Lesson 31: Topic 27 - Glucose Reabsorption

Question 1

summary of glucose reabsorption in the tubular epithelial cell

Answer 1

1. Na+ enters cell down electrochemical gradient using the Na+-glucose co-transporter 2 (SGLT-2) (Glucose comes in with Na+ against concentration gradient
2. Na+ is pumped to basolateral side of cell by Na+/K+ ATPase
3. Glucose passively diffuses out of cell using GLUT2 down the concentration gradient
4. GLUT1 passively transports glucose into peritubular capillaries

Question 2

what is SGLT-2?

Answer 2

a secondary active transporter
- it is actively moving glucose across a concentration gradient and it is being powered by sodium moving and co-transporting through the active transporter into the tubular epithelial cells

Question 3

what is the primary dictator of glucose reabsorption from the tubule back into the peritubular capillary?

Answer 3

the SGLT-2 transporter

Question 4

where is the GLUT2 facilitated diffusion transporter located?

Answer 4

on the basolateral membrane

Question 5

what transporter in the peritubular capillary wall?

Answer 5

a GLUT1 transporter

Question 6

what does SGLT-2 dictate?

Answer 6

how much glucose is entering into the tubular epithelial cell essentially for transport and reabsorption

Question 7

what does the GLUT-2 transporter do?

Answer 7

moves glucose out of the tubular epithelial cell

Question 8

what does the GLUT-1 transporter do?

Answer 8

moves glucose from the interstitial fluid into the peritubular capillary

Question 9

the amount of glucose entering filtrate is _______ to plasma glucose concentration

Answer 9

proportional

Question 10

what determines the maximum rate of absorption of glucose that is going to be entering into our tubular epithelial cells and entering into our peritubular capillaries?

Answer 10

SGLT-2
- referred to as a transport maximum

Question 11

what is transport maximum?

Answer 11

the maximum rate of reabsorption of glucose in the tubule

Question 12

what is the tubular maximum of glucose?

Answer 12

370mg/min of glucose
- essentially: maximum amount of glucose that can be reabsorbed at the tubule. And that is dictated by the SGLT-2 transporters

Question 13

the more SGLT-2 transporters we have = the more ______________.

Answer 13

the more glucose that we can reabsorb in the tubule

Question 14

true or false: SGLT-2 transporter is sensitive to insulin and the SNS

Answer 14

true

Question 15

if you have insulin present and the SNS is active, is the SGLT-2 transporter going to move glucose through into the tubule to be reabsorbed faster or slow?

Answer 15

faster

Question 16

what is renal threshold?

Answer 16

• the plasma concentration of glucose that results in saturation of the transporters, detected as spillover of glucose into the urine (essentially you have maximized the amount of glucose that is being transported by the SGLT transporters and it is completely being reabsorbed)

Question 17

what is the renal threshold?

Answer 17

300mg/100mL plasma concentration of glucose

Question 18

what is the plasma concentration of glucose in healthy individuals?

Answer 18

less than 100mg/100mL

Question 19

true or false: diabetes can be determined when the renal tubular glucose concentration exceeds 300mg/100mL

Answer 19

true

Question 20

true or false: tubular maximum is determined by the number of SGLT-2 transporters

Answer 20

true

Question 21

true or false: glucose filtered by the glomerulus can exceed what is reabsorbed in healthy individuals

Answer 21

false

Question 22

true or false: GLUT1 facilitates glucose transport from the interstitial fluid into the peritubular capillaries

Answer 22

true

Question 23

is the proximal tubule very permeable to H20?

Answer 23

yes

Question 24

at the proximal tubule, are Na+, Cl- and H20 reabsorbed at similar or different rates?

Answer 24

similar

Question 25

is there reabsorption of glucose and amino acids at the proximal tubules?

Answer 25

yes

Question 26

in the descending loop of henle, it is permeable to H20, but there is no sodium reabsorption. what is the case for the ascending loop of henle?

Answer 26

opposite - impermeable to H20 - there is Na+ reabsorption (it is controlled by Na+Cl-K+ cotransporter)

Question 27

is water reabsorbed in the collecting duct?

Answer 27

yes if it bypasses the loop of henle - permeability is controlled by vasopressin in the kidneys

Question 28

all of the underlying processes that are happening at the loop of henle, the purpose of it is to?

Answer 28

reabsorb water. or else we have too much water in our tubule which makes us urine too much and we would need to constantly drink more water to keep ourselves hydrated - main function is to reabsorb H20 by generating hyper osmotic interstitial fluid within the medulla

Question 29

what is osmolarity?

Answer 29

of solutes per given volume of liquid

Question 30

in the renal cortex, the interstitial fluid is what type of osmotic?

Answer 30

iso-osmotic (300 milliosmoles/L)

Question 31

what is iso-osmotic?

Answer 31

the interstitial fluid has the same number of solutes as in the tubule

Question 32

what is the osmolarity in the interstitial fluid in the renal medulla region?

Answer 32

hyper-osmotic - gradient extending from 300 mosm/L - 1200 mosm/L (closest to renal pelvis) (very concentrated)

Question 33

is there aquaporins in the descending limb of the loop of henle? what does this mean?

Answer 33

yes. this means we can move water into the interstitial fluid

Question 34

is there aquaporins in the ascending loop of henle?

Answer 34

no

Question 35

why can you move sodium in the ascending loop of henle?

Answer 35

because there is the a sodium chloride potassium pump present

Question 36

in summary, what are the unique characteristics of the Loop of Henle that allow for generation of hyper-osmotic interstitium?

Answer 36

1. the descending loop of Henle is H20 permeable (aquaporins) 2. the ascending loop of Henle is H20 impermeable (no aquaporins), and has Na+Cl-K+ PUMPS 3. the loop of Henle is a hairpin loop, so the actions on one side of the loop will affect the other side

Question 37

how is the osmotic gradient in the loop of henle generated?

Answer 37

1. in the ascending loop, NaClK pumps move salts into the interstitial fluid which increases interstitial fluid osmolarity and reduces the osmolarity of the tubular fluid (no water can move out of the ascending loop) 2. this increases the osmolarity of the interstitial fluid 3. in the descending loop, H20 diffuses out of the tubule into the interstitial fluid, following osmotic gradient. It will equilibrate with osmolarity of the interstitial fluid 4. it goes from 400 --> 300 because we are moving solutes, removing NaCl out of the filtrate back into the fluid. so it becomes more concentrated because then we are moving more water out (removing dilution)

Question 38

NaClK pumps can achieve _______ difference between interstitial fluid and tubular fluid in the ascending loop

Answer 38

200 mosm/L

Question 39

the highest osmolarity is where on the loop of henle?

Answer 39

at the base of the loop

Question 40

what dictates the movement of water from an area of low to high solute concentration?

Answer 40

osmosis - this drives tubular flow

Question 41

what is countercurrent exchange?

Answer 41

it creates high osmolarity in Loop of Henle which is dictated by the movement of sodium from the ascending limb. concentrates the solute in the loop of Henle in the interstitial fluid which helps to draw water in from the descending limb and then concentrates urine - countercurrent because it moves in the opposite direction

Question 42

the longer the loop of henle, the more ____ it can reabsorb

Answer 42

water

Question 43

in the loop of henle, we concentrate the solutes in?

Answer 43

in the interstitial fluid

Question 44

what does the vasa recta do?

Answer 44

maintains the osmotic gradient. NOT generates it

Question 45

is the vasa recta a capillary?

Answer 45

yes. it is an extension of the efferent arteriole

Question 46

the osmotic gradient is created by?

Answer 46

the loop of henle

Question 47

true or false: the flow of blood is counter to the movement of filtrate through the tubule

Answer 47

true

Question 48

as a capillary, vasa recta are freely permeable to?

Answer 48

water and salts

Question 49

blood flow in the vasa recta is?

Answer 49

slow and hydrostatic pressure is low (to favour movement of fluid from interstitial fluid into the capillary)

Question 50

what is the function of the vasa recta?

Answer 50

to remove H20 from the medullary interstitial fluid, maintaining osmolarity interstitium required for producing concentrated urine - essentially it is moving water back into our blood and restoring our blood plasma volume

Question 51

true or false: hyperosmolarity in the base of the loop is due to H20 reabsorption in the interstitum

Answer 51

true

Question 52

which part of the loop of henle is aquaporins in?

Answer 52

descending loop of henle