Download - Chapter 20a
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Chapter 20a
Integrative Physiology II:
Fluid and Electrolyte Balance
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About this Chapter
• Fluid and electrolyte homeostasis• Water balance• Sodium balance and ECF volume• Potassium balance• Behavioral mechanism in salt and water
balance• Integrated control of volume and osmolarity• Acid-base balance
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Na+ and water ECF volume and osmolarity
K+ Cardiac and muscle function
Ca2+ Exocytosis, muscle contractions, and other functions
H+ and HCO3– pH balance
Body must maintain mass balance
Excretion routes: kidney and lungs
Fluid and Electrolyte Homeostasis
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Fluid and Electrolyte Homeostasis
• The body’s integrated responses to changes in blood volume and blood pressure
Figure 20-1a
Blood volume
Blood pressure
Volume receptors in atria andcarotid and aortic baroreceptors
Cardiovascularsystem
Cardiac output,vasoconstriction
Thirst causeswater intake
ECF and ICFvolume
Behavior Kidneys
Conserve H2Oto minimize
further volumeloss
Bloodpressure
trigger homeostatic reflexes
Stimulus ReceptorEffectorTissue responseSystemic response
(a)
KEY
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Blood volume
Blood pressure
Volume receptors in atria,endocrine cells in atria, and
carotid and aortic baroreceptors
Cardiac output,vasodilation
Excrete saltsand H2O in urine
KidneysCardiovascularsystem
ECF and ICFvolume
Bloodpressure
trigger homeostatic reflexes
Stimulus
Receptor
Effector
Tissue response
Systemic response(b)
KEY
Fluid and Electrolyte Homeostasis
Figure 20-1b
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Urine
Lungs
Feces
Skin
Water lossWater gain
Totals
1.5 L/day
0.1 L/day
Food and drink
Metabolism
2.2 L/day
2.5 L/day 2.5 L/day
0.3 L/day
Insensiblewater loss0.9 L/day
Intake 2.2 L/day
Metabolic production0.3 L/day
Output2.5 L/day+ – = 0
Water Balance
Figure 20-2
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Water Balance
• The kidneys conserve volume but cannot replace lost volume
Figure 20-3
Volume gain Volume loss
GFR canbe adjusted.
Glomerularfiltration rate(GFR)
Ifvolumefallstoo low,GFRstops.
Regulated H2Oreabsorption
Volumeloss in
the urine
Body fluidvolume
Kidneysconservevolume.
Kidneysrecyclefluid.
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Urine Concentration
• Osmolarity changes as filtrate flows through the nephron
Figure 20-450–1200 mOsMurine excreted
300 mOsM300 mOsM
600 mOsM
900 mOsM
1200 mOsM1200
300 100
Distaltubule
Proximaltubule
Collectingduct
Loopof
Henle
CORTEX
MEDULLA
Permeability towater and solutesis regulated byhormones.
Variable reabsorptionof water and solutes
Ionsreabsorbedbut nowaterOnly water
reabsorbed
Isosmotic fluid leaving theproximal tubule becomesprogressively more concentratedin the descending limb.
Removal of solute in the thickascending limb createshyposmotic fluid.
Hormones control distal nephronpermeability to water and solutes.
Urine osmolarity depends onreabsorption in the collectingduct.
1
23
4
1
2
3
4
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Urine Concentration
Figure 20-4, step 1
50–1200 mOsMurine excreted
300 mOsM300 mOsM
600 mOsM
900 mOsM
1200 mOsM1200
300 100
Distaltubule
Proximaltubule
Loopof
Henle
CORTEX
MEDULLA
Permeability towater and solutesis regulated byhormones.
Variable reabsorptionof water and solutes
Ionsreabsorbedbut nowaterOnly water
reabsorbed
Isosmotic fluid leaving theproximal tubule becomesprogressively more concentratedin the descending limb.
1
1
Collectingduct
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Water Reabsorption
• Vasopressin makes the collecting duct permeable to water
Figure 20-5a
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Water Reabsorption
Figure 20-5b
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Collecting duct cell
Secondmessengersignal
Collectingduct
lumen
Medullaryinterstitial
fluid
Vasarecta
Filtrate300 mOsM
cAMP
Exocytosisof vesicles
Vasopressin receptor
700 mOsM
600 mOsM
Aquaporin-2water pores
600 mOsM
Cross section ofkidney tubule
Vasopressin
Vasopressin binds tomembrane receptor.
Receptor activates cAMPsecond messenger system.
Water is absorbed byosmosis into the blood.
Storage vesicles
Cell inserts AQP2 waterpores into apical membrane.
H2O H2O
H2O
H2O
1
2
3
41
2
3
4
Water Reabsorption
• Vasopressin causes insertion of water pores into the apical membrane
Figure 20-6
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Water Reabsorption
Figure 20-6, steps 1–4
Collecting duct cell
Secondmessengersignal
Collectingduct
lumen
Medullaryinterstitial
fluid
Vasarecta
Filtrate300 mOsM
cAMP
Exocytosisof vesicles
Vasopressin receptor
700 mOsM
600 mOsM
Aquaporin-2water pores
600 mOsM
Cross section ofkidney tubule
Vasopressin
Vasopressin binds tomembrane receptor.
Receptor activates cAMPsecond messenger system.
Water is absorbed byosmosis into the blood.
Storage vesicles
Cell inserts AQP2 waterpores into apical membrane.
H2O H2O
H2O
H2O
1
2
3
41
2
3
4
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Factors Affecting Vasopressin Release
Figure 20-7
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Water Balance
• The effect of plasma osmolarity on vasopressin secretion by the posterior pituitary
Figure 20-8
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Countercurrent Heat Exchanger
Figure 20-9
Warmblood
(a) (b)
Limb
Warmblood
Warmblood
Coldblood
Heat lostto externalenvironment
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H2O =
Cl– =
KEY
Na+ =
K+ =
Blood in thevasa recta
Filtrate entering thedescending limb
The ascending limb pumpsout Na+, K+, and Cl–
100mOsM
300mOsM
300mOsM
300mOsM
1200mOsM
1200mOsM
600 600 600
900900
500 500
600
900
900
1200
Loop of Henle
(a)
Vasa recta
Water Balance
• Countercurrent exchange in the medulla of the kidney
Figure 20-10a
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Ion reabsorption
• Active reabsorption of ions in the thick ascending limb creates a dilute filtrate in the lumen
Figure 20-10b
(b)
KEY1200 mOsmenteringascendingloop of Henle
Saltreabsorption
Water cannotfollow solute
Cells of ascendingloop of Henle
Interstitialfluid
100 mOsmleavingthe loop
H2O =
Cl– = Na+ =
K+ =
1
2
3
4
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Fluid and Electrolyte Balance
• Vasa recta removes water• Close anatomical association of the loop of
Henle and the vasa recta• Urea increases the osmolarity of the
medullary interstitium
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Sodium Balance
• Homeostatic responses to salt ingestion
Figure 20-11
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Sodium Balance
Figure 20-12
Newchannels
P cell of distal nephron
Translation andprotein synthesis
Proteins modulateexisting channels and pumps
New pumps
K+
Na+
K+ secreted
Na+ reabsorbed
Lumenof distaltubule
Interstitialfluid
Blood
Aldosterone
Aldosteronereceptor
K+
Na+
Na+
Aldosterone combines witha cytoplasmic receptor.
Hormone-receptor complexinitiates transcription inthe nucleus.
New protein channels andpumps are made.
Aldosterone-inducedproteins modify existingproteins.
Result is increased Na+
reabsorption andK+ secretion.
K+
ATP
ATP
1
2
3
4
5
12
3
4
5
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Sodium Balance
• The renin-angiotensin-aldosterone system (RAAS)
Figure 20-13
Bloodpressure
Angiotensinogenin the plasma
ANG I in plasma
Granular cells
(kidney)Renin
Liver
constantlyproduces
produce
containsBlood vesselendothelium
ACE(enzyme)
Volumeand maintain
osmolarity
HypothalamusCardiovascularcontrol center
in medullaoblongata
Adrenal cortex
Bloodpressure
Arterioles
Vasoconstrict Cardiovascularresponse
Na+ reabsorptionThirstVasopressin
Aldosterone
ANG II inplasma
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Sodium Balance
• Decreased blood pressure stimulates renin secretion
Figure 20-14
Bloodpressure
Cardio-vascularcontrolcenter
Paracrines Granular cells ofafferent arteriole
Macula densaof distal tubule
Sympatheticactivity
NaCltransport
Reninsecretion
GFR
across
direct effect
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Increasedblood volume
causes increasedatrial stretch
Myocardialcells
stretch andrelease
Natriuretic peptides
Kidney Adrenalcortex
MedullaoblongataHypothalamus
Lessvasopressin
Decreasedrenin Less aldosterone
Decreasedblood pressure
IncreasedGFR
NaCl andH2O excretion
Sodium Balance
• Natriuretic peptides promote salt and water excretion
Figure 20-15