Liver and billiary system Histo

• Liver is enclosed in a capsule of fibrous CR > glissons capsul > covered by mesothelial layer
• Functions of Liver

  1. Vitamin A: uptake storage and blood levels
  2. Vitamin D: Metabolism by converting Vit D. to 25hydroxycholecalciferol
  3. Synthesis almost all of proteins involved in iron transport and metabolism including transferrin haptoglobin and hemopexin
• General structure of Liver:

  1. Parenchyma > plates of hepatocytes 1 cell thick and are separated by sinusoidal capillaries
  2. Stroma > continues with fibrous capsule of Glisson > bunch of innervation
  3. Sinusoisdal capillaries > vascular channles between plates of hepatocytes
  4. Peisinusoidal spaces (spaces of Disse) > between the sinusoidal endotheloum and hepatocyte
  5. Bile ducts and canaliculi
• Hepatic lobule - Hexagonal 2 x 7 mm

  Central vein (Terminal hepatic venule) - where sinusoids drain

  Portal triad - portal canals with loose CT > continues with fibrous capsule of liver

  
• Classic Lobule > stacks of anastomosing plates of hepatocytes one cell thick

  Are seperated by anatomosing system of sinusoids that perfuse cells with the mixed portal and arterial blood
• The plates of cells radiate from central vein to the periphery of lobules (like sinusoids)
• At the edges of portal canal (b/w) CT stroma and hepatocytes is a small space called pperiportal space (Space of mall)
• Hepatocytes > polygonal cells 20-30 mewm

  80% of liver

  Large nuclei and spherical in the centre of cell

  Eosinophillic with granular cytoplasm > 5 months lifespan
• Hepatocytes regeneration due to reenetering cell cycle > stimulated by quiescent cells
• Limiting plate hepatocytes bordering the portal tracts are joined together and form a distinct row called limiting plates

  
• Blood from branches of portal vein and hepatic artery mixes in sinusoids of liver lobules
• Hepatic sinusoids > emerge from branches of portal vein and hepatic artery and converge on the lobule's central vein
• Sinosoids are bigger and have a thinner wall than capillaries
• Hepatic sinusoids

  1. Flattened endothelial cells
  2. Kupffer cells

  Has a discontinous basal lamina (exchange happens much quicker)
• Kupffer cells (stellate sinusoidal macrophage) - part of vessel lining, have active phagocytes, do not form junctions with neighboring endothelial cells
• Perisinusoidal space (space of disse)

  B/W basal surfaces of hepatocytes and endothelial cells and kkupffer cells

  Small irregular microvilli that project into this space forming basal surface of hepatocytes
• Proteins and lipoporteins synthesised by hepatocyte are transferred in space of disse > secretions other than bile
• Space of disse

  contains type I, II and IV collagen fibres
• Space of Disse

  1. Hepatic stellate cell (ito cell) are present here
  2. Mesenchymal in origin for hepatic vitmain A
  3. Becoming myofibroblasts after liver injury
• Bile canaliculi

  1. Where bile is secreted
  2. no descrete structure
  3. Aproximately 0.5 mewm isolated by tight junctions
• Bile flow from central vein towards the portal canal ( opposite to blood flow )

  bile canaliculi transform into the short canals of hering
• Blood flow from liver is regulated by hormonal (CCK gastrin and motilin) and neural
• Biliary tracy (Canal of Hering) > bile canaliculi with much large bile canals of hiring lined by chalongiocytes eventuall join the bile ductules which drains into biliary tree
• Biliary tract (tree)

  Bile canaliculi and ductules and ducts lined by cholangiocytes that has microvilli and each one has primary cilium (sense changes in luminal flow)
• Small bile ductules are lined by small cholangiocytes which are cuboidal in shape as the daimeter of the bile duct increases they become columnar in shape
• Lymphatic pathway any plasma that remains in periportal space (space of mall) > found between stroma of portal canal and outermost hepatocytes (limiting plate)

  fluid travels with the portal traid
• Liver reticulin > meshwork of ECM in form of a fine meshwork of reitculin fibres Type III collagen in the space of disse
• Liver lobules

  A) Classical

  B) Liver acinus

  C) Portal Lobule

  
• The portal lobule

  • Interlobular bile duct of the portal triad of the classical lobule
  • Outer margins are imaginary lines
  • The lines include those portions of three classic lobules that secrete the bile that drains into its asial bile duct
• Liver acinus > lozenge shaped smallest functional unit of hepatic parenchyma

  • Zone 1 is closest to short axis and blood supply branches of the portal vein and hepatic artery
  • Zone 3 farthest from short axis and closest to the terminal hepatic vein (central vein)
• Liver capsule - dense CT capsule > glissons capsule

  Mesothelium covers the capsule

  Compromises of collagen and elastic fibres and provides external support and shape to the liver
• Function of gallbladder > 50ml in humans > remove 90% if water > hormones secreted by enteroendcorine cells of small intestine > stimulate contractions of smooth muscle of gallbladder
• Structure of Gallbladder

  • Mucosa - simple columnar AND Lamina propia
  • Wall of gallbladder lacks a muscularis mucosa and submucosa
  • Muscularis with bundles of muscle fibres oriented in several directions
  • Thick adventitia or serosa
• Structure of gallbladder

  1. deep diverticula of mucosa called rokitansky-aschoff sinuses > sometimes extend to muscularis externa
  2. Presage pathologic changes and develop as the result of hyperplasia and herniation
• Liver and gallbladder innervation > sympathetic and parasympathetic > autonomic nervous > nerves enter porta hepatis along with portal triad
• Sympathetic innervate blood vessels > rapid increase of serum levles of glucose
• Parasympathetic fibres are assumed to innervate large ducts > promotes glucose uptake and utilisation