RENAL 06: TUBULAR FXNS ALONG NEPHRON Flashcards
What is euvolemia the condition of
Salt (and therefore water) intake matches salt (and therefore water) excretion
Most sodium is reabsorbed in the
Proximal tubule
The place of second-most sodium reabsorption
Thick ascending limb of loop of henle
How much sodium is reabsorbed in the distal tubule and collecting duct?
Not much (fine control)
Cortical nephrons are mostly in the business of doing what?
Making sure we hve the proper balance of sodium reabsorption
How do the early and late proximal tubule differ from each other, with regard to sodium reabsorption?
In the early proximal tubule, sodium is reabsorbed with bicarbonate and organic solutes (ex. glucose, amino acids); in late proximal tubule, Na is reabsorbed with Cl
What protein provides the driving force for sodium reabsorption in proximal tubule
Na/K-ATPase
How are we reabsorbing sodium in the early proximal convoluted tubule?
After the gradient has been set up by NKA, we transport Na into the proximal convoluted tubule via
- antiporting with hydrogen ions
- symporting with glucose (SGLT2)
From there, it gets from the proximal cell into blood lumen via a bicarb/Na symporter (as well as Na/K-ATPase)
How does glucose get from proximal tubule cell to blood lumen in early proximal convoluted tuble?
GLUT2
In late proximal tubule, sodium reabsorption is primarily coupled to what? (transcellular and paracellular)
Transcellularly, bicarbonate
Paracellularly, chloride
Due to high amount of ions moving in late proximal tubule, what happens to fluid in tubule?
Water follows
What happens to charge in late proximal tubule?
There is a slight negative charge due to reabsorbing so much sodium (sets up driving force for reabsorption of chloride paracellularly)
How does sodium get across the late proximal tubule barrier to get to blood on basolateral side?
Primarily chloride, but also bicarb. SHe seems to really want us to understand though the chloride connection because it’s in the picture she gave us.
Can chloride also move into the blood with potassium?
Yes, this can happen on the basolateral membrane in the late distal tubule cells with a K/Cl transporter.
Are the proximal tubule aquaporins that allow water equilibration aquaporin type 2 (the same as in collecting duct and distal tubule)?
No
In the proximal tubule, what do we say about the reabsorption of water with regard to osmolarity?
It is isosmotic
How much glucose is left in the urine by the end of the early proximal tubule?
Theoretically, nothing
3 segments of loop of henle
thin descending limb, thin ascending limb, thick ascending limb
Thin descending limb is ____(permeable / impermeable) __ to sodium and chloride, but __(permeable/impermeable)__ to water
Impermeable, permeable
Thick ascending limb is __(permeable/impermeable) _ to ions, and __(permeable/impermeable)__ to water.
Permeable, impermeable
This is called the diluting segment - NaCl is reabsorbed into blood, but water is not reabsorbed along with it. Therefore, the urine becomes more dilute.
The thin ascending limb is (permeable/impermeable) to solutes, and (permeable/impermeable) to water
Permeable, impermeable
Thick ascending limb ion transport
Active pumping by Na/K-ATPase in basalateral membrane sets up gradient and causes low intracellular Na, this leads to a favorable chemical gradient for Na from tubular fluid to come into the cell alongside Cl and K, or in an antiporter with hydrogen ions as part of the carbonic acid cycle. Na can also travel paracellularly (as well as K, Ca, and Mg) between cells. Water doesn’t follow any of these.
Where do diuretics like furosemide work
In the thick ascending limb by blocking the Na/K/Cl transporter, which will stop the reabsorption of ions. This means you hold onto water later on, and you pee all of it out. Lop diuretics are organic acids and are related to PAH, therefore they compete for binding sites and interfere with a transporter. If we gave a patient a really high dose, we could see them excrete so much as 25% of filtered sodium (maximum for this area)
In the early distal tubule, how do we set up the energy that is going to allow for transport of sodium?
NKA
How is sodium moving across the distal tubule cell to be reabsorbed?
In cotransport with chloride, and extruded into blood by NKA (cl will leave through channels and K/Cl transporters)
how can we modulate ion/water balance in early distal tubule?
You can use a diuretic that blocks that sodium/calcium transporter from lumen into cell
What cells in the collecting duct an late distal tubule are responsible for Na reabsorption and K secretion, as well as water reabsorption?
Principal cells
What is the effect of late distal tubule and collecting duct principal cells on K
They cause K secretion
What is the driving force for ion movemetn in the late collecting duct and distal tubule principal cells
NKA
What is the membrane potential in late distal tubule and collecting duct
quite negative-due to ENaC
What cells are repsonsible for K reabsorption and H secretion in late distal tuble and collecting duct
alpha intercalated cells
What cells in late distal tubule and collecting duct are responsile for bicarb secretion and hydrogen ion and chloride reabsorption?
beta intercalated cells
What cells are targets of K sparing diuretics
Late distal tubule and collecting duct cells
