Physio L35- Fluid Balance

  1. Balance Concept
    • The ECF is the pool of available material for cells
    • Input occurs from ingestion or metabolic production
    • Output occurs from excretion or consumption
    • Balance must occur the long run, with input= output
    • X-OH....HO-Y
    • X-O-Y
    • H2O
  2. Negative Balance
    • Output is greater than input
    • Net reduction in pool concentration
  3. Positive Balance
    • Input is greater than output
    • Net increase in pool concentration
  4. Fluid Balance
    • Balance of water in the body
    • 60% of the body is water, with adipose tissue causing variation
    • Plasma is 90% water, soft tissues 70-80% water, bone 22%, adipose 10%
  5. Intracellular Fluid
    • 2/3 of total body water
    • K+ dominated, with protein
  6. Extracellular Fluid
    1/3 of total body water, Na+ dominated
  7. Plasma
    20% ECF, with protein
  8. Interstitial Fluid (ISF)
    80% of ECF, with protein
  9. Minor ECF Components
    Relatively small volumes: lymph, CSF, saliva (release bicarbonate to neutralize acid and kill off bacteria), etc.
  10. ECF Volume Regulation
    • Regulation of volume needed for long-term BP control
    • Changes in BP cause shifts of fluid between plasma and IF
  11. Blood Pressure Control
    • Short term, a drop in pressure causes: auto-transfusion: Movement of fluid from IF to plasma to maintain BP- changes in baroreceptor activity
    • Long term control of volume is balance of thirst/ intake and kidney fluid excretion
  12. Salt Intake
    • The kidneys need 0.5g NaCl/ day for fluid loss in sweat, feces
    • Intake is 10.5g NaCl/day, excess excreted in urine
    • Cl- follows Na+
  13. Salt Excretion
    • Kidneys good at eliminating Na+, nut increase retention increases BP
    • Must balance 10.5g/ day input
    • Fitness reduces Na+ content in sweat
  14. Renin- Angiotensin- Aldosterone System
    • Long term control of Na+ excretion controls BP
    • Everyone has their own set point for BP
  15. ECF Osmolarity Control
    • Needed to prevent swelling or shrinking of cells
    • Total amount of material in a volume, regardless of composition, produces its osmolarity
  16. Ions
    • Na+ and K+ dominate the osmolarity of ICF and IF
    • Other non-penetrating substances, like proteins, also contribute to osmolarity
    • Water moves by osmosis if there are differences in ICF and IF osmolarity
    • Normal ICF and IF osmolarity is 300 mOSM
  17. Tonicity
    • The standard for tonicity is not the number of dissolved particles, but the behavior of cells in the solution
    • Cells swell in hypotonic solutions- ECF is rarely hypotonic (ex: IV solution with not enough material-> pure water into blood stream)
  18. Hypertonicity
    • Cells shrink in hypertonic solutions (>300 mOsm)
    • Dehydration- low intake, excess loss, diabetes
  19. Vasopressin
    • Controls osmolarity of urine
    • VP adds aquaporins to collecting duct to increase water reabsorption
  20. Water Intake
    • Fluid drinking, food intake, metabolism adds water
    • Balance water loss from lungs, skin, sweat (huge variable), feces, urine
  21. Osmoreceptors
    • Receptors in hypothalamus that control VP release
    • Increase osmolarity, Increase VP release, Increase water retention
    • Decrease osmolarity, Decrease VP release, Increase water excretion
Card Set
Physio L35- Fluid Balance
MSU physio