure 8.8).


The classic Rappaport acinus concept can be appreciated under the light microscope. It subdivides the parenchyma into zones 1 (periportal), 2 (between periportal and pericentral/perivenular), and 3 (area around hepatic venule), with decreasing oxygenation and increasing susceptibility to ischemia and toxic/drug‐induced injury toward zone 3. Biliary drainage runs parallel to the vascular sinusoidal circulation (Figure 8.9).

The portal tract (Figure 8.10) includes a portal venule, an interlobular bile duct, and a hepatic arteriole of the same size as the duct. The hepatic artery is responsible for the blood supply of the bile duct. The fibrous tissue surrounding the portal structures varies in amount depending on the distance of the portal tract from the hepatic hilum. This is important in the determination of how much pathological fibrosis is present in staging a liver biopsy.

Schematic illustration of developing embryo.

Figure 8.1 Developing embryo. (a) The drawing represents a 9 mm embryo, estimated at about 36 days of gestation. The liver is derived from the hepatic diverticulum (midline outgrowth stalk of the distal foregut) and projects cranially into the septum transversum and caudally into the abdominal wall. (b) The drawing represents an embryo that is slightly older, with the falciform ligament noted between the hepatic parenchyma and the anterior abdominal wall.

Source: Langman J. Medical Embryology, 2nd edn. Baltimore, MD: Williams & Wilkins, 1969. Reproduced with permission of Wolters Kluwer Health. Illustrated by Robin Kunkel.

Schematic illustration of anatomical and functional subdivisions.

Figure 8.2 Anatomical and functional subdivisions. The liver is divided into eight functional anatomical segments, each having its own vascular flow and biliary drainage. The caudate lobe is segment I. Segments II and III are the left lobe lateral subdivisions, while segment IV is the left lobe’s medial subdivision. The quadrate lobe is considered a part of segment IV, deemed IVb. The right lobe is subdivided into lateral (segments VI and VII) and medial (segments V and VIII) divisions.

Source: Moore KL, Dalley AF II. Clinically Oriented Anatomy, 4th edn. Philadelphia: Lippincott, Williams & Wilkins, 1999. Reproduced with permission of Wolters Kluwer Health. Illustrated by Robin Kunkel.

Schematic illustration of intrahepatic branches of the portal vein.

Figure 8.3 Intrahepatic branches of the portal vein.

Source: Adapted from Skandalakis LJ, Colborn GL, Gray SW, et al. Surgical anatomy of the liver and extrahepatic biliary tract. In: LM Nyhus, RJ Baker (eds.). Mastery of Surgery, 2nd edn. Boston, MA: Little, Brown; 1992.

Photo depicts embryonic development of the duct plate.

Figure 8.4 Embryonic development of the duct plate. Ductal plates form by invasion of hepatoblasts into the portal mesenchyme.

The hepatic lobules (Figure 8.11

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Nov 27, 2022 | Posted by in GASTROENTEROLOGY | Comments Off on 8: Liver

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