Digestion and absorption

Question 1

Role of the oesophagus?

Answer 1

carries food from the mouth to the stomach

Question 2

Role of the stomach?

Answer 2

stores and digests food. Has glands which produce enzymes for protein digestion

Question 3

Role of the ileum (small intestine)?

Answer 3

food is digested by enzymes produced in the walls and glands of the small intestine. Inner walls are folded into villi, with small projections called microvilli which give a large surface area, for rapid absorption into the bloodstream

Question 4

Role of the large intestine?

Answer 4

absorbs water

Question 5

Role of the salivary glands?

Answer 5

secrete amylase, which hydrolyses starch into maltose

Question 6

Role of the pancreas?

Answer 6

secretes pancreatic juice containing protease, lipase and amylase

Question 7

Why is it necessary to digest polymers?

Answer 7

• need to be small enough to pass into the bloodstream from the small intestine
• need to be soluble for absorption

Question 8

What are physical and chemical digestion?

Answer 8

physical - large pieces of food are broken down into smaller pieces by physical structures, which increases surface area for chemical digestion

chemical - large, insoluble molecules are broken down into smaller, soluble molecules by enzymes through hydrolysis reactions

Question 9

What is the substrate of amylase?

Answer 9

starch

Question 10

What is the substrate of maltase?

Answer 10

maltose

Question 11

What is the substrate of lactase?

Answer 11

lactose

Question 11

What is the substrate of lipase?

Answer 11

triglycerides

Question 11

What is the substrate of sucrase?

Answer 11

sucrose

Question 12

What is the substrate of exopeptidase?

Answer 12

polypeptides and dipeptides

Question 13

What is the substrate of endopeptidase?

Answer 13

polypeptides

Question 14

What is the product of starch?

Answer 14

maltose

Question 14

What is the substrate of dipeptidase?

Answer 14

dipeptides

Question 15

What is the product of maltose?

Answer 15

glucose

Question 16

What are the products of sucrose?

Answer 16

glucose and fructose

Question 17

What are the products of triglycerides?

Answer 17

glycerol and 3 fatty acids

Question 17

What are the products of lactose?

Answer 17

glucose and galactose

Question 18

What are the products of polypeptides?

Answer 18

shorter polypeptide chains and dipeptides

Question 19

What are the products of dipeptides?

Answer 19

amino acids

Question 20

Where is amylase produced?

Answer 20

salivary glands and pancreas

Question 21

Where dissacharidases (maltase, lactase, sucrase) produced?

Answer 21

epithelial lining of ileum

Question 22

Where is lipase produced?

Answer 22

pancreas

Question 23

Where is endopeptidase produced?

Answer 23

stomach and pancreas

Question 24

Where is exopeptidase produced?

Answer 24

pancreas

Question 25

Where is dipeptidase produced?

Answer 25

epithelial lining of ileum

Question 26

What is the site of digestion of starch?

Answer 26

mouth and duodenum

Question 27

What is the site of digestion for disaccharides?

Answer 27

epithelial lining of ileum

Question 28

What is the site of digestion of triglycerides?

Answer 28

duodenum

Question 29

What is the site of digestion of short polypeptide chains and dipeptides broken down by endopeptidase?

Answer 29

stomach and duodenum

Question 30

What is the site of digestion of dipeptides and amino acids broken down by exopeptidase?

Answer 30

dueodenum

Question 31

What is the site of digestion of amino acids broken down by dipeptidase?

Answer 31

epithelial lining of ileum

Question 32

How are carbohydrates digested?

Answer 32

- amylase produced in the salivary glands and pancreas will begin to hydrolyse polysaccharides into maltose by hydrolysing glycosidic bonds - food is swallowed and enters the stomach where conditions are acidic. The acid denatures amylase which prevents further hydrolysis - maltose is hydrolysed into alpha glucose by maltase produced in the lining of the ileum

Question 33

How are lipids digested?

Answer 33

- lipids are hydrolysed by lipase enzymes produced in the pancreas which breaks ester bonds found in triglycerides to form monoglycerides and fatty acids - lipids are firstly split into micelles by bile salts produced in the liver - this is called emulsification and increases surface area for faster digestion of lipids

Question 34

How are proteins digested?

Answer 34

- endopeptidases hydrolyse peptide bonds between amino acids in the centre of a polypeptide - exopeptidase hydrolyse peptide bonds on the terminal amino acids of a peptide molecule - dipeptidases hydrolyse peptide bonds between 2 amino acids in a dipeptide - digestion starts in the stomach, continues in the duodenum and fully digested in the ileum

Question 35

How is the small intestine adapted for efficient exchange?

Answer 35

- microvilli provide a large surface area which accelerates the rate of absorption - one cell thick epithelial layer/villi for a short diffusion distance - constant movement of internal medium (blood constantly flowing and good blood supply) and external medium (food in lumen of gut) so concentration gradient remains steep

Question 36

How is the small intestine specialised for exchange?

Answer 36

- membrane bound disaccharides and dipeptidases - muscle tissue for contraction to move along food - elastic tissue for expansion and stretching to fit more food - lacteals to absorb fat - lots of mitochondria for active transport and energy release

Question 37

How are amino acids absorbed into the bloodstream from the epithelial cells?

Answer 37

Through co-transport - sodium potassium pump - sodium moves out of cell by active transport, low concentration of Na+ inside and high concentration of Na+ in the blood - sodium ions and amino acids move from the lumen into epithelial cells. Larger di/tripeptides move in by H+ ions - these proteins are not fully digested - di/endo/exopeptidases break down dipeptides into amino acids - amino acids move out of epithelial cells into the bloodstream through a carrier protein - they are too large to move out through diffusion

Question 38

How are lipids absorbed and transported from the ileum into the lymph vessels?

Answer 38

- lipase enzymes hydrolyse lipids into glycerol and fatty acids - micelles contain bile salts and fatty acids - micelles make fatty acids more soluble - micelles come into contact with epithelial cells lining the villi of the ileum and maintain a higher concentration of fatty acids and monoglycerides to the lining of the ileum - fatty acids and monoglycerides absorbed by diffusion into epithelial cells - monoglycerides and fatty acids are transported to the endoplasmic reticulum where they are recombined to form triglycerides - exocytosis of vesicles

Question 39

What is the role of micelles in the absorption of fats in the ileum?

Answer 39

- micelles include bile salts and fatty acids - make fatty acids more soluble in water - carry fatty acids to the lining of the ileum which maintains a high concentration - fatty acids absorbed by diffusion