Lecture 16: Renal Physiology 3 Flashcards
Describe the pathway of urine production in the nephron
Glomerulus > PCT > PST > thin descending > loop of Henle > thin ascending > thick ascending > DCT > CT > CD
The glomerulus _____ while the Bowman’s capsule ______
Filters
collects
Proximal convoluted and straight tubule: Actively absorbs? Passively absorbs? Main transporter? What is secreted here?
NaHCO3, NaCl, K+, glucose, AA
H2O
Na/K ATPase, Na+/H+ antiporter
drugs and creatinine
Why is carbonic anhydrase important at the PCT?
Why is the Na/H antiporter important at the PCT?
Lumen: converts HCO3- and H+ to CO2+H2O that enters the PCT cell
PCT cell: converts CO2+H2O into HCO3- and H+
H+ made by carbonic anhydrase equation exchanged out of PCT for Na+ in lumen
Thin descending loop reabsorbs _____
Permeability of thin ascending loop?
Status of urine after leave thin descending to thin ascending?
H2O
Impermeable to everything
Concentrated
Thick ascending loop reabsorbs ______
What is the main transporter?
Status of urine here?
Na, Cl, impermeable to H2O
Na/K ATPase, NKCC2
Diluted
What is the importance of the NKCC2 transporter?
Takes 1 Na/2Cl/1K into the thick ascending limb cell in exchange for K+ flowing out through the K+ channels
Distal convoluted tubule:
What is reabsorbed here?
Is H2O permeable here?
What is the main transporter?
Na, Cl, Ca2+
No
NCC, Na/K ATPase
What hormone acts at the DCT? What does it do?
PTH. Upregulates expression of Ca2+ channels to allow Ca2+ into the blood
Early collecting tubule:
What is reabsorbed?
What is secreted?
What is the main transporter?
Na, H2O
K
ENac, Na/K ATPase, proton pump
What hormone acts at early CT? What does it do?
Aldosterone. Upregulates ENac and Na/K ATPase expression to allow Na+ and H2O to be reabsorbed, and K+ to be excreted
How is the early CT important for K+ secretion?
Basically the main control point for deciding how much Na+ absorbed, because it decides how much K+ is excreted in exchange. Diuretics will decrease K+ excretion here to decrease the reabsorption process.
-too much Na+ absorbed = too much K+ secreted (hypokalemia)
Late collecting tubule:
Reabsorbs?
Main transporter?
H2O
AQ 2
What hormone acts at the late CT and what does it do?
What controls it?
What substance can inhibit its release?
ADH, binds V2 receptors on CT > upregulates AQ2 expression
Serum osmolarity and volume status
Alcohol, leads to diuresis since H2O isn’t reabsorbed
What is the purpose of diuretics?
Decrease fluid load on the heart by excreting excess fluid
How does a natriuretic end up acting like a diuretic?
It increases salt excretion, causing water to follow it out = diuresis
How do carbonic anhydrase inhibitors work and what is its effect?
What do these commonly treat?
- No CA reaction, no H+ to couple to the Na/H antiporter = can’t absorb Na+ and H+ can’t get out
- increased Na, HCO3- in urine (basic urine), acidic body
High altitude sickness
How do loop diuretics work and what are its effects?
Inhibits NKCC2 which halts ion transport since K+ isn’t brought in so it can’t flow out to form the concentration gradient for Na+/Cl-/Ca2+/Mg2+ to enter.
No Na+ absorption, water follows it out (diuresis)
How do thiazide diuretics work and what are its effects?
Inhibits NCC, blocking NaCl reabsorption @ DCT
-increased Na and Cl in lumen leading to diuresis, Ca2+ reabsorption increases (PTH action not affected)
How do K sparing diuretics work?
Acting at collecting duct to regulate K+ excretion to influence Na+ reabsorption
How do aldosterone receptor (MR) antagonists work?
How do E-Nac inhibitors work?
- blocks E-Nac expression = Increase Na excretion = diuresis, decreased K+ excretion
- inhibits E-Nac, same effects
Both increase urine pH and decrease body pH
Factors that affect Na+ resorption?
Factors that affect Na+ secretion?
- High aldosterone or angiotensin II
- Any process that causes Na+ loss
-increased blood Na+, increased tubular flow rate
Factors affecting K+ resorption
Factors affecting K+ secretion
- K+ deficiency, diarrhea (any process that lowers body K+)
- Increased blood K+, aldosterone, increased tubular flow rate or Na+ delivery to CD
How does ADH act on the collecting duct?
Act on principal cells of CT by binding V2 receptor > increase AQ2 expression > more H2O reabsorption
What effect does ADH have on urea?
Increases urea permeability at the IMCD, causing it to flow back into the loop of henle (urea basically gets detoured, still comes back to the CD to be excreted)
What effect does ADH have on NKCC2?
Increases its activity to promote NaCl absorption
Explain why the medulla is salty (countercurrent flow)
- NaCl flows into interstitium at thick ascending limb
- Water in thin descending limb flow into interstitium to dilute it
- Filtrate going into medulla is concentrated (up to 1200 mOsm)
- Gets diluted at the thick ascending limb by the next “group” of filtrate
What is osmolar clearance?
How do you calculate it?
Total clearance of solute in blood
Cosm = Uosm x V / Posm
What is obligatory urine volume?
How is it calculated?
-Minimal amount of urine needed to excrete the solutes that need to be expelled
OUV = minimum solutes excreted per day/maximum urine concentrating ability
What is the difference between natriuresis, diuresis and antidiuresis?
N: excrete excessive sodium
D: large urine output, excessive water excretion
A: keep all the water, small urine volume (due to high ADH)
