chapter 20b integrative physiology ii: fluid and electrolyte balance
TRANSCRIPT
Chapter 20b
Integrative Physiology II:
Fluid and Electrolyte Balance
Potassium Balance
• Regulatory mechanisms keep plasma potassium in narrow range• Aldosterone plays a critical role
• Hypokalemia • Muscle weakness and failure of respiratory
muscles and the heart
• Hyperkalemia • Can lead to cardiac arrhythmias
• Causes include kidney disease, diarrhea, and diuretics
Behavioral Mechanisms
• Drinking replaces fluid loss• Low sodium stimulates salt appetite• Avoidance behaviors help prevent
dehydration• Desert animals avoid the heat
Disturbances in Volume and Osmolarity
Figure 20-16
Volume and Osmolarity
Table 20-1 (1 of 3)
Volume and Osmolarity
Table 20-1 (2 of 3)
Volume and Osmolarity
Table 20-1 (3 of 3)
Blood volume/Blood pressure
Osmolarityaccompanied by
osmolarity inhibits
CVCC+
Para-sympathetic
outputSympathetic
output
Heart
ForceRate
Cardiacoutput
Vasoconstriction
Peripheralresistance
Distalnephron
Vasopressinrelease from
posterior pituitary
Arterioles
VolumeH2O
reabsorption
+
+
H2Ointake
Thirst
+
+
Volumeconserved
DEHYDRATION
CARDIOVASCULARMECHANISMS
RENIN-ANGIOTENSINSYSTEM
RENALMECHANISMS
HYPOTHALAMICMECHANISMS
Carotid and aorticbaroreceptors
Hypothalamicosmoreceptors
Osmolarity
andBloodpressure
Granularcells
GFRFlow at
macula densa
+
++
+
+
Angiotensinogen ANG I
ACE
ANG II
Aldosterone
Na+
reabsorption
Distalnephron
+
Hypothalamus
Adrenalcortex
Atrial volumereceptors; Carotid
and aorticbaroreceptors
Renin
Volume and Osmolarity
• Homeostatic compensation for severe dehydration
Figure 20-17
Volume and Osmolarity
Figure 20-17 (5 of 6)
Blood volume/Blood pressure
Osmolarityaccompanied by
osmolarity inhibits
CVCC+
Para-sympathetic
outputSympathetic
output
Vasoconstriction
Peripheralresistance
Distalnephron
Vasopressinrelease from
posterior pituitary
Arterioles
VolumeH2O
reabsorption
+
H2Ointake
Thirst
+
Volumeconserved
DEHYDRATION
RENIN-ANGIOTENSINSYSTEM
RENALMECHANISMS
Osmolarity
andBloodpressure
Granularcells
GFRFlow at
macula densa
+
++
+
+
Angiotensinogen ANG I
ACE
ANG II
Aldosterone
Na+
reabsorption
Distalnephron
+
Adrenalcortex
Renin
Volume and Osmolarity
Figure 20-17 (6 of 6)
Blood volume/Blood pressure
Osmolarityaccompanied by
osmolarity inhibits
CVCC+
Para-sympathetic
outputSympathetic
output
Heart
ForceRate
Cardiacoutput
Vasoconstriction
Peripheralresistance
Distalnephron
Vasopressinrelease from
posterior pituitary
Arterioles
VolumeH2O
reabsorption
+
+
H2Ointake
Thirst
+
+
Volumeconserved
DEHYDRATION
CARDIOVASCULARMECHANISMS
RENIN-ANGIOTENSINSYSTEM
RENALMECHANISMS
HYPOTHALAMICMECHANISMS
Carotid and aorticbaroreceptors
Hypothalamicosmoreceptors
Osmolarity
andBloodpressure
Granularcells
GFRFlow at
macula densa
+
++
+
+
Angiotensinogen ANG I
ACE
ANG II
Aldosterone
Na+
reabsorption
Distalnephron
+
Hypothalamus
Adrenalcortex
Atrial volumereceptors; Carotid
and aorticbaroreceptors
Renin
Acid-Base Balance
• Normal pH of plasma is 7.38–7.42• H+ concentration is closely regulated• Changes can alter tertiary structure of proteins
• Abnormal pH affects the nervous system• Acidosis: neurons become less excitable and
CNS depression• Alkalosis: hyperexcitable
• pH disturbances • Associated with K+ disturbances
Acid-Base Balance
• Hydrogen ion and pH balance in the body
Figure 20-18
Fatty acidsAmino acids
CO2 (+ H2O)Lactic acidKetoacids
CO2 (+ H2O)
H+ input
H+ output
Plasma pH7.38–7.42
Buffers:• HCO3
– in extracellular fluid• Proteins, hemoglobin, phosphates in cells• Phosphates, ammonia in urine
H+
Acid and Base Input
• Acid• Organic acids • Diet and intermediates
• Under extraordinary conditions • Metabolic organic acid production can increase• Ketoacids • Diabetes
• Production of CO2
• Acid production• Base• Few dietary sources of bases
pH Homeostasis
• Buffers• Moderate changes in pH• Combines with or releases H+
• Cellular proteins, phosphate ions, and hemoglobin
• Ventilation • Rapid response• 75% of disturbances
• Renal regulation • Slowest of the three mechanisms• Directly excreting or reabsorbing H+
• Indirectly by change in the rate at which HCO3– buffer is
reabsorbed or excreted
pH Disturbances
• The reflex pathway for respiratory compensation of metabolic acidosis
Figure 20-19
Respiratorycontrol centers
in themedulla
Plasma H+
( pH)Plasma
PCO2
Carotid and aorticchemoreceptors
Centralchemoreceptors
PlasmaPCO2
Plasma H+
( pH)
by Law of Mass Action
by Law of Mass Action
Action potentials in somaticmotor neurons
Muscles of ventilation
Rate and depth of breathing
Neg
ati
ve f
ee
db
ac
k Neg
ative
fee
db
ac
k
Sensory neuron Interneuron
pH Disturbances
• Overview of renal compensation for acidosis
Figure 20-20
CO2 + H2O
Carbonic Anhydrase
Nephroncells
AcidosispH = H+
HCO3–
reabsorbed
HCO3– buffer
added toextracellular
fluid
Amino acids + H+
NH4+
H+ + HCO3–H+
secreted
H+
HPO42–
filtered
H2PO4–
Excretedin urine
Blood
Renal Compensation: Transporters
• Apical Na+-H+ exchanger (NHE)
• Basolateral Na+-HCO3– symport
• H+-ATPase• H+-K+-ATPase
• Na+-NH4+ antiport
Renal Compensation
• Proximal tubule H+ secretion and the reabsorption of filtered HCO3
–
Figure 20-21
8
5
7
6
3
2
4
1
Na+-H+ antiportsecretes H+.
H+ in filtrate combineswith filtered HCO3
– toform CO2.
CO2 diffuses into celland combines with waterto form H+ and HCO3
–.
H+ is secreted againand excreted.
HCO3– is reabsorbed.
Glutamine is metabolizedto ammonium ion and HCO3
–.
NH4+ is secreted and
excreted.
HCO3– is reabsorbed.
Peritubularcapillary
Interstitialfluid
Reabsorbed
Filtration
Glomerulus
HCO3–
H+ + HCO3–
HCO3–
CO2 + H2O
Na+
Secreted H+
Na+
H+
Na+
HCO3–
Na+
Bowman’scapsule
H2O + CO2
Filtered HCO3– + H+
Na+
CA
CA
Na+ Na+ Na+
KG HCO3–
Glutamine
NH4+ HCO3
–Secreted H+ and NH4+
will be excreted
Proximal tubule cell
1
2
3
4
5
6
7
8
Intercalated Cells
• Type A intercalated cells function in acidosis
Figure 20-22a
Intercalated Cells
• Type B intercalated cells function in alkalosis
Figure 20-22b
Acid-Base Balance
Table 20-2
Summary
• Fluid and electrolyte homeostasis• Water balance• Vasopressin, aquaporin, osmoreceptors,
countercurrent multiplier, and vasa recta
• Sodium balance• Aldosterone, principal cells, ANG I and II, renin,
angiotensinogen, ACE, and ANP
• Potassium balance• Hyperkalemia and hypokalemia
Summary
• Behavioral mechanisms• Integrated control of volume and osmolarity• Acid-base balance• Buffers, ventilation, and kidney• Acidosis and alkalosis• Intercalated cells