Lesson 31: Topic 27 - Glucose Reabsorption Flashcards
summary of glucose reabsorption in the tubular epithelial cell
- Na+ enters cell down electrochemical gradient using the Na+-glucose co-transporter 2 (SGLT-2) (Glucose comes in with Na+ against concentration gradient
- Na+ is pumped to basolateral side of cell by Na+/K+ ATPase
- Glucose passively diffuses out of cell using GLUT2 down the concentration gradient
- GLUT1 passively transports glucose into peritubular capillaries
what is SGLT-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
what is the primary dictator of glucose reabsorption from the tubule back into the peritubular capillary?
the SGLT-2 transporter
where is the GLUT2 facilitated diffusion transporter located?
on the basolateral membrane
what transporter in the peritubular capillary wall?
a GLUT1 transporter
what does SGLT-2 dictate?
how much glucose is entering into the tubular epithelial cell essentially for transport and reabsorption
what does the GLUT-2 transporter do?
moves glucose out of the tubular epithelial cell
what does the GLUT-1 transporter do?
moves glucose from the interstitial fluid into the peritubular capillary
the amount of glucose entering filtrate is _______ to plasma glucose concentration
proportional
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?
SGLT-2
- referred to as a transport maximum
what is transport maximum?
the maximum rate of reabsorption of glucose in the tubule
what is the tubular maximum of glucose?
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
the more SGLT-2 transporters we have = the more ______________.
the more glucose that we can reabsorb in the tubule
true or false: SGLT-2 transporter is sensitive to insulin and the SNS
true
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?
faster
what is renal threshold?
- 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)
what is the renal threshold?
300mg/100mL plasma concentration of glucose
what is the plasma concentration of glucose in healthy individuals?
less than 100mg/100mL
true or false: diabetes can be determined when the renal tubular glucose concentration exceeds 300mg/100mL
true
true or false: tubular maximum is determined by the number of SGLT-2 transporters
true
true or false: glucose filtered by the glomerulus can exceed what is reabsorbed in healthy individuals
false
true or false: GLUT1 facilitates glucose transport from the interstitial fluid into the peritubular capillaries
true
is the proximal tubule very permeable to H20?
yes
at the proximal tubule, are Na+, Cl- and H20 reabsorbed at similar or different rates?
similar
is there reabsorption of glucose and amino acids at the proximal tubules?
yes
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?
opposite
- impermeable to H20
- there is Na+ reabsorption (it is controlled by Na+Cl-K+ cotransporter)
is water reabsorbed in the collecting duct?
yes if it bypasses the loop of henle
- permeability is controlled by vasopressin in the kidneys
all of the underlying processes that are happening at the loop of henle, the purpose of it is to?
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
what is osmolarity?
of solutes per given volume of liquid
in the renal cortex, the interstitial fluid is what type of osmotic?
iso-osmotic (300 milliosmoles/L)
what is iso-osmotic?
the interstitial fluid has the same number of solutes as in the tubule
what is the osmolarity in the interstitial fluid in the renal medulla region?
hyper-osmotic
- gradient extending from 300 mosm/L - 1200 mosm/L (closest to renal pelvis) (very concentrated)
is there aquaporins in the descending limb of the loop of henle? what does this mean?
yes. this means we can move water into the interstitial fluid
is there aquaporins in the ascending loop of henle?
no
why can you move sodium in the ascending loop of henle?
because there is the a sodium chloride potassium pump present
in summary, what are the unique characteristics of the Loop of Henle that allow for generation of hyper-osmotic interstitium?
- the descending loop of Henle is H20 permeable (aquaporins)
- the ascending loop of Henle is H20 impermeable (no aquaporins), and has Na+Cl-K+ PUMPS
- the loop of Henle is a hairpin loop, so the actions on one side of the loop will affect the other side
how is the osmotic gradient in the loop of henle generated?
- 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)
- this increases the osmolarity of the interstitial fluid
- 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
- 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)
NaClK pumps can achieve _______ difference between interstitial fluid and tubular fluid in the ascending loop
200 mosm/L
the highest osmolarity is where on the loop of henle?
at the base of the loop
what dictates the movement of water from an area of low to high solute concentration?
osmosis
- this drives tubular flow
what is countercurrent exchange?
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
the longer the loop of henle, the more ____ it can reabsorb
water
in the loop of henle, we concentrate the solutes in?
in the interstitial fluid
what does the vasa recta do?
maintains the osmotic gradient. NOT generates it
is the vasa recta a capillary?
yes. it is an extension of the efferent arteriole
the osmotic gradient is created by?
the loop of henle
true or false: the flow of blood is counter to the movement of filtrate through the tubule
true
as a capillary, vasa recta are freely permeable to?
water and salts
blood flow in the vasa recta is?
slow and hydrostatic pressure is low (to favour movement of fluid from interstitial fluid into the capillary)
what is the function of the vasa recta?
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
true or false: hyperosmolarity in the base of the loop is due to H20 reabsorption in the interstitum
true
which part of the loop of henle is aquaporins in?
descending loop of henle
