L19

Question 1

The normal plasma osmolality (Posm) is ~… mosmol.kg-1H2O and very small variation by (~ … ) is sufficient to activate compensatory mechanisms.

Answer 1

290

±3 mosmol.kg-1H2O

Question 2

HOW The kidneys regulate the osmolality of the plasma by producing urine of varying osmolality?

Answer 2

1. The establishment of the osmotic gradient in the renal medulla by:
   •Transport of NaCl by the ascending loop of Henle
   •The counter-current multiplier in the thin descending, hairpin bend & ascending loop of Henle
   2.The regulation of the absorption of water from the collecting ducts by ADH.

Question 3

Ascending loop of Henle: describe transport of ions: (3)

●Transport is via….
●About …..% of the filtered ……- is reabsorbed
●The Na+/K+/2Cl-co-transporter is …..by loop diuretics -….

Answer 3

●Transport is via an apical Na+/K+/2Cl-co-transporter and a baso-lateral Na-pump
●About 20% of the filtered Na+, K+ and Cl- is reabsorbed
●The Na+/K+/2Cl-co-transporter is blocked by loop diuretics - frusemide, bumetamide.

Question 4

In the ascending limb of the loop of Henle …….. flows into the interstitium,…..

Answer 4

solute but not water

increasing its osmolality

Question 5

Przypomnienie: Producing Urine of Varying Osmolality

Answer 5

• The descending limb of the loop is permeable to water and so tubular fluid is concentrated
• Fluid continues to enter the loop so the concentrated fluid formed in the decending limb enters the ascending limb.
• A gradient is starting to develop in the interstitium and the nephron
• Solute fluxes continue to increase interstitial osmolality.
• Water fluxes from the descending limb concentrate tubular fluid.
• Repetition of the process generates an osmotic gradient in the medullary interstitium.

Question 6

The collecting ducts are….. to Na ….to water except in the presence of ….

Answer 6

relatively permeable
impermeable
ADH

Question 7

ADH - rozwin skót

Answer 7

Antidiuretic Hormone / vasopressin,

Question 8

ADH, or ….. is produced by….

Answer 8

vasopressin,

the posterior pituitary gland.

Question 9

•It is also called …. to distinguish it from ADH produced by ….

Answer 9

arginine vasopressin

other species.

Question 10

ADH: Actions on the kidney: (3)

+ the net effect

Answer 10

• ↑water permeability of the collecting duct
• ↑urea permeability in the inner medullary region of the collecting duct
• ↑NaCl reabsorption in the thick ascending limb.

The net effect is to aid water reabsorption by the kidney!

Question 11

ADH is produced in cells in….

Answer 11

the supraoptic and paraventricular nuclei

Question 12

ADH is transported to and released from ….

Answer 12

the posterior pituitary

Question 13

• ADH is released by …. as small as

1%. Release is reduced when ….

Answer 13

a rise of plasma osmolality

osmolality falls

Question 14

Plasma [ADH] between ….. accounts for the

range of urine osmolalities i.e. ….

Answer 14

0.5 and 5 pg.ml-1

100 -1250 mosmol.kg H2O-1.

Question 15

describe Mode of Action of ADH

Answer 15

Increased water permeability

                             ^
                             I This increases the insertion of water channels, aquaporins(AQP2), into the apical surface of the cell

                             ^
                             I Stimulation of adenylyl cyclase (AC) to generate cAMP and activate protein kinase A (PKA)

                             ^
                             I In the collecting duct ADH binds to a receptor on the baso-lateral surface of the tubule cell

Question 16

LO: The establishment of the osmotic gradient in the renal medulla by the counter-current multiplier

Answer 16

.

Question 17

LO: Transport of NaCl by the ascending loop of Henle

Answer 17

.

Question 18

LO: The role of ADH in the regulation of plasma osmolality

Answer 18

.

Question 19

LO: The mechanism by which ADH regulates water uptake by distal tubule and collecting ducts

Answer 19

.