1.2 Digestion of Carbohydrates

• What are the three major sources of carbohydrates in the human diet?

  Sucrose, lactose, and starches
• What is sucrose commonly known as?

  Cane sugar
• Where is lactose found?

  In milk
• What are starches primarily found in?

  Non-animal foods like potatoes and grains
• What are some other carbohydrates ingested in small amounts?

  Amylose, glycogen, alcohol, lactic acid
• Why can't cellulose be considered food for humans?

  Humans lack enzymes to hydrolyze cellulose
• Where does carbohydrate digestion begin?

  In the mouth and stomach
• What enzyme in saliva begins starch digestion?

  Ptyalin (α-amylase)
• What does ptyalin hydrolyze starch into?

  Maltose and small glucose polymers
• How much starch is hydrolyzed in the mouth before swallowing?

  About 5 percent
• How long can starch digestion continue in the stomach?

  Up to 1 hour
• What inhibits the activity of salivary amylase in the stomach?

  Acid from gastric secretions
• At what pH does salivary amylase become inactive?

  Below pH 4.0
• What percentage of starches can be hydrolyzed before mixing with gastric secretions?

  30 to 40 percent
• What enzyme is found in pancreatic secretion for carbohydrate digestion?

  Pancreatic α-amylase
• How does pancreatic α-amylase compare to salivary α-amylase?

  It is more powerful
• How long after chyme enters the duodenum does carbohydrate digestion occur?

  15 to 30 minutes
• What are carbohydrates converted into before passing beyond the duodenum?

  Maltose and small glucose polymers
• What enzymes do enterocytes in the small intestine contain?

  Lactase, sucrase, maltase, α-dextrinase
• What do these enzymes split disaccharides into?

  Monosaccharides
• What does lactose split into?

  Galactose and glucose
• What does sucrose split into?

  Fructose and glucose
• What do maltose and small glucose polymers split into?

  Multiple molecules of glucose
• What are the final products of carbohydrate digestion?

  Monosaccharides
• How are monosaccharides absorbed after digestion?

  They are water soluble and absorbed into portal blood
• What percentage of carbohydrate digestion products is glucose?

  More than 80 percent
• What percentage of carbohydrate digestion products is galactose and fructose?

  Each seldom more than 10 percent
• What are the major steps in carbohydrate digestion?

  1. Digestion begins in the mouth with ptyalin.
  2. Starch hydrolysis occurs in the stomach.
  3. Pancreatic amylase continues digestion in the small intestine.
  4. Disaccharides are split into monosaccharides by intestinal enzymes.
  5. Monosaccharides are absorbed into the portal blood.