Overview of the Maintenance of Water and Ions

Overview of the Maintenance of Water and Ions Osmoreceptors Baroreceptors Kidneys

Starting point 3. Shifting fluid along loop 2. Equilibration of osmolality between descending limb and Interstitium 1. Generation of 200 mOsm gradient 200 300 300 300 300 400 200 400 400 200 300 300 200 400 400 200 300 300 300 300 200 400 400 400 200 400 200 400 300 300 300 200 300 400 400 400 200 300 300 300 300 400 200 400 400 400 400 400 200 150 300 350 150 350 350 150 100 300 300 300 200 300 350 400 350 200 400 200 400 400 200 500 700 700 Cycle 2 400 400 200 400 400 200 400 400 300 800 1000 1000 400 500 300 500 500 300 400 400 500 1200 1200 1000 after a few cycles Generation of a high interstitial osmolality Cycle 1

Blood Movement of: Osmolality (mOsm/l) Salt Water 300 Anti Diuretic hormone 300 300 100 300 500 300 500 500 ADH ADH ADH 700 700 700 500 900 900 700 900 1100 1100 900 1100 300

Blood Movement of: Osmolality (mOsm/l) Salt Water 100 300 Anti diuretic hormone 90 300 100 300 80 500 300 500 ADH ADH ADH 700 700 500 70 900 700 900 65 1100 900 1100

100 VU= 16 ml·min-1 Max. diuresis : Max. antidiuresis : VU= 0,3 ml·min-1 80 Normal : VU= 1 ml·min-1 60 H2O (% of GFR) 40 35 % max. water diuresis 20 % } 20 Under control of ADH 0 max. antidiuresis Proximal Late distal and Collecting duct Diuresis and Antidiuresis

1200 diluting segment late distal with ADH 1000 800 ADH effect Osmolality (mOsm/l) 600 400 200 without ADH 0 Proximal tubule Thin loop Distal tubule Collecting duct Urine Osmolality of tubular fluid (effect of ADH)

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): average value 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;

GFR = 120 ml·min-1 M = GFR · P Diuresis: V = 16 ml·min-1 120 @ 7,5 times concentrated 16 H2O Antidiuresis: V = 0,3 ml·min-1 120 @ M = V · U 400 times concentrated 0,3 ( ) GFR U = is a measure for H2O reabsorption ! P V Inulin Concentrating of substances in Urine example: (Inulin)

Maximal concentration (mOsm) Urine / Plasma ratio 2 4 5 10 14 25 Beaver Pig Human White rat Kangaroo rat Desert spring mouse 520 1100 1400 3000 5500 9400 Ability of urine concentration Schmidt-Nielsen, 1979

Cell Blood Tubular fluid Protein kinase H2O ATP A ADH R C cAMP H2O Phosphoproteins Effects of ADH

Max Max Plasma [ADH] 0 0 270 -20 0 10 280 290 300 310 -30 -10 20 Plasma osmolality (mOsm/kg H2O) Changes in blood volume or blood pressure ( %) Stimuli releasing ADH A: Osmolality B: Blood volume

Max Urinosmolality Total excretion of electrolytes Urine excretion rate Min Max 0 Plasma ADH ADH effects on urine osmolality and urine excretion rate

ADH (= Antidiuretic hormone = vasopressin) Ncl. supraopticus and paraventricularis (Hypothalamus) Synthesis: Neurohypophysis Storing : Osmoreceptors (III. Ventricle) : Releasing stimuli : Osmolarity ADH Stretch receptors in low pressure system (right atrium) : Pressure ADH ADH deficiency: Diabetic insipidus

Overview of the Maintenance of Water and Ions