Acid and base balanceHarliansyah, Ph.D

Feb2011

THE BODY FLUIDSA solution of solvent and solutesOur body is made up of fluids and solidsAbout 50-60% of the body weight is WATERIn a 70 Kg adult male: 60% X 70= 40-42 LitersNote that 1 kg body weight= 1 liter of waterThe body has two major compartments:1 Intracellular2. Extracellular

Just Start MaintenanceMaintenance fluid provide the water and electrolytes equal to those lost simply for being alive and having a basal metabolic rate

Metabolism makes heat and solute that you need to get rid of to maintain homeostasisInsensible fluid loss dissipates heat by evaporation of water from skin and URT (50% of maintenance needs)Soluble waste is excreted in urine (50% of maintenance needs)

The Proportion of Body Fluids

Intracellular fluid40% Interstitial15%

Intravascular5%Transcellular 1-2%

The Intracellular FluidFound inside the cell surrounded by a membrane.

This is compartment with the highest percentageof water in adults.

The Extracellular FluidFluid found outside the cells

1. INTERSTITIAL FLUIDFound in between the cells2. INTRAVASCULAR FLUIDFound inside the blood vessels and lymphatic vessels 3. TRANSCELLULAR FLUIDFound inside body cavities like pleura, peritoneum, CSF

Sources of Fluids: Fluid Input1. Exogenous sourcesFluid intake- water from foodstuffsIVFMedicationsBlood products2. Endogenous sourcesBy products of metabolismsecretions

Fluid LossesRoutes of Fluid outputUrineFecal lossesSweatInsensible losses though the skin and lungs aswater vaporSensible losses

Fluid DynamicsThe movement of fluids (solutes and solvents) inthe body compartmentDiffusionOsmosisFiltrationActive transport

Principles of Acid-base balance interpretationBases can be defined as a proton (H+) acceptorMolecules capable of accepting a H+ ion Physiologically important bases include :Bicarbonate (HCO3-)Biphosphate (HPO4-2)

Principles of Acid-base balance interpretationAcids can be defined as a proton (H+) donorMolecules that dissociate in solution to H+Physiologically important acids include :Carbonic acid (H2CO3)Phosphoric acid (H3PO4)Pyruvic acidLactic acid

Principles of Acid-base balance interpretationE.C.F. acceptable pH range maintained by :1) Chemical buffersreact very rapidly (< 1 sec)2)Respiratory regulationreacts rapidly (sec to min)3)Renal regulationreacts slowly (min to hr)

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