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Lipids Digestion and Absorption

Chapter 8 / Lesson 15
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  • 0:05 Lipids
  • 0:54 Bile Salts and…
  • 1:59 Epithelial Cells
  • 2:54 Chylomicrons and Lacteals
  • 4:23 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Lipids, or fats, are digested and absorbed in the small intestine. In this lesson you will learn how bile salts emulsify fat so pancreatic lipase can digest it. You will also learn how fats first enter lymphatic capillaries, called lacteals, before entering your blood circulation.

Lipids

Foods, such as meats, dairy products, seeds, nuts, and oils, contain dietary fat. Fat is a common example of a lipid, and in this lesson you will learn about the unique way lipids, such as fats, are broken down and absorbed out of the digestive tract.

A lipid is defined as a fat-like molecule that does not have the ability to dissolve in water. This inability to dissolve in water adds an element of difficulty to fat digestion. Because fat does not like water, it tends to clump together and form large droplets as it moves through your digestive system. By the time fat reaches your small intestine, it has not been digested at all. So dietary fat in the small intestine looks like a fairly large glob of fat.

Lipids are fat-like molecules that cannot dissolve in water
Lipids

Bile Salts and Pancreatic Lipase

These globs remain until bile that is produced in the liver and stored in the gallbladder mixes with the large fat droplets. Bile contains bile salts, which act as an emulsifier of lipids. The term 'emulsify' means to break large fat droplets into smaller droplets. And that is exactly what we see happening here in the small intestine. The bile salts break up and coat the fat to form much finer droplets. These finer droplets have more surface area, and this aids digestion because the fat-digesting enzyme pancreatic lipase can only act on the surface of the fat droplet.

The enzymes of the small intestine are responsible for almost all of the fat digestion. When pancreatic lipase acts on the lipid, it breaks it down, which results in free fatty acids and monoglycerides, the two digestive products of lipids. These products are much easier for your small intestine to handle, and they have very little trouble being absorbed out of your digestive tract.

Pancreatic lipase breaks lipids down into free fatty acids and monoglycerides
Digestive Products of Lipids

Epithelial Cells

Absorption takes place through the mucosal lining of the small intestine, and when these products pass through the mucosa, they enter the epithelial cells. Once inside the cells, the free fatty acids and monoglycerides enter the endoplasmic reticulum, which is a system inside the cell whose functions include synthesis and transport of lipids. Here, the digested products are resynthesized into triglycerides. Triglycerides are the major form of fat stored by the body. So an important fact to point out is that fats are reassembled in the epithelial cells of the small intestine. This makes fat absorption different than absorption of proteins and carbohydrates. With protein and carbohydrate absorption, we see their basic units, which are amino acids and monosaccharides, are able to pass through the intestinal epithelial cells without being altered.

Chylomicrons and Lacteals

Before triglycerides actually leave the epithelial cells, they're coated by proteins, which results in the formation of chylomicrons. So we see that chylomicrons are small globules composed of protein and lipid. The coating of protein gives the triglyceride a water-soluble coat, and this allows the chylomicron to travel outside of the cell. The newly formed chylomicrons leave the epithelial cell and enter the lymphatic capillaries, which are called lacteals. The lacteals are found in the fingerlike projections of the intestinal wall, called the villi. The lacteals represent another unique way fats are absorbed because lipids pass through the lymphatic system before they make their way back to your bloodstream.

Chylomicrons enter the lymphatic capillaries, which are called lacteals
Chylomicrons

This differs from protein and carbohydrate digestion because amino acids and monosaccharides do not enter the lymphatic system; instead they travel directly into the blood capillaries and then into the hepatic portal vein that leads to the liver.

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