Topic 3 - Digestion & Absorption

Question 1

What is the small intestine responsible for?

Answer 1

Nutrient absorption

Question 2

How is the small intestine adapted to its function?

Answer 2

Epithelium lining contains villi that contains a network of capillaries.

Question 3

What does pancreatic amylase do?

Answer 3

Enzyme that breaks down carbohydrates in the pancreas.

Question 4

What does trypsin and chymotripsin do?

Answer 4

Break down proteins and peptides

Question 5

What does lipase do?

Answer 5

Enzyme that digests lipids into glycerol and fatty acids.

Question 6

What is the main reaction used in digestion?

Answer 6

Hydrolysis

Question 7

What does amylase do?

Answer 7

Catalyse the breakdown of starch

Question 8

What do membrane bound disaccharidases do?

Answer 8

Help the breakdown of disaccharides into monosaccharides

Question 9

What does lipase do?

Answer 9

Capitalise the breakdown of lipids into monoglycerides and fatty acids

Question 10

What are bile salts?

Answer 10

Produced by the liver and emulsify lipids causing them to form small droplets

Question 11

What are micelles?

Answer 11

Tiny structures formed when monoglycerides and fatty acid stick with the bile salts

Question 12

How is fructose absorbed?

Answer 12

Facilitated diffusion through a transporter protein

Question 13

How are monoglycerides and fatty acids absorbed?

Answer 13

Through diffusion

Question 14

How are amino acids absorbed?

Answer 14

Facilitated diffusion

Question 15

What is the role of amylase?

Answer 15

Hydrolyses starch into maltose.

Question 16

Where can amylase be found?

Answer 16

In the saliva, pancreas and small intestine. Enters the small intestine via the ‘common duct’

Question 17

Where does the digestion of carbohydrates take place?

Answer 17

1) Begins in the mouth (saliva).

2) Some takes place in the stomach, however amylase in rapidly inactivated due to low pH of HCl.

3) In the epthelial cells of the small intestine.

Question 18

What is the role of maltase?

Answer 18

Hydrolyses maltose to glucose - breaking glycosidic bonds

Question 19

What is the role of lactase?

Answer 19

Hydrolyses lactose into glucose and galactose - breaking glycosidic bonds

Question 20

What is the role of sucrase?

Answer 20

Hydrolyses sucrose to glucose and fructose - breaking glycosidic bonds

Question 21

What is step 1 in the digestion of lipids?

Answer 21

Emulsification

Question 22

What happens in the emulsification of lipids in the stomach?

Answer 22

Solid lipids are turned into fatty acid liquid containing fat droplets.

Question 23

What happens in the emulsification of lipids in the small intestine?

Answer 23

Bile, containing bile salts are secreted. Bile salts bind to fatty acids and breaks the fatty droplets into smaller ones via emulsification. This increases the surface area of the fatty droplets for action of digestive enzymes (lipase).

Question 24

What is step 2 in the digestion of lipids?

Answer 24

Digestion of the lipids

Question 25

Where does the digestion of lipids take place?

Answer 25

Takes place in the lumen of the small intestine

Question 26

What happens in lipid digestion in the small intestine?

Answer 26

Lipase breaks down lipids into glycerol and fatty acids. (breaks ester bonds)

Question 27

Where is lipase produced?

Answer 27

Produced in the pancreas and secreted into the small intestine by the pancreas.

Question 28

Where does protein digestion begin?

Answer 28

Begins in the lumen of the stomach by protease enzymes.

Question 29

What is the role of endopeptidases?

Answer 29

Hydrolyse peptide bonds within the polypeptide chain, creating smaller polypeptides.

Question 30

What is the role of exopeptidases?

Answer 30

Hydrolyse the penultimate peptide bonds at the ends of the polypeptide chain to produce dipeptides.

Question 31

What is the role of dipeptidases?

Answer 31

Hydrolyse dipeptides into amino acids which are then released into the cytoplasm.

Question 32

Through what process are amino acids and monosaccharides absorbed?

Answer 32

Through a co-transport mechanism with Na+ ions, then facilitated diffusion into the blood.

Question 33

How does glucose enter the cells?

Answer 33

By diffusion, co-transported using co-transporter proteins or co-transport with Na+ ions. (Sodium enters down an electrochemical gradient)

Question 34

How are lipids absorbed?

Answer 34

1) The monoglycerides and fatty acids associate with phospholipids and bile salts to form micelles.

2) Micelles diffuse across the cell membrane.

3) Once inside the epithelial cell, they are resynthesised to triglycerides inside the ER and golgi. This produces a golgi vesicle (chylomicron).

4) Chylomicron then binds to membrane and is released by exocytosis.

5) Chylomicron enters a lacteal and this transports the chylomicron away from the intestine, and into the blood.

Question 35

How are amino acids/glucose absorbed via co-transport?

Answer 35

1) Sodium ions are actively transported out of the epithelial cell into the blood.

2) This reduces the sodium ion concentration in the epithelial cell.

3) Sodium ions can then diffuse from the lumen down their concentration gradient into the epithelial cell.

4) The protein the sodium ions diffuse through is a co-transporter protein, so either glucose or amino acids also attach and are transported against their concentration gradient.

5) Glucose then moves by facilitated diffusion from the epithelial cell to the blood.