Lipid digestion, absorption

III. THE INTERACTION OF LIPOPHILIC DRUGS WITH THE LIPID DIGESTION/ABSORPTION CASCADE... 

In order to better understand the individual lipoprotein functions, let us go through an overview of lipid digestion, absorption and distribution ... 

D. Lipid digestion, absorption and transport in the bloodstream and delivery to tissues... 

II. DIGESTION, ABSORPTION, SECRETION, AND UTILIZATION OF DIETARY LIPIDS ... 

II. Digestion, Absorption, Secretion, and Utilization of Dietary Lipids... 

These agents are administered to aid in the digestion of food. The primary digestant preparations contain pancreatic enzymes or bile salts. Pancreatic enzymes such as amylase, trypsin, and lipase are responsible for digestion of carbohydrates, proteins, and lipids, respectively. These enzymes are normally synthesized in the pancreas and secreted into the duodenum via the pancreatic duct. Bile salts are synthesized in the liver, stored in the gallbladder, and released into the duodenum via the common bile duct. Bile salts serve to emulsify lipids in the intestinal tract and are important in lipid digestion and absorption. 

Lipids, unlike many excipients, whether present in food or as discreet pharmaceutical additives, are processed both chemically and physically within the GIT before absorption and transport into the portal blood (or mesenteric lymph). Indeed, most of the effects mediated by formulation-based lipids or the lipid content of food are mediated by means of the products of lipid digestion—molecules that may exhibit very different physicochemical and physiological properties when compared with the initial excipient or food constituent. Therefore, although administered lipids have formulation properties in their own right, many of their effects are mediated by species that are produced after transformation or activation in the GIT. An understanding of the luminal and/or enterocyte-based processing pathways of lipids and lipid systems is therefore critical to the effective design of lipid-based delivery systems. 

Solubilization of lipid digestion products in intestinal mixed micelles enhances their dissolution and dramatically increases the GI lumen-enterocyte concentration gradient that drives absorption by means of passive diffusion. Micelles, however, are not absorbed intact [8, 9], and lipids are thought to be absorbed from a monomolecular intermicellar phase in equilibrium with the intestinal micellar phase [10], The dissociation of monomolecular lipid from the micellar phase appears to be stimulated by the presence of an acidic microclimate associated with the enterocyte surface [11,12], In addition to passive diffusion, growing evidence suggests that active uptake processes mediated by transport systems located in the enterocyte membrane are also involved in the absorption of (in particular) fatty acids into the enterocyte [4],... 

Understand the mechanisms involved in lipid digestion and absorption, including bile salt metabolism. 

Noble, R.C. 1978. Digestion, absorption and transport of lipids in ruminant animals. Prog. Lipid Res., 17, 55-91. 

Sufficient absorption of macronutrients to maintain energy supply requires prior hydrolysis by pancreatic enzymes. Thus, complete absence of pancreatic enzymes (e.g., due to pancreatectomy) is, if untreated, incompatible with life. Normally, however, in healthy individuals the cumulative postprandial pancreatic enzyme response exceeds by far (10- to 15-fold) the quantity required to prevent overt maldigestion. In particular, lipid digestion is fast and... 

This could include retinol, cholecalciferol/ergocalciferol, a-tocopherol, vitamin K from food, all of which are more readily absorbed when they can be part of a normal mixed micelle process that occurs with lipid digestion and absorption... 

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