Intestine II: Nutrient Absorption (6)

Question 1

What are the soluble lumenal salivary enzymes?

Answer 1

Amylase and lingual lipase

Question 2

What are the soluble lumenal pancreatic enzymes?

Answer 2

Amylase, endopeptidases, exopeptidases, lipase/ colipase, phospholipase A2, cholesterol esterase

Question 3

What are intestinal ectoenzymes?

Answer 3

Membrane bound brush border whose catalytic side faces the lumen

Question 4

What activates trypsin?

Answer 4

Enterokinase (it converts trypsinogen released by the pancreas into trypsin)

Question 5

What can active trypsin activate?

Answer 5

1- Trypsinogen
2- Chymotrypsinogen
3- Proelastase
4- Procarboxypeptidase A
5- Procarboxypeptidase B

Question 6

Which peptidases cleave proteins from the C terminus?

Answer 6

the exopeptidases (carboxypeptidase A and B)

Question 7

In terms of amino acids and oligopeptides….lumenal digestion yeild what percent of each?

Answer 7

Amino acids= 40%

Oligopeptides (2-6 AA long)= 60%

Question 8

What is the main transporter for single amino acids?

Answer 8

Na dependent amino acid transprter

Question 9

What is the main transporter for oligopeptides?

Answer 9

H+/ oligopeptide transporter

Question 10

What size peptides do oligopeptide transporters transport?

Answer 10

Di-, Tri-, tetra-

Question 11

What is the form that amino acids leave enterocyes and enter the blood?

Answer 11

As single amino acids only

Question 12

What is the name of the H+/ oligopeptide transporter?

Answer 12

PepT1

Question 13

What is the function of brush border peptidases?

Answer 13

To digest small oligopeptides

Question 14

What sterospecific form of amino acids is absorbed preferentially?

Answer 14

L isomers

Question 15

True or false:

Most amino acids requires an inward Na+ concentration gradient

Answer 15

True

Question 16

What type of transport kinetics does Amino acid transport show?

Answer 16

Saturation kinetics

Question 17

What is amino acid transport into the enterocyte limited by?

Answer 17

The Vmax is limited by the number of transporters in the membrane and the turnover time of a single transporter

Question 18

If enterocytes exhibited free diffusion for amino acids what would the kinetics plot look like?

Answer 18

linear plot/ slope

Question 19

Which of the following carrier systems are Na dependent? (apical membrane)

Neutral AA transport system
y+ AA transport system
PHE AA transport system
Acidic AA transport system
Imino AA transport system
L AA transport system

Answer 19

Neutral, PHE, Acidic, Imino

Question 20

Which of the following carrier systems are Na dependent? (basolateral membrane)

A AA transport system
L AA transport system
y+ AA transport system
ASC AA transport system

Answer 20

A and ASC

Question 21

If oligopeptidases enter enterocytes via PepT1 receptors, how are they digested once in the cell?

Answer 21

Peptidaes in the cytoplasm

Question 22

What is an important pump in the basolateral membrane of enterocytes? Why?

Answer 22

Na+/ K+ pump is important because it allows the apical Na+/ H+ transporter on the apical membrane to bring in Na+ nd push out H+

This allows the H+/ Oligopeptide cotransporter to bring in H+ and oligopeptides into the cell

Question 23

What is defective in Hartnup Disease?

Answer 23

“System B” apical membrane AA transporter

Question 24

What absorption (and where) is affected in Hartnup Disease?

Answer 24

Neutral AA (namely Phe) transport is impaired in the intestine and kidneys

Question 25

Excessive amounts of what are excreted in the urine of of a patient with Hartnup disease?

Answer 25

Tryptophan

Question 26

What is defective in cystinuria?

Answer 26

"System B" apical membrane AA transporter that absorbs basic amino acids (like cystein)

Question 27

What two areas are affected by cystinuria?

Answer 27

intestine and kidneys

Question 28

What is the function of brushboarder ectoenzymes?

Answer 28

Convert discaccharides to monosaccharides

Question 29

How are glucose and Galactose absorbed by enterocytes?

Answer 29

SGLT1 transporters (Na coupled)

Question 30

How does fructose enter the enterocyte?

Answer 30

GLUT 5 transporter (Na independent)

Question 31

What monosaccharide transporter is found on the basolateral membrane?

Answer 31

GLUT 2 transporter

Question 32

What is the composition of carbohydrates?

Answer 32

60% starch 30% sucrose 10% lactose

Question 33

Where and how is the majority of starch digested?

Answer 33

In the intestine via pancreatic amylase

Question 34

Why does lactose intolerance result in diarrhea?

Answer 34

Because lactose is osmotically active

Question 35

What does a glucose tolerance test measure?

Answer 35

Lactose found in the blood and H2 in breath

Question 36

Will H2 in breath be higher or lower in a patient with lactose intolerance? Why?

Answer 36

It will be higher because of lactose catabolism in the gut by bacteria

Question 37

What is the problem in glucose/ galactose malabsorption?

Answer 37

Defective/ missing SGLT1 transporter

Question 38

How is glucose/ galactose malabsorption treated?

Answer 38

fructose only diet

Question 39

What is the importance of CCK? | 5 important functions

Answer 39

``` 1- slows gastric motility 2- stimulates pancreatic enzyme secretion 3- stimulates intestinal fluid secretion 4- stimulates gall bladder contraction 5- Relaxes sphincter of oddi ```

Question 40

Presence of fat in duodenum causes: | 2 things

Answer 40

1- release of GIP which decreases gastric acid secretion 2- release of CCK

Question 41

Where does the majority of lipid digestion occur? And what are the enzymes involved in this area?

Answer 41

In the jejunum and it is usually complete by mid jejunum Pancreatic phospholipase A2 Cholesterol Esterase Pancreatic lipase

Question 42

What is the function of colipase?

Answer 42

It anchors lipase to micells and provides access to neutral TGs inside micelles

Question 43

Where does pancreatic lipase hydrolyze?

Answer 43

At 1 & 3 position of TGs

Question 44

How is glycerol absorbed?

Answer 44

Free diffusion

Question 45

What is the function of bile salts?

Answer 45

They are amphipathic and emulsify fat globules into smaller micelles

Question 46

What stabilizes micelles?

Answer 46

Mutual charge repulsion...because micelles have a negative surface charge

Question 47

What are micelles? What can a micelle be composed of?

Answer 47

Aggregates of amphipathic molecules: ``` 1- Long chain FAs 2- Fat soluble vitamins 3- cholesterol 4- monoglycerides 5- phospholipids 6- bile salts ```

Question 48

How are FAs with short or medium chains absorbed into portal blood?

Answer 48

As FAs...they don't need to be reesterified

Question 49

How do long chain FAs enter the Enterocyte and what binds to them when they enter?

Answer 49

Need Fatty acid transport proteins (FATP) and they are bound by Fatty acid binding protein (FABP)

Question 50

What is the function of FABP?

Answer 50

To minimize FA reflux back into the lumen of the intestine

Question 51

Where are FAs reesterified?

Answer 51

ER

Question 52

What is NCP1L1?

Answer 52

a cholesterol transporter

Question 53

Where are bile salts absorbed?

Answer 53

ileum

Question 54

How are chylomicrons formed?

Answer 54

Apoproteins from the RER associate with lipid droplets in the SER and this complex then travels through the golgi to the cell membrane via transport vesicles to the lymphatic system