Drewes: Transporters in the GI System Flashcards Preview

GI- Week 3 > Drewes: Transporters in the GI System > Flashcards

Flashcards in Drewes: Transporters in the GI System Deck (55):
1

Transcellular route

across plasma membrane

2

paracellular route

across tight junctions (vary in permeability; impermeable to large organic molecules - AA and glucose)

3

What establishes electrochemical gradients?

Na/K/ATPase

4

What is used to move substances against their concentration gradient?

ATP

5

What is simple diffusion?

Compound diffusing DOWN its gradient b/c its LIPID SOLUBLE

6

What is facilitated diffusion?

Pores- channel
Gates- ligand binds> temporary pore
Transport molecules- help move other molecules across the membrane

7

What is endocytosis?

Part of the membrane buds off to allow entry into the cell

8

What transporter has 12 transmembrane segments and bindings sites where substrates bind and are carried to the other side of the membrane?

GLUTs

9

How many types of GLUTs are there?

13 types in 3 classes

10

GLUT4

insulin sensitive

11

GLUT1

RBC

12

How many segments make up MCTs? What do htey do?

12

carry lactate and beta hydroxybuterate in and out of cells

13

What are ATP binding cassette transporters?

Hydrolyze ATP to transport molecules across membrane

14

What transporters in the GI tract are involved w/ MDR and CFTR?

ATP binding cassette transporters

15

What are 3 transporters of the GI tract?

GLUTs
MCTs
ATPases

16

What is the single most important process in the SI to make absorption possible?

Electrochemical gradient of Na

LOW Na is maintated by Na/K/ATPases on basolateral membrane

Accumulation of Na outside cells is responsible for absorption of Water, AA and Carbs

17

How much water does the SI absorb daily?

9 L

18

Abosrption of water in the SI is dependent on?

Na co-transported w/ glucose and AA

19

How is water absorbed?

Transcellular and paracellular

Na gradient set up d/t uptake of Na>
water diffuses across membrane d/t osmotic gradient>
diffuses into blood

20

What enzymes at the brush border act on polysaccharides? What does this form?

Maltase
lactase
sucrase

Glucose and galactose which are then absorbed in the SI via a Na dependent transporter

21

SGLUT1

glucose and galactose

22

GLUT5

fructose

23

GLUT 2

transports glucose, galactose and fructose OUT of the enterocyte across basolateral membrane DOWN conc grad into capillaries

24

What enzymes are used for the digestion of proteins?

1. Stomach> PEPSINOGEN> coverted by H to PEPSIN

2. Pancreatic proteases: trypsin, chymotrypsin, carboxypeptidase

3. SI peptidases- covert free AA at brush border

25

What is the difference between lumenal and basolateral AA transporters?

Lumenal- Na dependent AA transporters

Basolateral- NON- Na dependent AA transporters

26

How are di and tri-peptides absorbed?

Absorbed into the SI via cotransport w/ H ions>
once inside the enterocytes they're digested by CYTOPLASMAIC PEPTIDASES

27

What is emulsification?

Bile acids (derivatives of cholesterol) have both
hydrophilic and hydrophobic domains which intercalate into the
lipid --> smaller droplets

28

What is hydrolysis?

Accomplished by PANCREATIC LIPASE which clips FAs at
positions 1 & 3 from triglyceride >
2 FAs and a 2-monoglyceride.

29

What is micelle formation?

liberated FAs and monoglycerides maintain
association with bile acids and complex with other lipids to form micelles. These micelles bump into the brush border and lipids are taken up into the cells.

30

How do FA and 2-MG enter enterocytes?

simple diffusion

31

Once insde the enterocyte, FA and MGs are transported to the ER to synthesize...

TGs

32

What are chylomicrons?

TG packaged w/ cholesterol, lipoproteins and other lipids into particles (by ER and golgi)

33

What happens to chylomicrons extruded from the Golgi?

Golgi>
exocytotic vesicles>
basolateral side of enterocyte>
exocytosis into lymphatic vessels

34

What is cholesterol homeostasis?

Balance of:
cholesterol synthesis
absorption of dietary cholesterol
elimination of cholesterol by excretion in the bile

35

Specific transport of nutrients and water occurs primarily in the...

jejunum

36

Active secondary transport usually occurs on the...

apical side

37

Carrier mediated transport usually occurs on the ...

basolateral side

38

Active ABC-type transport usually occurs on...

both sides

39

What is the mechanism of acid secretion?

1) Hydrogen ions generated within parietal cell from dissociation of water. The hydroxyl ion combines with CO2 to form bicarbonate (catalyzed by CA)
2) Bicarb is transported out of the basolateral membrane in exchange for Cl-
3) Cl- and K+ ions are transported into the lumen of the stomach via conductance channels
4) H+ ions are pumped out of the cell in exchange for K+ through a proton pump
5) The accumulation of H+ sets up an osmotic gradient > outward diffusion of H2O

40

What are the 3 stimulators for acid secretion?

ACh
Gastrin
Histamine

41

ACh

(Muscarinic receptor)> increases intracellular Ca concentration

42

Gastrin

Increases intracellular Ca concentration

43

Histamine (H2 receptor)

Activates adenylate cyclase>
increases cAMP>
activates PKA>
phosphorylation of cytoskeletal proteins involved in transport of H/K/ATPase from cytoplasm to plasma membrane

44

Ca and bombesin stimulate...

gastrin release

45

PGE2, secretin, GIP, glucagon and somatostatin all decrease...

gastric acid secretion

46

What drug therapy is used for gastric acid secretion?

H2 receptor antagonists
PPIs

47

f a patient had an intolerance to proteins with high lysine and/or arginine and they excreted the amino acid in the stool (and/or urine) what may be the transporter defect.

That defect might be in a cationic amino acid transporter. You might also think about where the transporter is localized in the epithelial cell.

48

How are AA transporters distributed along the GI tract?

greatly varies!

49

How are lactate transporters distributed along the GI tract?

MCT1 is variably distributed but is OVEREXPRESSED in the COLON

50

What does MCT1 transport?

short carboxylic aicds

51

How do bacteria in the colon relate to hte MCT1 transporter?

Bacteria in the colon digest cellulose and things that haven't been digested>
forms carboxylic acids>
bacteria produce butyrate>
MCT1 transfers butyrate across the lumen>
coloncytes use butyrate as fuel

52

Mutations in MCT1 is linked to what types of cancer?

colon cancer

53

What drug delivery issues are related to ABC transporters?

First barrier to noxious compounds (drugs)

Act as drug EFFLUX transporters by pumping noxious molecules back OUT into the lumen

*transporters are located on BOTH sides of hte epithelial cells

54

How does the transport of TG/lipids differ from that of most dietary nutrients?

Transported in chylomicrons into lymphatic vessels before entering the blood stream

55

What are the two main processes that establish an osmotic gradient that pulls water into the lumen?

1. influx/digestion of foodstuffs> Increase in luminal osmotic pressure

2. Crypt cells secrete electrolytes> water follows (ie. CFTR and cholera> Cl efflux and diarrhea)