Biology
Biology
11th Edition
ISBN: 9781259188138
Author: Peter H Raven, George B Johnson Professor, Kenneth A. Mason Dr. Ph.D., Jonathan Losos Dr., Susan Singer
Publisher: McGraw-Hill Education
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Textbook Question
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Chapter 47, Problem 1U

How is the digestion of fats different from that of proteins and carbohydrates?

a. Fat digestion occurs in the small intestine, and the digestion of proteins and carbohydrates occurs in the stomach.

b. Fats are absorbed into cells as fatty acids and monoglycerides but are then modified for absorption; amino acids and glucose are notmodified further.

c. Fats enter the hepatic portal circulation, but digested proteins and carbohydrates enter the lymphatic system.

d. Digested fats are absorbed in the large intestine, and digested proteins and carbohydrates are absorbed in the small intestine.

Expert Solution & Answer
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Summary Introduction

Introduction:

In the digestion all the food ingested is broken down to smaller absorbable forms. These are then absorbed into blood or lymph and carried to the rest of the body according to the requirements.

Answer to Problem 1U

Correct answer:

Fat absorption is different from the absorption of proteins and glucose. Therefore, option b. is correct.

Explanation of Solution

Reason for the correct statement:

Fats consumed normally are triglycerides. These are digested broken into the constituent fatty acids and glycerol molecules. These smaller parts diffuse into the epithelial cells lining the interior of the small intestine. Here they combine together again and a protein is added too to make chylomicrons. Chylomicrons then enter the lymphatic system instead of the hepatic portal system.

Option b. is given as “Fats are absorbed into cells as fatty acids and monoglycerides but are then modified for absorption; amino acids and glucose are not modified further”.

As, “the digestion of fats differ from that of proteins and carbohydrates because fats are taken into absorptive cells as fatty acids and glycerol which are then modified to chylomicrons for absorption but amino acids and glucose are not any modified further”, is the right answer.

Hence, option b. is correct.

Reasons for the incorrect statements:

Option a. is given as “Fat digestion occurs in the small intestine, and the digestion of proteins and carbohydrates occurs in the stomach”.

Fats, proteins and carbohydrates are all digested in the stomach as well as the small intestine. So, it is a wrong answer.

Option c. is given as “Fats enter the hepatic portal circulation, but digested proteins and carbohydrates enter the lymphatic system”.

Digested fats go into the lymphatic system and digested polypeptides (proteins) and sugar (carbohydrates) go into the hepatic portal circulation, not the other way around. So, it is a wrong answer.

Option d. is given as “Digested fats are absorbed in the large intestine, and digested proteins and carbohydrates are absorbed in the small intestine”.

Digested fats are also absorbed in the small intestine along with the digested carbohydrates and proteins. So, it is a wrong answer.

Hence, options a., c. and d. are incorrect.

Conclusion

A fat molecule is digested into the constituent three chains of fatty acids and one glycerol molecule which reassemble in the epithelial cells that line the lumen of small intestine and aggregate with proteins to form chylomicrons that enter the lymphatic circulation.

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