What is the Difference Between Chylomicrons and VLDL

The main difference between chylomicrons and VLDL is that enterocytes synthesize chylomicrons from the triglycerides absorbed in the small intestine whereas liver cells synthesize VLDL. Furthermore, the main function of chylomicrons is to transport absorbed triglycerides from the intestine to the skeletal muscles, adipose tissue, and liver while the main function of VLDL is to transport newly-synthesized triglycerides from the liver to the adipose tissue. Therefore, chylomicrons transport exogenous products while VLDL transports endogenous products.

Chylomicrons and VLDL are two types of lipoproteins responsible for the transport of lipids throughout the body.

Key Areas Covered

1. What are Chylomicrons
     – Definition, Structure, Role
2. What is VLDL
     – Definition, Structure, Role
3. What are the Similarities Between Chylomicrons and VLDL
     – Outline of Common features
4. What is the Difference Between Chylomicrons and VLDL
     – Comparison of Key Differences

Key Terms

Chylomicrons, Lipoproteins, Transport Lipids, Triglycerides, VLDL

What are Chylomicrons

Chylomicrons are the largest form of lipoproteins responsible for the transportation of lipids throughout the body. Generally, lipoproteins are carrier molecules, which transport hydrophobic molecules inside their core, especially lipids such as triglycerides and cholesterol esters. Moreover, chylomicrons are the form of lipoproteins that contain the highest amount of triglycerides. The source of their triglycerides is dietary triglycerides and cholesterol. Usually, chylomicrons are responsible for the transport of these triglycerides into the peripheral tissues and liver for storage.

Figure 1: Chylomicron

Furthermore, the diameter of a chylomicron particle depends on the amount of fat in the diet. Therefore, a high-fat meal results in the formation of large chylomicrons due to the increased amount of triglycerides absorbed by the intestine. On the other hand, the diameter of a chylomicron particle is reduced while fasting.

What is VLDL

VLDL or very low-density lipoproteins are the second largest type of lipoproteins responsible for the transport of lipids. Most importantly, VLDL contains the second highest amount of triglycerides. However, it transports triglycerides produced by the liver. Similarly, when the production of triglycerides increases in the liver, the diameter of the VLDL particle increases and vice versa.

Figure 2: Lipoprotein Metabolism

Moreover, in the bloodstream, some VLDL particles are converted either into LDL (low-density lipoproteins) or IDL (intermediate density lipoproteins). However, the main function of VLDL is to transport endogenous triglycerides into the storage tissues. LDL transport triglycerides throughout the body and can cause the formation of atherosclerotic plaques. Therefore, they are known as bad cholesterol. On the other hand, IDL appears in the blood during fasting.

Similarities Between Chylomicrons and VLDL

• Chylomicrons and VLDL are two types of lipoproteins responsible for the transport of lipids through the blood.
• They are the larger forms when compared to other lipoproteins such as HDL, LDL, and IDL.
• Also, they are rich in triglycerides when compared to  other lipoproteins.
• Furthermore, their main function is to transport triglycerides from the sources to the tissues that store them.
• Besides, the enzyme lipoprotein lipase is responsible for the digestion of triglycerides into fatty acids and monoglycerides, which can diffuse into cells.
• And, their diameter depends on the number of triglycerides carried by the lipoprotein.

Difference Between Chylomicrons and VLDL

Definition

Chylomicrons refer to the lipoproteins rich in triglyceride and common in the blood during fat digestion and assimilation while VLDL refers to the plasma lipoproteins produced primarily by the liver with lesser amounts contributed by the intestine. Thus, this is the fundamental difference between chylomicrons and VLDL.

Also Known as

Chylomicrons are also known as ULDL or ultra-low density lipoproteins while VLDL refers to the very low-density lipoproteins.

Synthesis

Furthermore, the main difference between chylomicrons and VLDL is that the enterocytes synthesize chylomicrons in the small intestine while the liver cells synthesize VLDL.

Origin of Triglycerides

Importantly, triglycerides in food are used to synthesize chylomicrons while triglycerides produced by the liver are used to synthesize VLDL.

Composition

Also, another difference between chylomicrons and VLDL is their composition. Chylomicrons contain 1-2% protein, 8% cholesterol, 7% phospholipid, and 83-84% triglycerides and cholesterol esters while VLDL contain 10% protein, 22% cholesterol, 18% phospholipid, and 50% triglycerides and cholesterol esters.

Size

Size is another difference between chylomicrons and VLDL.  The diameter of a chylomicron is 75-1200 nm while the diameter of a VLDL is 30-80 nm.

Density

Moreover, the density of a chylomicron is <0.930 g/ml while the density of a VLDL is 0.930- 1.006 g/ml. Hence, this is also a difference between chylomicrons and VLDL.

Major Apoproteins

Besides, the major forms of apoproteins in a chylomicron are Apo B-48, Apo C, Apo E, Apo A-I, Apo A-II, and Apo A-IV while the major forms of apoproteins in a VLDL are Apo B-100, Apo E, and Apo C.

Role

Functionally, chylomicrons are responsible for the transport of triglycerides from the intestine to the skeletal muscles, adipose tissue, and liver for storage while the main function of VLDL is to transport newly-synthesized triglycerides from the liver to the adipose tissue. Thus, this is the functional difference between chylomicrons and VLDL.

Conclusion

Chylomicrons are the largest form of lipoproteins, containing triglycerides absorbed by the small intestine. They are responsible for the transport of these triglycerides to the storage tissues including skeletal muscles, adipose tissue, and liver. On the other hand, VLDL is the second largest form of lipoproteins. It contains triglycerides produced by the liver. The main function of VLDL is to transport triglycerides from the liver to the adipose tissue. Both chylomicrons and VLDL are two types of lipoproteins mainly composed of triglycerides and they are responsible for the transport of triglycerides to the storage tissues. However, the main difference between chylomicrons and VLDL is their structure and function.

References:

1. Feingold KR, Grunfeld C. Introduction to Lipids and Lipoproteins. [Updated 2018 Feb 2]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000-. Available Here. 

Image Courtesy:

1. “Chylomicron” By Xvazquez – Own work (CC BY-SA 3.0) via Commons Wikimedia 
2. “Lipoprotein metabolism” By Npatchett – Own work (CC BY-SA 3.0) via Commons Wikimedia