3.3.3 Digestion & Absorption

Question 1

Digestion of carbohydrates

Answer 1

• amylase hydrolyses starch to maltose
  Produced in salivary glands
  Produced in pancreas (duodenum)
• maltase hydrolyses maltose to glucose
• sucrose hydrolyses sucrose to glucose and fructose
• lactase hydrolyses lactose to glucose and galactose

Question 2

Where are disaccharides produced

Answer 2

By the duodenum wall and bound to cell membranes

Question 3

Protein digestion process - role of exopeptidases

Answer 3

• hydrolyse peptide bonds at the end of chains, producing dipeptides

Question 4

Digestion of protein - endopeptidases

Answer 4

Hydrolyse peptide bonds in the middle of chains, producing shorter polypeptides

Both found in the stomach wall and the pancreas (in duodenum)

Question 5

Digestion of proteins - role of dipeptidase

Answer 5

Hydrolyses dipeptides to amino acids

• Produced by the duodenum wall and bound to cell membranes

Question 6

Digestion of lipids - role of lipase

Answer 6

Lipase hydrolyses triglycerides to monoglycerides and 2 fatty acids

• produced in the pancreas (acts in the duodenum

Question 7

Functions of bile

Answer 7

1. Emulsifies lipids to smaller droplets
   - increases S.A for lipase activity
   - increases rate of hydrolysis
2. Forms micelles
   - bile shell around monoglycerides & fatty acids to keep dissolved in ileum contents
   - transports digestion products to cell membrane for absorption

Question 8

Absorption of amino acids and glucose in ileum - active transport

Answer 8

• sodium activity transported (A.T) out of the ileum epithelial cells into blood by sodium / potassium pump - uses ATP
• produces Na+ conc gradient from higher conc in ilium contents to lower conc in epithelial cells

Question 9

Absorption of amino acids and glucose in ileum - co-transport

Answer 9

Glucose / a.a co-transported into epithelial cells with Na+
- glucose / a.a move against their conc gradient
- Na+ moves down its conc gradient

Question 10

Absorption of amino acids and glucose in ileum - facilitated diffusion

Answer 10

• glucose / a.a move by facilitated diffusion from epithelial cells into blood

Question 11

Absorption of lipids in the ileum

Answer 11

• Movement of ileum contents brings micelles into contact with brush border and micelle breaks down
  
  • Monoglycerides & fatty acids diffuse across membrane into cell (simple diffusion)
  • Monoglycerides and fatty acids transported to smooth endoplasmic reticulum, where they are recombined to form triglycerides
  • Triglycerides are transported to Golgi, where the triglycerides associate with cholesterol and lipoproteins to form chylomicrons
  • Chylomicrons transported by vesicle to the cell membrane & released by exocytosis
  • Chylomicrons enter the lacteal. These transport the lipids via lymphatic vessels into the blood vessels