(4) Reabsorption and secretion in the loop of henle

In about –% of juxtamedullary nephrons, the loops descend into the deepest section of the kidney medulla (near the duct of belline). What do they play a huge role in?

15; generating a concentrated environment in the interstitium

Ultrastructure of the thin descending limb and ascending limb

no amplified surface areas, no abundant mitochondria. Less complex and not very active in absorption or secretion

Ultrastructure of the thick ascending limb

mitochondria associated with extensive basal membrane interdigitations. More complex and cuboidal and more involved in absorption and secretion (like PT)

The PT is the primary — segment of the nephron that produces a fluid —- to plasma

reabsorbing; isosmotic

The loop of henle and distal nephron are responsible for producing a fluid that is either — or — when compared to plasma

hypo- or hyperosmotic

Describe the permeabilities of the tDLH

highly permeable to water, somewhat permeable to urea and less permeable to NaCl.

t/f there is a lot of transport in the tDLH

false, there is little transport in the tDLH

Describe the permeabilities of the tALH and TAL

tALH is highly permeable to NaCl and not permeable to H2O (so NaCL passively diffuses out) . In the TAL, NaCL is actively transported out of lumen and into interstitium by Na/K/2Cl cotransporter.

Fluid moving down the tDLH towards the — medulla becomes more (dilute or concentrated). Fluid moving up the ascending limb becomes more —

hyperosmotic; concentrated; dilute

Show how NaCl is reabsorbed in the TAL

NaCL is actively transported out of lumen by Na/K/2Cl cotransporter. Positive Vte due to abundance of apical K+ channels which stimulates paracellular cation movement

Bartter syndrome

defective Na/K/Cl cotransporter, K+ channel or Cl- channel which decreases potassium recycling and lowers the positive potential. Slows down cation reabsorption

Na+ reabsorption in the TAL occurs via what routes? What about Cl-?

transcellular and paracellular; transcellular only

Loop diuretics

inhibit Na/K/2CL cotransporter to decrease overall sodium reabsorption. Also decreases other cation reabsorption (like calcium)

–% of potassium reabsorption in the TAL is transcellular and –% is paracellular

50;50

–% of calcium reabsorption in the TAL is transcellular and –% is paracellular

50;50

How is calcium reabsorbed in the TAL

50/50 split between transcellular and paracellular route

Show how calcium and magnesium reabsorption is regulated in the TAL

may be inhibited by loop diuretics and activation of a Ca2+ - sensing receptor (which also sense Mg2+

The TAL is responsible for reabsorption of about —% of filtered Mg2+, predominantly by — diffusion

70; paracellular

Paracellin 1

increases tight junction permeability to Mg2+. necessary for Mg2+ diffusion through tight junctions in the TAL where it is mainly reabsorbed through paracellular routes