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unit 6: physiology > Intestine II: Nutrient Absorption (6) > Flashcards

Intestine II: Nutrient Absorption (6) Flashcards

1
Q

What are the soluble lumenal salivary enzymes?

A

Amylase and lingual lipase

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2
Q

What are the soluble lumenal pancreatic enzymes?

A

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

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3
Q

What are intestinal ectoenzymes?

A

Membrane bound brush border whose catalytic side faces the lumen

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4
Q

What activates trypsin?

A

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

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5
Q

What can active trypsin activate?

A 
1- Trypsinogen
2- Chymotrypsinogen
3- Proelastase
4- Procarboxypeptidase A
5- Procarboxypeptidase B
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6
Q

Which peptidases cleave proteins from the C terminus?

A

the exopeptidases (carboxypeptidase A and B)

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7
Q

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

A

Amino acids= 40%

Oligopeptides (2-6 AA long)= 60%

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8
Q

What is the main transporter for single amino acids?

A

Na dependent amino acid transprter

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9
Q

What is the main transporter for oligopeptides?

A

H+/ oligopeptide transporter

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10
Q

What size peptides do oligopeptide transporters transport?

A

Di-, Tri-, tetra-

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11
Q

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

A

As single amino acids only

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12
Q

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

A

PepT1

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13
Q

What is the function of brush border peptidases?

A

To digest small oligopeptides

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14
Q

What sterospecific form of amino acids is absorbed preferentially?

A

L isomers

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15
Q

True or false:

Most amino acids requires an inward Na+ concentration gradient

A

True

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16
Q

What type of transport kinetics does Amino acid transport show?

A

Saturation kinetics

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17
Q

What is amino acid transport into the enterocyte limited by?

A

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

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18
Q

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

A

linear plot/ slope

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19
Q

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
A

Neutral, PHE, Acidic, Imino

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20
Q

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

A

A and ASC

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21
Q

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

A

Peptidaes in the cytoplasm

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22
Q

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

A

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

23
Q

What is defective in Hartnup Disease?

A

“System B” apical membrane AA transporter

24
Q

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

A

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

25
Q

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

A

Tryptophan

26
Q

What is defective in cystinuria?

A

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

27
Q

What two areas are affected by cystinuria?

A

intestine and kidneys

28
Q

What is the function of brushboarder ectoenzymes?

A

Convert discaccharides to monosaccharides

29
Q

How are glucose and Galactose absorbed by enterocytes?

A

SGLT1 transporters (Na coupled)

30
Q

How does fructose enter the enterocyte?

A

GLUT 5 transporter (Na independent)

31
Q

What monosaccharide transporter is found on the basolateral membrane?

A

GLUT 2 transporter

32
Q

What is the composition of carbohydrates?

A

60% starch
30% sucrose
10% lactose

33
Q

Where and how is the majority of starch digested?

A

In the intestine via pancreatic amylase

34
Q

Why does lactose intolerance result in diarrhea?

A

Because lactose is osmotically active

35
Q

What does a glucose tolerance test measure?

A

Lactose found in the blood and H2 in breath

36
Q

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

A

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

37
Q

What is the problem in glucose/ galactose malabsorption?

A

Defective/ missing SGLT1 transporter

38
Q

How is glucose/ galactose malabsorption treated?

A

fructose only diet

39
Q

What is the importance of CCK?

5 important functions

A 
1- slows gastric motility
2- stimulates pancreatic enzyme secretion
3- stimulates intestinal fluid secretion
4- stimulates gall bladder contraction 
5- Relaxes sphincter of oddi
40
Q

Presence of fat in duodenum causes:

2 things

A

1- release of GIP which decreases gastric acid secretion

2- release of CCK

41
Q

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

A

In the jejunum and it is usually complete by mid jejunum

Pancreatic phospholipase A2
Cholesterol Esterase
Pancreatic lipase

42
Q

What is the function of colipase?

A

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

43
Q

Where does pancreatic lipase hydrolyze?

A

At 1 & 3 position of TGs

44
Q

How is glycerol absorbed?

A

Free diffusion

45
Q

What is the function of bile salts?

A

They are amphipathic and emulsify fat globules into smaller micelles

46
Q

What stabilizes micelles?

A

Mutual charge repulsion…because micelles have a negative surface charge

47
Q

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

A

Aggregates of amphipathic molecules:

1- Long chain FAs
2- Fat soluble vitamins
3- cholesterol
4- monoglycerides
5- phospholipids
6- bile salts
48
Q

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

A

As FAs…they don’t need to be reesterified

49
Q

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

A

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

50
Q

What is the function of FABP?

A

To minimize FA reflux back into the lumen of the intestine

51
Q

Where are FAs reesterified?

A

ER

52
Q

What is NCP1L1?

A

a cholesterol transporter

53
Q

Where are bile salts absorbed?

A

ileum

54
Q

How are chylomicrons formed?

A

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

unit 6: physiology (13 decks)

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