Lipids are hydrophobic and therefore, it is hard to break them down in the hydrophilic environment of our body. Bile salts are used to separate lipids and increase their surface area for better digestion and absorption. They are excellent at separating lipids thanks to being amphipathic, having both hydrophobic and hydrophilic groups. Lipid digestion begins in the tongue and is completed in the small intestine with the help of pancreatic enzymes. Bile salts allow lipids to form micelles and penetrate the water layer surrounding small intestine cells. The contents of micelles (lipids, cholesterol, and cholesterol esters) diffuse out of micelles and into the enterocytes. Bile salts do not diffuse through but rather are returned to the liver.
After being absorbed, long fatty acids come together to reform triacylglycerides and cholesterol esters. Short fatty acids pass directly into the blood where they bind albumin protein and get transported to the liver.
Lipids that are resynthesizes form big fat particles in the endoplasmic reticulum and are covered with lipoprotein. They then get send to the golgi apparatus where a carbohydrate gets attached to them, forming a chylomicron (a compound from the family of lipoproteins). Chylomicrons exit the cell and travel from tissue to tissue to supply needed lipids for different cells. The protein portion of lipoprotein is called apolipoprotein and functions to stabilize lipoproteins are they circulate the aqueous environment.
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