VAN 211: Veterinary Histology and Embryology (2+2)

LIVER

• Liver is an endodermal derivative. Its primordium lies between the pericardial cavity and attaching yolk stalk. Here the floor of the future duodenum continues to give rise to definite sacculations named hepatic diverticulum. This consists of a cranial portion which will differentiate into the glandular tissue and its bile ducts.
• The caudal portion will become the gall bladder and cystic duct. The hepatic diverticulum forces its way to splanchnic mesoderm which forms the primitive diaphragm, the septum transversum.
• A little later, the region of the septum occupied by the liver becomes drawn out as ventral mesentery and the final relation to the liver is more related to the mesentery than the diaphragm.
• The cranial portion of the hepatic diverticulum buds off epithelial cords which invade the septum transversum and continue to proliferate into a spongy work.
• The paired vitelline veins flanking the gut and send the branches into the region of proliferation. The result is a mutual, intimate intergrowth of tortuous liver cords and sinusoidal channels.
• The diverticulum in the meanwhile elongates and differentiates into duct system. The main portion of the diverticulum forms the hepatic duct and ductus choledochus.
• From the hepatic duct, large intra hepatic ducts buds off and from these small inter lobular ducts arise. The system of branching of vitelline veins are responsible for creation of hepatic lobules from the parenchyma.
• The gall bladder and cystic duct develop from caudal portion of hepatic diverticulum. The septum transversum furnishes the peritoneal covering and the connective tissue framework.