Module 24: Unit 1. Triacylglycerols (Fats) Digestion
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| The human body lipids contain more than 80% triacylglycerols (neutral fats). The triacylglycerols are stored in the adipose tissues as lipids droplets and they contribute to energy reserve for the human body.Lipids Droplets are shown in the figure below: |
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| Reference: http://pr.shmu.ac.ir/data/profinfo/5/0074743181/files/27617.pdf |
| Triacylglycerols lipids are water insoluble and chemically not reactive and therefore they do not interact with other cells or tissues and can be utilized by the human body as compounds storage reservoir for energy.This energy storage is very important in case of human body starvation for long time. The North Pole bears are utilizing this fact to survive the long month’s hibernation period during the whole winter.Triacylglycerols are digested within the small intestine of the gastrointestinal tract (shown in the figure below): |
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| Reference: https://www.nursingtimes.net/clinical-archive/gastroenterology/gastrointestinal-tract-4-anatomy-role-jejunum-ileum-19-08-2019/ |
| Three Sources of energy due to triacylglycerols (Fats) Digestion:Triacylglycerols (fats) are coming from daily dietTriacylglycerols (fats) are stored in adipose tissuesTriacylglycerols (fats) are produced in the liver due to carbohydrates large amountThe hydrophobic (water insoluble) triacylglycerols are converted into small micelles to increase their solubility. This is done by the formation of bile salts generally released in the small intestine after eating food with large amount of fats. The activation of the bile salts is utilized by the cholecystokinin. Bile salts produced in this way in the liver from cholesterol and stored in gall bladder. These steps are shown in the figure below: |
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| Reference: https://pharmaxchange.info/2013/10/digestion-of-fats-triacylglycerols/ |
| The mixed micelles (increased solubility) are converted into triacylglycerols in the presence of lipase enzyme, which are converted into several products of monoacylglycerols, diacylglycerols, free fatty acid and cholesterol. The products are aggregated with cholesterol and apolipoproteins to form chylomicrons, very low density lipids (VLDL) and very high density lipids (VHDL).productsThese products enter the lymphatic system and then enter the blood. From there they are distributed and enter the muscles and adipose tissue capillaries. The apolipoproteins activates the enzyme lipoprotein lipase in the capillaries of the adipose tissues and muscles. This enzyme is breaking down the chylomicrons and further hydrolyses the triacylglycerols and fatty acids and glycerol (see figure below: The hydrolysis of triacylglycerols in the small intestine).These products are then utilized by the muscles for energy. Also these products are converted to triacylglycerols through re-esterification reactions inside the adipose tissues.The remaining of chylomicrons which still have the cholesterol and apolipoproteins enter the liver through the blood main stream and through specific receptors taken up by the endocytosis.Some triacylglycerols might enter the liver through left over chylomicrons. They are used to produce other cellular components. The composition and the structure of chylomicrons is given in the figure below).The figure below illustrates the structure and the composition of the chylomicrons: |
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| Reference: https://www.mm3admin.co.za/cms/cpd/articles/f849a651-157e-4dc4-b9d9-9e29ce73aa6b.pdf |
| In the small intestine, the hydrolysis of triacylglycerols follows the scheme below: |
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| Reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3996833/ |
The Triacylglycerols Digestion is illustrated in the video below: