Lecture 12 fluid, electrolyte and acid base balance

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Lecture 12 fluid, electrolyte and acid base balance

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Lecture 12 fluid, electrolyte and acid base balance

  1. 1. Copyright 2010, John Wiley & Sons, Inc. Chapter 22 Fluid, Electrolyte and Acid-Base Balance
  2. 2. Copyright 2010, John Wiley & Sons, Inc. End of Chapter 22  Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.
  3. 3. Copyright 2010, John Wiley & Sons, Inc. Fluid Compartments  Total body water = 55-60% of lean body mass  Remainder: solid parts of bone, muscles, tendons  Major compartments (3): ICF, IF, plasma  Intracellular fluid (ICF): inside cells= 2/3  Extracellular Fluid (ECF): outside cells = 1/3  Interstitial fluid (IF): 80% of ECF  Includes: lymph; cerebrospinal, synovial, pericardial, pleural and peritoneal fluids; fluid in eyes and ears  Blood plasma: 20% ECF
  4. 4. Copyright 2010, John Wiley & Sons, Inc. Fluid Compartments
  5. 5. Copyright 2010, John Wiley & Sons, Inc. Barriers Between Compartments  Plasma membrane: between ECF and ICF  Blood vessel walls: between plasma and interstitial fluid  Fluid balance correct distribution of water & solutes  Water redistributes rapidly by osmosis  Thus fluid balance depends on solute (electrolyte) balance
  6. 6. Copyright 2010, John Wiley & Sons, Inc. Fluid Balance  Fluid balance requires  Appropriate total volume of body fluid  Appropriate distribution of water and solutes  Fluid balance depends on solute (electrolyte and nonelectrolyte) balance  Fluids and electrolytes are closely linked  Water redistributes rapidly by osmosis
  7. 7. Copyright 2010, John Wiley & Sons, Inc. Fluid Balance Interactions Animations  Water and Fluid Flow You must be connected to the internet to run this animation.
  8. 8. Copyright 2010, John Wiley & Sons, Inc. Water Gain and Loss  Gain: ingestion + metabolic reactions  Ingestion (food and drink): 2300 mL/day  Metabolism: 200 mL/day  Gain should = loss  Daily intake = daily output. Both 2500 mL/day  Loss: skin, lungs, kidneys, GI tract  Kidneys: ~1500 mL/day  Skin: sweat evaporates ~600 mL/day  Lungs: 300 mL/day; more if fever  GI tract: ~100 mL/day; more if diarrhea
  9. 9. Copyright 2010, John Wiley & Sons, Inc. Water Balance
  10. 10. Copyright 2010, John Wiley & Sons, Inc. Regulation of Gain  Thirst center in hypothalamus  ~2% dehydration will cause ↓ BP  Increase in body osmolality  dry mouth  thirst  Hormonal responses  High osmolality  hypothalamus releases ADH  water retention by kidneys  ↓ BP  renin released from kidney  angiotensin II  aldosterone  water retention by kidneys  Sensation of thirst may be decreased, especially in elderly
  11. 11. Copyright 2010, John Wiley & Sons, Inc. Regulation of Gain
  12. 12. Copyright 2010, John Wiley & Sons, Inc. Regulation of Salt and Water Loss  Urinary NaCl loss mainly determines body fluid volume  Na+ = main solute in ECF determining osmosis  Fluid intake varies so loss must vary also  ANP, angiotensin II and aldosterone regulate  ADH regulates water loss
  13. 13. Copyright 2010, John Wiley & Sons, Inc. Regulation of Salt and Water Loss
  14. 14. Copyright 2010, John Wiley & Sons, Inc. Movement of Fluid  ICF and ECF are normally at the same osmolality  Water moves freely  ↓ interstitial fluid osmolality  cell swelling and vice versa  Most often due to Na+ change  ADH responds rapidly: prevents significant cell change
  15. 15. Copyright 2010, John Wiley & Sons, Inc. Electrolytes in Body Fluids  Functions of electrolytes 1. Confined to compartments; control osmosis 2. Help maintain acid-base balance 3. Carry electrical currents 4. Serve as cofactors for enzymes
  16. 16. Copyright 2010, John Wiley & Sons, Inc. Electrolyte Distribution  Electrolyte content of ICF and ECF differ significantly  ICF: K+ major cation; protein, HPO4 2- : anions  ECF: Na+ major cation; Cl- major anion  Na+ /K+ pump maintains the cation difference  The two ECF fluids are similar  Electrolytes in plasma similar to those in IF  One difference: plasma contains more protein than interstitial fluid (IF)  Colloid osmotic pressure (due largely to plasma proteins) “holds onto” fluid in capillaries
  17. 17. Copyright 2010, John Wiley & Sons, Inc. Electrolyte Distribution
  18. 18. Copyright 2010, John Wiley & Sons, Inc. Other Electrolytes  K+ high in ICF, low in ECF  Regulated by aldosterone  Mg2+ and SO4 2- high in ICF, low in ECF  Ca2+ high in ECF, low in ICF  Regulated in plasma (PTH, calcitriol, and calcitonin)  Bones serve as Ca2+ reservoir
  19. 19. Copyright 2010, John Wiley & Sons, Inc. Acid- Base Balance  Input: diet, products of metabolism  Such as lactic acid, ketones  Output  Lungs: exhale CO2  Kidney: can eliminate H+ or HCO3 -  Regulatory mechanisms 1.Buffers: fastest but incomplete 2.Respiratory responses: fast but incomplete 3.Renal responses: slowest but compete elimination
  20. 20. Copyright 2010, John Wiley & Sons, Inc. 1: Buffer Systems  Protein in cells or plasma  Carboxyl and amino groups of amino acids  Hemoglobin (protein) in red blood cells  Carbonic acid-bicarbonate  Especially important in plasma  CO2 + H2O  H2CO3 ↔ HCO3 - + H+  Phosphate  H2PO4 -  H+ + HPO4 2-
  21. 21. Copyright 2010, John Wiley & Sons, Inc. 2: Exhalation of Carbon Dioxide  H+ + HCO3 - ↔ H2CO3 ↔ CO2 + H2O  Decrease of CO2 ↔ decrease of H+  Increase of CO2 ↔ increase of H+  Change of rate and depth of ventilation rapidly alters plasma pH  Negative feedback loop regulates
  22. 22. Copyright 2010, John Wiley & Sons, Inc. 2: Exhalation of Carbon Dioxide
  23. 23. Copyright 2010, John Wiley & Sons, Inc. 3. Renal Responses  Kidney Excretion of H+  Slow but only way to actually eliminate acid or base  Secrete H+ and replace with HCO3 -
  24. 24. Copyright 2010, John Wiley & Sons, Inc. Imbalances  Acidosis: arterial blood pH < 7.35   Depresses CNS  Below pH 7.0 can be fatal  Alkalosis: arterial blood pH > 7.45   Overexcitation of CNS  Muscle spasms, convulsions  Compensation  Respiratory or renal mechanisms  Respiratory very rapid; renal slower
  25. 25. Copyright 2010, John Wiley & Sons, Inc. Aging  Decrease in control of water and electrolyte balance can lead to pH problems  Decreases in respiratory and renal functioning  Decreased capacity to sweat

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