Distal Nephron

Question 0

Na-K ATPase effect on intracellular space

Answer 0

Pumps 3Na out and 2K+ in rendering the intracellular space more negative and allowing for Na to pump in on the apical side

Question 1

Character of fluid entering thin loop of henle

Answer 1

• Na in same concentration as plasma
• Cl in higher concentration than in plasma due to bicarb reabs in the PT
• Little if any glucose, AAs, or protein
• Minimal K+
• Lots of NH4+ which was synthesized in the PT
• 20% of filtered phosphate (rest was absorbed in the PT)

Question 2

How much active transport is there in the thin limbs?

Answer 2

Little if any, not even many Na-K ATPases

Question 3

Permeability properties of the thin descending limb

Answer 3

• Permeable to water with low perm to Na and Cl

- Water is extracted from the lumen and goes into the hypertonic interstitium of the medulla

Question 4

Permeability properties of the thin ascending limb

Answer 4

Impermeable to water and largely permeable to Na and Cl so salt DIFFUSES out of the tubule

Question 5

What is the net effect of the thin descending and thin ascending loops?

Answer 5

To reabsorb water and Na isotonically

Question 6

Tubular fluid content by the end of the thin limbs

Answer 6

• 15% of NaCl, 15% water and 15% of Ca2+ remains (70% was reabs in the PT, 15% in the thin limbs)
• 10% filtered K+ and phosphate remains
• 80% mg
• no glucose, little bicarb

Question 7

Permeability and charge of the thick ascending limb

Answer 7

• Water impermeable
• Powerful NaCl channels that dilute the urine
• Lumen is positive as compared to blood side

Question 8

What channel is key to thick ascending loop fxn?

Answer 8

NKCC2 channel

• Na, K and Cl are pumped into the cell
• Na is actively pumped out via Na/K ATPase
• Cl leaves the cell because the inside of the cell is negative
• K+ is recycled through ROMK

The lumen positive potential pushes Mg and Ca out to the blood to get reabs here

Question 9

What % of filtered solute is reabs in the thick ascending limb?

Answer 9

about 25%

Question 10

What is responsible for the pos potential in the thick ascending limb? What are the consequences of a more negative lumen?

Answer 10

The ROMK channel (ie K+ is responsible)

–if you block ROMK or have a defect here, the lumen will not have a pos potential and Mg and Ca won’t get reabs

Question 11

Characteristics of the luminal fluid at the end of the thick ascending limb?

Answer 11

• 10% of NaCl was reabs and now 5% remains
• 0% of water was reabs because it was water impermeable, so now a hypotonic fluid remains
• No glucose or phosphate
• 70-80% of Mg is reabs and now 5% remains

Question 12

Consequences of a defect in the thick ascending limb?

Answer 12

• More NaCl delivered to the distal tubule
• More Ca delivered to distal tubule
• Leads to a decrease in fluid retention, inc in aldosterone–>inc in K+ and H+ excretion

Question 13

What charge does the tubular lumen have in the DCT?

Answer 13

Weakly + due to active Cl uptake and some K+ recycling

Question 14

What channel is key to the DCT?

Answer 14

NCCT (Na-Cl co transporter)

Cl then passively exits the cell and goes into the blood

Question 15

Ca and Mg handling in the distal nephron

Answer 15

Only place where active reabs occurs (DCT, CNT to CD). Mg is reabs earlier than Ca

Question 16

Once in the cell, what buffers intracellular Ca2+?

Answer 16

Calbindin binds to it after it enters through the TRPV5 channel from the lumen and transports it to the blood side to be actively pumped out (ie the BLM side)

-process is controlled by vit D and PTH

Question 17

Character of fluid leaving the DCT?

Answer 17

• Hypotonic
• 1-5% of filtered NaCl and K+ remaining
• Minimal Ca and Mg
• Some acid
• 20% of filtered phosphage

Question 18

What is the major ion process in the cortical collecting duct?

Answer 18

Na passively enters through ENaC, K passively leaves through ROMK on the apical side
–>last bit of Na is reabs here

Question 19

What is the charge of the lumen in the cortical collecting duct?

Answer 19

negative

Question 20

Via what channels is K+ reabs in the cortical collecting duct?

Answer 20

Through low or intermediate conductance K channels

Question 21

Effects of aldosterone

Answer 21

Work on the CCD to increase ENaC channels, stimulate the Na-K ATPase, ROMK and increase H+ transport into the lumen

Question 22

What type of cell secretes H+?

Answer 22

Intercalated cell in the CCD

Question 23

What enzyme makes bicarb

Answer 23

Carbonic Anhydrase

Question 24

Where does active urea transport occur?

Answer 24

CD. Urea concentration here helps with urinary concentration and inc tonicity of inner medulla. ADH increases its transport.

Question 25

Functions of the collecting duct

Answer 25

• Regulate final urine composition of Na, K, bicarb and H+
• Regulate water retention/elim
• Contributes to the formation of high renal interstitial osmol so that the concentration of urine is ideal

Question 26

Content of fluid leaving the CD

Answer 26

All depends on what the organism needs!