In this video we discuss how fats are digested and absorbed in the body. We look at how the body breaks down fats into smaller masses and then how the body absorbs them in the small intestine.



Transcript/notes

Fat digestion

The main types of fats we get from food are triglycerides so, in this video we are going to go through a very basic look at how our bodies digest and absorb these molecules.

A triglyceride consists of a glycerol unit and 3 fatty acid chains. Triglyceride molecules are non-polar molecules, meaning they don’t mix with water, so they are hydrophobic or water fearing so to speak.

When we eat some fat molecules, an enzyme called lingual lipase is released in saliva in the mouth. However, this enzyme is not actually activated in the mouth. Next the fat molecules and the saliva with the lingual lipase enzymes is swallowed and enters the stomach.

The highly acidic environment of the stomach activates the lingual lipase enzymes, which are also joined by gastric lipase, which are enzymes released by chief cells in the stomach. These enzymes begin the digestion of the fat molecules, by breaking some of them into a diglyceride and a fatty acid. These lipases act on about 30% of the triglycerides.

Next the fat molecules enter the small intestine from the stomach. Because the fat molecules are hydrophobic or water fearing, they enter into the small intestine as large fat or lipid masses, so the body must first breakdown the larger masses into smaller droplets, which is called emulsification.

They are broken down into smaller segments by bile salts and phospholipids, which are part of bile that is released by the gallbladder into the small intestine. Bile salts and phospholipids have a hydrophilic water loving region and a hydrophobic water fearing region.

So, the hydrophobic water fearing region of the bile salts position themselves around the hydrophobic water fearing fat, as you can see here forming what is called emulsion droplets.

Now, pancreatic lipase, which is an enzyme released from the pancreas into the small intestine has greater access to the fat and can digest or break them down into mainly monoglycerides and free fatty acids. These then associate with bile salts and phospholipids to form micelles, which are much smaller than emulsion droplets.

Basically the micelles transport the monoglycerides and fatty acids to the membranes of the enterocyte cells of the small intestine, where they diffuse, or are absorbed across the cell membrane into the cell.

Once inside the enterocyte cell, the fatty acids are reattached with the monoglycerides to re-form triglycerides. The triglycerides, along with other lipids are then sort of wrapped with protein to form a lipoprotein called a chylomicron.

On the other side of the enterocyte cells, these chylomicrons are too large to enter into blood capillary walls, so they enter into lacteals which are lymph capillaries.

The chylomicrons are then transported through lymphatic vessels and eventually enter blood where they are delivered to the liver, fat tissue, muscle tissue and to other tissues as well where they can be stored, or used by cells.

Timestamps
0:00 Intro
0:11 The structure of a triglyceride
0:22 Fat/lipid digestion in the mouth
0:30 Fat/lipid digestion in the stomach
0:55 Emulsification in the small intestine
1:37 Pancreatic lipase breaks down fats further
1:56 Fat/lipids are absorbed into enterocyte cells
2:22 Chylomicrons transport fat

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