Fluid-Electrolyte _amp; Acid-Base Balance

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					Fluid-Electrolyte &
Acid-Base Balance

     Chapter 19
                Water Compartments
   Fluid compartments
       Intracellular fluid—about 2/3 of total
       Extracellular fluid—plasma, lymph,
        tissue fluids
           Cerebrospinal fluid in central nervous
            system, synovial fluid in joints,
            aqueous humor of eye, serous fluids
            between organs & membranes
            Movement of Water

   Water moves via two processes
       Filtration
       Osmosis
Fluid compartments




   Figure 22-1
          Water Intake & Output

   Intake: 2500 ml/day
       Oral liquids: 1600 ml/day (about 6½
        8 oz glasses)
       Food: 700 ml/day (about 3 glasses)
       Internal source: 200 ml (less than 1
        glass)
           Water Intake & Output

   Output: 2500 ml/day
       Urine 1500 ml/day
       Sweat 500 ml/day
       Exhaled water vapor 300 ml/day
       Feces 200 ml/day

   Intake & output SHOULD BE EQUAL
       Sweating, vomiting or diarrhea: DRINK
        MORE
       Too much intake: urinate more
Intake and output




                • Intake of water
Figure 22-2     • Output of water
            Regulation

 Hypothalamus   of brain
  Regulates water content
  Osmolarity—concentration of
   dissolved materials in a fluid
  Osmoreceptors in hypothalamus
   detect changes in blood osmolarity
       Regulation of Body Water

 If   body is dehydrated
   Osmolarity   of blood increases
   Less fluid in body makes body
    fluids more concentrated
        Person   feels thirsty & drinks fluids for
         relief
        Water absorbed by intestines
        Osmolarity of blood decreases
            Regulation of Water

   ADH (antidiuretic hormone)
       Produced by hypothalamus, stored in
        posterior pituitary
          Function: tells kidneys to save
           (reabsorb) water to relieve dehydrated
           state
          Result: less urine is produced
      Regulation of Water

 Aldosterone
  Produced   by adrenal cortex
  Function: tells kidneys to conserve
   (reabsorb) water to relieve a
   lowered blood pressure or a
   lowered blood Na+ level
        Regulation of Water

 Water intoxication—lowers
  concentration of dissolved
  materials
 Blood volume & blood pressure
  increase
     Atria   natriuretic peptide (ANP) from
     heart
       Function:tells kidneys to excrete Na+
       & water to lower BP & blood volume
                 Electrolytes

   Electrolytes are formed when
    molecules in water dissociate
   Electrolytes are either positive or
    negative
   Positive ions are called cations
       Na+, K+, Ca2+
   Negative ions are called anions
       Cl-, HCO3-, HPO42-
                 Electrolytes
   Most are inorganic molecules
       Salts (NaCl, KCl, CaCl)
       Acids (H2CO3 or HCl)
       Bases (NaHCO3 or Na2HPO4)
   Are part of tissues like bones, muscle &
    nerves
   Are part of proteins like enzymes or insulin
                  Electrolytes

   Help to establish the osmolarity of body
    fluids
   AND, their presence helps regulate an
    important process
       Movement of water: osmosis
       Water moves to attempt at diluting
        concentrated fluids
       Moves from LOW concentration to HIGH
                   Electrolytes
   K+ is most predominant ICF cation
    (remember “KICK”)
   Na+ is most predominant ECF cation
    (remember “NECK”)
   Cl- is most predominant anion in ECF
       Few protein anions found in tissue fluid
       Many protein anions found in plasma
   HPO4-2 (phosphate) & protein anions
    are found in ICF
        Regulation of Electrolytes

   We eat & drink these molecules daily
   We lose these in urine & feces but also in
    sweat
       Sweat is mostly NaCl (ever taste it??)
       Electrolytes end up in urine if there is too
        much of that substance in the blood
    Regulation of Electrolytes
   Hormonal regulation
       Aldosterone:
         Increases Na+ reabsorption
          (conservation) by kidneys
         Increases K+ excretion by kidneys

         Urine ends up with less Na+ but
          more K+ in it
        Regulation of Electrolytes
   ANP
       Increases excretion of Na+ by kidneys
       Urine has more Na+ ions in it
   Parathyroid (PTH)
       Increases Ca2+ & P reabsorption from
        bones into blood
       Results in weaker bones & increased
        values of both ions in blood
        Regulation of Electrolytes

   Calcitonin
       Increases Ca2+ & P removal from blood (into
        bones)
       Results in lowered blood values of both ions &
        stronger bones
Acid-Base pH
    scale
             Acid-Base Balance
   Normal blood pH: 7.35 – 7.45 (slightly
    alkaline)
       ICF is slightly acidic: 6.8 – 7.0
       Tissue fluid pH is closer to blood but varies
   pH scale: 7.0 is neutral
   Acidic: pH < 6.99
   Alkaline: pH > 7.01
                   Buffers

   Recall: substances that are able to deflect
    drastic changes in body pH
   Consist of weak acid, weak base
   When they react with STRONG acid or
    STRONG base, the resultant substance
    have little effect on overall pH of body
   3 systems in body: bicarbonate,
    phosphate & protein systems
          Bicarbonate system

   Recall: weak acid (H2CO3) & weak base
    (NaHCO3)
   Each easily dissociates in blood plasma,
    ready to give up or take up H+ ions
    whenever the need exists
         Adding HCl to body
    HCl + NaHCO3  NaCl + H2CO3

 Salt (NaCl) has no effect on pH
 Weak acid (H2CO3) makes little
  change to pH
Adding Sodium Hydroxide to body

NaOH + H2CO3  H2O + NaHCO3

   Water has no effect on pH
   Weak base (NaHCO3 which is sodium
    bicarbonate) has little effect on pH.
            Phosphate System
   Phosphate system—sodium dihydrogen
    phosphate (NaH2PO4), a weak acid & sodium
    monohydrogen phosphate (NaHPO4), a weak
    base.
           HCl + NaHPO4  NaCl + NaH2PO4
   Adding strong acid does not have major effect
    on pH (NaCl = no effect on pH)
          NaOH + NaH2PO4  H2O + NaHPO4

   Adding strong base does not have major effect
    on pH (water = no effect on pH)
       Protein Buffer System
   Important in ICF
   Amino acids may act as either acid or
    base
      Carboxyl (COOH) can act as an
       acid & donate H+ ions to  pH
      Amine group (NH2) can act as a
       base & pick up extra H+ ions to 
       pH
   React immediately but little long-term
    capacity
    Respiratory Regulation of pH

   Can regulate CO2 in body by increasing or
    decreasing respiratory rate
   CO2 Can form H2CO3 with water in body
    fluids; H+ ion affects pH
        CO2 + H2O  H2CO3  H+ + HCO3-
     Respiratory Regulation of pH
   Respiratory Acidosis
     CO2 (waste product) is retained in
      system
     Occurs with respiratory diseases
      (pneumonia, emphysema, asthma)
     Any decrease in respiratory rate or
      breathing efficiency
     Excess H+ ions are produced by
      reaction on previous slide
     This lowers pH of body fluids
    Respiratory Regulation of pH

   Respiratory Alkalosis
     Usually caused by hyperventilation
     Less common
     Exhale too much CO2
     Fewer H+ ions are produced
     Result in rise in body fluid pH
    Respiratory Compensation—
        Metabolic Acidosis
   Caused by kidney disease, diabetic
    ketoacidosis, excessive diarrhea or
    vomiting
   Respiratory rate  in response
   Exhale more CO2, less H+ ion produced
   pH increases back up toward normal
    Respiratory Compensation—
        Metabolic Alkalosis
   Not common, caused by overingestion of
    antacids or vomiting of stomach contents
    only
   Respiratory rate slows breathing
   Exhale LESS CO2 (more retained)
   More H+ ions produced, result is
    lowering of pH in body fluids back to
    normal
   Works within a few minutes
  Respiratory
system control of
      pH
           Renal Mechanisms

   Best ability for long-term control of pH in
    acidosis situation
   Take hours to days to reach full capacity
     Compensating for acidosis: will excrete H+
      ions, conserve Na+ & HCO3- ions
     Compensating for alkalosis: will excrete Na+
      & HCO3- ions while conserving H+ ions
                 Compensation

   First line is ECF buffers
       Bicarb, phosphate and protein
   Second line is respiratory system
       Breathing rate  to exhale more CO2, to  H+
        formation (which would lead to acidic pH)
       This  is limited, however
   Lastly, renal system
       Keep patient alive
       Excrete H+ ions in urine (urine very acidic)
Manifestations of Acidosis & Alkalosis

 Acidosis: depression of nerve
  transmissions results in confusion
  & disorientation, finally coma, death
 Alkalosis: irritability, muscle
  twitches & progression leads to
  severe muscle spasms &
  convulsions.

				
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posted:4/6/2013
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