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Chapter 20b

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

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Chapter 20b

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

  2. 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. Volume and Osmolarity • Homeostatic compensation for severe dehydration Blood volume/Blood pressure accompanied by DEHYDRATION Osmolarity RENALMECHANISMS HYPOTHALAMICMECHANISMS CARDIOVASCULARMECHANISMS RENIN-ANGIOTENSINSYSTEM Hypothalamicosmoreceptors + Atrial volumereceptors; Carotidand aorticbaroreceptors Carotid and aorticbaroreceptors + + Flow atmacula densa Granularcells GFR + CVCC + Hypothalamus Volumeconserved Renin + ANG I Angiotensinogen Vasopressinrelease fromposterior pituitary Para-sympatheticoutput Sympatheticoutput ACE + + + + Heart Arterioles ANG II Thirst + osmolarity inhibits Adrenalcortex Vasoconstriction Rate Force Aldosterone Peripheralresistance Distalnephron Distalnephron Na+reabsorption Cardiacoutput Bloodpressure H2Oreabsorption and H2Ointake Volume Osmolarity Figure 20-17

  9. Volume and Osmolarity Blood volume/Blood pressure accompanied by DEHYDRATION Osmolarity RENALMECHANISMS RENIN-ANGIOTENSINSYSTEM + + + Flow atmacula densa Granularcells GFR + CVCC + Volumeconserved Renin ANG I Angiotensinogen Vasopressinrelease fromposterior pituitary Para-sympatheticoutput Sympatheticoutput ACE + + + Arterioles ANG II Thirst + osmolarity inhibits Adrenalcortex Vasoconstriction Aldosterone Peripheralresistance Distalnephron Distalnephron Na+reabsorption Bloodpressure H2Oreabsorption and H2Ointake Volume Osmolarity Figure 20-17 (5 of 6)

  10. Volume and Osmolarity Blood volume/Blood pressure accompanied by DEHYDRATION Osmolarity RENALMECHANISMS HYPOTHALAMICMECHANISMS CARDIOVASCULARMECHANISMS RENIN-ANGIOTENSINSYSTEM Hypothalamicosmoreceptors + Atrial volumereceptors; Carotidand aorticbaroreceptors Carotid and aorticbaroreceptors + + Flow atmacula densa Granularcells GFR + CVCC + Hypothalamus Volumeconserved Renin + ANG I Angiotensinogen Vasopressinrelease fromposterior pituitary Para-sympatheticoutput Sympatheticoutput ACE + + + + Heart Arterioles ANG II Thirst + osmolarity inhibits Adrenalcortex Vasoconstriction Rate Force Aldosterone Peripheralresistance Distalnephron Distalnephron Na+reabsorption Cardiacoutput Bloodpressure H2Oreabsorption and H2Ointake Volume Osmolarity Figure 20-17 (6 of 6)

  11. 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. Acid-Base Balance • Hydrogen ion and pH balance in the body CO2 (+ H2O)Lactic acidKetoacids Fatty acidsAmino acids H+ input Plasma pH7.38–7.42 Buffers:• HCO3– in extracellular fluid• Proteins, hemoglobin, phosphates in cells• Phosphates, ammonia in urine CO2 (+ H2O) H+ output H+ Figure 20-18

  13. 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 • 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. pH Disturbances • The reflex pathway for respiratory compensation of metabolic acidosis Plasma H+( pH) PlasmaPCO2 by Law of Mass Action Carotid and aorticchemoreceptors Centralchemoreceptors Sensory neuron Interneuron Respiratorycontrol centersin themedulla Negative feedback Negative feedback Action potentials in somaticmotor neurons Muscles of ventilation Rate and depth of breathing PlasmaPCO2 Plasma H+( pH) by Law of Mass Action Figure 20-19

  16. pH Disturbances • Overview of renal compensation for acidosis Nephroncells Blood Acidosis pH = H+ CO2 + H2O HPO42–filtered Carbonic Anhydrase H+ + HCO3– HCO3–reabsorbed H+secreted H+ HCO3– bufferadded toextracellularfluid Amino acids + H+ H2PO4– Excretedin 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. Glomerulus Bowman’scapsule Interstitialfluid Peritubularcapillary Na+-H+ antiportsecretes H+. 1 Filtration H+ in filtrate combineswith filtered HCO3– toform CO2. 2 Proximal tubule cell HCO3– Na+ CO2 diffuses into celland combines with waterto form H+ and HCO3–. 3 1 Na+H+ Na+Secreted H+ H+ is secreted againand excreted. 4 4 Na+ Na+ 5 HCO3– is reabsorbed. Filtered HCO3– + H+ 5 HCO3– HCO3– 2 CA Glutamine is metabolizedto ammonium ion and HCO3–. 6 CA 3 H2O + CO2 CO2 + H2O H+ + HCO3– Reabsorbed 6 Glutamine 7 NH4+ is secreted andexcreted. 7 HCO3– 8 HCO3– Secreted H+ and NH4+will be excreted NH4+ KG Na+ Na+ Na+ 8 HCO3– is reabsorbed. Renal Compensation • Proximal tubule H+ secretion and the reabsorption of filtered HCO3– Figure 20-21

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

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

  21. Acid-Base Balance Table 20-2

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

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