19.7 Liver, gall bladder and passages



Development and function of the liver

Quiz

Quiz 17


In stage 13 (ca. 32 days, 13) 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, 11) (pars cystica), which also grows into the transverse septum.

Quiz

Quiz 19


Quiz

Quiz 20


Fig. 32 - Liver bud (side view) Fig. 33 - Liver bud (front view)  Legenda

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Capillary network of the
omphalomesenteric vein
Liver bud
Intestinal tube (duodenum)
Gall bladder
Dorsal pancreas anlage


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Capillary network of the
omphalomesenteric vein
Liver bud
Intestinal tube (duodenum)
Gall bladder
Omphalomesenteric vein
Omphalaomesenteric duct
Umbilical vein

Fig. 32
Through sprouting and divisions of the intestinal bud, the first liver acini arise in the capillary network of the omphalo-
mesenteric vein.

Fig. 33
Through the relocation of the entire cardiac circulation system to the right the liver also is shifted more into that position.



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.


Fig. 34 - Overview of the liver's passage system  Legenda

Fig. 34
All intrahepatic bile passages stem from the cells of the hepatic bud. The liver cells form canaliculi between them and also the extrahepatic hepatic duct that joins with the cystic duct to become the bile duct.



Meer info

The central vein-lobule is considered the classic histological structural unit of the liver, whereby the lobule consists of radially organized sheets of hepatocytes separated by the sinusoids converging toward the central vein. Some physiologic and pathologic observations on the liver cannot be explained based on the classic liver lobule concept. For this reason further functional concepts of the histological organization have been suggested.



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. Fig. 35 - Cross section (perspective) through a liver lobule  Legenda

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Branch of the portal vein
Branch of the hepatic artery
Bile duct
Boundary lamina of hepatocytes
Central vein
Liver acinus
Sinusoid

Fig. 35
The classic liver lobule is enveloped by a limiting plate of hepatocytes, surrounded by various vessels embedded in connective tissue. The blood flows from the periphery via the sinusoids into the central vein (violet arrow). The bile flows in the opposite direction (green arrow).



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.


Fig. 36 - Liver lobule Fig. 37 - Liver beam with sinusoids  Legenda


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Ito cells with fat vacuoles
Sinusoidal space
Disse's space
Bile canaliculi
Hepatocyte
Tight junction
Kupffer's cells while phagocytizing
Discontinuous endothelial layer

Fig. 36
Section of a classic liver lobule with a sheet of hepataocytes.

Fig. 37
The enlargement shows a sheet of hepatocytes, the sinusoids and a variety of specialized cells close to (Ito-
cells) or inside (macrophages) the sinusoids.



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