Water Balance

Question 0

Osmol of fluid as it leaves PT?

Answer 0

300mosmols/kg

Loop is initially filled with iso-osmotic fluid

Question 1

How do the juxtamedullary and superficial nephrons differ in their ability to concentrate urine?

Answer 1

JM: Thin predominates
S: Thick ascending loop predominates (ie more NaCl pumps)

Question 2

Max gradient of water in asc loop?

Answer 2

200mosm/kg

Question 3

Describe the passive model of inner medulla osm?

Answer 3

Thin desc: only water can leave, leaves due to urea concentration in the interstitium of the inner medulla

Thin asc: only NaCl can leave

–>impt to get “the last drop” of water out of urine in cases of severe dehydration (countercurrent mult is MORE impt and includes the outer medulla–aka the thick asc limb)

NOTE: thick asc limb is in the OUTER medulla. Thins are in the INNER medulla

Question 4

Vasa recta surround which type of nephron?

Answer 4

Juxtamedullary

Question 5

Net effect of countercurrent mult?

Answer 5

Blood exiting medulla is less hypertonic than if there was a straight tube (rather than a hairpin loop) so kidney better preserves osmotic gradient in medulla

Question 6

Most impt stimulus for rise in ADH release?

Answer 6

Inc serum osmol unless in diseased states where vol is impt too (released from post pit)

–>cells in the hypothal shrink in response to inc extracellular tonicity signaling for AVP release

Question 7

How do we assess max urine concentration fxn?

Answer 7

• Collect for 12 hrs after 24 hrs fasting

- or when pt has elevated plasma osm (>800?)