Canaliculi

Most bones of the human skeleton are composed of two structurally distinct types of tissue compact (dense) and trabecular (cancellous, spongy) bone. Both types contain the same elements cells ( osteocytes) embedded in a mineralised matrix and connected by small canals ( canaliculi ). In compact bone, which makes up 85% of the skeleton, these components form elongated cylinders of concentric lamellae surrounding a central blood vessel (called osteon or Haversian system). Cancellous bone, in contrast, forms thin,... 

Approximately 15 per cent of osteoblasts become entrapped in their own matrix to become osteocytes. Osteocytes have a vast three-dimensional network of cell processes (canaliculi), providing nourishment and cell-cell interactions. Because they are located throughout bone tissue and have an extensive canalicular network, osteocytes are assumed to be a vital component of sensing mechanical signals. Nutrients are essential for the vitality of bone tissue and are obtained from the blood supply, limiting most osteocytes to lie within 150 p.m of a blood vessel, resulting in a high cellular density 25000 osteocytes within a square millimetre of bone... 

Bone is a porous tissue composite material containing a fluid phase, a calcified bone mineral, hydroxyapatite (HA), and organic components (mainly, collagen type). The variety of cellular and noncellular components consist of approximately 69% organic and 22% inorganic material and 9% water. The principal constiments of bone tissue are calcium (Ca ), phosphate (PO ), and hydroxyl (OH ) ions and calcium carbonate. There are smaller quantities of sodium, magnesium, and fluoride. The major compound, HA, has the formula Caio(P04)g(OH)2 in its unit cell. The porosity of bone includes membrane-lined capillary blood vessels, which function to transport nutrients and ions in bone, canaliculi, and the lacunae occupied in vivo by bone cells (osteoblasts), and the micropores present in the matrix. 

Curtis LR. 1988. Chlordecone is a potent in vitro inhibitor of oligomycin-insensitive magnesium-ATPase of rat bile canaliculi-enriched fraction. J Biochem Toxicol 3(Winter) 321-328. 

Curtis LR, Mehendale HM. 1981. Hepatobiliary dysfunction and inhibition of adenosine triphosphatase activity of bile canaliculi-enriched fractions following in vivo mirex, photomirex, and chlordecone exposures. Toxicol Appl Pharmacol 61 429-440. 

Golgi, in early neuroanatomical studies (1898) staining neurones by silver impregnation, observed a reticular apparatus which was crescent shaped and appeared to be linked through canaliculi. The structure was also seen in secretory cells. Between 1949 and 1954, Baker reported the presence of similar systems in unfixed cells examined by phase contrast. The structures could be stained by osmium tetroxide and probably contained lipid. They also stained for glycoprotein and alkaline phosphatase. Baker s confirmation of the existence of the... 

As they secrete osteoid matrix around themselves, osteoblasts eventually become entrapped within lacunae ( spaces ) and mature into osteocytes. Although topographically isolated from each other, osteocytes maintain contact with neighbours by cell processes which run through tiny interconnecting fluid-filled canaliculi (channels) within the matrix. 

A familial deficiency in the bile-acid export pump, 103 which conveys bile acids from hepatocyte cytoplasm into bile canaliculi, increases the incidence of hepatocellular carcinoma in children. 

The hepatocyte secretes biliary fluid into the bile canaliculi (dark green), tubular intercellular clefts that are sealed off from the blood spaces by tight junctions. Secretory activity in the hepatocytes results in movement of fluid towards the canalicular space (A). The hepatocyte has an abundance of enzymes carrying out metabolic functions. These are localized in part in mitochondria, in part on the membranes of the rough (rER) or smooth (sER) endoplasmic reticulum. 

The liver secretes about 1 L of bile daily. Bile flow and composition depend on the secretory activity of the hepatic cells that line the biliary canaliculi. As the bile flows through the biliary system of ducts, its composition can be modified in the ductules and ducts by the processes of reabsorption and secretion, especially of electrolytes and water. For example, osmotically active compounds, including bile acids, transported into the bile promote the passive movement of fluid into the duct lumen. In the gallbladder, composition of the bile is modified further through reabsorptive processes. 

Liver biopsies showing bile plugs in the canaliculi, with eosinophilic infiltration in the periportal space... 

Bums of the lacrymal system. They are uneasy to evaluate, however looking for a stenosis of the lacrymal point or canaliculi is essential. Concerning serious chemical eye bums, a systematic wash of the lacrymal system also enables to check its permeability. 

The bile canaliculi form a network, which feed into ductules, which become bile ducts (Fig. 6.3). The structural and functional unit of the liver is the lobule, which is usually described in terms of the hepatic acinus (Fig. 6.5), based on the microcirculation in the lobule. When the lobule is considered in structural terms, it may be described as either a classical or a portal lobule (see "Glossary"). The acinus comprises a unit bounded by two portal tracts and terminal hepatic or central venules, where a portal tract is composed of a portal venule, bile ductile, and hepatic arteriole (Fig. 6.5). Blood flows from the portal tract toward the central... 

Moslen. M.T.. Dunsford. H.A., Kamasuta, C., Chieco, P. Kanz, M.F. (1989) Histochemical and immunocytochemical evidence of early, selective bile canaliculi injury after 1,1-dichlor-ethylene in rats. Am. J. Pathol., 134, 1099-1112... 

The most common change is a short-term rise in serum transaminases (208), which often abates if treatment is continued. An increase in serum alkaline phosphatase is usual, while serum transaminases can be normal to markedly increased (209). Long-term use leads to changes in hepatic ultrastructure, with involvement of the mitochondria, which develop crystalline inclusions. Furthermore, hypertrophy of the smooth endoplasmic reticulum and changes in the biliary canaliculi have been shown (210,211). These changes are not usually accompanied by any clinical symptoms. The Budd-Chiari syndrome can occur in connection with thromboembolism. 

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