Development and function of the liver
In stage 13 (ca. 32 days) the embryonic liver cells (pars hepatica) form themselves into acini and cords that grow into the capillary network that has arisen in the transverse septum between the two omphalomesenteric veins. Below it arises the gall bladder diverticulum (stage 11, ca. 29 days) (pars cystica), which also grows into the transverse septum.
The complex pattern of parenchyma and sinusoids arise in that sheets composed of liver cells are engendered from the cell cords and the capillares expand to become sinusoids. The hepatic laminas are ca. 5-7 cells thick. This organization is still retained until several years after birth. Until after birth no multi-nuclear hepatocytes are found.
It is to be noted that the blood and bile flows in opposite directions.
The blood flows from the periphery over the sinusoids into the central veins while the bile flows from the centrally located hepatocytes into the periphery and is collected by the bile capilaries in the portal fields.
If one observes a small section of a classic liver lobule one sees that the branches of the portal vein as well as the hepatic artery discharges their blood into the sinusoids while the bile flows via tiny bile canaliculi that are each formed by two neighboring hepatocytes into the bile canals of the portal fields.
In a liver cell, the blood pole (facing the sinusoid) can be distinguished from a bile pole (between two hepatocytes). The bile canaliculi are formed by the hepatocytes themselves and are sealed by tight junctions.On the boundary between the sinus and hepatocytes there are a number of specialized cells.