Biochemistry of Digestion and Absorption of Lipids

Biochemistry is a subdivision of these two subjects: biology and chemistry. It is the branch of science that investigates the chemical process within a living organism. Lipids are very large, organic, non-polar molecules. They are available naturally. They are not readily soluble in water but dissolve in non-polar solvents. They embody hydrogen, oxygen, and carbon atoms. Sometimes, lipids are confused with fats, but fats are a subgroup of lipids. They are separated into three categories: simple lipids, derived, and complex lipids.

Digestion is a process that takes place in a living organism where large food molecules form into smaller, simple molecules. There are two categories of digestion: mechanical digestion and chemical digestion. Absorption is the process of absorbing the nutrients from the smaller food particles. The nutrients are then transported into the bloodstream for purification.

Properties of lipids 

Lipids are responsible for various roles in our bodies. They also give out a high amount of energy for bodily functions. Some of the properties of lipids are listed below.

• They are a diverse group of compounds that mainly accommodate hydrocarbon chains.
• Adipose tissues are the place where the lipids are stored.
• They are known for their insoluble nature with water 
• They create a mechanical barricade in living organisms that separates the cell and its contents from the outer environment.

The biochemistry of digestion and absorption of lipids is subdivided into four parts: biochemistry of digestion in the mouth, biochemistry of digestion in the stomach, biochemistry of digestion in the small intestine, and biochemistry of absorption in the small intestine.

Biochemistry of lipid digestion in the mouth

The digestion by lipids begins in the mouth. It starts with chewing. Chewing is a process in which the food is broken down into small pieces to increase surface area. These small pieces of food are mixed with saliva. Lingual lipase is the enzyme responsible for triglyceride digestion and individual fatty acid cleaving from the glycerol backbone. The tongue produces the enzyme called lingual lipase. 

Biochemistry of lipid digestion in the stomach

After the digestion of lipids in the mouth, the digestion continues in the stomach. The food from the mouth is transported to the stomach by a movement called peristalsis in the oesophagus. The mixing and churning of food particles occur in the stomach—this aids in the dispersion of food contents and fat globules. The stomach produces the enzyme called gastric lipase. This enzyme helps in the digestion and disintegration of triglycerides. The lingual lipase from the mouth is still active in the stomach. However, these two lipases play only a minor role in digesting fats. A substantial part of lipid digestion takes place in the small intestine.

Biochemistry of lipid digestion in the small intestine

The food contents from the stomach enter into the small intestine. Most of the undigested dietary lipids are clustered to form large droplets. The hormone called bile from the liver is added. Bile hormone is said to be stored in the gallbladder. The bile is liberated into the first segment of the small intestine called the duodenum. There is a hydrophobic and hydrophilic fraction. This property makes it possible to attach to fats as well as water. They can break down large fat globules into tiny droplets. This process is known as emulsification. Lipids are more accessible to digestive enzymes because of emulsification. This is because emulsification increases the surface area to perform its functions. 

The pancreas liberates pancreatic lipases. It is released into the small intestine to digest triglycerides enzymatically. The triglycerides are split into fatty acids, mono-glycerides, and some free glycerol. The particles which do not need to be enzymatically digested are- cholesterol and fat-soluble vitamins.

Biochemistry of lipid absorption in the small intestine

After the digestion process in the stomach, absorption in the small intestine begins. The fat digested products have to enter the circulation system to help the cell function. In this process, bile helps. The salts of bile aggregate around the fat digested products to form unique micelles structures. 

Micelles are molecules that help the fat products get close to the microvilli, which are situated in the small intestine. The microvilli in the small intestine aid in the absorption process. The fat digested product moves across the intestinal cell membranes by diffusion. The bile salts will be recovered and sent to work on emulsification.

The medium and short-chain fatty acids, along with glycerol, will be absorbed directly into the bloodstream once they enter the inside of the intestinal cells. The larger lipids such as long-chain fatty acids, mono-glycerides, fat-soluble vitamins, and cholesterol will need help to be absorbed and transported to the bloodstream. 

The long-chain fatty acids and mono-glycerides are reconstructed back to triglycerides in the intestinal cells. The transporting vehicles called chylomicrons help transport the triglycerides and the fat-soluble vitamins and cholesterol. 

Chylomicrons have a core made of triglycerides, and the external membrane embodies apolipoproteins, phospholipids, and cholesterol. The outer membrane is water-soluble. This makes it possible to travel across the aqueous surroundings in the body. The chylomicrons travel from the small intestine to the lymph vessels; then, the contents are delivered to the bloodstream.

Conclusion  

Biochemistry is the branch of science that investigates the chemical process within a living organism. Lipids are very large, organic, non-polar molecules. The biochemistry of digestion and absorption of lipids is a complex process. They are a diverse group of compounds that mainly accommodate hydrocarbons. The biochemistry of digestion and absorption of lipids is subdivided into four parts: biochemistry of digestion in the mouth, biochemistry of digestion in the stomach, biochemistry of digestion in the small intestine, and biochemistry of absorption in the small intestine. The contents absorbed in the small intestine are transported to the bloodstream with the help of chylomicrons.