Digestion and Absorption

Question 1

What do salivary glands do?

Answer 1

Secrete enzymes in the mouth.Enzyme amylase which hydrolyses starch to maltose.

Question 2

What does the pancreas do?

Answer 2

Produces pancreatic juice which contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch

Question 3

Digestion of Carbohydrates

Answer 3

• Amylase catalyses conversion of starch to maltose
• Amylase produced in pancreas and salivary glands
• Membrane bound disaccharidases in ileum break down disacchirides into monosacchirides

Question 4

Digestion of lipids

Answer 4

• Lipase catalyses break down of lipids to monoglycerides and fatty acids
• Lipase made in pancreas
• Bile salts emulsify lipids, increasing SA.
• Monoglycerides and fatty acids combine with bile salts and phospholipids to form micelles

Question 5

Role of endopeptidases

Answer 5

• Hydrolyse peptide bonds
• Break down bonds inside the protein

Question 6

Role of exopeptidases

Answer 6

• Hydrolyse peptide bonds at ends of protein molecules - remove single amino acids from proteins
• Include dipeptidases that work specifically on dipeptides - located in ileum

Question 7

What is the structure of ileum and how is it adapted?

Answer 7

• Wall folded into projections called villi which have thin walls lined with epithelial cells and a large capillary network
• Contain muscle to move, maintaining diffusion gradient as contents mix
• Good blood supply maintains concentration gradient
• Epithelial cells in villi have microvilli, further increasing SA

Question 8

Absorption of amino acids and monosacchirides

Answer 8

• Specific co-transport proteins found within cell surface membrane of epithelial cells
• Only transport when sodium ions present
• For every sodium ion, a monosacciride/amino acid passes in via facilitated diffusion
• Monosacchirides/amino acids continue to diffuse into capillaries via facilitated diffusion
• Conc. gradient maintained by active transport of sodium ions into bloodstream via sodium-potassium pump

Question 9

What do micelles do and what is their structure?

Answer 9

Combined phospholipids and bile salts with fatty acids and monoglycerides. Aid transport through ileum as the fatty acids and monoglycerides are insoluble.

Question 10

Absorption of lipids

Answer 10

• Micelles break down near epithelial cells and fatty acids and monoglycerides absorb into epithelial cells via diffusion
• Short fatty acid chains easily enter bloodstream
• Long fatty acid chains recombine with monoglycerides and glycerol to form triglycerides

Question 11

What happens to long fatty acid chains in epithelial cells?

Answer 11

• Golgi apparatus modifies triglycerides packages them in chylomicrons for exocytosis
• These are then transported into a lacteal where they are later absorbed into the bloodstream