3.3.3 Digestion and absorption

Question 1

what is digestion

Answer 1

hydrolysis of polymers to monomers for absorption across cell membranes

Question 2

enzymes of carbohydrates

Answer 2

• amylase
• maltase
• sucrase
• lactase

Question 3

function of amylase

Answer 3

hydrolyses starch into maltose
- produced in salivary glands (act in mouth)
- produced in pancreas (acts in duodenum)

Question 4

function of maltase

Answer 4

hydrolyses maltose to glucose

Question 5

function of sucrase

Answer 5

hydrolyses sucrose into glucose and fructose

Question 6

function of lactase

Answer 6

hydrolyses lactose into glucose and galactose
- disaccharidases are produced by duodenum and bound to cell membrane

Question 7

what are enzymes of proteins

Answer 7

• exopeptidase
• endopeptidase
• dipeptidase

Question 8

function of exopeptidase

Answer 8

hydrolyse peptide bonds at the end of chains (produces dipeptides)

Question 9

function of endopeptidases

Answer 9

hydrolyse peptide bonds in the middle of chains, producing shorter polypeptidesw

Question 10

where are endopeptidases found

Answer 10

produced in stomach wall (act in the stomach)
produced in the pancreas
(act in the duodenum)

Question 11

function of dipeptidases

Answer 11

hydrolyse dipeptides into amino acids

Question 12

where are dipeptides found

Answer 12

produced by duodenum wall and bound to cell membrane

Question 13

what are enzymes of lipids

Answer 13

lipases and bile

Question 14

function of lipases

Answer 14

hydrolyse triglycerides to monoglycerides and 2 fatty acids

Question 15

where are lipases found

Answer 15

produced in pancreas (acts in the duodenum)

Question 16

what are the functions of bile

Answer 16

• emulsifies lipids into smaller droplets
• forms micelles

Question 17

what does emulsifying lipids do

Answer 17

• increases surface area
• increases rate of hydrolysis

Question 18

what do micelles do

Answer 18

• bile shell around monoglycerides and fatty acids to keep dissolved in ileum contents
• transports digestion products to cell membrane for absorption

Question 19

how do amino acids/glucose get absorbed in the ileum

Answer 19

• Sodium actively transported out of ileum epithelial cells into blood by sodium / potassium pump - uses ATP
• Produces Na+ concentration gradient from higher concentration in ileum contents to lower concentration in epithelial cells
• Glucose / amino acids co-transported into epithelial cells with Na+
  ○ Glucose / amino acids move against their concentration gradient
  ○ Na+ moves down it’s concentration gradient
• Glucose / amino acids move by facilitated diffusion from epithelial cell into blood

Question 20

how do lipids get absorbed in the ileum

Answer 20

• 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