Mechanisms of Urinary Concentration

Question 1

The production of concentrated urine (_____ urine) is done when ____ levels are high

Answer 1

The production of concentrated urine (hyperosmotic urine) is done when ADH levels are high

Question 2

When are ADH levels high?

Answer 2

in water deprivation, volume depletion, and SIADH

Question 3

ADH acts upon the ____ ____ of the nephron

Answer 3

ADH acts upon the collecting duct of the nephron

Question 4

What occurs in the loop of henle

Answer 4

In the TAL of the loop of Henle, H2O cannot be transferred but Na+ is reabsorbed by the Na/K/2Cl transporter, causing a dilution of the filtrate and concentration of the interstitial fluid (only good for about 600-700 mOsm/L)

Question 5

Where do we do urea recycling and what stimulates this?

Answer 5

occurs from the medullary collecting ducts and is stimulated by ADH

Question 6

Urea recycling results in:

Answer 6

results in cycling of urea into the interstitial space and subsequent concentration to form a gradient (makes up another 600-800 mOsm/L of the interstitial concentration)

Question 7

What acts on the distal tubules and what occurs there?

Answer 7

ADH increases the permeability of principal cells to H2O

increases reabsorption

Question 8

____ ____ are the capillaries that supply the loop of Henle; serve as ____ exchangers

Answer 8

Vasa recta are the capillaries that supply the loop of Henle; serve as osmotic exchangers

Question 9

For the countercurrent mechanism to work, the following must hold true:

Answer 9

The NaCl and H2O removed from the thick ascending limb and distal part of the tubules must be removed at the rate at which they are formed.

This is all accomplished by the countercurrent exchange mechanism of the vasa recta

Question 10

What is Free water clearance (Ch2o) and what do we use it for?

Answer 10

is used to estimate the ability to concentrate or dilute the urine

is produced in the diluting segments of the kidney (TAL and early distal tubule) where NaCl is reabsorbed and H2O is left behind

Question 11

in the absence of ADH water is ____ and therefore free water clearance is ____

Answer 11

in the absence of ADH water is excreted and therefore free water clearance is positive

Question 12

in the presence of ADH water is _____, and therefore free water clearance is ____.

Answer 12

in the presence of ADH water is not excreted, but reabsorbed in the late distal tubule and collecting ducts, therefore free water clearance is negative

Question 13

Calculation for Ch2O

Answer 13

= V - Cosm

V = urine flow rate
Cosm = osmolar clearence

Cosm = (Urine osmolarity x flow rate) / Plasma osmolarity

Question 14

If Ch2o is positive, it indicates (conditions/causes):

Answer 14

If Ch2o is positive: indicates high water intake, diabetes insipidus, or nephrotic DI

Question 15

If Ch2o is negative, it indicates (conditions/causes):

Answer 15

If Ch2o is negative: indicates water deprivation or SIADH