1. Integrative Physiology II: Fluid and Electrolyte Balance
Chapter 20b
Integrative Physiology II: Fluid and Electrolyte Balance

2. Regulatory mechanisms keep plasma potassium in narrow range
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

3. Behavioral Mechanisms
Drinking replaces fluid loss
Low sodium stimulates salt appetite
Avoidance behaviors help prevent dehydration
Desert animals avoid the heat

4. Disturbances in Volume and Osmolarity
Figure 20-16

5. Volume and Osmolarity
Table 20-1 (1 of 3)

6. Volume and Osmolarity
Table 20-1 (2 of 3)

7. Volume and Osmolarity
Table 20-1 (3 of 3)

8. Homeostatic compensation for severe dehydration
Volume and Osmolarity
Homeostatic compensation for severe dehydration
DEHYDRATION
Blood volume/ Blood pressure
accompanied by
Osmolarity
CARDIOVASCULAR MECHANISMS
RENIN-ANGIOTENSIN SYSTEM
RENAL MECHANISMS
HYPOTHALAMIC MECHANISMS
Hypothalamic osmoreceptors +
Carotid and aortic baroreceptors
Atrial volume receptors; Carotid and aortic baroreceptors + +
Granular cells
Flow at macula densa
GFR +
CVCC +
Volume conserved
Hypothalamus
Renin
Angiotensinogen
ANG I +
Para- sympathetic output
Sympathetic output
Vasopressin release from posterior pituitary
ACE + + +
Heart
Arterioles +
ANG II
Thirst +
Adrenal cortex
osmolarity inhibits
Vasoconstriction
Rate
Force
Aldosterone
Peripheral resistance
Distal nephron
Distal nephron
Na+ reabsorption
Cardiac output
Blood pressure
Volume
H2O reabsorption
and
H2O intake
Osmolarity
Figure 20-17

9. Volume and Osmolarity Figure 20-17 (5 of 6) DEHYDRATION
Blood volume/ Blood pressure
accompanied by
Osmolarity
RENIN-ANGIOTENSIN SYSTEM
RENAL MECHANISMS + + +
Granular cells
Flow at macula densa
GFR +
CVCC +
Volume conserved
Renin
Angiotensinogen
ANG I
Para- sympathetic output
Sympathetic output
Vasopressin release from posterior pituitary
ACE + + +
Arterioles
ANG II
Thirst +
Adrenal cortex
osmolarity inhibits
Vasoconstriction
Aldosterone
Peripheral resistance
Distal nephron
Distal nephron
Na+ reabsorption
Blood pressure
H2O reabsorption
Volume
and
H2O intake
Osmolarity
Figure (5 of 6)

10. Volume and Osmolarity Figure 20-17 (6 of 6) DEHYDRATION
Blood volume/ Blood pressure
accompanied by
Osmolarity
CARDIOVASCULAR MECHANISMS
RENIN-ANGIOTENSIN SYSTEM
RENAL MECHANISMS
HYPOTHALAMIC MECHANISMS
Hypothalamic osmoreceptors +
Carotid and aortic baroreceptors
Atrial volume receptors; Carotid and aortic baroreceptors + +
Granular cells
Flow at macula densa
GFR +
CVCC +
Volume conserved
Hypothalamus
Renin
Angiotensinogen
ANG I +
Para- sympathetic output
Sympathetic output
Vasopressin release from posterior pituitary
ACE + + + +
Heart
Arterioles
ANG II
Thirst +
Adrenal cortex
osmolarity inhibits
Vasoconstriction
Rate
Force
Aldosterone
Peripheral resistance
Distal nephron
Distal nephron
Na+ reabsorption
Cardiac output
Blood pressure
H2O reabsorption
Volume
and
H2O intake
Osmolarity
Figure (6 of 6)

11. H+ concentration is closely regulated
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

12. Hydrogen ion and pH balance in the body
Acid-Base Balance
Hydrogen ion and pH balance in the body
CO2 (+ H2O) Lactic acid Ketoacids
Fatty acids Amino acids
H+ input
Plasma pH 7.38–7.42
Buffers: • HCO3– in extracellular fluid • Proteins, hemoglobin, phosphates in cells • Phosphates, ammonia in urine
CO2 (+ H2O)
H+ output H+
Figure 20-18

13. Under extraordinary conditions
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

14. pH Homeostasis Buffers Ventilation Renal regulation
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

15. The reflex pathway for respiratory compensation of metabolic acidosis
pH Disturbances
The reflex pathway for respiratory compensation of metabolic acidosis
Plasma H+ ( pH)
Plasma PCO2
by Law of Mass Action
Carotid and aortic chemoreceptors
Central chemoreceptors
Sensory neuron
Interneuron
Respiratory control centers in the medulla
Negative feedback
Negative feedback
Action potentials in somatic motor neurons
Muscles of ventilation
Rate and depth of breathing
Plasma H+ ( pH)
Plasma PCO2
by Law of Mass Action
Figure 20-19

16. HCO3– buffer added to extracellular fluid
pH Disturbances
Overview of renal compensation for acidosis
Nephron cells
Acidosis
Blood
pH = H+
HPO42– filtered
CO2 + H2O
Carbonic Anhydrase
H+ secreted
H+ + HCO3–
HCO3– reabsorbed H+
HCO3– buffer added to extracellular fluid
Amino acids + H+
H2PO4–
Excreted in urine
NH4+
Figure 20-20

17. Renal Compensation: Transporters
Apical Na+-H+ exchanger (NHE)
Basolateral Na+-HCO3– symport
H+-ATPase
H+-K+-ATPase
Na+-NH4+ antiport

18. Peritubular capillary Secreted H+ and NH4+ will be excreted
Renal Compensation
Proximal tubule H+ secretion and the reabsorption of filtered HCO3– 8 5 7 6 3 2 4 1
Na+-H+ antiport secretes H+.
H+ in filtrate combines with filtered HCO3– to form CO2.
CO2 diffuses into cell and combines with water to form H+ and HCO3–.
H+ is secreted again and excreted.
HCO3– is reabsorbed.
Glutamine is metabolized to ammonium ion and HCO3–.
NH4+ is secreted and excreted.
Peritubular capillary
Interstitial fluid
Reabsorbed
Filtration
Glomerulus
HCO3–
H+ + HCO3–
CO2 + H2O
Na+ Secreted H+
Na+ H+
Na+
Bowman’s capsule
H2O + CO2
Filtered HCO3– + H+ CA
KG
Glutamine
NH4+
Secreted H+ and NH4+ will be excreted
Proximal tubule cell
Figure 20-21

19. Type A intercalated cells function in acidosis
Figure 20-22a

20. Type B intercalated cells function in alkalosis
Figure 20-22b

21. Acid-Base Balance
Table 20-2

22. Fluid and electrolyte homeostasis Water balance
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

23. Behavioral mechanisms Integrated control of volume and osmolarity
Summary
Behavioral mechanisms
Integrated control of volume and osmolarity
Acid-base balance
Buffers, ventilation, and kidney
Acidosis and alkalosis
Intercalated cells