(10) - Epithelial Transport

Question 1

(Key Points)

1. reabsorption (and secretion) involves crossing which 2 barriers?
2. The tubular epithelium can be crossed in how many steps?
3. Most metabolically important substances can not penetrate lipid membrances and must do what?

Answer 1

1. the tubule epithelium and the endothelial cells lining the peritubular capillaries
2. 1 or 2
3. must move via specific integral membrane proteins - transporters or channels

Question 2

(Key Points)

1. What is the lynchpin of reabsorption in the proximal tubule?
2. Hydraulic pressure in peritubular capillaries in peritubular capillaries is low and oncotic pressure high, thus facilitating what?
3. Are there limits to the max rate at which solutes can be reabsorbed?

Answer 2

1. movement of Na from the tubular lumen to the serosa
2. reabsorption of filtrate
3. yes

Question 3

how can you tell these apart - check blood levels (if high its diabetes)

Question 4

disease of the proximal tubule where all of this stuff is messed up

is genetic in this dog

Question 5

Answer 5

if he doesn’t go over this later might want to go back to this - cause he said a decent amount about this

Question 6

almost everything that is filtered will be reabsorbed

Answer 6

this varies a good amount

if you really want to get rid of something completely need to used secretion - cause not all blood subjected to filtration (?)

if you gave too much PAH - would still have some left becuase secretion can only get rid of so much because there is only so much energy and transporters

Question 7

Question 8

(Crossing the Epithelial Barrier)

1. how many steps?

(Paracellular route)

2. how many steps?
3. how does it get through?

(Transcellular route)

4. how many steps?

5-6. what are they?

Answer 8

1. one or two
2. single step
3. substance goes “around” cells through matrix of tight junctions
4. two steps
5. across apical membrance facing lumen
6. across basolateral membrane

Question 9

1-4. What four ways do substances move across membranes and cells?

Answer 9

1. diffusion
2. transporters
3. channels (a holes - things can move in bulk - aquaporin)
4. active transport (use ATP)

Question 10

(Movement by diffusion)

1. what kind of movement?
2. permeable membrane
3. what are the two driving forces?
4. applies to movement across what two things?

Answer 10

1. “brownian”
2. concentration, electrical
3. paracellular (some transcellular) and across capillary walls (endothelial barrier)

Question 11

(Movement by transporters)

1. are tranpsorters extremely specific?
2. faster or slower than channels?

why?

3. What are the 3 general types?

Answer 11

1. many of them are
2. slower

binds substance stronger (for specificity)

carrier protein undergoes more elaborate conformational change

3. uniport, symport and antiport, primary active transport

Question 12

(uniporters)

1. what kind of diffusion?

follows what?

what facilitates movement?

2. permit movement of single solute
3. solute binds to site alternately available to one side and then the other side of the membrane

Answer 12

1. facilitated

electrochemical gradient

transporter protein

Question 13

(Symporters and Antiporters)

Answer 13

Question 14

big picture thing to see here

Na is carrying glucose in, carrying AA in, bunch of metablic anions in, and exchange of Na for H (which will combine with HCO-3 - which makes CO2 and water)

thing that runs the whole system is the NA-K ATPase pump - this establishes the gradient (keeps Na low in intra and K high in intra

all movement based on very low Na in cell

Question 15

(Movement by channels)

1. Channels can move large amounts of substances how fast across membranes?
2. what is specificity like?
3. How is movement through the pore controlled?

(pic is slide before)

Answer 15

1. rapidly
2. low
3. opening and closing the pore

Question 16

(Secondary Active Transport)

1. Secondary because what?
2. energy from what?
3. energetics of Na distribution always favor what?

Answer 16

1. ATP not hydrolyzed
2. transport of another solute (often sodium)
3. entrance to the cell

Question 17

(Primary Active transporters)

1. Moves 1 or more solutes up electrochemical gradient using what?

(Sodium pump: Na-K-ATPase)

2. maintains what?

Answer 17

1. energy from ATP hydrolysis
2. low Na and high K intracellular stoichiometry (3 Na to K for every ATP)

Question 18

Question 19

Answer 19

C

Question 20

(Hydrostatic Flow, Osmosis and Oncotic Pressure)

Answer 20

Question 21

Answer 21

B

Question 22

(The Renal Tubular Epithelia Barrier)

1. solute permeability less than or more than that of water for all solutes?
2. thus.. what contribute to driving water flux?
3. What is net flux (the direction)?

Answer 22

1. less than
2. all solutes (small ions, glucose, proteins (oncotic pressure))
3. renal tubule –> capillary lumen

Question 23

(Reabsorption: Transport Mechanisms)

1. most transport in kidneys is what?
2. most reabsorption occurs where?

(most movement essentially iso-osmotic)

3. glomerular filtrate - same or different as plasma?
4. is proximal tublue reabsorption iso-osmotic?
5. Distal nephron - water and solute absorption are usually what?

Answer 23

1. reabsorption
2. PT
3. nearly the same
4. yes
5. divergent (this occurs because in the ascending limb there is no movement of water…Na can be moved without water following at around)

Question 24

(PT Reabsorption)

(Reabsorption in PT is mostly of what…)

1-2. what two things?

3. Are PT cells permeable to water?
4. what does water follow?

Answer 24

1. sodium
2. anions to maintain electoneutrality (chloride and bicarbonate)
3. highly permeable
4. the solute

Question 25

(Interstitium to Caps)

(Solute and water move into capillaries)

1-2. under what pressures?

3. Rapid blood flow in peritubular capillaries does what?

Answer 25

1. capillary hydraulic pressure
2. plasma oncotic pressure
3. sweeps away solute and electrolytes

Question 26

Question 27

Answer 27

C

Question 28

Answer 28

this happens over the entire body

Question 29

(Transcellular Transport)

1. Involves crossing how many membranes?
2. which ones?
3. are transporters same or different in each?
4. transcellular transport requires that the epithelial cells be what?

Answer 29

1. two
2. apical and basolateral
3. different
4. polarized (apical and basolateral membranes are not the same - promtoes net movement of Na from lumen to interstitium)

(in pictured he said something about loss of brush border causing change in polarity)

Question 30

he talked about this a fair amount

Question 31

(Key Points)

1. most transcellular transport in the proximal tubules results from what?

Answer 31

1. active transport of Na across basolateral surface of PT cells

Question 32

1-3. What are three kinds of passive reabsorption?

Answer 32

1. simple diffusion
2. paracellular transport
3. non-ionic transport

Question 33

(Passive reabsorption)

1. occurs by simple diffusion
   (example: urea)
2. urea reabsorbed in what tubular segments?
3. Reabsorption in proximal tubules is by what route?

3-4. Reabsprotion determind by what two things?

Answer 33

1. most of them
2. paracellular route
3. concentration gradient (tubular lumen –> interstitium)
4. permeability of tight junctions

Question 34

(Key point)

1. passive reabsorption fo urea is facilitated by what?
2. This causes urea concentration to increase where?

Answer 34

1. greater removal of sodium with water (isotonic) upstream
2. downstream (thus facilitating diffusion down concentration gradient)