Lecture 3 Histology GIT 3 (Liver) PDF

Faculty of Medicine Medical Education- Damietta University Level 2 Semester 3  Learning Outcomes By the end of the lecture, the students will be able to: 1. Define the concept of the classic liver lobule 2. Identify the structure of the hepatocytes...

Faculty of Medicine Medical Education- Damietta University Level 2 Semester 3  Learning Outcomes By the end of the lecture, the students will be able to: 1. Define the concept of the classic liver lobule 2. Identify the structure of the hepatocytes and other cells of the liver; Kupffer cells, endothelial cells and Ito cells. 3. Identify histological features of the gallbladder  Fatty liver disease is a reversible condition in which large lipid droplets containing triglycerides accumulate abnormally in hepatocytes via the process called steatosis. This disorder has multiple causes, but it occurs most commonly in individuals with alcoholism or obesity. Q1: What is wrong with fatty liver?  OVERVIEW OF THE LIVER The largest internal organ. The largest mass of glandular tissue in the body. The liver’s unique histologic organization and microvasculature allow hepatocytes to perform their diverse metabolic exocrine, and endocrine functions. Plays an important role in the uptake, storage, and distribution of nutrients. Produces the majority of circulating plasma proteins (e.g., albumins), stores iron, Converts vitamins, and degrades drugs and toxins. Acts as an exocrine organ (produces bile) performs endocrine-like functions by its ability to modify the structure and function of many hormones.  Histological organization of the liver: A. Stroma. 1. Capsule: thin connective tissue capsule called (Glisson's capsule). 2. Trabeculae (Septa): connective tissue septa extend from the capsule divided the liver into lobules. 3. Reticular network B. Parenchyma: The hepatic lobule is the main functional and structural unit of the liver, three main models of liver lobulation are present: 1-Classical hepatic lobule 2-Portal lobule 3-Hepatic acinus  1-Classical hepatic lobule Hexagonal in cross section, with a central vein at the center and portal areas (canal or triad) at the corners. The liver consists of about 1 million such units. Within each lobule, hepatocytes are arranged into branching and anastomosing plates (hepatic cords ) each plate thickness formed of two rows cells separated by adjacent blood sinusoids 1-Classical hepatic lobule portal areas (canal or triad) portal vein, hepatic artery and bile duct  Hepatocytes Constitute 80% of liver cells. Hepatocytes are long-lived for cells average life span is about 5 months. LM: ✓Large Polyhedral cell central rounded nucleus. ✓25% of hepatocytes are binucleated. ✓The cytoplasm of hepatocytes is acidophilic(due to SER, mitochondria) & vacoulated (due to glycogen) Hepatocytes EM The cell membrane of the hepatocytes: 1. Facing blood sinusoidal showing long microvilli. 2. Facing bile canaliculus showing short microvilli. 3. Facing adjacent hepatocytes showing junctional complex. The nucleus is euchromatic with prominent nucleolus. ✓The hepatocyte is a very active cell. It is very rich in most of the cell. 1. Mitochondria are numerous (up to 1000 in each cell). Responsible for the energy requirements for the metabolic activities. 2. Well developed RER. Synthesizes both plasma proteins and the protein part of lipoprotein 3. Free ribosomes responsible for the synthesis of the intrinsic proteins used by the cell. 4. Well developed SER. Forms the lipid portion of lipoprotein. Responsible for detoxification of alcohol and toxic drugs. 5. Golgi apparatus is located around the nucleus. Plasma proteins and lipoprotein are packaged into secretory vesicles. 6. Peroxisomes are numerous in hepatocytes. Responsible for : 1. Breakdown of fatty acids. 2. Detoxification of alcohol. 7. Lysosomes are occasionally seen in the cytoplasm. 8. Glycogen granules and lipid vacuoles are usually present in large numbers. Hepatic blood Sinusoids: ✓They are irregular blood spaces between adjacent plates of hepatocytes. ✓They are lined by : 1. Fenestrated endothelial cells on a discontinuous basal lamina. 2. Kupffer cells (sinusoidal macrophage). Hepatic blood Sinusoids:  The space of Disse or perisinusoidal space. -Site: lies between the basal surfaces of hepatocytes and the basal surfaces of endothelial cells and Kupffer cells that line the sinusoids.  The space of Disse or perisinusoidal space. It contains : 1. The blood plasma. 2. Von Kupffer cells (hepatic macrophages) 3. Ito cells ( fat storing cells ) (hepatic stellate cell ) NB: Microvilli project into this space from the basal surface of the hepatocyte increase the surface area available for exchange of materials between hepatocytes and plasma by as much as six times. The space of Disse or perisinusoidal space.  Blood supply of the liver: The liver has a dual blood supply: Branches of the hepatic artery carry oxygenated blood and provide about 20% of the blood flow within hepatic sinusoids. In contrast, branches of the portal vein carry nutrient rich blood from the G.I.T and contribute the remaining 80% of the sinusoidal blood flow.  Flow of blood and bile The direction of bile flow is opposite that of the blood flow. The direction of blood flow from the periphery to the centre. The direction of bile flow from the centre to the periphery.  THE PORTAL LOBULE ✓It is triangular in shape and contains parts of 3 adjacent hepatic lobules. ✓A portal canal at its center. ✓A central vein is located at each corner of this unit. ✓The bile produced by hepatocytes flows in a direction opposite that of blood toward the periphery of the classic hepatic lobule.  Hepatic acinus Diamond-shaped structure between two classic lobule organized around central vascular core (terminal branches of the hepatic artery) Cells at the center of the acinus are the first to receive blood, and cells located towards the periphery are the last to receive blood. Zone 1 : is closest to the blood supply from penetrating branches of the portal vein and hepatic artery. This zone corresponds to the periphery of the classic lobules. Zone 2 : lies between zones 1 and 3. Zone 3 : is closest to the central vein. This zone corresponds to the most central part of the classic lobules.  The zonation is important in the description and interpretation of patterns of degeneration, regeneration, and specific toxic effects in the liver parenchyma relative to the degree or quality of vascular perfusion of the hepatic cells. Cells in zone 1 are the first to receive oxygen, nutrients , and toxins from the sinusoidal blood. These cells are also the last to die if circulation is impaired and the first to regenerate.  On the other hand, cells in zone 3 are the first to show ischemic necrosis (centrilobular necrosis) in situations of reduced perfusion. They are the last to respond to toxic substances Cells in zone 2 have responses intermediate to those of zones 1 and 3. Bile canaliculi and bile ducts: Bile (produced by hepatocytes) is collected by the bile canaliculi and drains to the canals of Hering. From there, it continues to flow into the interlobular bile ducts (part of the portal triad). ✓ Interlobular ducts fuse together to form the left and right hepatic ducts that exit the liver. ✓ Common hepatic duct (formed by union of the left and right hepatic ducts ) carry the bile to the gallbladder.  The gallbladder is a pear-shaped, distensible sac that concentrates (removes 90% of water) and stores bile. Common bile duct formed by union of (common hepatic duct+ cystic duct from the gallbladder ). The common bile duct join pancreatic duct and open in the 2nd part of duodenum controlled by sphincter of Oddi.  GALL BLADDER 1-The mucosa: a) Simple columnar epithelium b) lamina propria. c) No muscularis mucosa. 2-NO Submucosa : in the gallbladder. 3-Musculosa : interlacing bundles of smooth muscle that spiral around the lumen of the gallbladder. 4-The serosa. The tall epithelial cells (cholangiocytes) exhibit the following features: a) Numerous short apical microvilli. b) Apical junctional complexes that join adjacent cells and form a barrier between the lumen and the intercellular compartment. c) Mitochondria in the apical and basal cytoplasm. NB Contraction of the smooth muscle in musculosa reduces the volume of the bladder, forcing its contents out through the cystic duct.  A human liver. The lobules of the human A pig liver with thick liver lack connective tissue septa. The plates interlobular connective of hepatocytes of one lobule merge with tissue septa (stained blue) those of adjacent lobules. The boundaries of surrounding the lobules. a lobule can be approximated, however, by The central vein is visible drawing a line (dashed line) from one portal in the center of the canal to the next, thus circumscribing the lobule. lobule.  Fatty liver disease is a reversible condition in which large lipid droplets containing triglycerides accumulate abnormally in hepatocytes via the process called steatosis. This disorder has multiple causes, but it occurs most commonly in individuals with alcoholism or obesity. Q1: What is wrong with fatty liver? Accumulation of fat in hepatocytes may produce a progressive inflammation of the liver, or hepatitis, in this case called steatohepatitis. Questions The space of Disse is located between: A. blood sinusoids and central vein. B. blood sinusoids and hepatic artery. C. blood sinusoids and liver cells. D. adjacent liver cells. E. liver cells and bile canals. Blood flow in liver lobules passes along sinusoids from the: A. central vein to the portal vein. B. hepatic artery and portal vein to the central vein. C. central vein to the hepatic artery. D. hepatic vein to the portal vein. E. portal vein to portal duct.