Dr. ANAND SRINIVASAN

 Good regenerative capacity  Hence used for transplantation

 Able to :  Describe, identify and draw the histological features of :  Liver  Gall bladder  Pancreas

 2 nd largest organ  2 types of blood vessels  Portal vein (70%)  Hepatic A. (30%)  Surrounded by fibrous capsule (GLISSON’s CAPSULE) deep to peritoneum  Capsule through trabeculae divides the liver into “lobules”  Portal tract / Portal space / Portal canal  Branches of Hepatic A, Portal V., Hepatic duct and lymphatics present in trabeculae

 Structural unit of liver  Hexagonal (polygonal) in shape  Central vein in the center  Liver lobules not completely demarcated by connective tissue septa (c.f. pig)  Lobules can be demarcated by connecting portal tracts

 Structural and functional component of liver “Hepatocytes”  Hepatic plates usually single layer thick (c.f. children 2 plates)  Radiate from central vein to periphery  “Sinusoids” – spaces between hepatic plates lined by fenestrated endothelial cells  Some endothelial cells modified as “Kupffer’s cells”  Hepatic stellate / Ito cells (perisinusoidal lipocytes) also present within hepatocytes – activated in certain pathological conditions.

 Sinusoids separated from hepatocytes by “Space of Disse”  Blood from portal vein and hepatic A. enter into sinusoid which then drains into central vein and finally to hepatic vein

 Atleast 2 surfaces of hepatocytes are in contact with sinusoids through space of disse  Rest of the hepatocytes contact with adjacent and has a intercellular space called “Bile canaliculus” – first part of the bile duct system  Pass through “Cana of Hering” to hepatic ducule  Flow of bile is in a opposite direction to that of blood.

 For studying certain pathological conditions it is useful to divide liver into portal lobule  Part of liver parenchyma that drains bile into hepatic ductule present in portal triad

 Another functional unit of liver which is irrigated by terminal distributing branches of portal vein and hepatic artery  Diamond shaped

 Exocrine and endocrine gland  EXOCRINE  Darkly stained serous acini  No myopeithelial cells but pancreatic stellate cells present  Some acini exhibit “Centroacinar cells” – cuboidal cells representing intra-acinar part of intercalated duct  Intercalated duct  intralobular ducts  interlobular duct  main pancreatic duct (epithelium varying from simple to stratified cuboidal)

 ENDOCRINE  Made of “Islets of Langerhans” – pale staining spherical bodies amongst serous acini  More in the tail of pancreas  1 – 2 million islets in pancreas

 ALPHA CELLS (20 %)  Secrete glucagon  BETA CELLS (70%)  Secrete insulin  DELTA CELLS (5%)  Secrete somatostatin  F CELLS / PP CELLS  Secrete pancreatic polypeptides

 Sac situtated close to the liver  Concentrate bile

 MUCOSA  Simple columnar epithelium  Lamina propria rich in elastic fibers  Microvilli – absorption of water  Muscularis mucosa and submucosa absent  FIBROMUSCULAR LAYER  Circular smooth muscle fibers intermixed with connective tissue  SEROSA / ADVENTITIA  Fundus & lower surface of body – serosa  Rest - adventitia

 Wheater’s Functional Histology  Cell Biology & Histology – Board Review Series  Microanatomy workbook – RAKMHSU