Where do fat-soluble nutrients enter the body’s transport system?

Fat-soluble nutrients, such as vitamins A, D, E, and K, are absorbed through the intestinal lining and enter the body's transport system via the lymphatic system. When dietary fats are ingested, they are emulsified by bile salts and packaged into structures called micelles in the small intestine. The intestinal cells then absorb these micelles, which contain the fat-soluble nutrients.

Once inside the intestinal cells, fat-soluble nutrients are incorporated into chylomicrons, which are lipoprotein particles that transport dietary lipids. Chylomicrons enter the lymphatic system through the lacteals, tiny lymph vessels in the intestinal villi. This pathway allows fat-soluble nutrients to bypass the bloodstream initially and directly enter the lymphatic system, eventually draining into the bloodstream through the thoracic duct.

Other options such as the bloodstream, stomach, and small intestine play different roles in the digestion and absorption processes but are not the initial transport route for fat-soluble nutrients. The bloodstream is primarily for water-soluble nutrients, while the stomach is mainly involved in the initial digestion of food, and the small intestine is where absorption occurs, but for fat-soluble substances, the lymphatic system is the correct pathway.