Digestion and absorption

Question 1

What is digestion?

Answer 1

Secretion of enzymes that hydrolyse large, insoluble molecules to smaller, soluble molecules for absorption and transport

Question 2

What is the stomach?

Answer 2

A muscular sac that secretes enzymes from the inner layer (specifically protease)

Question 3

What is the ileum?

Answer 3

A long muscular tube that further digests food molecules

Question 4

What does the large intestine do?

Answer 4

Absorbs water, most of which is from the secretions of many digestive glands

Question 5

What is egestion?

Answer 5

The removal of faeces from the anus after being stored in the rectum

Question 6

What enzyme(s) do salivary glands secrete?

Answer 6

Amylase, which hydrolyses starch into maltose

Question 7

What is the pancreas?

Answer 7

A large gland situated below the stomach, that produces pancreatic juices

Question 8

What enzymes are within pancreatic juices?

Answer 8

Protease, lipase and amylase

Question 9

What are the two stages of digestion?

Answer 9

Physical and chemical digestion

Question 10

What is physical digestion?

Answer 10

Breaking of large food, by structures such as teeth, which provide large surface area for chemical digestion, the churning in the stomach is also physical digestion

Question 11

What is chemical digestion?

Answer 11

Hydrolysis of large insoluble molecules into smaller soluble ones, carried out by enzymes

Question 12

What does amylase do?

Answer 12

Hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose

Question 13

How is maltose hydrolysed?

Answer 13

By the disaccharidase maltase, into alpha glucose molecules, in the ileum lining

Question 14

What do mineral salts in saliva do?

Answer 14

Maintain the pH at around neutral, which is optimum for amylase

Question 15

How does pancreatic amylase maintain a neutral pH?

Answer 15

Alkaline salts are produced by both the pancreas and the intestinal wall, so amylase can function

Question 16

Where are lipases produced and what do they do?

Answer 16

The pancreas, they hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides

Question 17

What is emulsification?

Answer 17

The production of micelles (droplets of fats and oils) by bile salts

Question 18

What are three different proteases?

Answer 18

Endopeptidase, exopeptidase and dipeptidase

Question 19

What does endopeptidase do?

Answer 19

Hydrolyse the peptide bonds between amino acids in the central region of a polypeptide chain, forming a series of peptide molecules

Question 20

What does exopeptidase do?

Answer 20

Hydrolyse the peptide bonds on the terminal amino acids of of the peptide molecules formed by endopeptidases, they progressively release dipeptides and single amino acids

Question 21

What does dipeptidase do?

Answer 21

Hydrolyse the bond between the two amino acids of a dipeptide

Question 22

Where are dipeptidases found?

Answer 22

They are membrane-bound, being part of the cell-surface membrane of epithelial cell lining the ileum

Question 23

How is the ileum adapted for its function?

Answer 23

1mm long villi and a rich network of blood capillaries

Question 24

How do the villi increase absorption?

Answer 24

Increase surface area, thin walled, contain muscles which mix contents of ileum and maintain concentration gradient, rich blood supply and microvilli

Question 25

How are amino acids and monosaccharides absorbed?

Answer 25

Diffusion and co-transport

Question 26

What's the average diameter of micelles?

Answer 26

4-7nm

Question 27

How are micelles broken down?

Answer 27

The come into contact with epithelial cells lining the ileum

Question 28

How do monoglycerides and fatty acids enter epithelial cells?

Answer 28

As they are non-polar molecules, they easily diffuse across the cell-surface membrane

Question 29

What happens once monogylcerides and fatty acids enter the epithelial cells?

Answer 29

They are transported to the endoplasmic reticulum, where they are recombined to form triglycerides

Question 30

What happens after triglycerides are formed by the endoplasmic reticulum?

Answer 30

Continue to the Golgi apparatus, where they associate with cholesterol and lipoproteins to form chylomicrons

Question 31

What are chylomicrons?

Answer 31

Special particles adapted for the transport of lipids

Question 32

How do chylomicrons move out of the epithelial cells and where do they go?

Answer 32

Exocytosis, they enter lymphatic capillaries called lacteals

Question 33

Where are lacteals found?

Answer 33

At the centre of each villus

Question 34

How do the chylomicrons move into blood vessels and how are they hydrolysed?

Answer 34

They pass via the lymphatic vessels into the blood system, they are hydrolysed by an enzyme in the endothelial cells of blood capillaries, from where they diffuse into cells