Final answer:
Short-chain fatty acids with less than 12 carbons long are absorbed directly into the portal blood through the intestinal wall by simple diffusion, while long-chain fatty acids require micelles and are transported via chylomicrons into lacteals.
Step-by-step explanation:
Lipid Absorption and Fatty Acid Chain Length
Lipid absorption in the human body is a vital process that occurs primarily in the small intestine, where about 95 percent of lipids are absorbed. Fatty acids with shorter chain lengths, specifically those that are less than 12 carbons long, can be absorbed directly into the portal blood through the intestinal wall. This is possible because short-chain fatty acids are relatively water soluble and can enter the absorptive cells, also known as enterocytes, directly. The small size of these molecules allows for simple diffusion across the cell membrane, after which they enter the blood capillary of a villus and follow the same path as monosaccharides and amino acids toward the hepatic portal vein and then to the liver.
In contrast, long-chain fatty acids are not as easily absorbed because of their larger and more hydrophobic nature. These require the assistance of bile salts and lecithin to form micelles, which can carry the fat particles to the surface of enterocytes. The lipids are then reassembled into triglycerides and transported as part of larger lipoprotein complexes known as chylomicrons into the lacteals, the lymphatic vessels situated in the villi of the intestine, eventually reaching the bloodstream.