digestion and absorption

Question 1

what enzymes are produced in the salivary glands?

Answer 1

salivary amylase

Question 2

what enzymes are produced in the stomach

Answer 2

endopeptidases (eg: pepsin)
exopeptidases

Question 3

what enzymes are produced in the pancreas?

Answer 3

pancreatic amylase
lipases
exopeptidases

Question 4

what enzymes are produced in the ileum

Answer 4

membrane bound dipeptidases
disaccharidases (eg: maltase)

Question 5

describe the role of the enzymes of the digestive system in the breakdown of starch.

Answer 5

• salivary amylases hydrolyse starch into maltose
• by hydrolysing glycosidic bonds
• maltose is hydrolysed into glucose
• by maltase enzymes in the membrane of the epithelium cell membrane of the ileum

Question 6

co transport of glucose

Answer 6

• Na ions are actively transported out of epithelial cell into the blood
• creates a concentration gradient of sodium ions between ileum and epithelial cell
• Na ions and glucose enter by facilitated diffusion using complementary co transporter proteins
• Na ions diffuse into the cell down the concentration gradient
• glucose moves into the cell against its concentration gradient
• glucose moves into the blood by facilitated diffusion

Question 7

describe the role of enzymes in the digestion of proteins in a mammal

Answer 7

• hydrolysis of peptide bonds
• endopeptidases act in middle of polypeptide, producing shorter polypeptide chains
• exopeptidases act at end of polypeptide to produce amino acids
  -dipeptidases produces two single amino acids, act on dipeptide

Question 8

describe how amino acids are absorbed from the ileum into the blood

Answer 8

Na ions are actively transported out of the epithelial cell into the blood
- creates a concentration gradient between the ileum and the epithelial cell
- Na ions and amino acids enter the epithelial cell via facilitated diffusion
- Na ions move down the concentration gradient
- amino acids move against their concentration gradient
- amino acids move into the blood via faciliated diffusion

Question 9

bile

Answer 9

• produced in the liver
• neutralises food
• emulsifies fat droplets to increase the surface area of lipids for lipase action

Question 10

lipid digestion and absorption

Answer 10

lipid droplets are mixed with bile salts and are emulsified
- small droplets increase SA for faster hydrolysis by lipase
- triglycerides hydrolysed into monoglycerides, glycerol and fatty acids
- bile salts and fatty acids and glycerol form micelles
- micelles make fatty acids more soluble in water and transport FA to epithelial cell membrane
- FA simply diffuse through the cell
- At the SER: FA, glycerol are recombined to form triglycerides
- at golgi body: triglycerides are modified and proteins are added to form lipoproteins (chylomicrons), packaged into vesicles
- chylomicrons transported into lymph vessel by exocytosis

Question 11

describe the processes involved in the absorption and transport of digested lipid molecules from ileum into the lymph vessels

Answer 11

• micelles contain bile salts and fatty acids
• make fatty acids more soluble in water
• carry FA to lining of ileum
• maintain a higher concentration of FA to the lining of ileum
• FA absorbed by diffusion
• triglycerides reformed in cells
• vesicles move to csm

Question 12

describe the role of micelles in the absorption of fats into the cells of the ileum

Answer 12

• micelles contain bile salts and fatty acids
• make fatty acids more soluble in water
• carry FA to lining of ileum
• maintain a higher concentration of FA to the lining of ileum
• FA absorbed by diffusion