Liver: anatomy, microscopic structure, and cell types

The liver is a unique organ with remarkable capabilities and a vast range of functions. This chapter outlines embryological development as well as the gross, histological, and electron microscopic characteristics of the liver with a practical, patient-oriented mindset. The primordial liver first appears toward the end of gestational week 3, and is called the "hepatic diverticulum." It is formed by an outpouching of the distal foregut (future duodenum), and is composed of proliferating endodermal cells. The liver size regresses at birth and only a few islands of hematopoietic cells are left; at that point, the liver weighs about 5% of body weight. Anatomically, the liver has four lobes: right, left, caudate, and quadrate. Grossly, the right lobe is divided from the left by the falciform ligament. Functional divisions of the liver follow the branching pattern of the portal structures (portal vein, hepatic artery, and bile duct).