Where is the Na/K ATPase located exclusively?
the basolateral membrane
Sodium transport is almost always…
active and via transcellular route
Sodium reabsorption mainly occurs via..
Na+ leak channels
What is the function of carbonic anhydrase?
it catalyzes the conversion of CO2 and H2O to bicarb and H+
Why does the concentration of chloride rise along the PCT?
because water and Na+ are leaving, and it’s staying (starts at 100mmol/L and goes to 120mmol/L)
Where do we find AQP1? AQP2? Which is under the control of ADH?
- PCT
- CD
- CD
*Aquaporins control trans cellular movement of water
What aquaporins are found in the ascending lim of the Loop of Henle?
NONE NONE NONE—> tons of tight junctions + no aquaporins = impermeable to H2O
What is responsible for glucose reabsorption?
90% SGLT2, 10% SGLT1
SGLT2–>low affinity, high capacity
SGLT1–>high affinity, low capacity (why it’s at the end; not much glucose left, but it can find the ones that are)
What is a treatment for diabetes?
SGLT2 inhibition (blood glucose levels drop because you don’t reabsorb the glucose)
What is the transport maximum for glucose?
200mg/dl
-past this point, extra glucose is excreted (glycosuria)
Of all the particles that enter the ascending limb, what percentage are reabsorbd?
75%
What is the permeability of the DCT to water?
DCT is relativity impermeable to water
What do thiazide diuretics work on?
- they block the Na/Cl pump in the DCT, and this increases the excretion of Na/Cl
- enhance Ca reabsorption in the DCT by increasing Na/Ca exchange
- reduce urinary excretion of Ca (and can be used to treat kidney stones/osteoporosis)
*natriuresis and decreases blood volume and pressure
What makes the Collecting Ducts impermeable to water?
lack of ADH
What conditions lead to aldosterone being released?
- decreased blood volume/blood pressure
- low EC Na+ (hyponatremia)
- high EC K+ (hyperkalemia)
- 1 and 2 promote renin/RAAS
- *3 directly stimulates adrenal cortex to secrete aldosterone
What two structures are impermeable to urea?
DCT, thick ascending limb
What is the function of UT-A?
it is stimulated by ADH to increase urea permeability in the inner medullary collecting duct
What triggers aldosterone release?
- angiotensin II (indirect in response to fall in Na+)
- increased plasma K+
- released from adrenal medulla
- *regardless of 1 or 2, it ALWAYS leads to Na+ reabsorption and K+ excretion
Loop Diuretics (furosemide)
MOA: inhibits Na/K/Cl co transporter in thick ascending LoH
- decreases reabsorption of Na, K, CL
- diuresis–>increases urine output (treat edema)
K+ sparing spironolactone
MOA: aldosterone dependent K+ sparing diuretic
- inhibits Na/K exchange in distal tubule and collecting duct
- promotes K+ retention of Na+ and water loss
- hypotensive effect
