Acid and Base Balance and
Imbalance

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pH Review
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pH = - log [H+]
H+ is really a proton
Range is from 0 - 14
If [H+] is high, the solution is acidic; pH < 7
If [H+] is low, the solution is basic or alkaline ; pH > 7

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• Acids are H+ donors.
• Bases are H+ acceptors, or give up OH- in solution. • Acids and bases can be:
– Strong – dissociate completely in solution • HCl, NaOH
– Weak – dissociate only partially in solution • Lactic acid, carbonic acid
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The Body and pH
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Homeostasis of pH is tightly controlled
Extracellular fluid = 7.4
Blood = 7.35 – 7.45
< 6.8 or > 8.0 death occurs
Acidosis (acidemia) below 7.35
Alkalosis (alkalemia) above 7.45

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Small changes in pH can produce major disturbances
• Most enzymes function only with narrow pH ranges
• Acid-base balance can also affect electrolytes (Na+, K+, Cl-)
• Can also affect hormones

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The body produces more acids than bases
• Acids take in with foods
• Acids produced by metabolism of lipids and proteins
• Cellular metabolism produces CO2.
• CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-

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Control of Acids
1. Buffer systems
Take up H+ or release H+ as conditions change Buffer pairs – weak acid and a base
Exchange a strong acid or base for a weak one
Results in a much smaller pH change
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Bicarbonate buffer
• Sodium Bicarbonate (NaHCO3) and carbonic acid (H2CO3)
• Maintain a 20:1 ratio : HCO3- : H2CO3
HCl + NaHCO3 ↔ H2CO3 + NaCl
NaOH + H2CO3 ↔ NaHCO3 + H2O
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Phosphate buffer
• Major intracellular buffer
• H+ + HPO42- ↔ H2PO4• OH- + H2PO4- ↔ H2O + H2PO42-

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Protein Buffers
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Includes hemoglobin, work in blood and ISF
Carboxyl group gives up H+
Amino Group accepts H+
Side chains that can buffer H+ are present on
27 amino acids.

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2. Respiratory mechanisms
• Exhalation of carbon dioxide
• Powerful, but only works with volatile acids • Doesn’t affect fixed acids like lactic acid
• CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3• Body pH can be adjusted by changing rate and depth of breathing
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3. Kidney excretion
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Can eliminate large amounts of acid
Can also excrete base
Can conserve and produce bicarb ions
Most effective regulator of pH
If kidneys fail, pH balance fails

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Rates of correction
• Buffers function almost instantaneously
• Respiratory mechanisms take several minutes to hours
• Renal mechanisms may take several hours to days

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Acid-Base Imbalances
• pH< 7.35 acidosis
• pH > 7.45 alkalosis
• The body response to acid-base imbalance is called compensation
• May be complete if brought back within normal limits
• Partial compensation if range is still outside norms.
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Compensation
• If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation.
• If problem is respiratory, renal mechanisms can bring about metabolic compensation. 20

Acidosis
• Principal effect of acidosis is depression of the
CNS through ↓ in synaptic transmission.
• Generalized weakness
• Deranged CNS function the greatest threat
• Severe acidosis causes
– Disorientation
– coma
– death
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Alkalosis
• Alkalosis causes over excitability of the central and peripheral nervous systems.
• Numbness
• Lightheadedness
• It can cause :
– Nervousness
– muscle spasms or tetany
– Convulsions
– Loss of consciousness
– Death
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Respiratory Acidosis
• Carbonic acid excess caused by blood levels of CO2 above 45 mm Hg.
• Hypercapnia – high levels of CO2 in blood
• Chronic conditions:
– Depression of respiratory center in brain that controls breathing rate – drugs or head trauma – Paralysis of respiratory or chest muscles
– Emphysema
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Respiratory Acidosis
• Acute conditons:
– Adult Respiratory Distress Syndrome
– Pulmonary edema
– Pneumothorax

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Compensation for Respiratory
Acidosis
• Kidneys eliminate hydrogen ion and retain bicarbonate ion

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Signs and Symptoms of
Respiratory Acidosis
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Breathlessness
Restlessness
Lethargy and disorientation
Tremors, convulsions, coma