Question 25.1: Describe how the fat in an ice cream cone gets from the ice ...
Describe how the fat in an ice cream cone gets from the ice cream to a liver cell.
ANALYSIS Dietary fat from animal sources (such as the whole milk often found in ice cream) is primarily triacylglycerides with a small amount of cholesterol present. Fat-digesting enzymes are secreted by the pancreas and delivered via the common duct to the small intestine, along with bile acids (
, Section 24.6). As discussed above, only free fatty acids, mono- and diacylglycerides can cross the intestinal cell wall before being passed on to the blood stream in special packaging called lipoproteins.
As the ice cream cone is eaten, it passes through the mouth to the stomach where mixing occurs. This mixing action promotes the formation of triacylglycerols into small droplets. No enzymatic digestion of lipids occurs in the stomach. When the stomach contents move to the small intestine, bile acids and pancreatic lipases are secreted into the mixture. The bile acids help to emulsify the fat droplets into micelles. Once micelles have formed, lipases hydrolyze the triacylglycerides to mono- and diacylglycerides; the hydrolysis also produces fatty acids. These three hydrolysis products cross into the cells lining the small intestine, are rearranged, and secreted into the bloodstream in the form of chylomicrons. Chylomicrons travel to the liver and enter cells for processing.