MCAT Content / Metabolism Of Fatty Acids And Proteins / Digestion Mobilization And Transport Of Fats

Digestion, mobilization, and transport of fats

Topic: Metabolism Of Fatty Acids And Proteins

Lipases in the mouth (lingual lipase), pancreas (pancreatic lipase), and bile in the liver facilitate the digestion of fats and enable their breakdown into fatty acids; fats are mobilized and transported via chylomicron, very low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL).

The digestion of fats (triglycerides) begins in the mouth, where lingual lipase breaks down short-chain lipids into diglycerides. The presence of fat in the small intestine produces hormones that stimulate the release of pancreatic lipase from the pancreas, and bile from the liver, to enable the breakdown of fats into fatty acids. The complete digestion of one molecule of fat results in three (3) fatty acid molecules and one (1) monoglyceride.

The free fatty acids and monoglycerides are reconstructed back into triglycerides, which are gathered into a lipoprotein assembly of fat and protein called a chylomicron that leaves the cell via exocytosis and is delivered to the blood circulation via lymphatic ducts. From the lymphatic system, the chylomicrons are then transported to the circulatory system. Once in the circulation, they can either move to the liver or be stored in fat cells (adipocytes) that comprise the adipose tissue found throughout the body.

In the liver, fats can be mobilized and transported via the blood protein albumin or other lipoproteins such as very low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Stored triglycerides are broken down in cells by the enzyme lipase for transport as free fatty acids.

 


Practice Questions

Khan Academy

Diabetes and hyperglycemia

Fat metabolism deficiencies

Cell membranes and trafficking disorders


MCAT Official Prep (AAMC)

Practice Exam 4 B/B Section Passage 2 Question 6

 

Key Points

• The digestion of fats begins in the mouth, where short-chain lipids break down into diglycerides because of lingual lipase; the fat present in the small intestine stimulates the release of lipase from the pancreas, and bile from the liver enables the breakdown of fats into fatty acids.

• The free fatty acids and monoglycerides are reconstructed back into triglycerides, which are gathered into a chylomicron that leaves the cell via exocytosis and is delivered to blood circulation via lymphatic ducts; chylomicrons are then transported to the circulatory system.

• Fats can also be mobilized and transported via the VLDL, LDL, and HDL.


Key Terms

Lipases: Enzymes that catalyze the hydrolysis of fats.

Fatty acids: Lipids that contain a carboxylic acid functional group attached to a long-chain hydrocarbon tail.

Chylomicron: Lipoprotein assemblies containing cholesterol and triglycerides that transport lipids out of the intestinal cells and into the lymphatic and circulatory systems.

Very low-density lipoproteins (VLDL): A molecule that transports cholesterol from the liver to the tissues of the body.

Low-density lipoproteins (LDL): A molecule that transports cholesterol from the liver to the tissues of the body.

High-density lipoproteins (HDL): A molecule that transports cholesterol from the liver to the tissues of the body.

Triglycerides: Lipids, or fats, consisting of three fatty acid chains attached to a glycerol backbone.

Lipoprotein: An assembly of proteins and lipids that transports hydrophobic lipid molecules in hydrophobic water (such as blood).

Exocytosis: The transport of substances out of a cell.

Lymphatic system: An organ system that is part of the circulatory system and the immune system, and is made up of a network of lymphatic vessels that carry lymph.

Adipocytes: Fat cells.

Albumin: A water-soluble family of proteins that can transport fats in the blood.

Bile salts: Salts that are released from the liver in response to lipid ingestion and surround the insoluble triglycerides to aid in their conversion to monoglycerides and free fatty acids.



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