Fat absorption and transport

See also Adipocytes, Fat Absorption and Transport, Bile Salts and Emulsion of Fats, Mobilization of Stored Fat, Energy Storage, Triacylglycerol Synthesis, Action of Insulin, Lipids... 

See also Cholesterol, Fat Absorption and Transport, Lipoprotein Complexes in Fat Transport... 

Martin, J.C., C. Caselli, S. Broquet, P. Juaneda, M. Nour, J.L. Sdb dio, and A. Bernard. 1997. Effect of cyclic fatty acid monomers on fat absorption and transport depends on their positioning within the ingested triacylglycerols. Journal of Lipid Research 38 1666-79. 

The relative solubility of materials is relevant to most of the subjects covered in this book. The biochemical "machinery" used for digestion, absorption, and transport of nutrients throughout the body depends on whether the nutrients are water soluble or fat soluble. Relative solubilities are also crucial to the function, composition, and architecture of cells and their surrounding membranes. 

Vitamins K and Kj are absorbed by an active process in the proximal small intestines. Bile of normal composition is necessary to facilitate the absorption. The bile component principally concerned in the absorption and transport of fat-soluble vitamin K from the digestive tract is thought to be Jcoxycholic acid. The molecular compound of vitamin K with deoxycholic acid was effective on oral administration to rats with biliary fistula. Vitamin K is absorbed through the lymph in chylomicrons. It is tran.sportcd to the liver, where it is concentrated, but no significant storage occurs. 

Nelson, G.J. and Ackman, R.G. (1988) Absorption and transport of fat in mammals with emphasis on n-3 polyunsaturated fatty acids. Lipids. 23 1005-1014. 

G, L. P. Fernando-Wamakulasuriya, J. E. Staggers, S. C. Frost. M. A. Wells, Studies on fat digestion, absorption and transport in the suckling rat. i. Fatty acid composition and concentration of major Upis components. J Lipid Res 22 668-674. 1981. 

Phospholipides.— Lecithin and other phospholipides of the diet are important nutritional somces of choUne and of phosphoric acid, and are resolved into their components by the esterases of the small intestine previous to absorption. Within the intestinal mucosa, a re-synthesis occiun, or a new phospholipide is assembled containing units derived from the saponified fats of the diet, and as such participates in the lipide transport in the lymph and the portal blood. By use of a phosphate containing a radioactive isotope of phosphorus as indicator, Artom and his colleagues (1937) have shown that phospholipides of the lecithin and cephalin type are synthesised in large quantities during fat absorption, and accumulate in the intestinal mucosa, the liver, and to a lesser extent, the kidney, but not in the spleen, heart or skeletal muscles. 

Figure 10. Numbers of Golgi vacuoles per cell during fat absorption and after abrupt termination of fat absorption by flushing the lumen of the bowel with isotonic saline ( SD, n = 5). During absorption, Golgi vacuoles containing lipid progressively increase in both size and number a maximum is reached at 1 h. With the abrupt termination of lipid transport, there is a gradual decline in the quantity of Golgi vacuoles. From Friedman and Cardell (1977) with permission of the publisher.

Bile is produced continuously by the liver bile salts are secreted by the hepatocytes and the water, sodium bicarbonate, and other inorganic salts are added by the cells of the bile ducts within the liver. The bile is then transported by way of the common bile duct to the duodenum. Bile facilitates fat digestion and absorption throughout the length of the small intestine. In the terminal region of the ileum, the final segment of the small intestine, the bile salts are actively reabsorbed into the blood, returned to the liver by way of the hepatic portal system, and resecreted into the bile. This recycling of the bile salts from the small intestine back to the liver is referred to as enterohepatic circulation. 

Vitamin E, like neutral lipids, requires apoB lipoproteins at every stage of its transport (Fig. 27-2). Dietary vitamin E becomes emulsified in micelles produced during the digestive phase of lipid absorption and permeates the intestinal epithelium, similar to fatty acids and cholesterol. Uptake of vitamin E by enterocytes appears to be concentration dependent. Within intestinal cells, vitamin E is packaged into chylomicrons and secreted into lymph. During blood circulation of chylomicrons, some vitamin E may be released to the tissues as a consequence of partial lipolysis of these particles by endothelial cell-anchored lipoprotein lipase. The rest remains associated with chylomicron remnants. Remnant particles are mainly endocy-tosed by the liver and degraded, resulting in the release of fat-soluble vitamins. 

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