fluids electrolytes and acid base balance n.
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Fluids, Electrolytes, and Acid - Base Balance. Chapter 26. Body Fluids. Body Water Content. Largest component in body Fxn of age, mass, sex, and body fat Adipose tissue ~ 20% Skeletal muscle ~ 75% Infants ~ 73% Low fat and mass Young men and women ~ 60% and 50%

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body water content
Body Water Content
  • Largest component in body
  • Fxn of age, mass, sex, and body fat
    • Adipose tissue ~ 20%
    • Skeletal muscle ~ 75%
  • Infants ~ 73%
    • Low fat and mass
  • Young men and women ~ 60% and 50%
    • Relationship of adipose to muscle
fluid compartments
Fluid Compartments
  • Intracellular fluid (ICF) ~ 2/3 H20 volume
  • Extracellular fluid compartment (ECF) ~ 1/3 H2O volume
    • Plasma
    • Interstitial fluid (IF)
  • Other ECF
    • Lymph
    • CSF
    • GI secretions
    • Synovial fluids
composition of body fluids
Composition of Body Fluids
  • Nonelectrolytes
    • Bonds prevent dissociation in H2O = no charge
    • Glucose, lipids, and urea
  • Electrolytes
    • Dissociate in H2O = charge = conduct electricity
      • Inorganic salts, acids and bases, and some proteins
      • Cations w/ (+) charge, anions w/ (-) charge
    • Greater contribution to fluid shifting (osmolality)
comparing compartments ecf vs icf
Comparing Compartments (ECF vs ICF)
  • All ECF similar
    • Exception proteins b/c to big to diffuse
    • [Na+] and [Cl- ] predominate
    • Non-electrolytes ~ 90% & 60% in plasma & IF
  • ICF
    • [K +] and [phosphate] (HPO42-) predominate
    • [Na+] and [Cl- ] lowest
      • Na +/K + pumps
      • Renal reabsorption enhances
    • Non-electrolytes ~ 97%
  • Fig 26.2
fluid movement
Fluid Movement
  • Blood and IF exchange at capillaries*
    • HPb forces protein-free plasma out into IF
    • OPb sucks H2O out of IF (nondiffusible proteins)
    • Lymph removes minimal excess
  • IF and ICF more complex b/c of PM
    • H20 responds bidirectionally to [gradients]
    • Ions by active or facilitated transport
    • Nutrients, gases, and wastes move unidirectionally
hydration
Hydration
  • Intake must equal output ~2500 ml
  • Increased plasma osmolality (high solutes) = thirst and ADH release  dark urine
  • Decreased plasma osmolality = inhibits above  light/clear urine
regulating intake
Regulating Intake
  • Thirst mechanism stimulates drinking
    • Regulated by hypothalamic osmoreceptors
      • Increased plasma osmolality causes H2O loss to ECF
    • Dry mouth from decreased saliva production
    • Decreased plasma volume
    • Angiotensin II (Na+ reabsorption)
  • Moistening of GI mucosaand distension GI tract inhibit
    • Prevents overconsumption or overdilution
    • Not fail proof (exercise, heat, athletic events)
regulating output
Regulating Output
  • Obligatory H2O losses are unavoidable, but necessary
    • Insensible from lungs and skin
    • Sensible w/ sweat, urine, and feces
      • Kidneys must excrete ingested solutes w/ H2O = urine
  • Fluid intake, diet, and sweating regulate too
    • Increased sweating decreases urine output
    • Relationship of Na+ and H2O
regulating adh s role
Regulating ADH’s Role
  • Hypothalamic osmoreceptors
    • Decreased ECF osmolality inhibits ADH release
    • Increased ECF osmolality enhances ADH release
  • Collecting duct reabsorption reflects ADH release
    • High ADH = little concentrated urine  why?
    • Low ADH = dilute urine & reduced body fluid volume
  • Large blood volume and pressure changes also influence
    • Prolonged fever, vomiting, sweating, diarrhea, burns
    • Signals arteriole constriction = increasing BP
dehydration
Dehydration
  • Output > intake
  • H2O loss from ECF  H2O from ICF to ECF to equalize
    • Electrolytes move out too
    • Causes: hemorrhage, severe burns, vomiting and diarrhea, profuse sweating, H2O deprivation, diuretic abuse
  • Signs/symptoms
    • Early: ‘cottonmouth’, thirst, decreased micturition
    • Prolonged: weight loss, fever, confusion, hypovolemic shock
hypotonic hydration
Hypotonic Hydration
  • Intake > output
    • Increases fluid in ALL compartments
    • Diluted ECF w/normal Na+ H2O from ECF to ICF
      • Excessive intake of H2O
      • Reduced renal filtration (renal failure)
  • Excessive H2O in ICF swells cells
  • Signs/symptoms
    • Early: nausea, vomiting, muscular cramping, cerebral edema
    • Prolonged: disorientation, convulsions, coma, death
  • IV’s of hypertonic saline to reverse
edema
Edema
  • Fluid accumulation in IF (only) swells tissues
    • Increased fluid flow out of blood into IF
      • Increased BP and permeability
      • Increases filtration rate
    • Hindrance of fluid flow from IF into blood
      • Blocked/removed lymphatic vessels
      • Low plasma [proteins]
  • Disruptions
    • Increased distance for O2 and nutrient diffusion
    • Blood volume and BP drop = circulation impairment
sodium na balance
Sodium (Na+) Balance
  • Primary renal function
    • No known transport maximum
    • ~ 65% in PCT and ~ 25% in loop of Henle
  • Controls ECF volume and H2O distribution
    • Only cation creating OP
    • Na+ leaks into cells, but pumped out against electrochemical gradient
    • Water follows salt
  • [Na+] relatively stable in ECF
  • Changes effect plasma volume, BP, ICF and IF volumes
  • Transport coupled to renal acid-base control
regulating na balance aldosterone
Regulating Na+ Balance: Aldosterone
  • Effects
    • High  all Na+ reabsorbed
      • Decrease urinary output and increase blood volume
    • Inhibited  no Na+ so excreted w/dilute urine
  • Renin-angiotensin mechanism primary trigger
    • JG apparatus releases renin  aldosterone release
      • Decreased BP, [NaCl], or stretch, or SNS stimulation stimulates
regulating na balance anp
Regulating Na+ Balance: ANP
  • Reduces BP and blood volume
    • Inhibits vasoconstriction
    • Inhibits Na+ and H2O retention
      • Inhibit collecting duct Na+ reabsorption
      • Suppresses ADH, renin, and aldosterone release
  • Atrial stretch releases
regulating na balance other hormones
Regulating Na+ Balance: Other Hormones
  • Estrogens
    • Enhance NaCl reabsorption by renal tubules
    • Enhance H2O retention during menstrual cycles
    • Cause edema w/ pregnancy
  • Progesterone
    • Promotes Na+ and H2O loss
    • Blocks aldosterone effects at renal tubules  diuretic
  • Glucocorticoids
    • Enhance Na + reabsorption
    • Increase GFR
    • Promote edema
regulating k balance
Regulating K+Balance
  • Cortical collecting ducts change K+ secretion
    • [K+] in plasma primarily influences
      • High K+ in ECF increases secretion for excretion
        • Stimulates adrenal cortical release of aldosterone
  • Aldosterone enhances K+ secretion
    • High ECF K+ stimulates adrenal cortex for release
    • Renin-angiotensin mechanism
regulating ca 2 and po 4 2
Regulating Ca2+ and PO42-
  • PTH from parathyroid gland
    • Activates osteoclast activity in bones
    • Enhances intestinal absorption of Ca2+
      • Kidneys to transform vitamin D to active state
    • Increases Ca2+and decreases PO42- reabsorption
  • Calcitonin from thyroid gland
    • Released w/ increased Ca2+ levels to encourage deposit
    • Inhibits bone reabsorption
acid base review
Acid – Base Review
  • Acids
    • Electrolytes that release H+ in solution
    • Low pH (1 – 6.9)
    • Proton donors
    • Acidosis: pH decrease below homeostatic range
  • Bases
    • Electrolytes that release OH- in solution
    • High pH (7.1 – 14)
    • Proton acceptors
    • Alkalosis: pH increase above homeostatic range
  • Homeostatic ranges
    • Arterial blood 7.4
    • Venous blood and IF 7.35
    • ICF 7.0
acid base abnormality
Acid-Base Abnormality
  • Respiratory imbalances
    • Respiratory acidosis
      • Increase in CO2 = increased H+ = decreased pH
      • From shallow breathing or inhibition of gas exchange
    • Respiratory alkalosis
      • Decrease in CO2 PCO2 = decreased H+ = increased pH
      • From hyperventilation
  • Metabolic imbalances
    • Metabolic acidosis
      • Decrease in HCO3 = lowered pH
      • From excessive alcohol, diarrhea, starvation
    • Metabolic alkalosis
      • Decrease in HCO3 = lowered pH
      • Excessive vomiting or intake of bases (antacids)
chemical buffering systems
Chemical Buffering Systems
  • Resist shifts in pH from strong acids and bases
  • Bicarbonate
    • Only ECF buffer, but supports ICF
    • Mixture of H2CO3, NaCl, and NaHCO3
      • HCl + NaHCO3 = NaCl + H2CO3
      • NaOH + H2CO3 = NaHCO3 + H2O
  • Phosphate
    • Mimics bicarbonate
    • Mixture of dihydrogen (H2PO4-) and monohydrogen phosphate (PO3-)
    • Effective in urine and ICF
  • Protein
    • Plasma and ICF w/highest concentrations
    • Mixture of carboxyl (COOH) and amine (NH3) groups
    • Amphoteric molecules can fxn as weak acids or bases