Nutrition Science and Everyday Application - beta v 0.1

LIPID TRANSPORT, STORAGE, AND UTILIZATION 287
Table 5.1. Comparison of composition, size, density, and function of lipoproteins. (TG =
triglycerides)
Except for chylomicrons, the names of the lipoproteins refer to their density. Of the four
components of lipoproteins, protein is the most dense and triglyceride is the least dense.
(This is why one pound of muscle is much more compact in size than one pound of adipose
or fat tissue.) High-density lipoproteins are the most dense of the lipoproteins, because they
contain more protein and less triglyceride. Chylomicrons are the least dense, because they
contain so much triglyceride and relatively little protein.
Chylomicrons Deliver Lipids to Cells for Utilization and Storage
On the previous page, we learned that chylomicrons are formed in the cells of the small
intestine, absorbed into the lymph vessels, and then eventually delivered into the
bloodstream. The job of chylomicrons is to deliver triglycerides (originating from
digested food) to the cells of the body, where they can be used as an energy source or
stored in adipose tissue for future use.
How do the triglycerides get from the chylomicrons into cells? An enzyme called lipoprotein
lipase sits on the surface of cells that line the blood vessels. It breaks down triglycerides into
fatty acids and glycerol, which can then enter nearby cells. If those cells need energy right
away, they’ll oxidize the fatty acids to generate ATP. If they don’t need energy right away,
they’ll reassemble the fatty acids and glycerol into triglycerides and store them for later use.