Digestion and Absorption

Question 1

Define physical breakdown.

Answer 1

Food being mechanically broken into smaller parts by the teeth or churning of the stomach, to increase surface area to volume ratio for chemical digestion to take place.

Question 2

Define chemical digestion.

Answer 2

Hydrolysation of large, insoluble molecules into smaller, soluble ones. Carried out by enzymes.

Question 3

Which enzyme hydrolyses starch?

Answer 3

Amylase

Question 4

What is starch hydrolysed into?

Answer 4

Maltose.

Question 5

Which enzyme hydrolyses maltose?

Answer 5

Maltase.

Question 6

Where is amylase produced?

Answer 6

.Salivary amylase in the salivary glands,
.Pancreatic amylase in pancreas.

Question 7

Where is maltase produced?

Answer 7

The epithelial lining in the ileum; it remains bound to the membranes of the epithelial cells.

Question 8

What do mineral salts in the saliva do?

Answer 8

Maintain a neutral pH optimum for amylase.

Question 9

What do alkaline salts in the pancreas do?

Answer 9

Maintain a neutral pH for amylase.

Question 10

What does maltose break down into?

Answer 10

Alpha glucose

Question 11

Which enzyme hydrolyses sucrose?

Answer 11

Sucrase.

Question 12

Describe the action of sucrase.

Answer 12

.Membrane bound enzyme,
.Hydrolyses the singly glycosidic bond in sucrose,
.Produces fructose and alpha-glucose.

Question 13

Where is sucrase secreted?

Answer 13

The epithelial villi of the ileum.

Question 14

Describe the action of lactase.

Answer 14

.Membrane-bound enzyme,
.Hydrolyses the single glycosidic bond in lactose,
.Produces alpha-glucose and beta-galactose.

Question 15

Where is lactase secreted?

Answer 15

The epithelial villi in the ileum.

Question 16

Which enzymes hydrolyse lipids?

Answer 16

Lipases.

Question 17

Describe the action of lipases.

Answer 17

.Hydrolyse the ester bond in triglycerides to form fatty acids and glycerol.

Question 18

How do bile salts speed up the action of lipases?

Answer 18

Through emulsification- they split up lipids into micelles, which have a higher surface area to volume ratio, so lipase acts faster.

Question 19

Where are bile salts produced?

Answer 19

The liver.

Question 20

Where are lipases produced and secreted?

Answer 20

Produced in the liver, secreted in the small intestine.

Question 21

Which group of enzymes break down proteins?

Answer 21

Peptidases.

Question 22

What do endopeptidases do?

Answer 22

Hydrolyse the peptide bonds between amino acids in the centre of the protein.

Question 23

What do exopeptidases do?

Answer 23

Hydrolyse the peptide bonds between amino acids on the terminal ends of the peptide molecules formed by endopeptidase.

Question 24

What do dipeptidases do?

Answer 24

They are exopeptidases which work specifically on dipeptides. They are bound to the membranes of ileum epithelial cells.

Question 25

What is a sodium potassium pump?

Answer 25

A mechanism where 3 sodiums and ATP bind to a carrier protein, ATP changes the shape of the protein, sodium is released on the outside of the cell and potassium binds to the carrier protein, then it reverts back to its original shape, releasing potassium on the inside of the cell.

Question 26

Why is co-transport necessary for the digestion of glucose and amino acids.

Answer 26

.Diffusion alone would mean only 50% is absorbed- equilibrium. .The sodium potassium pump means that glucose can move in down the sodium gradient, which is always maintained.

Question 27

What is the first stage of triglyceride absorption?

Answer 27

Bile salts emulsify lipids into smaller triglyceride droplets, which are then hydrolysed into a monoglyceride and 2 fatty acids.

Question 28

How do the monoglyceride and 2 fatty acids move into the epithelial cells?

Answer 28

The diffuse, meet the rough ER and turn back into a triglyceride. Meet the golgi which attached cholesterol and lipoproteins, making it a chylomicron. Chylomicron exocytoses into lacteal lymph vessel, where is diffuses into capillary endothelium and is hydrolysed back into triglyceride.

Question 29

Describe adaptations of the ileum.

Answer 29

.Villi and microvilli increase surface area for absorption, .Thin walls- one epithelial cell thick, so short diffusion distance, .Large network of capillaries so constant blood flow and concentration gradient.