 Digestion and absorption of lipids occurs in various stages where lipids first undergo emulsification that is they are broken down into small small particles. Then there is digestion in which there is hydrolysis of ester linkages of lipids and then there is micelle formation and then finally there is absorption. So the major lipids which are present in our diet is a long-chain triglyceride which consists of basically a glycerol molecule which is attached to three molecules of fatty acid by ester linkages and since the name is long chain so these fatty acids are long chain and generally they are like 16 to 18 carbon atoms are there in these fatty acids. Now digestion is basically breakdown of these ester linkages of the long chain triglycerides. But for digestion to occur we want that large lipid molecules should be broken down into smaller molecules. Why? This is because our digestive enzymes for lipids that is the lipase which is the main enzyme then there are others also we will see but they act only on the surface of the fat globule. So if they act only on the surface to digest this big fat globule it will take a long time. So it is important that they are broken down into smaller particles so that these enzymes can act on the surface of all these smaller particles. This will speed up the digestion of the lipids. So that process of breaking down of lipids into smaller particles is known as emulsification. So how this emulsification occurs? Basically emulsification occurs by mechanical processes that is our mastication when our bolus is in the mouth. So we are breaking down by chewing it into smaller particles right. Then there is gastric churning movements they also lead to breaking down of these large particles into smaller particles plus intestinal movements they are also responsible for that. So all these are mechanical events but see like when you put oil in the water what happens? Even if there are separate separate droplets all the oil particles will soon come together isn't it? So despite this breaking down of lipids into smaller particles we want that these smaller particles should remain separate. So that is done by bile salts. So these bile salts are released from liver and what happens that once the larger globule is broken down into smaller smaller particles these bile salts attach on the surface of this smaller globules and these bile salts have two ends. One is which is hydrophilic so which remains towards the water side and one which is lipophilic so which attaches to the surface of the lipids. So that keeps these smaller particles away from each other. So bile salts are important for emulsification of the lipids and as we have already discussed that this is essential for the speedy digestion of the lipids. Okay now the digestion of the lipids starts in mouth itself because our saliva consists of salivary lipase. So that starts the digestion however it is responsible for only very less digestion of the lipids that is only 3%. Plus our stomach also has lipase that is the gastric lipase and together they are responsible for 10% of fat digestion. Now physiologically it is not that important. Then what is the need of this? Well what happens that they release some fatty acids from triglycerides they break down that ester linkages and some fatty acids are released. Now when the chyme reaches into the intestine these fatty acids act on the intestine and cause release of the enzyme CCK, cholecystokinin and as you might be aware that cholecystokinin is responsible for release of the pancreatic enzyme. So it enters into the blood the CCK and it via blood it acts on pancreas causing release of pancreatic enzymes which further act on the our long-chain triglycerides. So the physiological importance of this salivary lipase and gastric lipase is release of free fatty acids which stimulate the release of cholecystokinin. So further digestion is brought about by pancreatic enzymes. So what are these pancreatic enzymes? These pancreatic enzymes consist of most important lipase which is responsible for major digestion of the lipids. And one thing to remember is this lipase is active in alkaline pH. So pH when it is greater than 8 this lipase is active and we know. Then deodorant pH is alkaline isn't it? Then there is another enzyme cholesterol esterase and phospholipase A2. So these are the various enzymes which cause the digestion of the lipids. Majorly we will concentrate on this lipase only because that is responsible for the digestion of the long-chain triglycerides. Okay so what do these lipase 2 is that are long-chain triglycerides which consist of glycerol and ester linkages with the free fatty acids. It breaks down this into free fatty acids. So two of these fatty acids are released and we get free fatty acids as well as a monoglyceride. So this is the monoglyceride. So this is the action of the lipase. Now if you remember we had said that our bile salts they have attached to the smaller globules of the fat isn't it? So what happens though these bile salts are helpful in emulsification they prevent the action of this lipase on the fat globules. So it is not able to attach to the fat globules and how this lipase will act. Well there comes the role of another substance known as colipase. So this colipase binds with the lipase and helps it to attach to the fat globule. So without colipase lipase will not be able to act. So from the pancreas this lipase and colipase are released in a ratio of 1 is to 1 so that the digestion is possible. Now with digestion it causes the release of the free fatty acids plus it also causes release of the monoglyceride is already told but all these are what insoluble okay and what has happened that digestion has taken place in the lumen of the intestine and the absorption has to occur from the via the cells which are lining the intestine. So these digested products must travel from here to the surface of the cell and pass from that. Now these cells are covered by a lining of unstirred aqueous layer. So there is a water layer over that which is quite thick you can understand like that. So they have to pass through it then how this will pass through it that is brought about by myself. Again what we have discussed before are bile salts which were helpful in emulsification they are also helpful in myself formation. So because they have a hydrophilic part as well as a lipophilic part it's kind of they carry all the digested products inside and they attach on the outside. So these are bile salts so it is looking like the same diagram which we draw in emulsification but that droplet was little bigger in size it is like around micrometer but the digested products are now in nanometer. So this is a very small droplet kind of thing surrounded by our bile salts. So they act as a carrier and transport the digested products along the unstirred water layer which is lining the cells. So thing to remember is our bile salts help in emulsification that is useful for digestion as well as for micelle formation which is important for absorption because it acts as a carrier. Okay so let's see now what happens at the absorption level. So basically all the products of digestion have reached till here. Now at this level they bind to certain carrier proteins and they are transported inside the cell. Now once inside the cell whatever digestion had taken place inside the lumen is reversed that is these fatty acids again bind with our glycerol so our monoglyceride is there they will bind with that and again there is production of triglycerides. Then you may think that what was the use of all the digestion. Well it's simple triglycerides are big molecules they are not absorbed directly so they are broken down into smaller particles and then they are absorbed and re-synthesized within the intestinal cell. So these triglycerides need to be transported exited out of the cell for that they bind with a protein this protein is known as beta lipoprotein. So this protein binds with that and forms chylomicrons and these chylomicrons exit via the lymphatics into the circulation. So this is important because triglycerides again they are water insoluble so they need to bind to a protein which needs to be carried in solution. So this was a simple process of digestion and absorption of lipids just a quick revision because in our next video we'll see that what are the abnormalities which can lead to steatoria. So first of all basically long chain triglycerides are present then emulsification breaking down of particles occurs by mechanical events and these are kept separated by bile salts then digestion mainly occurs because of the pancreatic enzyme so that is important which is active in alkaline pH that is pH greater than 8. Then again for micelle formation we need bile salts otherwise absorption cannot occur bile salts act as a carrier and for absorption it binds to the certain proteins then there is re-synthesis of the triglycerides which are transported by formation of the chylomicrons which enter into lymphatics. So just remember that if there is a problem in any of these events then it will lead to steatoria that we are going to see in detail in another video. 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