Copyright 2010, John Wiley & Sons, Inc. Chapter 22 Fluid, Electrolyte and Acid-Base Balance

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 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  Ingestion (food and drink): 2200 mL/day  Metabolism: 200 mL/day Gain should = loss  Daily intake = daily output. Both 2400 mL/day Loss: skin, lungs, kidneys, GI tract  Kidneys: ~1400 mL/day  Skin: sweat evaporates ~450 mL/day  Lungs: 350 mL/day; more if fever  GI tract: ~200 mL/day; more if diarrhea

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 Sensation of thirst may be decreased, especially in elderly

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 ADH regulates water loss

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

Copyright 2010, John Wiley & Sons, Inc. Acid- Base Balance Input: diet, products of metabolism  Such as lactic acid, ketones (fatty acids in the blood) Output  Lungs: exhale CO 2  Kidney: can eliminate H + or HCO 3 - Regulatory mechanisms 1.Buffers: fastest but incomplete (sweating) 2.Respiratory responses: fast but incomplete 3.Renal responses: slowest but compete elimination (nephrons in kidneys)

Copyright 2010, John Wiley & Sons, Inc. Imbalances Acidosis: arterial blood pH < 7.35   Depresses CNS  Caused by abundance of a macromolecule in the blood (example: DKA – diabetic ketoacidosis)  Below pH 7.0 can be fatal Alkalosis: arterial blood pH > 7.45   Overexcitation of CNS  Muscle spasms, convulsions, seizures 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