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Elements of Continuum Mechanics
Published in Clement Kleinstreuer, Biofluid Dynamics, 2016
Apart from a patch where it is connected to the diaphragm, the liver is covered entirely by a thin, double-layered membrane that reduces friction against other organs. Based on surface appearance, it can be divided into major folded lobes (see Fig. 4.3.1a). Surprisingly, there are only two types of cells forming the structure of the liver. The liver cells, called hepatocytes, form hepatic plates that are one to two cell-layers thick. These plates are separated by microchannels, called sinusoids (see Fig. 4.3.1b). The channel walls are lined with Kupffer cells which, like white blood cells, can “devour” toxins, bacteria, etc. As indicated in Fig. 4.3.1a, nutrients in the blood from the digestive system are carried via the hepatic partial vein to capillaries in the liver, as it receives arterial blood via the hepatic artery. The hepatic plates are arranged into active units called liver lobules, each with a central vein which collects the arterial/venous blood mixture flowing through the sinusoids (Fig. 4.3.1b). The central veins of all the lobules converge and deliver the blood to the inferior vena cava. In contrast, bile is produced by the hepatocytes and secreted into microchannels, called bile canaliculi, which empty into the bile duct (see Fig. 4.3.1).
Bioprinting of liver
Published in Ali Khademhosseini, Gulden Camci-Unal, 3D Bioprinting in Regenerative Engineering, 2018
Dong-Woo Cho, Hyungseok Lee, Wonil Han, Yeong-Jin Choi
Cholangiocytes are epithelial cells that form the biliary tree, a tubular network for the transport of bile acids [59]. In native liver tissue, hepatocytes synthesize bile-acid compounds and secrete them into the bile canaliculi, a process organized by the specific polarity of hepatocytes [5]. Then, bile acids are transported to the biliary network, where they are modified by cholangiocytes and finally secreted as a digestive juice [60]. Although cholangiocyte sources including primary cultured cells [61] and artificially immortalized cell lines [62] have been established, their application in liver bioprinting has not been reported to date (Table 13.2).
Micro- and Nanotechnology in Tissue Engineering
Published in Yubing Xie, The Nanobiotechnology Handbook, 2012
Jane Wang, Robert Langer, Jeffrey T. Borenstein
The liver comprises complex structures, an integrated microvasculature, and performs many critical functions. It is the largest gland of the body, normally weighing about 1.5 kg in adult. Primary hepatocytes constitute 60%–80% of the liver mass and play many important functions in our body. The intercellular channels between adjacent hepatocytes form bile canaliculi, thin tubes that collect bile secreted by hepatocytes. The bile canaliculi merge and form bile ductules, which eventually become bile ducts. In between each row of hepatocytes are small cavities called sinusoids comprising a fenestrated monolayer of liver sinusoidal endothelial cells. Each sinusoid is lined with Kupffer cells, macrophages that remove amino acids, nutrients, sugar, old red blood cells, bacteria, and debris from the blood that flows through the sinusoids. The main functions of the sinusoids are to destroy old or defective red blood cells, to remove bacteria and foreign particles from the blood, and to detoxify toxins and other harmful substances. ECM-producing stellate cells, biliary epithelial cells, hepatocyte precursor cells, and fibroblasts are also present and perform important metabolic functions. The main functions played by the liver include (1) bile production and secretion; (2) excretion of bilirubin, cholesterol, hormones, and drugs; (3) metabolism of fats, proteins, and carbohydrates; (4) enzyme activation; (5) storage of glycogen, vitamins, and minerals; (6) macromolecules and protein synthesis (i.e., albumin and bile acids); and (7) detoxification (Kobori et al. 2007, Lal et al. 2007). Exogenous and endogenous substances are detoxified in the liver, and hepatocyte-based hepatotoxicity testing is useful in rapid screening of chemicals and in mechanistic evaluation of toxicological phenomena.
A fully coupled porous media and channels flow approach for simulation of blood and bile flow through the liver lobules
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
As mentioned in Section 3, a transmission factor, Tbb is introduced on the edges of each bile canaliculi to connect the bile and blood flows. The effect of this transmission factor on the pressure profiles within the liver tissue (i.e the CV-CV line) as well as sinusoids (i.e. the CV-PV line) is investigated by changing the value of this parameter within 0.4 to 1.6. As shown in Figure 7e, this factor has a little effect on pressure distributions along the mentioned lines, which is mainly restricted to regions near the lobule central vein specially for the CV-CV line. While has no sensible effect on the velocity distribution along CV-CV, the value of transmission factor changes the magnitude of maximum velocity in such a way that it increases by decreasing Tbb (Figure 7f).