First of all let us try to understand how fat is metabolized in the stomach and then enters into our bloodstream.
In animals, these fats are obtained from food or are synthesized by the liver. Lipogenesis is the process of synthesizing these fats.The majority of lipids found in the human body from ingesting food are triglycerides and cholesterol. Lipid metabolism often begins with hydrolysis, which occurs with the help of various enzymes in the digestive system. The second step after the hydrolysis is the absorption of the fatty acids into the epithelial cells of the intestinal wall. In the epithelial cells, fatty acids are packaged and transported to the rest of the body.
- Digestion of fats begin in the mouth through chemical digestion by lingual lipase.
- Lipids then continue to the stomach where chemical digestion continues by gastric lipase and mechanical digestion begins.
- The majority of lipid digestion and absorption, however, occurs once the fats reach the small intestines. Chemicals from the pancreas (pancreatic lipase family and bile salt-dependent lipase) are secreted into the small intestines. It is the pancreatic lipase that is responsible for signaling for the hydrolysis of the triglycerides into separate free fatty acids and glycerol units.
- Short chain fatty acids can be absorbed in the stomach, while most absorption of fats occurs only in the small intestines.
- In the cytosol of epithelial cells, fatty acids and monoglycerides are recombined back into triglycerides. In the cytosol of epithelial cells, triglycerides and cholesterol are packaged into bigger particles called chylomicrons. Chylomicrons will travel through the bloodstream to enter adipose and other tissues in the body.
- Chylomicrons are Ultra low density lipoproteins that mainly carry triglycerides (fatty acids from your food). They are made in the digestive system and so are influenced by what you eat.
- Very-low-density lipoprotein (VLDL) particles also carry triglycerides to tissues. But they are made by the liver. As the body’s cells extract fatty acids from VLDLs, the particles turn into intermediate density lipoproteins, and, with further extraction, into LDL particles.
- Intermediate-density lipoprotein (IDL) particles form as VLDLs give up their fatty acids. Some are removed rapidly by the liver, and some are changed into low-density lipoproteins.
- Low-density lipoprotein (LDL) particles are even richer in pure cholesterol, since most of the triglycerides they carried are gone. LDL delivers cholesterol to tissues .
- High-density lipoprotein (HDL) particles are called “good” cholesterol because some of them remove cholesterol from circulation and from artery walls and return it to the liver for excretion.
Once across the intestinal barrier, the triglycerides are synthesized and transported to the liver or adipose tissue.
Fatty acids are oxidized through fatty acid or β-oxidation into two-carbon acetyl CoA molecules, which can then enter the Krebs cycle to generate ATP. If excess acetyl CoA is created and overloads the capacity of the Krebs cycle, the acetyl CoA can be used to synthesize ketone bodies. When glucose is limited, ketone bodies can be oxidized and used for fuel.
Excess acetyl CoA generated from excess glucose or carbohydrate ingestion can be used for fatty acid synthesis or lipogenesis. Acetyl CoA is used to create lipids, triglycerides, steroid hormones, cholesterol, and bile salts.
Lipolysis is the breakdown of triglycerides into glycerol and fatty acids, making them easier for the body to process.
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References:
https://en.wikipedia.org/wiki/Lipid_metabolism