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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). [27] [29]
Lipid metabolism is often considered the digestion and absorption process of dietary fat; however, there are two sources of fats that organisms can use to obtain energy: from consumed dietary fats and from stored fat. [5] Vertebrates (including humans) use both sources of fat to produce energy for organs such as the heart to function. [6]
These chylomicrons then pass into the lacteals, forming a milky substance known as chyle. The lacteals merge to form larger lymphatic vessels that transport the chyle to the thoracic duct where it is emptied into the bloodstream at the subclavian vein. [2] [3] At this point, the fats are in the bloodstream in the form of chylomicrons.
Chylomicron structure ApoA, ApoB, ApoC, ApoE (apolipoproteins); T (triacylglycerol); C (cholesterol); green (phospholipids). Chylomicrons transport lipids absorbed from the intestine to adipose, cardiac, and skeletal muscle tissue, where their triglyceride components are hydrolyzed by the activity of the lipoprotein lipase, allowing the released free fatty acids to be absorbed by the tissues.
In the body, stores of fat are referred to as adipose tissue. In these areas, intracellular triglycerides are stored in cytoplasmic lipid droplets. When lipase enzymes are phosphorylated, they can access lipid droplets and through multiple steps of hydrolysis, breakdown triglycerides into fatty acids and glycerol. Each step of hydrolysis leads ...
In contrast, the human body stores only about 400 g (0.9 lb) of glycogen, of which 300 g (0.7 lb) is locked inside the skeletal muscles and is unavailable to the body as a whole. The 100 g (0.2 lb) or so of glycogen stored in the liver is depleted within one day of starvation. [ 11 ]
Triglycerides are the main constituents of body fat in humans and other vertebrates as well as vegetable fat. [2] They are also present in the blood to enable the bidirectional transference of adipose fat and blood glucose from the liver and are a major component of human skin oils. [3] Many types of triglycerides exist.
Triglycerides are synthesized by esterification of fatty acids to glycerol. [1] Fatty acid esterification takes place in the endoplasmic reticulum of cells by metabolic pathways in which acyl groups in fatty acyl-CoAs are transferred to the hydroxyl groups of glycerol-3-phosphate and diacylglycerol. [ 7 ]