Overview of the Maintenance of Water and Ions

Kidneys

Baroreceptors

Osmoreceptors

Generation of a high interstitial osmolality

300

300

300

300

300 300

300 300

300 300

300 300

Starting point

400

400

400

400

400

400

400

400

200

200

200

200

2. Equilibration of osmolality between descending limb and Interstitium

200

200

400

400400

400 400

300 300

400 400 200

200

3. Shifting fluid along loop

Cycl

e 2

300

400

400

400

500 300

200400

350 150

400 200

500500

350

400

350

400

400 400

150

200

200

300

200

300

500

400400

400 400

300 300

350 350 200

150

after a few cycles

300 300

500700 700

1000 1000 800

100

10001200 1200

300

300

300

300

400

400

400

400

200

200

200

200

1. Generation of 200 mOsm gradient

Cycl

e 1

Osmolality(mOsm/l)

300

500

700

900

1100

300

300

500

700

900

1100

300

500

700

900

100

300

300

500

700

900

1100

ADH

Blood Movement of:SaltWater

ADH AntiDiuretichormone

ADH

Osmolality(mOsm/l)

300

500

700

900

1100

300

300

500

700

900

1100

300

500

700

900

100

Blood Movement of:SaltWater

100ADH Anti

diuretichormone

90

80

70

65

ADH

ADH

Diuresis and Antidiuresis

max. antidiuresis

max. water diuresis

Max. antidiuresis : VU= 0,3 ml·min-1

Max. diuresis : VU= 16 ml·min-1

Normal : VU= 1 ml·min-1

100

80

60

40

20

0

35 %

20 %

Proximal Late distaland

Collecting duct

H2O

(%

of G

FR)

Under control of ADH}

Osmolality of tubular fluid (effect of ADH)

Proximaltubule

Thinloop

Distal tubule Collecting duct Urine

1200

1000

800

600

400

200

0

Osm

olal

ity (m

Osm

/l)

dilutingsegment late

distal

ADHeffect

withoutADH

withADH

Normal values

Renal Blood flow RBF = 1100 ml·min-1

with hematocrit, Hct = 45%

Effective Renal Plasma flow ERPF = 600 ml·min-1

Urine flow (V):

1 ml·min-1 = 1,5 L·day-1

minimal value 0,3 ml·min-1

by extreme dehydratation

maximal value 16 ml·min-1 by extreme water intake;

average value

GFR = 120 ml·min-1

M = GFR · P

Diuresis: V = 16 ml·min-1

12016

@ 7,5 times concentrated

Antidiuresis: V = 0,3 ml·min-1

@ 400 times concentrated1200,3

M = V · U

Concentrating of substances in Urineexample: (Inulin)

H2O

( )UP Inulin

is a measure for H2O reabsorption !GFR

V=

Ability of urine concentration

Maximalconcentration

(mOsm)

Urine / Plasmaratio

BeaverPigHumanWhite ratKangaroo ratDesert spring mouse

52011001400 3000 55009400

245 10 14 25

Schmidt-Nielsen, 1979

Effects of ADHTubular

fluidCell Blood

R ADHCA

H2O

H2O

ATP

cAMP

Protein kinase

Phosphoproteins

Stimuli releasing ADH

A: Osmolality

270 280 290 310300Plasma osmolality

(mOsm/kg H2O)

Max

0

Plas

ma

[AD

H]

B: Blood volume

-30 -20 -10 0 10 20

Max

0

Changes in blood volume or blood pressure ( %)

ADH effects on urine osmolality and urine excretion rate

Urine excretionrate

Total excretion of electrolytes

Urinosmolality

0 Plasma ADH Max

Max

Min

ADH(= Antidiuretic hormone = vasopressin)

Synthesis: Ncl. supraopticus and paraventricularis(Hypothalamus)

Storing : Neurohypophysis

ADH deficiency: Diabetic insipidus

Releasing stimuli : Osmoreceptors (III. Ventricle) :

Osmolarity ADH

Stretch receptors in low pressure system (right atrium) :

Pressure ADH