Membrane Transporters in Action

Question 1

do RBCs have high or low permeabilit?

Answer 1

low

Question 2

respiration/RBC tranport

Answer 2

anion exchanger

Question 3

each individual transporter can exchange anions (which ones?) across the RBC membrane at rates that reach ( )

Answer 3

• Cl and HCO3

- 100,000 times per sec

Question 4

what is the drivers for anion exchangers

Answer 4

CO2

Question 5

anion exhanger: to be transported effectively in blood, CO2 must be converted to the musch more soluable ( )

Answer 5

HCO3

Question 6

anion exchanger: the enzyme that catalyzes this process

Answer 6

carbonic anhydrase

Question 7

anion exchanger: what is very membrane permeable, diffuses out of celss, into plasma, and then into RBCs

Answer 7

CO2

Question 8

anion exhcanger: In RBCs, CO2 reacts with water to form ( )

Answer 8

one proton and one HCO3 anion

Question 9

anion exchanger: the HCO3 anion is exchanged for a ( ) and the HCO3 anion in carried in plasms to ( )

Answer 9

• chloride anion

- lungs

Question 10

anion exchanger: as RBCs pass the lungs, what happens?

Answer 10

the entire reaction path functions in reverse to move CO2 out of the RBCs and into the alveoli of the lungs

Question 11

( )% of all cytoplasmic chloride ions in RBCs exchange across the plasmalemma in less that 50 ms

Answer 11

50%

Question 12

anions: all reactions are completely reversible so they can run in reverse as dictated by the ( ) in theperipheral ciriculation vs. the lungs

Answer 12

CO2 gradients

Question 13

epithelial cells are physically connected to each other via

Answer 13

tight junctions

Question 14

tight junctions: do not allow passage of ( ), and ( ) do not pass through them easily, their permeability to ( ) is limitied

Answer 14

• proteins
• small solutes
• ions

Question 15

often, tight junctions allow passage of ( ) while being relatively impermeable to ( )

Answer 15

• cations

- anions

Question 16

in some cases, tight junctions may be more impermeable to ( ) and in a few cases they are known to be more permeable to ( )

Answer 16

• ions

- anions than cations

Question 17

to accomplish transport across a cell layer, it is essential that cells are ( )

Answer 17

polarized (basolateral side and apical side)

Question 18

in the majority of epithelia, the Na/K pump is localized to what side of the cell membrane?

Answer 18

basolateral

Question 19

provides the initial driving force

Answer 19

Na/K pumps

Question 20

whenever solutes or ions move across a membrane or epithelium in one direction, water will tend to follow across in the same direction and therefore ( )

Answer 20

minimize osmotic gradients

Question 21

in an isoosmotic solutions, there are about how many molecules of water for each dissolved particle?

Answer 21

185 molecules

Question 22

most physiological secretions are ( )

Answer 22

hypotonic

Question 23

what is maintained?

Answer 23

electric neutrality (ex. Na will promote Cl movement and vice versa)

Question 24

the body attempts to absorb all nutrients from the gut, and to do so the body uses ( )

Answer 24

both cotransporters and uniporters

Question 25

glucose is absorbed from the gut by ( )

Answer 25

enterocytes

Question 26

it is critical for digestive function that these gut secretions have a high ( ) content

Answer 26

NaCl

Question 27

Since the Na concentration of the gut is high, Na/glucose transporters are used to move Na and glucose together into ( ), whereby all glucose in the gut can be absorbed

Answer 27

enterocytes

Question 28

On the opposite side of the enterocyte, simple glucose uniporters called ( ) are used to move glucose into the interstitial space

Answer 28

GLUT

Question 29

driving force in absoption of glucose in kidney

Answer 29

glucose gradient between the cytoplasm and interstitial space

Question 30

a hypotonic secretion is produced in two overall steps:

Answer 30

1) salt is secreted and water follows salt to generate a primary isotonic secretion 2) salt is reabsorbed to generate the final hypotonic secretion

Question 31

in the case of sweat gland, ( ) is secreted into the secretory tubule and water follows the movement of salt to generate an isotonic fluid

Answer 31

NaCl

Question 32

salt is reabsorbed as fluid moves through the ducts of the sweat gland, so that the final sweat is ( )

Answer 32

hypotonic

Question 33

secretory tubule contains a high density of water channels which is necessary to favor the movement of ( )

Answer 33

water into the tubule

Question 34

why do cells in the duct contain very few water channels?

Answer 34

so water movement out of the duct is minimized during salt reabsorption

Question 35

during the secretion of the primary sweat, the energy of the ( ) is used to pump Cl across both membranes into the tubule

Answer 35

Na and K

Question 36

sweat: Na, K, and Cl are transported across the basolateral membrane via ( ), driven mostly by the ( ) gradient into the cell

Answer 36

Na, K,Cl cotransporters; Na

Question 37

sweat: ( ) ions that enter across the basolateral side via pumps and transporters cycle back across the basolateral side via ( ), generating membrane potential across the basolateral side

Answer 37

K; K channels

Question 38

sweat: ( ) ions that enter via cotransporters cycle back across the basolateral membrane by being pumped out by ( )

Answer 38

Na; Na/K pumps

Question 39

sweat: ( ) leaves cells on the apical side via ( )

Answer 39

Cl; Cl channels

Question 40

Since Cl is negatively charged, its movement across the apical membrane generates an ( ); what is this called?

Answer 40

electrical field across the entire cell; transcellular potential

Question 41

sweat: it is critical that the tight junctions allow ( ) to move between cells, but not ( )

Answer 41

- cations | - anions

Question 42

sweat: the negative electrical field on the apical side attracts Na ions to pass through the tight junctions into the lumen. What is now established?

Answer 42

a flux of NaCl all the way across the epithelium

Question 43

sweat: this movement of NaCl generates an osmotic gradient, osmolatiy being higher in the ( ) than on the ( ), water therefore moves through water channels across the cell

Answer 43

- lumen | - basolateral

Question 44

sweat: secretion of NaCl and water depends on the coordinated function of ( )

Answer 44

Na/K pumps, Na/K/Cl co-transporters, K channels, and Cl channels

Question 45

as sweat passes through the duct of the sweat gland, what heppens?

Answer 45

ions are reabsorbed

Question 46

sweat: to avoid that water is reabsorbed with ions, what is important?

Answer 46

that these epithelial cells do NOT have water channels

Question 47

both apical and basolateral membranes of these cells contain ( )

Answer 47

CFTR Cl channels

Question 48

basolateral: K cycles back out of the cells through ( ), therefore making a large inside negative membrane potential across the membrane

Answer 48

basolateral K channels

Question 49

basolateral: this negative potential is used to drive ( ) out across the basolateral side through CFTR Cl channels, therefor making ( ) low

Answer 49

Cl; cytoplasmic Cl

Question 50

apical: contains both ( ) channels

Answer 50

CFTR Cl channels and Na channels

Question 51

apical: ( ) enter the cell from the duct lumen through these channels, diffusing down their concentration gradients

Answer 51

Na and Cl

Question 52

apical: the currents generated by ( ) influx tend to cancel each other out so there is very little membrane potential across the apical membrane side

Answer 52

Na and Cl

Question 53

what are the Na channels that are used for epithelia that are highly selective for Na but are very different from voltage gated Na channels used to make APs?

Answer 53

Epithelial Na Channels (ENAC)

Question 54

why can't CFTR can't reabsorb ion?

Answer 54

because Cl channels are not there

Question 55

Why is sweat salty when CFTR channels are lost?

Answer 55

because NaCl is not effectively reabsorbed