Digestion and Absorption

Question 1

What is the function of the mouth?

Answer 1

• Food is ingested
• Teeth physically digest the food

Question 2

What is the function of the salivary glands?

Answer 2

• Produce amylase, starting the chemical digestion of starch.

Question 3

What is the function of the oesophagus?

Answer 3

• Tube connecting mouth to the stomach

Question 4

What is the function of the stomach?

Answer 4

• Muscular bag that churns food (mechanical / physical digestion)
• Adds acid and pepsin to start protein digestion

Question 5

What is the function of the ileum (small intestine)?

Answer 5

• Long tube with villi
• Site of final stages of digestion and absorption of monomers

Question 6

What is the function of the liver?

Answer 6

• Produces bile, for the emulsification of fats, which is stored in the gall bladder

Question 7

What is the function of the pancreas?

Answer 7

• Produces many digestive enzymes released into the duodenum.

Question 8

What is the function of the caecum (large intestine)?

Answer 8

• Where water and ions are absorbed.

Question 9

What is the function of the rectum?

Answer 9

• Storage of faeces before being expelled from the anus.

Question 10

What are the four stages of digestion?

Answer 10

• Ingestion
• Digestion
• Absorption
• Egestion

Question 11

Define ingestion.

Answer 11

Food is taken into the body through the mouth.

Question 12

Define digestion.

Answer 12

Breakdown of large insoluble molecules into small, simple, soluble molecules by mechanical and chemical means.

Question 13

Define absorption.

Answer 13

The small soluble molecules can be absorbed through the lining of the small intestine (the ileum) into the blood.

Question 14

Define egestion.

Answer 14

Any food that can’t be digested is eliminated from the body (e.g. cellulose in plant cell walls).

Question 15

What is the role of digestive enzymes?

Answer 15

Digestive enzymes hydrolyse large insoluble molecules into smaller soluble ones which can then be absorbed and used in the body.

Question 16

What are the two types of digestion?

Answer 16

• Mechanical / physical
• Chemical

Question 17

What is physical / mechanical digestion?

Answer 17

• Large food is broken down into smaller pieces by chewing with teeth in the mouth (mastication) and churning of the stomach muscles.

Question 18

What is chemical digestion?

Answer 18

• Digestive enzymes hydrolyse large insoluble molecules into smaller soluble ones which can then be absorbed and used by the body.

Question 19

Describe the digestion of carbohydrates by amylases and membrane-bound disaccharides in mammals.

Answer 19

• Starch can exist in one of two forms: linear chains (amylose) or branched chains (amylopectin).
• Starch digestion begins in the mouth with the release of amylase from the salivary glands. It is broken down into maltose.
• Amylase is also secretes by the pancreas in order to continue carbohydrate digestion within the small intestine.
• Maltese is immobilised on the epithelial lining of the small intestine.

Question 20

What are the three different types of proteases?

Answer 20

• Endopeptidases
• Exopeptidases
• Dipeptidases

Question 21

What is the role of endopeptidases?

Answer 21

Hydrolyse peptide bonds in the middle of the polypeptide to produce shorter polypeptides.

Question 22

What is the role of exopeptidases?

Answer 22

Hydrolyse peptide bonds at the ends of the polypeptide to produce dipeptides or single amino acids.

Question 23

What is the role of dipeptidases?

Answer 23

Hydrolyse any remaining dipeptides into single amino acids.

Question 24

What are bile salts?

Answer 24

• Bile salts are made by the liver and stored in the gall bladder.
• Bile salts emulsify lipids from larger globules into smaller droplets producing a larger area for lipase to act on.

Question 25

What are micelles?

Question 26

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Question 27

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Question 28

Describe the role of micelles on the absorption of lipids.

Answer 28

- ***Bile salts?*** from micelles - Micelles help to move monoglycerides, glycerol and fatty acids towards the intestinal epithelium. - Monoglycerides, fatty acids and glycerol and small and non-polar enough to cross the cell-surface membrane by simple diffusion. - Fatty acids and monoglycerides are synthesised into triglycerides in the smooth endoplasmic reticulum. - Triglycerides are then packaged into chylomicrons in the Golgi. - Chylomicrons are then released from the cell by exocytosis.

Answer 29

- Fatty acids and monoglycerides are synthesised into triglycerides in the smooth endoplasmic reticulum. - Triglycerides are then packaged into chylomicrons in the Golgi. - Chylomicrons are then released from the cell by exocytosis.

Question 30

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Question 31

Describe the co-transport mechanisms for the absorption of amino acids.

Answer 31

- Sodium ions are actively pumped out of the intestinal cell by the Na^+K^+ATPase pump using ATP. - Sodium ions inside the cell are at a lower concentration than in the lumen. - Sodium moves into the cell from the lumen down its concentration gradient through a carrier protein. - Amino acids move in with it against their concentration gradient, creating a high concentration inside the cell. - Amino acids move onto the blood by facilitated diffusion from a high concentration inside to a low concentration in the blood where it is quickly removed by the flow, maintaining a concentration gradient.