Liver and Gallbladder
I. Introduction
§ The liver is involved in many biochemical and functional processes that are vital for homeostasis
§ No temporary mechanical or biochemical backup available
II. Macroscopic Anatomy and Function
§ Liver is the largest gland in the body (1400-1600 g)
§ 2% of body weight in adults, 5% in newborns
§ completely protected the rib cage
§ divided into four lobes- right, left, caudate and quadrate
§ functionally divided into segments according to the arterial and portal blood supply
§ covered b peritoneum except at three places on its surface: ‘bare area’ small trianglular area beneath diaphragm
§ afferent and efferent vessels, nerves and ducts enter and leave the liver at the porta hapatis (aka hilum)
Major afferent vessels:
§ hepatic artery
a branch of the celiac
1/3 blood flow to liver, 70% of the oxygen
§ hepatic portal vein
2/3 blood flow to liver, 30% of the oxygen
receives blood from the splenic, superior mesenteric, inferior mesenteric v. and v. from the duodenum and stomach
§ sympathetic nerves from the hepatic plexus
Major efferent vessels and ducts:
§ hepatic veins
segmentally drain the liver
enter into the inferior vena cava
§ common hepatic duct
made up of the right and left hepatic ducts
lymphatic vessels
Functions of the Liver
§ protein synthesis (clotting factors)
§ bile production
§ glycogen storage
§ fatty acid transportation
§ drug metabolism
§ hematopoiesis (fetal and neonatal liver)
§
III. Microscopic Liver Anatomy
Glisson’s Capsule
§ connective tissue capsule that covers the entire surface of the liver
§ contains a fair number of elastic fibers
§ capsule is enclosed by serosa of simple squamous epithelium
Liver parenchyma and CT frame work
The hepatocytes
§ makeup the majority of the liver parenchyma
§ hepatocytes are arranged in sponge-like plates that in the adult are one cell thick
§ plates are separated by sinusoids
§ in children up to 5 or 6 years, the liver cells are arranged in two cell thick plates
Individual hepatocytes
§ polygonal epithelial cells
§ has a well defined plasma membrane with differentiation into basolateral (75%) and bile canalicular (25%) regions
§ nucleus is centrally located, round and contains one or more nuclei
§ binucleate forms are common
§ mitotic activity is rare in normal state
§ abundant eosinophilic cytoplam with the basophilic granules representing RER
§ cytoplasmic glycogen is present and show distributional and amount variation with diet. Glycogen deposits in nuclei in certain conditions
§ small amounts of stainable iron common in normal hepatocytes
§ lipofuscin is the wear the tear pigment seen in cytoplasm of hepatocytes in zone 3, increases in individual hepatocytes and in the number of cells involved as individuals age
Hepatic sinusoids
§ separate cords of hepatocytes
§ lined by sinusoidal lining cells (endothelial and kupffer cells) which are supported by reticulin fibers
§ RBC can be seen in the sinusoids in the normal liver
§ Endothelial cells have a thin indistinct cytoplasm and an elongated nucleus
§ Kupffer cells have a bean shaped nucleus and plump cytoplasm and star shaped extensions; belong to mononuclear phagocytic system; respond to injury in the liver with proliferation and hypertrophy
Space of Disse
§ Between the endothelial cells and the hepatocytes
§ This space contains Ito cell (fat storage) and pit cells
§ Space is not discernible in normal fixed biopsy specimens
§ Ito cells are modified resting fibroblast that can store fat and vit A and produce collagen
§ Pit cells have not been characterized by light microscopy. They may have natural killer cell activity
Portal tracts
§ Roughly triangular to round in shape and contain three major elements: bile duct, portal vein branch, hepatic artery branch
§ Also contain lymphatics, nerves, and varying amounts of inflammatory cells
§ Amount of fibroconnective tissue and size of each portal tract depends on the location
§ Size of the structures within the portal tract also depends on the location
§ Normally contain few lymphocytes and macrophages
§ Few or no plasma cells or polymorphonuclear leuckcytes
§ Number of inflammatory cells increases with age and certain liver diseases
§ The “Limiting Plate” is the distinct row of hepatocyes joined together and forming a row which surrounds the portal tract; it is destroyed by inflammation in certain diseases
Hepatic veins or central veins
§ Valveless veins which are embedded in a thin shealth of CT and the intrahepatic course drains straight into the inferior vena cava
§ Blood flow in the liver is from the portal tracts to the hepatic veins
§ Normally have only a thin collagenous wall
§ Liver cell plates run between the central veins and portal areas; normally only one hepatocyte thick and separated by sinusoids lined by flattened endothelial cells and kupffer cells
§ Portal areas have a collagenous supporting stroma within which is one portal vein branch and one hepatic artery branch.
§ Ductile or canal of Hering can sometimes be found ta the edges of portal area, but are usually inconspicuous in normal liver
§ Layer of hepatocytes closest to portal area is called the limiting plate, a useful landmark in chronic hepatitis.
Microscopic structural liver organization
The classic liver lobule
§ Consists of an efferent central vein with radiating cords of hepatocytes, radiating to several peripheral portal tracts
§ Roughly a hexagon in shape
§ Divided into 3 zones: centrilobular, midzonal, peripheral
The hepatic acinus
§ Functional unit and a regular three dimensional structure
§ Blood flows from the portal tract into the sinusoids and empties into several terminal hepatic venules at periphery of the acinus
| Roughly Corresponding Terms | |
| Acius | Lobule |
| Central vein | Terminal hepatic venule |
| Portal area | Portal area |
| Centrilobular zone | Zone 3 |
| Midzonal | Zone 2 |
| Peripheral | Zone 1 |
§ Subdivided into 3 zones: zones 1, 2, 3 with decreasing oxygentaion.
§ Hepatocytes in zone 1 are nearest B to the portal tract (peripheral)
§ Hepatocytes in zone 2 are between the hepatic venule and the portal tract (midzone)
§ Hepatoctyes in zone 3 are nearest to the hepatic venule (centrilobular)
§ Hepatic blood flow is from the portal tracts to the terminal hepatic venules; blood flows through the sinusoids
§ Hepatic bile flow is from zone 3 area to portal tracts (opposite to blood flow)
§ Bile is produced in the hepatocytea and flows into bile canaliculi.
§ Bile canaliculus is an intercellular space with a diameter of 1 micron formed by the edges of hemicanals of adjacent surfaces of two hepatocytes; they connect to the small portal tract bile ducts via canals of Hering
§ The hepatocytes in the different zones have different functions.
§ Zone 1 hepatocytes receive the best oxygenated blood
| Bile flow | Lining cell |
| Bile canaliculi | Hepatocyte |
| Canal of hering | Cuboidal epithelium |
| Interlobular bile ducts in the portal tracts | Cuboidalà columnar |
| Right and left hepatic ducts | |
| Common hepatic ducts | |
| Cystic duct | |
| Gallgladder | |
| Common bile duct |
IV. The Gallbladder anatomy and function
§ Gall bladder is a pear shaped organ that occupies an area on the posterior aspect of the right lobe of liver
§ Measure up to 10 cm by 4 cm in normal adults
§ Wall measure up to 2 mm thick and varies with the distention of the gallbladder
§ Composed of a blindly ending fundus, a central body and a narrow neck
§ Concentrates, stores, and releases bile
§ Approximately 1000 ml of bile flows into the gall bladder daily from the liver
§ Microanatomy of gall bladder includes the surface epithelium, lamina propria, smooth muscle, subserosal CT and serosa.
§ Lacks a muscularis mucosae and submucosa
§ Luminal folds are lined by columnar epithelium; single layer of columnar cells lie above a basement membrane
§ Lamina propria contains loose connective tissue; smooth muscle does not form well developed layers; only one muscularis is present
§ Adventia consists of dense CT and is continuous with Glisson’s caspsule
§ Rokitandky-Aschoff sinuses are herniations of the epithelium into the underlying layers
§ Luschka’s ducts are small bile ducts that lie in the subserosal, found in approx 10% of routine cholescystectomy specimens; may represent embryonic remnants
Tags: acinus, bile canaliculi, disse, fibroconnective tissue, gallbladder, Glisson's Capsule, hematopoiesis, hepatic, hepatic artery, hepatic plexus, hepatocytes, inferior mesenteric, lamina propria, Limiting Plate, liver, lobule, Parenchyma, portaql tracts, Rokitandky-Aschoff, sinusoids, superior mesenteric
