6.10- ABSORPTION OF THE PRODUCTS OF DIGESTION

Question 1

What function is the ileum adapted for?

Answer 1

absorbing products of digestion

Question 2

What is done to the wall of the ileum?

Answer 2

wall of ileum folded

Question 3

What does the walls of the ileum possess?

Answer 3

finger-like projections, about 1mm long, called villi

Question 4

What are the walls of the ileum like?

Answer 4

thin walls, lined with epithelial cells on outer side of which is rich network of blood capillaries

Question 5

What do the villi do?

Answer 5

considerably increase SA of ileum + so accelerate rate of absorption

Question 6

Where are the villi situated?

Answer 6

at interface between lumen of intestines + blood and other tissues inside body

Question 7

What are the villi part of?

Answer 7

specialised exchange surface adapted for absorption of products of digestion

Question 8

What properties does the villi have to increase efficiency of absorption? (5)

Answer 8

increase SA for diffusion
very thin walled 
contain muscle so able to move 
well supplied with blood vessels 
epithelial cells lining villi possess microvilli

Question 9

How does the villi being thin walled increase efficiency of absorption?

Answer 9

reduce distance over which diffusion happens

Question 10

How does the villi containing muscle + so able to move increase efficiency of absorption?

Answer 10

helps maintain diffusion gradients as their movement mixes contents of ileum
this ensures that, as products of digestion absorbed from food adjacent to villi, new material rich in products of digestion replace it

Question 11

How does the villi being well supplied with blood vessels increase efficiency of absorption?

Answer 11

so blood carry away absorbed molecules + hence maintain diffusion gradient

Question 12

How does the epithelial cells lining the villi possessing microvilli increase efficiency of absorption?

Answer 12

further increase SA for absorption

Question 13

What does the digestion of proteins produce?

Answer 13

amino acids

Question 14

What does the digestion of carbohydrates produce?

Answer 14

monosaccharides i.e. glucose, fructose + galactose

Question 15

What are the methods of absorbing amino acids + monosaccharides?

Answer 15

diffusion + co-transport

Question 16

What do monoglycerides and fatty acids remaining doing after being formed in digestion?

Answer 16

remain in association with bile salts that initially emulsified the lipid droplets

Question 17

What are the structures of the monoglycerides and fatty in association with the bile salts called?

Answer 17

micelles

Question 18

What is the size of a micelle?

Answer 18

tiny, being around 4-7nm in diameter

Question 19

How do the micelles come into contact with the epithelial cells lining the villi of the ileum? (absorption of triglycerides)

Answer 19

through movement of material within lumen of ileum

Question 20

What happens to the micelles when in contact with the epithelial cells lining the villi of the ileum? (absorption of triglycerides)

Answer 20

micelles break down, releasing monoglycerides + fatty acids

Question 21

Why do the monoglycerides + fatty acids easily diffuse across the cell-surface membrane into the epithelial cells? (absorption of triglycerides)

Answer 21

non-polar molecules

Question 22

What happens to the monoglycerides + fatty acids once inside the epithelial cells? (absorption of triglycerides)

Answer 22

monoglycerides + fatty acids transported to ER where they’re recombined to form triglycerides

Question 23

Where do the triglycerides go to from the ER and what do they do? (absorption of triglycerides)

Answer 23

continue into Golgi apparatus, triglycerides associate with cholesterol + lipoproteins

Question 24

What is it called when the triglycerides associate with cholesterol + lipoproteins in the Golgi apparatus? (absorption of triglycerides)

Answer 24

chylomicrons

Question 25

What are chylomicrons? (absorption of triglycerides)

Answer 25

special particles adapted for transport of lipids

Question 26

How do chylomicrons move out of the epithelial cells? (absorption of triglycerides)

Answer 26

by exocytosis

Question 27

Where do the chylomicrons enter from the epithelial cells? (absorption of triglycerides)

Answer 27

lymphatic capillaries called lacteals found at the centre of each villus

Question 28

Where do the chylomicrons pass to from the lacteals? (absorption of triglycerides)

Answer 28

pass via lymphatic vessels + into blood system

Question 29

What happens to the triglycerides in the chylomicrons? (absorption of triglycerides)

Answer 29

hydrolysed by enzyme in endothelial cells of blood capillaries from where they diffuse into cells