Physiology - Renal Topic #1

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Physiology - Renal Topic #1
2011-03-04 21:14:19

Topic #1 - Volume and Osmolarity Homeostasis
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    • 1. fluid balance / plasma volume
    • 2. regulation of body fluid osmolarity (solute concentration)
    • 3. electrolyte balance (Na K HCO Cl Ca)
    • 4. regulates plasma pH
    • 5. waste excretion -(urea creatinine penicillin, saccharin)
    • 6. hormone production - erythro poetin (EPO) stimulates red blood cell synthesis, calcitriol- is the active vitaminD3 (1,25-dihydroxycholecalciferol) starts off as cholesterol but is then formed into calcitriol
  2. Body Fluid Compartments
    • total body water is 60% of their body wieght
    • (0.6xbody weight) (60 kg about 36L)
    • the ICF contains 2/3 (24L) and the ECF contains 1/3 (12L)
    • ISF contains 3/4 (9L) and plasma contains 1/4 (3L) of the ECF fluid
  3. Total body water varies among individuals
    • more fat = less body water (fat crowds out the water)
    • women have less water (breasts and hips are more fatty)
    • less body water with age (ISF diminishes)
    • plumpness of new borns due to water not fat
  4. Water Balance
    • Input=Output
    • INPUT (2.4L/d)
    • most from water/food. (2.1 L), some from metabolism (0.3 L)

    • OUTPUT (2.4L/d)
    • sweat (0.35L), lungs (0.35L), urine (1.5L), feces (0.2L)
  5. Osmolarity
    • Osmosis = diffusion of water down is gradient
    • each mole creates an OSMOTIC FORCE of 1mOsmol
    • Osmolarity - measured in: mOsmol/L
    • Osmolality - measured in: mOsmol/Kg (H2O)
    • Ionic solutions – measured in: mEq/L (milli equivalent)
    • 1 mol K+=1mEq/L 1mol Ca2+=2mEq/L (charge dependant)
    • ECF osmolarity is about 300mOsmol/L
  6. Osmolarity Depends On?
    • depends on number not size of solutes dissolved
    • (300 mM of solute= 300mOsM)
    • Salts (likeNaCl) dissociate into ions in water
    • osmolarity of 150 mM NaCl solution =300mOsM
    • (0.9g/dl or 0.9%) this is "normal saline"
  7. Penetrating Solutes and Osmolarity
    • not all dissolved molecules contribute to osmotic pressure
    • non penetrating solutes:
    • ethanol diffuses accross membranes
    • urea and glucose are transported into cells
    • cellular metabolsim creates solutes(glucose)
    • penetrating solutes are NOT effective osmoles (solutes which do NOT contribute to osmotic pressure):
    • tonicity= the ability to move water across membrane in response to osmotic change
    • hypertonic = higher conc outside, water moves out
    • hypotonic = lower conc outside, water moves in
    • isotonic =same conc outside, no net movement
  9. Forces Governing Fluid Movement
    • Plasma to ISFacross:
    • Starling Forces: capillary pressure, osmotic pressure, tissue pressure
    • ISF to ICF (across cell membrane):
    • osmotic effects alone
  10. Salt and water Balance
    • ECF volume maintains blood pressure
    • ICF volume (cell shrink/swell) is altered when ECF osmolarity changes
    • ECF volume depends on salt balance (retain salt=retain fluid)
  11. infusions of isosmotic NON-PENETRATING solutes
    will distribute into: ECF only

    effect on osmotic gradient across cell is unchanged (eg. normal saline)
  12. infusions of PENETRATING solutes
    • distribute into: ECF (1/3) and ICF (2/3)
    • used to increase ICF volume
    • hemolysis: too much water entering RBCs
    • slightly soluted solution prevent this (Eg 0.3=5% glucose solution)