Lesson 30: Topic 26 - Transepithelial Transport

Question 1

true or false: transepithelial transport is selective

Answer 1

true

Question 2

about how much of filtrate is entering glomerulus and tubules?

Answer 2

125mL

Question 3

what is the selective reabsorption of molecules and water in the tubule?

Answer 3

substances within the tubule (filtrate) are transferred to the peritubular capillaries = trans-epithelial transport

Question 4

why is the process of transepithelial transport high selective?

Answer 4

because there are certain specific channels that help to move some contents through the tubule and into the peritubular capillary

Question 5

is transepithelial transports selectivity constant throughout the nephron or variable?

Answer 5

variable throughout the length of the nephron and under physiological control

Question 6

what is renal plasma flow?

Answer 6

volume of plasma that passes through the kidneys per unit of time
- this encompasses the glomerular filtration rate(625mL/min renal plasma flow) (how much enters the kidneys, not how much is filtered)

Question 7

what is renal clearance?

Answer 7

• volume of plasma that is completely removed of a substance per unit of time
• selective reabsorption in the tubule
• we are talking about, how much of this volume of plasma is COMPLETELY removed of a substance per unit time

Question 8

in what case will we see no reabsorption?

Answer 8

where we have soluble molecules like inulin and creatinine, it just gets filtered into the filtrate and will not get reabsorbed. therefore it just goes straight into urine

Question 9

why is inulin important clinically?

Answer 9

we can determine what is going on with someone’s glomerular filtration rate because inulin determines how much plasma is entering through the glomeruli and into the urine

Question 10

when would complete reabsorption of the tubules happen?

Answer 10

with glucose
- we like to keep glucose to use as an energy source - one of the major fuel sources within the body

Question 11

what is renal clearance of no reabsorption?

Answer 11

125mL/min

Question 12

what is renal clearance of complete reabsorption?

Answer 12

0mL/min

Question 13

what are some substances that are partially reabsorbed in tubules?

Answer 13

sodium and urea
- if the body wants to retain sodium, it is going to be partially reabsorbed in different components of the tubule system

Question 14

why would we want to retain urea?

Answer 14

while it is a waste product, urea also contains nitrogen

Question 15

what does reabsorbing urea help with?

Answer 15

helps to concentrate our urine by concentrating urea within our renal medulla

Question 16

what is the renal clearance of partial reabsorption?

Answer 16

anywhere between 1-124mL/min (in between complete and no reabsorption)

Question 17

what molecules are going to not be able to reabsorb but will be able to secrete?

Answer 17

hydrogen ions, potassium ions and penicillin
- these are things that we will want to excrete but are not reabsorbed

Question 18

an accumulation of hydrogen ions and potassium ions are due to overexerted exercise, what can it lead to?

Answer 18

fatigue

Question 19

because penicillin is so efficiently cleared out of the body via urine, what does this mean clincially?

Answer 19

we need higher doses

Question 20

what is the renal clearance of no reabsorption but secretion in tubules?

Answer 20

• 126-625mL/min
• so high because not only are we not reabsorbing into the venous system, we are also secreting the substance into the tubules to really concentrate the urine

Question 21

what does the tubular reabsorption process start with?

Answer 21

sodium ions (positive charge) being absorbed by active transport from the tubule into the peritubular capillary

Question 22

by allowing sodium ions to be absorbed via active transport from the tubule into the peritubular capillary, what does this create?

Answer 22

an electrochemical gradient to allow for anion reabsorption

Question 23

after the electrochemical gradient is created and ions accumulate in the peritubular capillary, what happens?

Answer 23

accumulating ions in the interstitial fluid (peritubular capillary) creates an osmotic gradient

Question 24

by creating an osmotic gradient in the peritubular capillaries, what is going to happen?

Answer 24

it is going to want to draw in water, so water moved by osmosis, following solute reabsorption

Question 25

in summary, what is the basis concepts of the tubular reabsorption process?

Answer 25

1. Na+ absorbed by active transport 2. This creates an electrochemical gradient that allows anion reabsorption 3. accumulating ions in interstitial fluid (peritubular capillaries) creates an osmotic gradient 4. water moves by osmosis, following solute reabsorption

Question 26

as water is reabsorbed, remaining _______ in tubule become concentrated and _____ are reabsorbed by diffusion

Answer 26

solutes, SOME

Question 27

what is the osmotic gradient used for in the tubules?

Answer 27

to move water across

Question 28

what is between two adjacent tubular epithelial cells?

Answer 28

a tight junction

Question 29

there are two sides of the membrane on the tubular epithelial cells. what are they called?

Answer 29

1. luminal membrane (facing towards the tubular lumen) 2. basolateral membrane (facing towards the lateral space which is a specific space between the tubular epithelial cells that is part of the interstitial fluid)

Question 30

what are the five distance barriers that a substance must traverse in order to be reabsorbed (moving from the filtrate to the plasma)?

Answer 30

1. the luminal cell membrane 2. the cytosol (of the tubular epithelial cell) 3. the basolateral cell membrane 4. the interstitial fluid 5. the capillary wall

Question 31

how does sodium enter the tubular cell?

Answer 31

through a sodium channel - it is a dedicated channel that helps to move sodium into the tubular cell and that occurs passively(no energy required) by concentration and electrochemical gradients

Question 32

how does sodium passively enter the tubular cell via the centration gradient?

Answer 32

we have a high amount of sodium in our tubular lumen, but there is a low concentration of sodium in the tubular cell

Question 33

how is the concentration gradient of sodium in the tubule created?

Answer 33

with the basolateral sodium potassium ATPase carrier (sits in the basolateral membrane)

Question 34

how does the sodium potassium pump ATPase carrier work?

Answer 34

it is going to take energy and undergoes hydrolysis to produce ADP and then will pump 3Na+ ions out of the cell for every 2 K+ ions pumped in the cell

Question 35

how does sodium passively enter the tubular cell via the electrochemical gradient?

Answer 35

via sodium potassium pump - responsible for repolarization - negative electrochemical gradient because it pumps more positive ions out than it pumps in

Question 36

what is the net change in ions in the tubular cell?

Answer 36

net positive OUT

Question 37

what is the concentration gradient in the lumen?

Answer 37

usually -3mV

Question 38

what is the concentration gradient inside the tubular cell?

Answer 38

usually - 70mV

Question 39

the negative voltage inside the tubular cell does what?

Answer 39

attracts positive ions

Question 40

in summary, what are the three steps of sodium reabsorption?

Answer 40

1. Na+ passively enters through Na+ channels via concentration and electrochemical gradient 2. Na+ is actively pumped to basolateral side of cell by Na+/K+ ATPase 3. Na+ diffuses into peri-tubular capillary

Question 41

what is the purpose of the Na+//K+ ATPase in the tubular cell?

Answer 41

- actively pump Na+ to aid in Na+ efflux from tubular cell - maintain electrochemical gradient for passive Na+ influx into tubular cell - maintain concentration gradient for passive Na+ influx into tubular cell

Question 42

what % of filtered Na+ is reabsorbed?

Answer 42

99.5%

Question 43

80% of the kidneys total ATP use is devoted to?

Answer 43

transporting Na+

Question 44

why is it important to reabsorb Na+?

Answer 44

because the movement of Na+ drives the reabsorption of many other substances as well

Question 45

each area of the tubule is responsible for?

Answer 45

reabsorbing sodium in different amounts

Question 46

which part of the tubule reabsorbs the largest amount of sodium?

Answer 46

proximal tubule, reabsorbing 67% of sodium

Question 47

why is so much of sodium reabsorption important at the proximal tubule?

Answer 47

at the proximal tubule, it helps to reabsorb glucose, amino acids, water, chloride ions, and urea

Question 48

what tubule area is 25% of sodium being reabsorbed?

Answer 48

in the ascending limb of the loop of Henle

Question 49

what is the role of Na+ reabsorption at the ascending limb of the loop of Henle?

Answer 49

plays critical role in kidney's ability to produce urine of varying concentrations

Question 50

in the distal and collecting tubules, what % of sodium reabsorption happens here?

Answer 50

8%

Question 51

the sodium being absorbed at the distal and collecting tubules, what is its role?

Answer 51

- hormonal control and regulating ECF volume

Question 52

summary of how water is reabsorbed (how water enters through and across into the plasma of the peritubular capillary/

Answer 52

1. H20 moves through selective water channel (aquaporins) in the luminal membrane 2. H20 moves out of tubular cell into the interstitial fluid via osmosis due to [Na+] gradient in lateral space 3. H20 moves in peritubular capillary due to hydrostatic pressure + osmosis

Question 53

can water enter the tubular cell through tight junctions?

Answer 53

yes

Question 54

the interstitial fluid is confined, tight space. we bring water in there via osmosis so what happens to the interstitial space then?

Answer 54

we create a pressure gradient which will then move water into the peritubular capillary

Question 55

is water reabsorption active or passive?

Answer 55

all passive, no energy is required