Lecture 16: Renal Physiology 3

Question 1

Describe the pathway of urine production in the nephron

Answer 1

Glomerulus > PCT > PST > thin descending > loop of Henle > thin ascending > thick ascending > DCT > CT > CD

Question 2

The glomerulus _____ while the Bowman’s capsule ______

Answer 2

Filters

collects

Question 3

Proximal convoluted and straight tubule:
Actively absorbs?
Passively absorbs? 
Main transporter? 
What is secreted here?

Answer 3

NaHCO3, NaCl, K+, glucose, AA
H2O
Na/K ATPase, Na+/H+ antiporter
drugs and creatinine

Question 4

Why is carbonic anhydrase important at the PCT?

Why is the Na/H antiporter important at the PCT?

Answer 4

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

Question 5

Thin descending loop reabsorbs _____
Permeability of thin ascending loop?
Status of urine after leave thin descending to thin ascending?

Answer 5

H2O
Impermeable to everything
Concentrated

Question 6

Thick ascending loop reabsorbs ______
What is the main transporter?
Status of urine here?

Answer 6

Na, Cl, impermeable to H2O
Na/K ATPase, NKCC2
Diluted

Question 7

What is the importance of the NKCC2 transporter?

Answer 7

Takes 1 Na/2Cl/1K into the thick ascending limb cell in exchange for K+ flowing out through the K+ channels

Question 8

Distal convoluted tubule:
What is reabsorbed here?
Is H2O permeable here?
What is the main transporter?

Answer 8

Na, Cl, Ca2+
No
NCC, Na/K ATPase

Question 9

What hormone acts at the DCT? What does it do?

Answer 9

PTH. Upregulates expression of Ca2+ channels to allow Ca2+ into the blood

Question 10

Early collecting tubule:
What is reabsorbed?
What is secreted?
What is the main transporter?

Answer 10

Na, H2O
K
ENac, Na/K ATPase, proton pump

Question 11

What hormone acts at early CT? What does it do?

Answer 11

Aldosterone. Upregulates ENac and Na/K ATPase expression to allow Na+ and H2O to be reabsorbed, and K+ to be excreted

Question 12

How is the early CT important for K+ secretion?

Answer 12

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)

Question 13

Late collecting tubule:
Reabsorbs?
Main transporter?

Answer 13

H2O

AQ 2

Question 14

What hormone acts at the late CT and what does it do?
What controls it?
What substance can inhibit its release?

Answer 14

ADH, binds V2 receptors on CT > upregulates AQ2 expression
Serum osmolarity and volume status
Alcohol, leads to diuresis since H2O isn’t reabsorbed

Question 15

What is the purpose of diuretics?

Answer 15

Decrease fluid load on the heart by excreting excess fluid

Question 16

How does a natriuretic end up acting like a diuretic?

Answer 16

It increases salt excretion, causing water to follow it out = diuresis

Question 17

How do carbonic anhydrase inhibitors work and what is its effect?
What do these commonly treat?

Answer 17

• 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

Question 18

How do loop diuretics work and what are its effects?

Answer 18

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)

Question 19

How do thiazide diuretics work and what are its effects?

Answer 19

Inhibits NCC, blocking NaCl reabsorption @ DCT

-increased Na and Cl in lumen leading to diuresis, Ca2+ reabsorption increases (PTH action not affected)

Question 20

How do K sparing diuretics work?

Answer 20

Acting at collecting duct to regulate K+ excretion to influence Na+ reabsorption

Question 21

How do aldosterone receptor (MR) antagonists work?

How do E-Nac inhibitors work?

Answer 21

• blocks E-Nac expression = Increase Na excretion = diuresis, decreased K+ excretion
• inhibits E-Nac, same effects

Both increase urine pH and decrease body pH

Question 22

Factors that affect Na+ resorption?

Factors that affect Na+ secretion?

Answer 22

• High aldosterone or angiotensin II
• Any process that causes Na+ loss

-increased blood Na+, increased tubular flow rate

Question 23

Factors affecting K+ resorption

Factors affecting K+ secretion

Answer 23

• K+ deficiency, diarrhea (any process that lowers body K+)

- Increased blood K+, aldosterone, increased tubular flow rate or Na+ delivery to CD

Question 24

How does ADH act on the collecting duct?

Answer 24

Act on principal cells of CT by binding V2 receptor > increase AQ2 expression > more H2O reabsorption

Question 25

What effect does ADH have on urea?

Answer 25

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)

Question 26

What effect does ADH have on NKCC2?

Answer 26

Increases its activity to promote NaCl absorption

Question 27

Explain why the medulla is salty (countercurrent flow)

Answer 27

• 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

Question 28

What is osmolar clearance?

How do you calculate it?

Answer 28

Total clearance of solute in blood

Cosm = Uosm x V / Posm

Question 29

What is obligatory urine volume?

How is it calculated?

Answer 29

-Minimal amount of urine needed to excrete the solutes that need to be expelled
OUV = minimum solutes excreted per day/maximum urine concentrating ability

Question 30

What is the difference between natriuresis, diuresis and antidiuresis?

Answer 30

N: excrete excessive sodium
D: large urine output, excessive water excretion
A: keep all the water, small urine volume (due to high ADH)