Lecture 12 fluid, electrolyte and acid base balance
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Transcript of Lecture 12 fluid, electrolyte and acid base balance
Copyright 2010, John Wiley & Sons, Inc.
Chapter 22
Fluid, Electrolyte and Acid-Base Balance
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.
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
Copyright 2010, John Wiley & Sons, Inc.
Fluid Compartments
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
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
Copyright 2010, John Wiley & Sons, Inc.
Fluid BalanceInteractions Animations
Water and Fluid Flow
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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
Copyright 2010, John Wiley & Sons, Inc.
Water Balance
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
Copyright 2010, John Wiley & Sons, Inc.
Regulation of Gain
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
Copyright 2010, John Wiley & Sons, Inc.
Regulation of Salt and Water Loss
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
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
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
Copyright 2010, John Wiley & Sons, Inc.
Electrolyte Distribution
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
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 mechanisms1.Buffers: fastest but incomplete
2.Respiratory responses: fast but incomplete
3.Renal responses: slowest but compete elimination
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+ + HPO42-
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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
Copyright 2010, John Wiley & Sons, Inc.
2: Exhalation of Carbon Dioxide
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3. Renal Responses Kidney Excretion of H+
Slow but only way to actually eliminate acid or base
Secrete H+ and replace with HCO3-
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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
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