How is cholesterol absorbed from the intestinal pool into the body?
For cholesterol, the gateway into the body is a layer of cells lining the upper intestine known as enterocytes. The only way for cholesterol to get to this layer is to attach itself to a transporter called a micelle. Micelles are small, round transport packages formed by bile salts and phospholipids that carry cholesterol and fat (triglycerides) to the intestinal cell wall. The cholesterol must then take a second transport route - a protein channed called Niemann - Pick C1 Like 1, or NPC1L1 for short. The NPC1L1 traverses through the wall and into the intestinal cell where the cholesterol is packaged into chylomicrons for travel in the lymph system and ultimately the bloodstream. Zetia, the new cholesterol - lowering drug, blocks cholesterol absorption from the intestine by targeting the NPC1L1 protein.
Once in the bloodstream, chylomicrons off-load lots of triglycerides to needy cells, eventually arriving at the liver as small, cholesterol-rich particles known as chylomicron remnants. These remnants signal to the liver cells that they don't have to make more cholesterol, as a new cholesterol shipment has arrived - cholesterol that may have come from your breakfast omelet. The liver extracts the cholesterol from the remnants to make whatever is required for the day. Typically, the cholesterol is converted into bile acids for its launch into the body's cholesterol recycling system. But the liver could instead package the cholesterol up as a lipoprotein (primarily VLDL) and send it back into the bloodstream, ultimately increasing the amount of "bad" LDL cholesterol. Eat a huge amount of cholesterol and you increase the delivery of cholesterol to the liver by chylomicron remnants. Therefore, you should avoid foods with high cholesterol in order to lower the amount of cholesterol in your intestinal pool. Less cholesterol overloading the liver means less VLDL exported and less LDL produced.
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