Lecture 2: Na+ and H2O handling, Concurrent Multiplication, Generation of the hypertonic renal medullary ISF

is Na+ and H2O synthesized by the body

• Na+ not synthesized or degraded by body

• H2O ingested or synthesized by the body

what is the volume of the ECF determined by

amount of Na+ in the ECF

where are Na+ and H2O reabsorbed along the nephron?

in the renal tubule, ______ reabsorption follows ______ reabsorption (either directly or indirectly)

water, Na+/solute

the majority of reabsorbed solute is

Na+

lower osmolarity solutions have a

higher h2o concentration

higher osmolarity solutions have a

lower h2o concentration

how do the kidneys adjust osmolarity of plasma (Posm)

altering only water reabsorption

label the following:

• lumen and ISF

• apical and basolateral membranes

• ions/molecules transport, apical and basolateral side

• is transporter secondary active cotransporter, secondary active cotransporter, ATPase, or facilitated diffusion transporter, or channel

label the following:

• lumen and ISF

• apical and basolateral membranes

• ions/molecules transport, apical and basolateral side

• is transporter secondary active cotransporter, secondary active cotransporter, ATPase, or facilitated diffusion transporter, or channel

movement at the apical membrane is

downhill (passive), either by diffusion through a channel or via a transporter (i.e., Na+/glucose co-transporter, Na+/H+ exchanger)

movement at the basolateral membrane is

active via the Na+/K+ ATPase

secretion of Na+ and H2O

secretion of Na+ and H2O does not occur

normal plasma osmolality/osmolarity value

300 mOsm/L

why is the filtered load of Na+ and H2O not the same in the proximal tubule

there are other solutes being filtered out, but Na+ is the primary solute

what does ADH (antidiuretic hormone) do

alters H2O permeability, primarily at collecting duct

obligatory water loss

minimum amount of water that must be excreted via the urine in order to excrete waste products (~444 ml/day)

indirect coupling between solute and water starts at

loop of Henle

ascending limb of the loop of henle is permeable to

Na+ only

descending limb of the loop of henle is permeable to

H2O primarily

distal tubule is permeable to

Na+

steps of countercurrent multiplication in loop of henle

steps of urea recycling

1. urea is reabsorbed by facilitated diffusion in the inner medullary CD

2. urea is secreted into the ascending limb, and recycled back to inner medullary CD

3. urea is trapped by the recycling process in the inner medulla because very little urea is removed by vasa recta

apical urea transporters in inner medullary CD are increased when

ADH is high

role of vasa recta capillaries

• delivery of O2 and nutrients to medullary cells

• prevents dissipation of the medullary osmotic gradient

outer medulla vs inner medulla

• outer medulla concentration is mostly salt

• inner medulla is about 600-700 mOsm salt and the rest is urea

AQP2

carried by vesicles that fuse with apical membrane

AQP3 and AQP4

always present on the basolateral membrane