PSC1002/L29 Stomach

Question 1

Give 3 functions of the small intestine.

Answer 1

Digestion
Nutrient absorption
Electrolyte absorption
Water absorption
Secretion

Question 2

Which enzyme is involved in luminal digestion of starch-type polysaccharides?

Answer 2

Amylases

Question 3

Which enzymes are involved in membrane digestion by disaccharidases? (3)

Answer 3

Maltase
Sucrase-isomaltase
Lactase

Question 4

Why is amylase described as an endo-enzyme?

Answer 4

It can only break internal bonds so cannot produce monosaccharides

Question 5

Give 2 transporters of the apical membrane.

Answer 5

SGLT1
Glucose, galactose
Na+ coupled, secondary active transport

Question 6

Give a transporter of the basolateral membrane.

Answer 6

GLUT2
Facilitated diffusion

Question 7

Give 3 types of protein digestion and their related enzymes.

Answer 7

Luminal digestion by gastric and pancreatic proteases
Membrane digestion by brush-border peptidases
Cytosolic digestion within epithelium of small peptides

Question 8

Give 2 substances absorbed in the small intestine.

Answer 8

Amino acids
Peptides
Intact protein absorbed in antigenic quantities

Question 9

Describe digestion by gastric pepsin. (2)

Answer 9

10-20% digestion
Endopeptidases

Question 10

Describe digestion by pancreatic peptidases. (3)

Answer 10

E.g., trypsin
Endopeptidases and exopeptidases
Short peptides (2-6AA) and free amino acids

Question 11

Describe protein digestion by membrane and cytosolic peptidases. (3)

Answer 11

Endo, exo or dipeptidases
Many different types
Free amino acids

Question 12

What is acid microclimate used for?

Answer 12

Peptide absorption
H+ coupled di/tripeptide transport

Question 13

What follows peptide absorption?

Answer 13

Cytosolic peptide digestion or export by unknown basolateral transporter

Question 14

Give 3 drugs which utilise peptide carriers.

Answer 14

Angiotensin-converting enzyme (ACE) inhibitors
B-lactam antibiotics
Prodrugs (Val-acyclovir)

Question 15

Give 3 types of amino acid transporters.

Answer 15

Neutral
Cationic
Anionic

Question 16

Give the function of the apical membrane in amino acid absorption. (3)

Answer 16

Mainly coupled to ion uptake
Secondary active transport
Accumulation within epithelial cells

Question 17

What is the role of the basolateral membrane in amino acid absorption?

Answer 17

Mainly facilitated diffusion

Question 18

Give 3 key points in lipid digestion and absorption.

Answer 18

Low water solubility
Solubilisation
Digestion
Absorption
Re-esterification of fatty acids
Transport to blood

Question 19

Describe triglycerides (dietary lipids).

Answer 19

Triesters of glycerol and long-chain fatty acids

Question 20

Describe phospholipids (dietary lipids).

Answer 20

Subsitute 1 fatty acid chain with phospho-ester of organic base

Question 21

Describe short chain fatty acids.

Answer 21

Minor - dairy

Question 22

Describe lipid digestion. (5)

Answer 22

Detergent emulsification
Digestion by lipases produces micelles
Diffusion into epithelial cells
Resynthesis of triglycerides
Release as chylomicrons

Question 23

Describe emulsification (stage 1) of lipid digestion. (3)

Answer 23

Begins with chewing, grinding and mixing of food
Increases oil-water interface area
Stabilised by bile salts and phospholipids

Question 24

Describe digestion (stage 2) of lipids. (3)

Answer 24

Gastric and pancreatic lipases
Co-lipase
Triglycerides to 2 fatty acids and monoglyceride

Question 25

What are micelles? (3)

Answer 25

Polymolecular aggregates 5nm Monoglyceride, fatty acids, bile salts Cholestrol and fat-soluble vitamins Close approximation to enterocyte microvilli for absorption

Question 26

Describe stage 3 of lipid digestion.

Answer 26

Diffusion down gradient

Question 27

Describe stage 4 of lipid digestion.

Answer 27

Driven by re-esterification of fatty acids to triglycerides within epithelial cells

Question 28

Describe stage 5 of lipid digestion.

Answer 28

Released across basolateral membrane as chylomicrons

Question 29

How do digested lipids enter the blood?

Answer 29

Via lymph system

Question 30

What other molecules follow the same route of absorption as lipids?

Answer 30

Fat soluble vitamins (A, D, E, K)