Transcript Chapter 22
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 Fluid balance depends on solute (electrolyte and nonelectrolyte) balance Appropriate total volume of body fluid Appropriate distribution of water and solutes Fluids and electrolytes are closely linked Water redistributes rapidly by osmosis 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. Copyright 2010, John Wiley & Sons, Inc. Water Gain and Loss Gain: ingestion + metabolic reactions Gain should = loss Ingestion (food and drink): 2300 mL/day Metabolism: 200 mL/day 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 Fluid intake varies so loss must vary also Na+ = main solute in ECF determining osmosis 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. 2. 3. 4. Confined to compartments; control osmosis Help maintain acid-base balance Carry electrical currents 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, HPO42-: 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 SO42- 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 Output Such as lactic acid, ketones 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 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- 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 Copyright 2010, John Wiley & Sons, Inc. 2: Exhalation of Carbon Dioxide 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- Copyright 2010, John Wiley & Sons, Inc. Imbalances Acidosis: arterial blood pH < 7.35 Alkalosis: arterial blood pH > 7.45 Depresses CNS Below pH 7.0 can be fatal 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 Copyright 2010, John Wiley & Sons, Inc.