Editing Liver (section)

== '''Microscopic anatomy''' ==

* Structure of a lobule
** Each lobule is made up of a      central terminal hepatic venule, surrounded by 4-6 terminal portal triads      that form a polygonal unit
** In between the vein and      triad, hepatocytes are arranged in once-cell-thick plates, surrounded on      each side by endothelium-lined and blood-filled sinusoids - the      functional unit of the liver
** Blood flows from the portal      triad through the sinusoids into the terminal hepatic venule through      three zones, which have different enzymatic makeups and respond      differently to toxin exposure and hypoxia
*** Zone 1 (periportal): rich       in nutrients and oxygen
*** Zone 2 (intermediate):       poorer
*** Zone 3 (peri-venular zone):       poor, and most susceptible to decreases in oxygen delivery (explains the       phenomenon of centrilobular necrosis)
** Bile is formed within the      hepatocytes and empties into terminal canaliculi, which form on the      lateral walls of the intercellular hepatocyte, and ultimately coalesce      into bile ducts and flow toward the portal triads

* Hepatic microcirculation
** Arterial and PV flow varies      inversely in the sinusoids and can be compensatory. Local control likely      depends on arteriolar sphincters, and contraction of the sinusoidal      lining by endothelial cells and hepatic stellate cells or portal      myofibroblasts.
** Unidirectional flow from      zone 1 to zone 3 and then into the terminal hepatic venule
** Sinusoidal endothelial cells
*** The sinusoids are       7-15microm wide but can increase up to 10-fold
*** Should be a low-resistance       and low-pressure (2-3mmHg) system
*** Sinusoidal endothelial       cells account for 15-20% of the total hepatic cell mass
*** Sinusoidal endothelial       cells are separated from hepatocytes by the space of Disse       (peri-sinusoidal space), where hepatocytes project microvilli
*** Endothelial cells       fenestrated and have no intercellular junctions/basement membrane
** Kupffer cells
*** Derived from       macrophage-monocyte system, phagocytic
*** Line the sinusoids,       insinuating between endothelial cells
*** Trap foreign substances and       initiate inflammatory responses
*** Natural killer, CD4 T and       CD8 T cells also exist
** Hepatic stellate cells
*** Vitamin A storage and       synthesis of extracellular collagen and other ECM proteins
*** Activated to a       myofibroblast state in acute and chronic liver injuries
*** Key role in progression of       fibrosis to cirrhosis
** Hepatocytes
*** Make up 60% of the hepatic       cellular mass
*** Every hepatocyte has       contact with adjacent hepatocytes, the biliary space and the       peri-sinusoidal space
*** Functions
**** Uptake, storage and        release of nutrients
**** Synthesis of glucose,        fatty acids, lipids, and numerous plasma proteins (including CRP and        albumin)
**** Production and secretion        of bile for digestion of dietary fats
**** Degradation and        detoxification of toxins
*** Bile canaliculi form a ring       around the hepatocyte that drains into small bile ducts known as canals       of Hering, which empty into a bile duct at a portal triad
*** The monoclonal antibody       HepPar1 (hepatocyte paraffin 1) identifies a unique antigen on       hepatocyte mitochondria and can be used to identify hepatocytes on       immunohistochemical examination
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