ACIDS AND BASES

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ACIDS AND BASES

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pH Review

• ECF pH 7.4
• Tightly regulated
• Fatal if pH 7.25 gt pH gt 7.55
• Nec for proper enzyme activity
• May ? change protein shape (enzymes)
• Enzymes catalyze rxns by holding substrates
  properly for rxn to occur at active site of
  certain shape
• pH change ? ? ?? cell death

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pH Review contd

• pH - log H
• High H acidic soln low pH (1-6)
• Low H basic (alkaline) soln high pH
  (8-14)
• pH 7 neutral solution

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Acids

• H donors
• Body acids classified as
• Volatile (eliminated from the body as CO2)
• Most impt -- carbonic acid (H2CO3)
• Gives up H by reaction H2CO3 ? CO2 H2O
• Nonvolatile (eliminated through kidney tubules)
• Ex lactic acid, phosphoric acid, etc

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Acids contd

• Another classification of acids weak/strong
• Strong easily gives up H from molecular
  structure
• Ex HCl mostly (H Cl-)Note there are few
  strong acids in the body
• Weak most physiological acids may or may not
  easily give up H in solution
• Dissociation depends on molecular structure and
  conditions of solution

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Carbonic Acid Important

• CO2 H2O ?? H2CO3 ?? H
  HCO3-(carbon (water) (carbonic
  (hydrogen (bicarbonate)dioxide)
  acid) ion)Both reversible reactions
  catalyzed by enzyme carbonic anhydrase

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Bases, Buffers

• Bases -- H acceptors
• Overall negative (-) charge (ex OH-)
• Can also be weak or strong
• Buffer system of weak acid conjugate base
• Pairs of related molecules
• Conjugate base whats left of a weak acid
  molecule, once H dissociated
• React with either added base or added acid ? no
  significant change in pH
• Blood buffers -- first responders to changes in
  blood pH

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Buffers contd

• Four important body buffers
• Bicarbonate/carbonic acid
• Weak acid carbonic acid
• Conjugate base bicarbonate ion
• Hb/oxy-Hb
• Phosphate system works inside cells
• Protein system important in ISF

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Bicarbonate/Carbonic Acid Buffer System

• Henderson-Hasselbach equation (for any buffer)
• pH pKa log conjugate base/weak acid,
  where
• pH can be measured
• pKa is constant for any weak acid
• If pKa is known, concentration of conjugate base
  and weak acid can be calculated
• For carbonic acid buffer system
• pH pKa log HCO3-/H2CO3

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Bicarb/Carbonic Acid Buffer contd

• Blood concentrations of base, acid in proper
  blood buffer (REMEMBER 201)
• Substitute into H-H eqn
  (pH pKa log base/acid)
• Normal blood pH 7.4
• pKa for carbonic acid 6.1
• Solve for base/acid ratio
• HCO3-/H2CO3 20 / 1
• For every 1 carbonic acid molecule in
  bloodstream, body strives to maintain 20
  bicarbonate molecules
• Actual concentrations in healthy blood
  HCO3-24 mEq/L, H2CO31.2 mEq/L

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Bicarb/Carbonic Acid Buffer contd

• Respiratory component
• From overall carbonic acid rxn
• CO2 H2O ?? H2CO3 ?? H HCO3-
• Resp component is left side of equation
• CO2 H2O ?? H2CO3
• H2CO3 dependent on CO2, which is expired through
  lung
• Lung can rapidly decrease H2CO3 in blood by
  excreting CO2
• Body uses respiratory system to maintain H2CO3 at
  proper amounts to maintain 201 buffer ratio
• Fast mechanism
• Minutes to hours

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Bicarb/Carbonic Acid Buffer contd

• Respiratory component contd
• Acid/base disorders identified
• Incrd blood H2CO3 ? decrd blood pH
• Respiratory acidosis
• Due to retained CO2
• Decrd blood H2CO3 ? incrd blood pH
• Called respiratory alkalosis
• Due to too little CO2 in blood
• Note respiratory component disorders are based
  on the amount of one of the blood buffer
  components (H2CO3).

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Bicarb/Carbonic Acid Buffer contd

• Renal component
• HCO3- regulated by kidney, w/ H secreted to
  urine
• From overall carbonic acid rxn
• CO2 H2O ?? H2CO3 ?? H HCO3-
• Renal component is right side of equation
• H2CO3 ? ? H HCO3-
• Kidneys control excrn H and HCO3- from blood
• Body uses renal system to manipulate HCO3- part
  buffer system to maintain the 201 buffer ratio
• Slow
• Hours to days (so not sufficient in acute
  dysfunction or disease)

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Bicarb/Carbonic Acid Buffer contd

• Renal component contd
• Acid/base disorders identified
• Incrd blood HCO3-? incrd blood pH
• Metabolic alkalosis
• Decrd blood HCO3- ? decrd blood pH
• Metabolic acidosis
• Note metabolic dysfunctions focus on amount of
  conjugate base part of the buffer system (HCO3-)

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Importance of K -- It Can Exchange for H

• If blood acidosis (high concentration of H
  cant be neutralized by blood buffer base)
• H can leave IVF ? ISF
• If ISF H high enough, H will enter the cell
• ? cell with too high charge
• To maintain neutral ICF charge, K leaves cell,
  enters ISF

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K Exchange contd

• Opposite in alkalosis
• Too little H in ECF ? H from cell moves into
  ECF
• To maintain charge neutrality, ECF K moves into
  cell from ECF in exchange ? ECF hypokalemia

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Acid/Base Imbalances (Figs.4-10 4-13)

• Respiratory Acidosis
• Decrd ventilation (breathing or gas exchange) ?
  incrd PaCO2 (arterial pressure CO2)
• Lung dysfunction ? CO2 improperly excrd
• ? Build-up of CO2 in bloodstream
• Increased PaCO2 hypercapnia
• Due to
• Chronic conditions
• Depression of resp center of brain that controls
  breathing rate
• Paralysis of respiratory or chest muscles
• Acute conditions
• Adult Respiratory Distress Syndrome (ARDS)
• Occurs with trauma, acute infection ? high amts
  biochems impt to inflammatory response ? severe
  impact on the lungs ? inhibited breathing
• Pneumothorax (or collapsed lung)

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Acid/Base Imbalances contd

• Respiratory acidosis contd
• Causes differ for chronic/acute
• Acute airway obstruction
• Chronic chronic pulmonary disease
• Compensation differs for chronic/acute
• Acute compensation difficult
• Cant use resp system to adjust acid/base levels
• Renal component too slow to accommodate acute
  difficulty
• Chronic renal mechanism compensates
• Body senses increased CO2 in IVF
• ? Stimn kidney to increase reabsorption HCO3-
  from renal tubules
• Also incrd CO2 sensed stimulates kidney to
  incr excrn of H into urine
• Taken together, blood now will have less H (so
  will be less acidic) and more HCO3- (neutralizes
  any excess H remaining)

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Acid/Base Imbalances contd

• Respiratory acidosis contd
• Clinical
• Neurological effects if acidity increases
  enough, cerebrospinal fluid becomes acidic ? ? ?
  tremors, coma
• Treatment
• Restore ventilation
• Treat any underlying cause of chronic
  dysfunctions or diseases

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Acid/Base Imbalances contd

• Respiratory Alkalosis
• Most common acid/base imbalance
• Primarily caused by hyperventilation ? decrd
  PaCO2 (hypocapnia)
• Due to
• Pulmonary diseases
• Congestive heart failure
• Both ? hypoxia sensed at chemoreceptors in
  vasculature
• Chemoreceptors send signals to brain (respiratory
  center) ?
• ? incrd breathing to bring in more oxygen
• BUT incrd breathing ? incrd CO2 excrn so
  decrd PaCO2
• Now less CO2 H2O ? H2CO3, and too little acid
  defines alkalosis
• Acute anxiety ? hyperventilation

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Acid/Base Imbalances contd

• Clinical
• Frequent yawning
• Deep respirations
• Treatment
• Eliminate underlying disease
• Breathe into a paper bag (to decrease CO2 lost
  with breathing)

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Acid/Base Imbalances contd

• Metabolic acidosis
• Due to
• Incrd metabolic acids accumulating in blood
• With metabolic disorders
• With hypoxia
• Greatly incrd ingested acids
• Decrd excreted acids
• With renal dysfunction
• Decrd HCO3- in blood
• With chronic diarrhea

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Acid/Base Imbalances contd

• Metabolic acidosis contd
• Compensation - incr'd serum HCO3- K exch.
• Resp system responds to decrd H2CO3 in blood
  by decreasing CO2 in blood (or increasing excrn
  CO2)
• So hyperventilation
• Renal system must respond to incrd excrn H if
  possible
• K exchanges with excess H in ECF
• So K moves out of the cells into ECF as H moves
  out of ECF into the cells

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Acid/Base Imbalances contd

• Metabolic acidosis contd
• Clinical
• Headache, lethargy
• CNS depression
• Deep, rapid respirations
• Dysrhythmias
• Treatment
• Treat underlying cause
• Lactate solution IV
• In liver, lactate converted to HCO3-
• So incrs base available to bring buffer system
  ratio back to normal

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Acid/Base Imbalances contd

• Metabolic alkalosis
• Increased relative HCO3- in the blood
• Due to
• Chronic vomiting, g.i. suction, diuresis
• H lost to body fluids along with other
  electrolytes
• Problematic if concurrent renal dysfunction that
  allows incrd HCO3- reabsorption
• Heavy ingestion of antiacids

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Acid/Base Imbalances contd

• Metabolic alkalosis contd
• Compensation
• Renal compensation difficult (HCO3- reabs'd)
• Most commonly occurs with renal dysfunction, so
  patient cant count on kidney to compensate
• Resp. compensation difficult (limited hypovent'n)
• Body needs to increase PaCO2 (? increased
  H2CO3)
• Patient must hypoventilate (to decrease excretion
  of CO2)
• BUT hypoventilation is only temporary (through
  breathing reflex at resp center)
• So the patient cant count on the respiratory
  system to compensate

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Acid/Base Imbalances contd

• Metabolic alkalosis contd
• Clinical
• Respirations slow, shallow
• Symptoms often related to depletion of
  electrolytes (if cause is vomiting, etc.)
• Atrial tachycardia
• Dysrhythmias
• Treatment
• Electrolytes to replace those lost
• Treat underlying renal disorder if possible

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