Embryonic liver development is a process with several stages in which the bile ducts and gallbladder are formed in addition to the liver. The epithelial bud serves as the output and undergoes proliferation until it becomes a functional organ. Embryonic developmental abnormalities may occur during liver development.
What is embryonic liver development?
Embryonic liver development is a process with several stages; it occurs as early as the first trimester of pregnancy. In embryogenesis, the individual tissues of the later individual develop from omnipotent cells to their final morphology. Part of this development is embryonic liver development. This multistep process corresponds to the formation of the liver and hepatobiliary system. The bile ducts and gallbladder are thus included in development. The liver is considered the central organ of metabolism. Its starting material is the epithelial bud, which gradually undergoes proliferation until it becomes the final functional organ. The embryonic development of the overall hepatobiliary system can be divided into two steps. First, the parenchyma of the liver, bile ducts and gallbladder develops. The second step is the development of the intrahepatic vessels. It is the development of the vasculature that helps the components achieve their final function.
Function and task
Initially, endoderm cells sprout in the duodenal region of embryonic liver development. At the embryonic stage with seven somites, the liver anlage, known as the hepatopancreatic ring and comprising two distinct sections, is formed in this manner. The lower section develops by strangulation and serves as the originating material of the gallbladder, the ductus cysticus, and some bile duct parts. The upper section develops into the other bile ducts in addition to the liver parenchyma. The cells to form the liver parenchyma grow into the mesogastrium ventrale and also infiltrate the septum transversum to attach the diaphragm. After this step, reorganization into plates and bars takes place. The blood-filled sinus wraps around the structures in a seam-like fashion. Sinus endothelial cells form its walls and originate from the septum transversum. Hematopoiesis of the embryonic liver reaches its climax in the seventh month of gestation and drops to zero by birth. The intrahepatic vasculature forms in the second stage of embryonic liver development. The yolk veins take their course within the immediate intestinal tubular neighborhood. They form anastomoses both anteriorly and posteriorly. Following subsequent remodeling processes, the venae vitellinae and their anastomoses give rise to the outflow and inflow hepatic veins and the intrahepatic blood sinus. The liver parenchyma grows around the vitelline veins and their anastomoses, giving the resulting sinusoid connection to the venous system. The cranial vascular network becomes the intrahepatic portion of the inferior vena cava and the venae efferentes. The latter veins become the venae hepaticae. This is followed by obliteration of the left vitelline vein, which gives rise to a unitary feeding venous trunk. Later, the venous trunk becomes a source vessel of the vena portae hepatis. Along the vena portae hepatis lies connective tissue of mesenchyme, which from the seventh week of development is involved in a proliferation process and thus spreads along intrahepatic branches. Portions of the hepatic artery grow into the resulting storehouse of connective tissue, branching to form septa. With the hepatic orifice as the starting point, the process continues into the interior of the liver. To the left and right of the hepatic anlage lie the blood-bearing venae umbilicales. Their blood originates from the placenta. The left-sided vena umbilicalis receives connection to the sinus system in its later course. The right-sided umbilical artery regresses. From then on, the arterialized placental blood is transferred to the liver. This is followed by remodeling of the intrahepatic vasculature to allow blood to be delivered directly to the heart via the venae efferentes hepatis and through the vena cava.
Diseases and disorders
During embryonic development, various disorders can occur, also known as embryonic developmental disorders. Some of these have internal factors as their cause, and these are usually genetic mutations or hereditary factors.Other developmental disorders are due to external factors and may be related, for example, to exposure to toxins or malnutrition of the mother during pregnancy. In connection with the liver, cysts of the organ, for example, may be due to such a developmental disorder. Cystic liver degeneration is, for example, a consequence of embryonally disturbed biliary tract development. In most cases this phenomenon is associated with cystic degeneration of the kidneys and manifests itself already in the newborn inform of a strongly enlarged liver. A disturbance of embryonic liver development is also the cause of the so-called Von Meyenburg complex. The leading symptom in this disease is a hamartoma of the liver with dilated structures of the bile ducts and parts of the connective tissue. The Von-Meyenburg complex results from an embryonic malformation at the ductal plate. This formation of tissue is the starting point in the development of the individual bile ducts in the liver. This disease is also associated with cystic changes of the liver and kidneys. The complex, apart from the cysts, consists mainly of macroscopically visible grayish-white foci, usually no more than one centimeter in size, occurring either singly or in groups. Often, these foci lie immediately beneath the capsule of the liver. Fine tissue analysis reveals groups of moderately dilated ducts of the bile. Atypia do not usually exist. The changes are embedded in connective tissue. In isolated cases, they contain bile.
