Digestion And Absorption (3.3.3)

Question 1

What is digestion?

Answer 1

• The hydrolysis of large molecules into smaller molecules that can be absorbed

Question 2

What are membrane-bound disaccharides?

Answer 2

• Enzymes attached to the cell-surface membranes of epithelial cells lining the ileum

Question 2

Where are the types of amylases produced?

Answer 2

• Salivary amylase is produced by the salivary glands and secreted into the mouth
• Pancreatic amylase is produced by the pancreas and secreted into the small intestine

Question 3

What do the enzymes maltase, lactase and sucrase do?

Answer 3

• Hydrolyses maltose to two alpha glucose molecules
• Hydrolyses lactose to glucose and galactose
• Hydrolyses sucrose to glucose and fructose

Question 4

Where are bile salts produced?

Answer 4

• In the liver

Question 4

Where is lipase produced?

Answer 4

• Produced in the pancreas and secreted into the small intestine

Question 4

What do bile salts do?

Answer 4

• They emulsify lipids to form tiny droplets called micelles
• This increases the surface area for lipase to act on

Question 5

What does lipase do

Answer 5

• Hydrolyses the ester bonds in triglycerides to form monoglycerides and fatty acids

Question 6

What are the types of protein enzymes?

Answer 6

• Endopeptidases (stomach)
• Exopeptidases (secreted by the pancreas and small intestine)
• Membrane-bound dipeptidases

Question 7

What do endopeptidases do?

Answer 7

• They hydrolyse the internal peptide bonds between the amino acids of proteins to form small polypeptides and peptides

Question 8

What do exopeptidases do?

Answer 8

• They hydrolyse bonds at ends of polypeptide to produce dipeptides or individual amino acids

Question 9

What do membrane-bound dipeptidases do?

Answer 9

• Hydrolyse dipeptides into two single amino acids

Question 9

Describe the process of protein digestion

Answer 9

• Peptide bonds hydrolysed
• Endopeptidase hydrolyses internal peptide bonds
• Exopeptidases hydrolyses terminal peptide bonds
• Membrane-bound dipeptidases break dipeptides into amino acids

Question 10

How is the ileum adapted for absorption?

Answer 10

• Large surface area due to its long length
• Single layer of epithelial cells providing short diffusion pathway
• Rich blood supply in the villi maintains a concentration gradient
• Epithelial cells have many mitochondria for active transport

Question 11

How are lipids absorbed?

Answer 11

• Bile salts emulsify lipids into smaller droplets
• Bile salts combine with fatty acids and monoglycerides to form micelles
• Micelles transport fatty acids and monoglycerides to the surface of the epithelial cell
• Micelles release fatty acids and monoglycerides, which diffuse into the epithelial cells
• Inside the epithelial cells, fatty acids and monoglycerides are transported to the SER and recombined to form triglycerides
• They are packaged in protein and phospholipid to form chylomicrons
• Chylomicrons are absorbed into the lacteals

Question 12

How does co-transport work?

Answer 12

• Sodium ions are actively transported out of the epithelial cells into the blood
• This maintains a low concentration of sodium ions inside the epithelial cell, creating a concentration gradient between the lumen of the ileum and the inside of the cell
• Sodium ions then diffuse from the lumen of the ileum into the epithelial cell through a co-transport protein
• Glucose also moves into the epithelial cells against their concentration gradient through the same co-transport protein
• Glucose diffuses out of the epithelial cell, into the blood, by facilitated diffusion through a protein channel