Lecture 12 - Anatomy (Anatomy - histology of the exocrine foregut) Week 7 PDF

ANATOMY & HISTOLOGY OF THE LIVER & BILIARY SYSTEM Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & A...

ANATOMY & HISTOLOGY OF THE LIVER & BILIARY SYSTEM Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & Abrahams Clinical Atlas of Anatomy, Human Anatomy Colour Atlas & Textbook [email protected] Goal: Understand the anatomy & histology of the excretory organs of the foregut, & relate their structure to their respective functions Outline: Outcomes: Lobes & ligaments of the liver Describe the difference between the anatomical and functional lobes of the liver. Identify and describe the series of ligaments of the coronary ligament Histology of liver lobules and (ventral mesogastrium), which connect the stomach and liver to the cells anterior body wall. Describe the flow of bile and blood through the liver, in relation to the The ducts of the biliary system liver lobules, triads and central veins. Identify and describe the features of the liver, gall bladder and pancreas Histology of the gall bladder in histological sections, and relate their respective features to their specific functions. Histology of the EXOCRINE Identify and define the different sections of bile duct from left and right hepatic to common bile and pancreatic ducts, relating this to the pancreas embryological development of the hepatic diverticulum. The Liver: Explained via the coronary ligament Anterior end: Falciform ligament… Posterior end: Lesser omentum… Surrounds the ‘bare area’ Creates the 4 ‘anatomical’ lobes: Left & Right, Caudate & quadrate lobes Anterior component: Starts where falciform separates & attaches to diaphragm Peritoneum of falciform lig continues laterally to form left / right triangular lig. Posterior component: Formation of the lesser omentum From the triangular ligaments: Left coronary will form left side of lesser omentum Right coronary: Moves anteriorly to IVC: IVC impression creates caudate lobe Encompasses porta hepatis Quadrate lobe: created by gallbladder impression and Lig. Teres Joins the left coronary lig, Where the Round lig. dives deeper into liver tissue Functional anatomy of the liver 4 anatomical lobes: Left & Right, Caudate & quadrate lobes 8 Functional segments (*don’t need to memorise each!*) Defined by portal triads = Hepatic artery, portal vein, and bile duct Each a branch of original Porta Hepatis structure 2 functional lobes defined by the Principal Line Traces the line of the middle hepatic vein Imaginary line roughly from gall bladder fossa  IVC Important surgical consideration Histology of the liver Overview: An unusual exocrine gland No secretory units as in salivary glands/pancreas Organised plates of hepatocyte parenchyma Outer fibrous CT capsule continuous with inner stroma Not much CT in human liver Contains BVs, nerves, lymphatics, bile ducts Sinusoidal capillaries (sinusoids…) Vascular channels between plates of hepatocytes All cells in contact with blood, many products delivered directly into bloodstream Hexagonal lobules: aren’t clearly defined Reflect the joining of the porto-caval systems 2 vascular inputs & 2 outputs (1 vasc. / 1 excretory) Triads are at peripheral corners (3 of the above) Portal vein, Hepatic artery, Bile duct Central vein (CV) part of Hepatic veins (Caval; output) Lobule concepts Blood & bile move in opposite directions Blood (portal venous & hepatic arterial): Triad  CV Bile: Hepatocytes around CV  Triads Bile canaliculi run between hepatocytes to bile ducts of the triads Canaliculi spaces between neighbouring hepatocytes Bile ducts in triads are lined with simple cuboidal epithelium Lobule concept based on central drainage with CT partitions Each portal triad supplies portal venous blood & afferent hepatic arterial blood towards 3 central veins ‘Classical’ lobule idea outlines the flow to & from a central vein Concerned mainly with venous drainage ‘Portal’ lobule idea outlines the flow to & from a ‘centralised’ triad Concerned mainly with bile drainage to a centralised triad Blood from centralised triad can flow towards one of the 3 CVs nearby Liver Acinus: Emphasises the secretory function of the liver Zones with respect to portal axis Short axis: Line joining two triads Long axis: Line joining two CVs Important in disease processes and recovery 3 zones defined by proximity to hepatic arterioles Zone 1: Closest Cells are last to die if circulation is impaired & first to regenerate First to show morphological changes after bile duct occlusion Metabolic gradient exists between zones for many hepatic enzymes Zone 2: Intermediate transitional zone Zone 3: Furthest from hepatic arterioles First to show ischemic necrosis & fat accumulation Last to respond to toxic substances Site of drug & alcohol detoxification Hepatocytes ~80% of cells in the liver Separated from bloodstream by discontinuous simple squamous Large polyhedral cells with large round nuclei epithelium of the sinusoids Secrete bile (up to ~1L/day) Space between hepatocytes and epithelial cells: Apical surface has microvilli Narrow perisinusoidal space (of Disse) Bile canaliculi run between neighbouring hepatocytes Plasma can freely enter through openings in sinusoids Tight junctions between cells Macrophages (Kupffer cells) attached to epithelium Stellate cells: Role in regeneration & Vit A storage & transport Can’t see in H&E, need special stain Images from Yale medical school Importance of liver capsule Liver is covered with visceral peritoneum Except for where it contacts the diaphragm directly: Bare area Provides external support and shape to the liver Liver has jelly-like consistency Capsule continuous with CT of porta hepatis Supports internal vessels Capsule contains its own blood & lymphatic supply Connects with parenchyma of liver and supporting CT Subcapsular hepatic hematomas Liver is a large, highly vascular, blood reservoir Earliest haematopoietic organ in embryonic development Capsule can contain bleeding  rupture is life threatening Mostly from blunt and penetrating traumas Also a complication of preeclampsia, or parasitic infection Anatomy: Biliary system An outpouching system of the foregut, mostly derived from the hepatic diverticulum Bile is: Made in the liver, Stored in the gallbladder Released into duodenum  Emulsifies dietary fats Energetic efficiency Reabsorbed through colon Transported back to liver via portal system Components are specific Right & Left hepatic ducts Common HEPATIC duct Cystic duct Common bile duct Main pancreatic duct May have an accessory pancreatic duct Major duodenal papilla Histology of the Gall bladder Concentrates bile by reabsorbing fluid Bile is ~97% water and ~0.5-1% bile salt Fills due to vacuum pressure Empties using SM contraction, via cystic duct  Common bile duct Simple columnar epithelium with microvilli Helps with water reabsorption NO mucous cells (relate structure to function) Some mucous glands near the neck More common in inflamed GBs Highly folded mucosa, when not full No muscularis mucosa, or submucosa Thin outer fibromuscular coat Irregular orientation of muscular bands Can have adventitia on one side and serosa on the other Think about the gross anatomy Histology of the Exocrine Pancreas No distinct outer capsule, surrounded by a thin layer of CT only Exocrine pancreas is a series of tubuloacinar glands Lobules with serous secretory units (acini) Very short intralobular ducts Apical cytoplasm full of secretory vesicles Precursors of digestive enzymes First portion of duct system extends into centre of acini lined by centroacinar cells: first part of intercalated ducts Flattened cuboidal epithelium Intercalated ducts: Low cuboidal epithelium No striated ducts in the pancreas: No sodium & bicarbonate reabsorption Result?... Intercalated  Intralobular  interlobular duct (columnar epithelium) Interlobular ducts  Pancreatic duct (‘tall’ columnar epithelium) Different types of ducts Different types of pancreatic ducts