Chapter 12, Problem 1Q

Summary Introduction

To review:

The path of movement of fatty acids present in a cheeseburger to the fat cells or adipocytes.

Introduction:

Oils and fats are constituted by triacylglycerol (TAG). These molecules are essential for the body as they provide energy, but when the levels of these molecules become high, the body is at a risk of a heart attack. Food rich in fats includes avocados, nuts, butter, red meat, and vegetable oil.

Explanation of Solution

When a person eats a cheeseburger, the mouth mixes the crushed food with the saliva that is termed as the bolus. It then enters the stomach. Digestion of fats does not occur in either of these organs. Instead, fat digestion starts in the small intestines when it receives food from the stomach mixed with the secretions of the pancreas and liver. Bile salts from the liver break the fat to fat droplets. The pancreatic lipases from the pancreas act on the TAGs to break them into fatty acids and glycerol molecules. These molecules are small enough to diffuse in the cells of the intestines. For the fats to be stored, these molecules again have to be converted back to TAG and then be packaged.

The body packages TAG into the core of a protein molecule. This lipoprotein is thus called a chylomicron. The lymphatic capillaries of the intestines called lacteals take up the chylomicrons, which then travel through the veins, enter the heart, the heart pumps it to the lungs, and then they reach the arteries. The arteries drain into capillary beds. These capillary beds are the site of absorption. The chylomicrons of the arteries are broken down by lipase to fatty acid and glycerol. The adipose cells pick these up from the capillaries and get converted to TAGs again for storage. The chylomicrons that are not absorbed are referred to as the chylomicron remnants and are taken up by the liver.

Conclusion

Thus, it can be concluded that digestion of fats starts in the small intestines, where they are broken down into fatty acids and glycerol that are then absorbed by the lymphatic system. To store the fats, these molecules are converted to TAG again and then stored in the cytoplasm of the adipose cells.