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About this Chapter

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. Fluid and Electrolyte Homeostasis.

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About this Chapter

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  1. 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

  2. Fluid and Electrolyte Homeostasis • 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

  3. Fluid and Electrolyte Homeostasis The body’s integrated response to changes in blood volume and blood pressure Figure 20-1a

  4. Fluid and Electrolyte Homeostasis Figure 20-1b

  5. Water Balance in the Body Figure 20-2

  6. Water Balance A model of the role of the kidneys in water balance Figure 20-3

  7. Urine Concentration Osmolarity changes as filtrate flows through the nephron Figure 20-4

  8. Water Reabsorption Water movement in the collecting duct in the presence and absence of vasopressin Figure 20-5a

  9. Water Reabsorption Figure 20-5b

  10. Water Reabsorption Cross-section of kidney tubule Medullary interstitial fluid Collecting duct lumen Vasa recta Collecting duct cell 600 mOsM Filtrate 300 mOsm H2O 600 mOsM H2O H2O H2O 700 mOsM 4 Storage vesicles Second messenger signal 2 Exocytosis of vesicles 1 Vasopressin Aquaporin-2 water pores cAMP 3 Vasopressin receptor Water is absorbed by osmosis into the blood. Receptor activates cAMP second messenger system. Cell inserts AQP2 water pores into apical membrane. Vasopressin binds to mem- brane receptor. 4 1 2 3 The mechanism of vasopressin action Figure 20-6

  11. Water Reabsorption Cross-section of kidney tubule Medullary interstitial fluid Collecting duct lumen Vasa recta Collecting duct cell 600 mOsM Filtrate 300 mOsm 600 mOsM 700 mOsM 1 Vasopressin Vasopressin receptor Vasopressin binds to mem- brane receptor. 1 Figure 20-6, step 1

  12. Water Reabsorption Cross-section of kidney tubule Medullary interstitial fluid Collecting duct lumen Vasa recta Collecting duct cell 600 mOsM Filtrate 300 mOsm 600 mOsM 700 mOsM Second messenger signal 2 1 Vasopressin cAMP Vasopressin receptor Vasopressin binds to mem- brane receptor. Receptor activates cAMP second messenger system. 1 2 Figure 20-6, steps 1–2

  13. Water Reabsorption Cross-section of kidney tubule Medullary interstitial fluid Collecting duct lumen Vasa recta Collecting duct cell 600 mOsM Filtrate 300 mOsm 600 mOsM 700 mOsM Storage vesicles Second messenger signal 2 Exocytosis of vesicles 1 Vasopressin Aquaporin-2 water pores cAMP 3 Vasopressin receptor Cell inserts AQP2 water pores into apical membrane. Vasopressin binds to mem- brane receptor. Receptor activates cAMP second messenger system. 1 2 3 Figure 20-6, steps 1–3

  14. Water Reabsorption Cross-section of kidney tubule Medullary interstitial fluid Collecting duct lumen Vasa recta Collecting duct cell 600 mOsM Filtrate 300 mOsm H2O 600 mOsM H2O H2O H2O 700 mOsM 4 Storage vesicles Second messenger signal 2 Exocytosis of vesicles 1 Vasopressin Aquaporin-2 water pores cAMP 3 Vasopressin receptor Vasopressin binds to mem- brane receptor. Receptor activates cAMP second messenger system. Cell inserts AQP2 water pores into apical membrane. Water is absorbed by osmosis into the blood. 4 1 2 3 Figure 20-6, steps 1–4

  15. Factors Affecting Vasopressin Release Figure 20-7

  16. Water Balance The effect of plasma osmolarity on vasopressin secretion by the posterior pituitary Figure 20-8

  17. Countercurrent Heat Exchanger Figure 20-9

  18. Water Balance Countercurrent exchange in the medulla of the kidney Figure 20-10

  19. Ion reabsorption Active reabsorption of ions in the thick ascending limb creates a dilute filtrate in the lumen Figure 20-11

  20. Fluid and Electrolyte Balance • Vasa recta removes water • Close anatomical association of the loop of Henle and the vasa recta • Urea increase the osmolarity of the medullary interstitium

  21. Sodium Balance Homeostatic responses to salt ingestion PLAY Animation: Urinary System: Late Filtrate Processing Figure 20-12

  22. Sodium Balance Aldosterone combines with a cytoplasmic receptor. 1 Interstitial fluid P cell of distal nephron Blood 2 Hormone-receptor complex initiates transcription in the nucleus. Lumen of distal tubule Transcription Aldosterone 2 1 mRNA Translation and protein synthesis 3 Aldosterone receptor 3 New protein channels and pumps are made. New channels New pumps ATP 4 Proteins modulate existing channels and pumps. Aldosterone- induced proteins modify existing proteins. 4 K+ secreted K+ K+ K+ 5 ATP Na+ reabsorbed Na+ Na+ Result is increased Na+ reabsorption and K+ secretion. 5 Na+ Aldosterone action in principle cells Figure 20-13

  23. Sodium Balance Aldosterone combines with a cytoplasmic receptor. 1 Interstitial fluid P cell of distal nephron Blood Lumen of distal tubule Aldosterone 1 Aldosterone receptor Figure 20-13, step 1

  24. Sodium Balance Aldosterone combines with a cytoplasmic receptor. 1 Interstitial fluid P cell of distal nephron Blood 2 Hormone-receptor complex initiates transcription in the nucleus. Lumen of distal tubule Transcription Aldosterone 2 1 mRNA Aldosterone receptor Figure 20-13, steps 1–2

  25. Sodium Balance Aldosterone combines with a cytoplasmic receptor. 1 Interstitial fluid P cell of distal nephron Blood 2 Hormone-receptor complex initiates transcription in the nucleus. Lumen of distal tubule Transcription Aldosterone 2 1 mRNA Translation and protein synthesis 3 Aldosterone receptor 3 New protein channels and pumps are made. New channels New pumps ATP Figure 20-13, steps 1–3

  26. Sodium Balance Aldosterone combines with a cytoplasmic receptor. 1 Interstitial fluid P cell of distal nephron Blood 2 Hormone-receptor complex initiates transcription in the nucleus. Lumen of distal tubule Transcription Aldosterone 2 1 mRNA Translation and protein synthesis 3 Aldosterone receptor 3 New protein channels and pumps are made. New channels New pumps ATP 4 Proteins modulate existing channels and pumps. Aldosterone- induced proteins modify existing proteins. 4 ATP Figure 20-13, steps 1–4

  27. Sodium Balance Aldosterone combines with a cytoplasmic receptor. 1 Interstitial fluid P cell of distal nephron Blood 2 Hormone-receptor complex initiates transcription in the nucleus. Lumen of distal tubule Transcription Aldosterone 2 1 mRNA Translation and protein synthesis 3 Aldosterone receptor 3 New protein channels and pumps are made. New channels New pumps ATP 4 Proteins modulate existing channels and pumps. Aldosterone- induced proteins modify existing proteins. 4 K+ secreted K+ K+ K+ 5 ATP Na+ reabsorbed Na+ Na+ Result is increased Na+ reabsorption and K+ secretion. 5 Na+ Figure 20-13, steps 1–5

  28. Sodium Balance The renin-angiotensin-aldosterone pathway Figure 20-14

  29. Sodium Balance Decreased blood pressure stimulates renin secretion Figure 20-15

  30. Sodium Balance Action of natriuretic peptides Figure 20-16

  31. 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

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

  33. Disturbances in Volume and Osmolarity PLAY Animation: Fluid, Electrolyte, and Acid/Base Balance: Water Homeostasis Figure 20-17

  34. Volume and Osmolarity

  35. Volume and Osmolarity

  36. Volume and Osmolarity

  37. Volume and Osmolarity Blood volume/ Blood pressure Osmolarity accompanied by DEHYDRATION CARDIOVASCULAR MECHANISMS RENIN-ANGIOTENSIN SYSTEM RENAL MECHANISMS HYPOTHALAMIC MECHANISMS Hypothalamic osmoreceptors + Atrial volume receptors; carotid and aortic baroreceptors Carotid and aortic baroreceptors + + Flow at macula densa Granular cells GFR + CVCC + Hypothalamus Volume conserved Renin + Angiotensinogen ANG I Vasopressin release from posterior pituitary Sympathetic output Parasympathetic output ACE + + + + Heart Arterioles ANG II Thirst + osmolarity inhibits Adrenal cortex Vasoconstriction Rate Force Aldosterone Peripheral resistance Distal nephron Distal nephron Na+ reabsorption H2O intake H2O reabsorption Cardiac output Blood pressure Volume Osmolarity Homeostatic compensation for severe dehydration Figure 20-18

  38. Volume and Osmolarity Blood volume/ Blood pressure DEHYDRATION CARDIOVASCULAR MECHANISMS Carotid and aortic baroreceptors CVCC Sympathetic output Parasympathetic output Heart Arterioles Vasoconstriction Rate Force Peripheral resistance Cardiac output Blood pressure Figure 20-18 (1 of 6)

  39. Volume and Osmolarity Blood volume/ Blood pressure Osmolarity accompanied by DEHYDRATION HYPOTHALAMIC MECHANISMS Hypothalamic osmoreceptors Atrial volume receptors; carotid and aortic baroreceptors Hypothalamus + Vasopressin release from posterior pituitary + Thirst Distal nephron H2O intake H2O reabsorption Blood pressure Volume Osmolarity Figure 20-18 (2 of 6)

  40. Volume and Osmolarity Blood volume/ Blood pressure DEHYDRATION RENIN-ANGIOTENSIN SYSTEM RENAL MECHANISMS + + Flow at macula densa Granular cells GFR Volume conserved Renin Angiotensinogen ANG I ACE ANG II Figure 20-18 (3 of 6)

  41. Volume and Osmolarity Blood volume/ Blood pressure Osmolarity accompanied by DEHYDRATION RENIN-ANGIOTENSIN SYSTEM + Granular cells CVCC + Renin Angiotensinogen ANG I Vasopressin release from posterior pituitary ACE + + + Arterioles ANG II Thirst + osmolarity inhibits Adrenal cortex Aldosterone Distal nephron Na+ reabsorption Figure 20-18 (4 of 6)

  42. Volume and Osmolarity Blood volume/ Blood pressure Osmolarity accompanied by DEHYDRATION RENIN-ANGIOTENSIN SYSTEM RENAL MECHANISMS + + + Flow at macula densa Granular cells GFR + CVCC + Volume conserved Renin Angiotensinogen ANG I Vasopressin release from posterior pituitary Sympathetic output Parasympathetic output ACE + + + Arterioles ANG II Thirst + osmolarity inhibits Adrenal cortex Vasoconstriction Aldosterone Distal nephron Distal nephron Na+ reabsorption H2O intake H2O reabsorption Blood pressure Volume Osmolarity Figure 20-18 (5 of 6)

  43. Volume and Osmolarity Blood volume/ Blood pressure Osmolarity accompanied by DEHYDRATION CARDIOVASCULAR MECHANISMS RENIN-ANGIOTENSIN SYSTEM RENAL MECHANISMS HYPOTHALAMIC MECHANISMS Hypothalamic osmoreceptors + Atrial volume receptors; carotid and aortic baroreceptors Carotid and aortic baroreceptors + + Flow at macula densa Granular cells GFR + CVCC + Hypothalamus Volume conserved Renin + Angiotensinogen ANG I Vasopressin release from posterior pituitary Sympathetic output Parasympathetic output ACE + + + + Heart Arterioles ANG II Thirst + osmolarity inhibits Adrenal cortex Vasoconstriction Rate Force Aldosterone Peripheral resistance Distal nephron Distal nephron Na+ reabsorption H2O intake H2O reabsorption Cardiac output Blood pressure Volume Osmolarity Figure 20-18 (6 of 6)

  44. 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

  45. Acid-Base Balance Hydrogen balance in the body Figure 20-19

  46. 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

  47. pH Homeostasis • Buffers moderate changes in pH • Cellular proteins, phosphate ions, and hemoglobin • Ventilation • Rapid • 75% of disturbances • Renal regulation • Directly excreting or reabsorbing H+ • Indirectly by change in the rate at which HCO3– buffer is reabsorbed or excreted

  48. pH Disturbances The reflex pathway for respiratory compensation of metabolic acidosis Figure 20-20

  49. pH Disturbances Overview of renal compensation for acidosis Figure 20-21

  50. Renal Compensation: Transporters • Apical Na+-H+ antiport • Basolateral Na+-HCO3– symport • H+-ATPase • H+-K+-ATPase • Na+-NH4+ antiport

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