12.3.3 Chemical Digestion in the Small Intestine

Question 1

Chemical Digestion in the Small Intestine

Answer 1

• The digestion of food molecules occurs primarily in the small intestine. Accessory organs secrete digestive fluids into the duodenum of the small intestine that aid in digestion.
• Polysaccharides are broken down into disaccharides by pancreatic amylase in the pancreatic juice.
• Proteins are broken down by the action of several enzymes, including trypsin, carboxypeptidases, chymotrypsin, and aminopeptidase.
• Bile aids in lipid digestion by breaking fats into smaller droplets.

Question 2

stomach

Answer 2

• Review: Chewing food increases the surface area of the food that will be exposed to digestive agents and lubricates it for easy passage down the esophagus.
• In the stomach, HCl disrupts the extracellular matrix of
  ingested tissues and the enzyme pepsinbreaks down proteins.
• From the stomach, food passes through the pyloric sphincter and enters the duodenum, which is located at the beginning of the small intestine.

Question 3

acessory organs

Answer 3

• Accessory organs form and/or secrete digestive fluids into the duodenum that aid in digestion. Accessory organs include the liver, gall bladder, and pancreas.
• The liver produces bile, while the gall bladder stores and secretes bile. The pancreas produces several digestive enzymes in a basic solution that help neutralize acid chyme from the stomach.

Question 4

digestion of carbohydrates

Answer 4

• The digestion of carbohydrates begins in the mouth where large polysaccharides are broken down to smaller polysaccharides by the enzyme salivary amylase found in saliva.
• It is not until these small polysaccharides enter the small intestine that they will be broken down into disaccharides by pancreatic amylase. The disaccharides will be broken down into their respective monosaccharides in the epithelium of the small intestine by enzymes such as maltase, sucrase, and
  lactase.

Question 5

protein digestion

Answer 5

• Protein digestion begins in the stomach where the enzyme pepsin breaks down proteins into smaller polypeptides.
• These smaller polypeptides will continue to be broken down in the small intestine. Protein-digesting enzymes are secreted into the lumenof the small intestine in an inactive form. The enzyme enteropeptidase, which is bound to the membrane of cells of the epithelium, is able to activate trypsinogen (an inactive enzyme) to trypsin, the active form. Trypsin, in turn, is able to convert procarboxypeptidase to carboxypeptidase and chymotrypsinogento chymotrypsin.
• Tripsin and chymotrypsin are enzymes that cut specific
  peptide bonds in a polypeptide. Carboxypeptidase, the
  enzyme represented on the right of the diagram, only cuts amino acids off from the carboxyl end of a polypeptide. Aminopeptidase, the enzyme represented on the left of the diagram, breaks down a polypeptide from the amino end of a polypeptide.

Question 6

fat digestion

Answer 6

• Fat digestion begins in the lumen of the small intestine. Bile, a substance produced by the liver, is secreted into the small intestine. Bile acts as a natural detergent by breaking fat into small droplets. The small size of the fat droplets increases the surface area of fat that is exposed to digestive enzymes.

Question 7

Food arriving in the duodenum is best described as

Answer 7

• an acidic, lubricated fluid mass with a disrupted extracellular matrix, poly- and dipeptides, some simple sugars and disaccharides, and lipids.

Question 8

The digestion of proteins is catalyzed by all of the following enzymes except

Answer 8

• maltase

Question 9

Enzymes

Answer 9

• catalyze the chemical reactions of digestion.

Question 10

Digestive enzymes are named according to the molecule they break down, which is also called the substrate. Which enzyme-substrate pair below is incorrect?

Answer 10

• glucase / glucose

Question 11

Pancreatic amylase continues the chemical digestion begun by

Answer 11

• salivary amylase in the mouth.

Question 12

Which organ or structure manufactures bile?

Answer 12

• liver

Question 13

The primary digestion of food molecules occurs in the

Answer 13

• small intestine.

Question 14

Trypsin activates which of the following inactive enzymes?

i. enteropeptidase
ii. procarboxypeptidase
iii. chymotrypsinogen
iv. aminopeptidase

Answer 14

• ii, iii