Lecture 3: Transport Along The Nephron Flashcards
Tubular renal epithelial cells exhibit:
Membrane polarity
What are the 2 sides of a renal epithelial cell?
- Apical/tubular - faces urine
2. Basal/basolateral - faces blood
Movement of solutes between the cells
Paracellular
Movement of solutes across the cell
Transcellular
Movement of solutes against gradient, required ATP
Active transport
Movement of solutes with gradient, no ATP
Passive transport
Simple diffusion vs carrier-mediated
Simple- due to gradient, bulk flow (ultrafiltration)
Carrier- needs a carrier protein (has a Tm)
Kidney filters about ____ L of plasma per day.
180L
Nearly everything that is filtered is…
Reabsorbed
What’s an example of glomerulotubular balance?
If you eat more Na, then you will excrete more Na.
The ability to adjust reabsorption rate to match the filtered load
What is solvent drag?
The things in H2O usually want to move with it.
Most Na transport is…
Transcellular
Reabsorption of Na and its co-transported solutes causes:
Osmotic gradient and reabsorption of H2O
Na is reabsorbed with what molecule and enzyme in the PCT?
HCO3-
Carbonic anhydrase
Na is usually cotransported with what solutes? In the PCT
Glucose, AAs, phosphate, lactate (and of course HCO3-)
Which of the following could explain why untreated diabetic patients have increased urine flow?
Increased tubular fluid osmotic pressure
What effect would a carbonic hydrase inhibitor have on urine volume and osmolarity?
Increase volume and decrease osmolarity
REMEMBER: carbonic hydrase is required to reabsorb sodium and HCO3, which will cause water to follow
We reabsorb a lot of Pi- and HCO3- at the expense of what in the PCT?
Cl-
Organic Anion Secretion in the PCT
PCT secretes organic anions. MK.
Reabsorb alpha-ketoglutarate to excrete organic anions like PAH and penicillin.
The organic anions charge is neutralized by H+ or other cations.
Transporters are non-selective.
What happens if you have both procanimide and cimetidine?
YOU DIE
Because they counteract each other.
BTW.. PAH and penicillin is good.
Organic Cation Secretion in the PCT
PCT secretes organic cations into the tubular fluid. WOW, NO WAY.
Little bit of creatinine, dopamine, epi/NE
Morphine, atropine, blah
Trades this shit for H+
Fuck
When there is too much solute and not enough transporters
The transport process that utilizes a transport protein becomes saturated
Where the lines are not linear on the filtered load vs plasma glucose graph
Splay area
What is the transport maximum of glucose? Tm
325 mg/min
If plasma glucose is 400 mg/do and GFR is 125 ml/min….how much glucose is secreted?
Tm= 325 mg/min
Excretion = FL - Tm
FL = Xa * GFR
Exc = (4 * 125) - 325 = 175 mg/min
FUCKING WONDERFUL
Thin descending loop (DTL) of henle is permeable ONLY to:
Water.
Reabsorbed due to osmotic forces.
“The concentrating segment”
The Thin ascending loop (ATL) of henle is impermeable to…
Water.
No water movement, no volume change.
Will always have less volume than DTL
The Thick ascending loop (TAL) is impermeable to…
Water.
Not water movement, no volume change.
“The diluting segment” due to LOTS of transport.
Helps generate hyperosmotic gradient in tissue.
TAL is called the “diluting segment” because…..
There’s lots of transport, but no water movement.
-active, passive, paracellular and transcellular
1000mOsm to 100mOsm*
Where is the Na-Cl-K symporter found?
What blocks this?
Thick ascending loop
Lasix
This is how the macula densa senses Na to adjust GFR
Where is the site of macula densa and juxtaglomerular apparatus?
Between ascending loop and distal tubule
Senses tubular sodium load by measuring transport rate, and adjust GFR
Early distal tubule is impermeable to…
Water.
Continues diluting tubular fluid.
Lots of transport.
Where is the Na-Cl symporter found and what blocks this?
Early distal tubule
Thiazides
