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Electrolyte Homeostasis Part 4 Cheat Sheet by

NURS601 Week 1 Concept 3: Acid-base balance (too much/too little acid)

Blood pH levels

Dependent on H+ concen­tration
Normal pH: 7.35-7.45
Alkalosis: 7.45-7.8
Acidosis: 7-7.35
Anything >7.8 or <7 is deadly


Buffering is the primary regulator of acid-base balance.
Buffers act chemically to change strong acids into weaker ones, or bind them to neutralise them
Different buffer systems assume dominant roles in different parts of the body:
Extrac­ellular Fluid (ECF)
Major buffer: Bicarb­onate buffer system
Minor buffers: Intrac­ellular problems, Phosphate buffer system
Major buffers: Bicarb buffer system, Hemoglobin
Minor buffers: Plasma proteins, Phosphate buffer system
Intrac­ellular fluid (ICF)
Major buffers: Proteins, Phosphate
Minor buffers: None
Major buffers: Ammonia, Phosphate
Minor buffers: None


Secretes free hydrogen ions into renal tubules
Excretes weak acid
Excretes HCO3 (if there is metabolic acidosis)

Reading arterial blood gases (ABG)

Respir­atory Acidosis
Decreased pH, increased PaCO2, normal HCO3
Respir­atory Alkalosis
Increased pH, decreased PaCO2, normal HCO3
Metabolic Acidosis
Decreased pH, normal PaCO3, decreased HCO3
Metabolic Alkalosis
Increased pH, normal PaCO2, increased HCO3
Normal ABG figures

Acid-base homeos­tasis

How is it mainta­ined?
Bicarb­onate (HCO3) - reacts rapidly, less than an second. Chemically change strong aicds to weaker acids or bind to neutralise effect
Resipr­atory system
Reacts rapidly - seconds to minutes
Renal system
Reacts slowly - hours


CO2 formed and excreted in lungs
Lungs excrete CO2 + H2O as by-pro­ducts of cellular metabolism
CO2 is regarded as an acid
Homeos­tasis cycle of CO2 in the body:
During exercise or other activity, cell metabolism increases and produces more CO2, then:
More CO2 dissolves in blood, forming carbonic acid which lowers blood pH slightly, then:
Receptors in the brain sense the drop in pH and send nerve signals to increase breathing rate, then:
Increased breathing rate quickly removes more CO2 from blood. Blood pH rises slightly, returning to normal - cycle starts again

Continuous mixing of body fluids­/gases



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