Chylomicrons are particles with lipoprotein coatings that transport cholesterol and triglycerides into the bloodstream. They are broken down by lipoprotein lipase and can be stored by fat cells or used for energy. Elevated levels can cause health problems and can be treated with medication.
Once the food is digested, the cholesterol and triglyceride particles must be absorbed into the bloodstream. These particles generally cannot pass into the bloodstream on their own and do not dissolve on their own. Cells in the intestine called enterocytes typically take up proteins and fatty acids and form chylomicrons, which are particles with lipoprotein coatings that can pass fat-based substances into the bloodstream. Cholesterol and fat-soluble vitamins are typically contained within the particle.
Within their lipoprotein outer coat, chylomicrons are usually 90% triglycerides. About 10% of the particle content is cholesterol. These particles are typically large compared to the smaller substances that can pass through most blood capillaries. Instead they travel in lymphatic capillaries in the intestinal wall called lacteals. After traveling through the lymphatic system, the particles enter the blood through the veins in the neck and can then be broken down.
The triglyceride component of chylomicrons is usually broken down by a protein called lipoprotein lipase. Various fatty acids along with monoglycerides become free in the blood and can be absorbed by cells. The same substances are often released into the digestive system with the bile, in particles called micelles. These are broken down in the intestine and then absorbed together with fatty acids from food as chylomicrons,
A cyclical process of transporting cholesterol around the body is often aided by the liver; some of the fatty substances are used to break down the food. Half of the cholesterol is typically absorbed from the small intestine and the rest is usually excreted from the body. The fatty acids that are released into the blood can be stored by fat cells as triglycerides, or be used directly for energy from muscles. The removal of chylomicrons is usually done by the liver, which removes the particles and processes the compounds before they are released back into the blood.
Chylomicrons help transport triglycerides, which at high levels can cause health problems. Elevated levels can be caused by common or rare genetic conditions such as chylomicron retention disease. Absorption of cholesterol, fat and vitamins is usually inhibited, which can affect childhood development and stunt growth. Neurological problems often occur later. Conditions that affect triglycerides and chylomicrons, including genetic factors, kidney problems, some types of diabetes, and heavy alcohol consumption, can usually be treated with a variety of medications.
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