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Chapter 20

Chapter 20. Integrative Physiology II: Fluid and Electrolyte Balance. Body Water Balance. Urine concentration: Dilute: 300 mOsM Concentrated: 1200 mOsM. Figure 20-3: Role of the kidneys in water balance. What is “put back” and where in the nephron. Proximal tubule

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Chapter 20

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

  2. Body Water Balance Urine concentration: Dilute: 300 mOsM Concentrated: 1200 mOsM Figure 20-3: Role of the kidneys in water balance

  3. What is “put back” and where in the nephron. • Proximal tubule • Glucose (those carriers) & Na+ (Primary active transport) urea (passive transport) • Loop of Henle • H2O and ions ( Na+, K+ & Cl-) • Distal tubule • Na+ & H2O • Collecting duct • H2O, Na+ & urea (again)

  4. Overview: starts off isosmotic 300 mOsM (saltiness) Figure 20-4: Osmolarity changes as fluid flows through the nephron

  5. VASOPRESSIN:If we NEED water, we can get it from the collecting duct!

  6. Vasopressin (a.k.a. ADH) regulates urine OsM:Let’s make concentrated uring part I Figure 20-5: Water movement in the collecting duct in the presence and absence of vasopressin

  7. Formation of Water Pores: Mechanism of Vasopressin Action

  8. Figure 20-7: Factors affecting vasopressin release

  9. Countercurrent exchanger. Loop of HenleLet’s make concentrated uring part II • Medullary osmotic gradient; more salty Collecting duct Figure 20-10: Countercurrent exchange in the medulla of the kidney

  10. The players: • Loop of Henle • Descending/ascending • vasa recta • Ions: which ones? • H2O • Why is it, countercurrent?

  11. Key facts: • 1. descending LOH is water permeable, ascending LOH is NOT. • 2. Ascending LOH actively pumps out ions. • 3. water goes to where the most stuff is!!! • 4. vasa recta removes water so it doesn’t dilute the medullary gradient.

  12. SODIUM BALANCE: • What happens to the body’s OsM after eating salty fries? Increase/decrease • This triggers two responses; can you guess?

  13. Vassopressin and thirst; both decrease OsM, but raise blood pressure. • To lower blood pressure our kidneys excrete sodium. • How does excreting sodium lower BP?

  14. WATER GOES TO WHERE THE MOST STUFF IS. • When sodium leaves, water follows, decreasing ECF volume, and BP.

  15. Sodium Balance: Intake & Excretion Figure 20-11: Homeostatic responses to eating salt

  16. Sodium is regulated by aldosterone from the adrenal cortex. • Aldosterone is actually secreted in response to blood pressure, blood volume and OsM. • More aldosterone: more sodium reabsorption. • Aldosterone target: principal cell (P cell) of the distal tubule & collecting duct.

  17. Mechanism of Na+ Selective Reabsorption in Collecting Duct !water does not follow! Vassopressin must be present Figure 20-12: Aldosterone action in principal cells

  18. How does aldosterone get released? RAAS: renin-angiotensin-aldosterone-system Figure 20-13: The renin-angiotensin-aldosterone pathway

  19. Artial Natruretic Peptide: Regulates Na+ & H2O Excretion Figure 20-15: Atrial natriuretic peptide

  20. Potassium Balance: Critical for Excitable Heart & Nervous Tissues • Hypokalemia – low [K+] in ECF, Hyperkalemia - high [K+] • Reabsorbed in Ascending Loop, secreted in Collecting duct

  21. Potassium Balance: Critical for Excitable Heart & Nervous Tissues Figure 20-4: Osmolarity changes as fluid flows through the nephron

  22. Potassium Balance: Critical for Excitable Heart & Nervous Tissues Figure 20-12: Aldosterone action in principal cells

  23. Chapter 20, part B Integrative Physiology II: acid-base balance

  24. Acidosis:  plasma pH Protein damage CNS depression Alkalosis:  plasma pH Hyperexcitability CNS & heart Buffers: HCO3- & proteins H+ input: diet & metabolic H+ output: lungs & kidney Neutral pH is 7.0 Biological pH is 7.4 Determined based upon H+ concentration. Acid/Base Homeostasis

  25. Acid/Base Homeostasis: Overview Figure 20-18: Hydrogen balance in the body

  26. Low pH – acidosis – nervous tissue becomes less exciteable – respiratory centers shut down. • High pH – alkalosis – neurons become hyperexciteable – twitching, numbness – tetenay and paralyzed respiratory muscles.

  27. pH homeostasis depends on 3 things: • 1. buffers • 2. the lungs • 3. the kidneys

  28. Buffer systems • Bicarbonate, phosphate ions, and proteins (Hb) • Buffers prevent significant changes in pH by binding or releasing H+ CO2 + H2O H2CO3 H+ + HCO3- carbonic anhydrase

  29. What will drive the equation to the right? • What will drive the equation to the left? CO2 + H2O H2CO3 H+ + HCO3- carbonic anhydrase How can ventilation compensate for pH disturbances? Pg. 647.

  30. Acidosis prevention at the Proximal Tubule: H+ excreted, bicarbonate reabsorption. • Na+ - H+ antiport activity • Glutamine metabolism Figure 20-21: Proximal tubule secretion and reabsorption of filtered HCO3-

  31. Kidney Hydrogen Ion Balancing: Collecting Duct • Type A Intercalated cells excrete H+ absorb HCO3- • Type B intercalated cells absorb H+ secrete HCO3-

  32. Kidney Hydrogen Ion Balancing: Collecting Duct The polarity of the two cells is reversed with the transport proteins on opposite sides. Figure 20-22: Role of the intercalated cell in acidosis and alkalosis

  33. Acid-base disturbances: respiratory or metabolic • Respiratory acidosis – • hypoventilation & CO2 retention. • COPD- loss of alveolar tissue • Metabolic acidosis • Metabolic acids increase protons • Lactic acid from anaerobic metabolism burn sugar not oxygen. • Respiratory alkalosis • Hyperventilation rids CO2 • Hysterical hyperventilation • Renal compensation can occur • Metabolic alkalosis • Vomiting stomach acids and taking bicarbonate-containing antacids. • Respiratory compensation takes place rapidly.

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