Structure of the liver

The histological features of the liver are summarized below.
         Structural component of liver include
        Connective tissue stroma
        Portal triad
        Bile canaliculi

         There are three way to describe the structure of liver
        The classic lobule
        The portal lobule
        Portal acinus

Classical lobule

         Connective tissue stroma
     liver is covered by a thin connective tissue capsule (Glisson's capsule) and extends into its interior as numerous branching septa.
        Blood vessels, nerves, lymphatic vessels and bile ducts travel within these septa.


    In cross section, the substance of liver appears to be made up of hexagonal areas that constitute  the hepatic lobules. In certain animals (eg, pigs micrograph b in adjacent figure), the lobules are separated by connective tissue septa (C). But in human (micrograph c in adjacent figure) the septa are not distinct and the lobules appear to merge with each other making it difficult to establish the exact limits between different lobules. 

     Each lobule consists of interconnected plate of liver cells (hepatocytes). These plates are one cell thick that branch and anastomose with each other to form network.

        The center of the lobule is occupied by a central vein (V) which is a tributary of hepatic vein

   Along the periphery of each lobule there are angular intervals filled by connective tissue. These intervals are called portal canal/tract (T). Each portal tract contains a venule (a branch of the portal vein), an arteriole (a branch of the hepatic artery), a duct (part of the bile duct system).These three structures collectively form a portal triad.

   venule contains blood coming from the superior and inferior mesenteric and splenic veins.
   The arteriole contains oxygen-rich blood coming from the celiac trunk of the abdominal aorta.
  The duct, carries bile synthesized by the hepatocytes and eventually empties into the hepatic duct

Bile canaliculi

    Each liver cell is cuboidal presenting six surfaces, out of which two surfaces are related to the sinusoids and the remaining surface are in contact with the wall of adjacent hepatocyte. Wherever two hepatocytes are in contact, they make a tubular space between them known as the bile canaliculus
        Bile is synthesised by hepatocytes and secreted into bile canaliculi
        Bile canaliculi of adjacent hepatocyte plates merge to form canals of Hering or bile ductules which latter finally drain into the bile duct in the portal canal

Portal lobule

    The portal lobule emphasizes the exocrine functions of the liver
   The portal lobule includes the territory of liver tissue centered around a portal triad, and is drawn by joining the central veins of the three adjacent liver lobules
    The territory of portal lobule includes those portion of three classic lobules that secrete the      bile that drains into its axial bile duct.

Liver acinus

    Liver acinus is the structural unit that provides the best correlation between blood perfusion and metabolic activity
         It consists of the area of liver tissue supplied by one hepatic arteriole running along the line of junction of two hepatic lobule. Two central veins lie at the ends of the acinus.

Structure of Gall Bladder

The histological features of the gallbladder are summarized below.

  consists of a mucosa composed of simple columnar epithelium and lamina propria, fibromuscular layer, and a serous membrane

         Mucous membrane:
   lined by is a single layer of tall columnar absorptive cells bearing numerous short irregular microvilli . Goblet cells are absent.
      Mucosa is highly folded, and the folds are called rugae.The submucosa (S) is relatively loose. 

     The fibromuscular coat: is composed of fibrous tissue (A) mixed with smooth muscle cells (M)  which are arranged loosely in longitudinal, circular and oblique bundles but do not form distinct layers. 

Gray's Anatomy
K. L. Moore's Clinically Oriented Anatomy
R. Snell's Clinical Anatomy
Wheater's Functional Histology