Triacylglycerol digestion

The products of triacylglycerol digestion, mainly monoacylglycerol and long-chain fatty acids, interact with bile salts to form micelles, which comprise bile salts/ monoacylglycerols/phospholipids and fatty acids. The micelle aids the absorption of monoacylglycerol and fatty... 

Bernback, S., Blackberg, L. and Hernell, O. (1989) Fatty acids generated by gastric lipase promote human milk triacylglycerol digestion by pancreatic colipase-dependent lipase. Biochim. Biophys. Acta 1001, 286— 291. 

Recall that the exocrine pancreas, in addition to secreting proteolytic zymogens, also secretes amylase for starch digestion and lipase and co-lipase for dietary triacylglycerol digestion. 

The human fat-digestive enzymes include triacylglycerol Kpases and phosphohpases. The triacylglycerol digestive enzymes comprise the... 

Four major groups of lipoproteins are recognized Chylomicrons transport lipids resulting from digestion and absorption. Very low density lipoproteins (VLDL) transport triacylglycerol from the liver. Low-density lipoproteins (LDL) deliver cholesterol to the tissues, and high-density lipoproteins (HDL) remove cholesterol from the tissues in the process known as reverse cholesterol transport. 

Figure 44-2. Digestion and absorption of triacylglycerols.The values given for percentage uptake may vary widely but indicate the relative importance of the three routes shown.

Phospholipids are digested and absorbed in a similar manner to that of triacylglycerol. Pancreatic lipase has some hydrolytic activity towards phospholipids and removes the fatty acid from the 1-position. The product is a lysophospholipid such as lysolecithin (Figure 4.12). It also acts as a detergent and contributes to the stability of the mixed micelles. 

Medium-chain fatty acids are also present in bovine milk and some plant oils (e.g. coconut). After digestion of the triacylglycerol, they are taken up by the enterocytes in the small intestine but are not esterified. Instead they pass directly into the hepatic portal blood, from where they are taken up by the liver for complete oxidation or conversion to ketone bodies. 

In developed conntries, fat provides about 40% of the total energy consnmed but in some individuals this percentage may be mnch higher. Almost all of this is in the form of triacylglycerol, containing mainly long-chain bnt also some short-chain fatty acids. The stractnre, digestion, absorption and eventual fate of the products of absorption are described in Chapters 4 and 5 and the metabolism of fat is discussed in Chapter 7. 

The absorptive state continues for 2-4 hours after food intake. As a result of food digestion, the plasma levels of glucose, amino acids, and fats (triacylglycerols) temporarily increase. 

FIGURE 17-1 Processing of dietary lipids in vertebrates Digestion and absorption of dietary lipids occur in the small intestine, and the fatty acids released from triacylglycerols are packaged and delivered to muscle and adipose tissues. The eight steps are discussed in the text. 

An adult ingests about 60 to 150 g of lipids per day, of which more than n nety percent is normally triacylglycerol (formerly called triglyceride). Uhe remainder of the dietary lipids consists primarily of cholesterol, cholesteryl esters, phospholipids, and unesterified ("free") fatty acids. "The digestion of dietary lipids is summarized in Figure 15.2. 

The dietary triacylglycerol, cholesteryl esters, and phospholipids are enzymically degraded ("digested") by pancreatic enzymes, whose secretion is hormonally controlled. 

Digestion of dietary lipids Dietary lipids DIGESTION OF DIETARY LIPIDS (p. 171) Dietary lipids consist primarily of triacylglycerol, with some cholesterol, cholesteryl esters, phospholipids, and free (nonesterified) fatty acids. 

A. Digestion, Synthesis, and Distribution of Triacylglycerols in the Human Body... 

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