Digestion & Absorption

Question 1

Main contents of food?

Answer 1

1. Carb
2. Lipids
3. Proteins

Question 2

What are the two forms of digestion occurring in the small intestine?

Answer 2

1. Luminal

2. Membrane

Question 3

What is luminal digestion mediated by? Where is it secreted into?

Answer 3

Pancreatic enzymes, into the duodenum

Question 4

What is membrane digestion mediated by? Where is it secreted into?

Answer 4

Mediated by enzymes situated at brush border of epithelial cells

Question 5

What are enterocytes?

Answer 5

Absorptive cells of intestinal epithelium

Question 6

What two membranes do the breakdown products have to cross to get into the interstittium?

Answer 6

1. Apical

2. Basolateral

Question 7

What is assimilation?

Answer 7

Digestion + absorption

Question 8

What are the 3 types of carbohydrates?

Answer 8

1. Polysaccharides
2. Oligosaccharides
3. Monosaccharides

Question 9

Basic building blocks of carbs?

Answer 9

D dimer glucose monomers

Question 10

Main chemical bonds formed in carbs?

Answer 10

1. a-1,4

2. a-1,6

Question 11

Can polysaccharides be absorbed into the gut?

Answer 11

No. Need to be broken down into monosaccharides for absorption

Question 12

What is the sequence of carb breakdown?

Answer 12

Starch–> Oligosaccharides–> Monosaccharides

Question 13

What is the action of A-amylase?

Answer 13

Endoenzyme

Breaks Internal a-1,4 linkages but not Terminal a-1,4 bonds. Hence no Glucose produced

Question 14

What is the role of Oligosaccharidases?

Answer 14

Breaks down oligosaccharides along the lumen of GI tract

Question 15

Role of lactase?

Answer 15

Lactose–> glucose + galactose

Question 16

Role of maltase?

Answer 16

breaks a-1,4 bonds in oligomers

Question 17

Role of sucrase?

Answer 17

Sucrose–> Glucose + fructose

Question 18

What is lactose intolerance?

Answer 18

Unable to digest lactose. Due to enzyme lactase insufficiency.

Question 19

What is primary lactase deficiency?

Answer 19

Lack of lactase persistence allele. Most common cause world wide

Question 20

What is secondary lactase deficiency?

Answer 20

caused by damage to/ infection of proximal small intestine

Question 21

What is congenital lactase deficiency?

Answer 21

Austosomal recessive.

Unable to digest lactose from birth

Question 22

What are the effects of undigested lactose? (2)

Answer 22

1. Colon acidification

2. increased osmotic load- diarrhoea, loose stool

Question 23

What are the two types of glucose transporters in the intestine?

Answer 23

1. Sodium dependent

2. Sodium independent

Question 24

What is the important transporter of Sodium dependent transporters?

Answer 24

SGLT1

Question 25

What does SGLT1 do?

Answer 25

active transport of Glucose and galactose across brush border

Question 26

What are the sodium independent transporters?

Answer 26

GLUT 1-5

Question 27

Role of GLUT5?

Answer 27

Transports fructose

Question 28

What is the mechanism of SGLT1 (6 steps)

Answer 28

1. 2 Na bind
2. Glucose affinity increases, glucose binds
3. Na and glucose translocate from extra to intracellular
4. 2 Na dissociate, affinity for glucose falls
5. Glucose dissociates

Repeat

Question 29

What must proteins be converted to to allow digestion?

Answer 29

Protein–> oligopeptides-> amino acids

Question 30

What are the two types of peptidases ?

Answer 30

1. Endo- cleaves middle of chains

2. Exo- cleaves ends of chains

Question 31

Subtypes of exopeptidase?

Answer 31

Carboxypeptidase A & B. Both produce single amino acids

Question 32

What does HCL do in stomach?

Answer 32

Acid- denatures proteins

Question 33

Role of pepsin in stomach?

Answer 33

Protein–> Peptides (main stomach enzyme, endopeptidase)

Question 34

What are the two types of protein transporters needed for absorption?

Answer 34

1. 5 Na dependent

2. 2 Na independent

Question 35

Ho are amino acids absorbed into the basolateral membrane?

Answer 35

1. Mediate efflux of amino acids, Na independent

2. Mediate Influx of amino acids. Na dependent