<P> These triglycerides, cannot be absorbed by the intestine . They are broken down into mono - and di - glycerides plus free fatty acids (but no free glycerol) by pancreatic lipase, which forms a 1: 1 complex with a protein called colipase (also a constituent of pancreatic juice), which is necessary for its activity . The activated complex can work only at a water - fat interface . Therefore, it is essential that fats are first emulsified by bile salts for optimal activity of these enzymes . The digestion products consisting of a mixture of tri -, di - and monoglycerides and free fatty acids, which, together with the other fat soluble contents of the diet (e.g. the fat soluble vitamins and cholesterol) and bile salts form mixed micelles, in the watery duodenal contents (see diagrams on the right). </P> <P> The contents of these micelles (but not the bile salts) enter the enterocytes (epithelial cells lining the small intestine) where they are resynthesized into triglycerides, and packaged into chylomicrons which are released into the lacteals (the capillaries of the lymph system of the intestines). These lacteals drain into the thoracic duct which empties into the venous blood at the junction of the left jugular and left subclavian veins on the lower left hand side of the neck . This means that the fat soluble products of digestion are discharged directly into the general circulation, without first passing through the liver, as all other digestion products do . The reason for this peculiarity is unknown . </P> <P> The chylomicrons circulate throughout the body, giving the blood plasma a milky, or creamy appearance after a fatty meal . Lipoprotein lipase on the endothelial surfaces of the capillaries, especially in adipose tissue, but to a lesser extent also in other tissues, partially digests the chylomicrons into free fatty acids, glycerol and chylomicron remnants . The fatty acids are absorbed by the adipocytes, but the glycerol and chylomicron remnants remain in the blood plasma, ultimately to be removed from the circulation by the liver . The free fatty acids released by the digestion of the chylomicrons are absorbed by the adipocytes, where they are resynthesized into triglycerides using glycerol derived from glucose in the glycolytic pathway . These triglycerides are stored, until needed for the fuel requirements of other tissues, in the fat droplet of the adipocyte . </P> <P> The liver absorbs a proportion of the glucose from the blood in the portal vein coming from the intestines . After the liver has replenished its glycogen stores (which amount to only about 100 g of glycogen when full) much of the rest of the glucose is converted into fatty acids as described below . These fatty acids are combined with glycerol to form triglycerides which are packaged into droplets very similar to chylomicrons, but known as very low - density lipoproteins (VLDL). These VLDL droplets are handled in exactly the same manner as chylomicrons, except that the VLDL remnant is known as an intermediate - density lipoprotein (IDL), which is capable of scavenging cholesterol from the blood . This converts IDL into low - density lipoprotein (LDL), which is taken up by cells that require cholesterol for incorporation into their cell membranes or for synthetic purposes (e.g. the formation of the steroid hormones). The remainder of the LDLs is removed by the liver . </P>

Where is the energy stored in a fatty acid molecule