fluid electrolyte balance
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Fluid, Electrolyte Balance. Chapter26. Body Fluids & Fluid Compartments. Figure 26.1. Approximately 60% of body weight is H 2 O. Fluid Compartments Intracellular fluid (ICF): fluid within the cells Extracellular fluid (ECF): fluid outside the cells Plasma Interstitial fluid (IF). ICF.

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body fluids fluid compartments
Body Fluids & Fluid Compartments

Figure 26.1

  • Approximately 60% of body weight is H2O.
  • Fluid Compartments
    • Intracellular fluid (ICF): fluid within the cells
    • Extracellular fluid (ECF): fluid outside the cells
      • Plasma
      • Interstitial fluid (IF)



what are electrolytes
What are electrolytes?????


body fluids
Body Fluids
  • Composition (solutes):
    • Electrolytes
      • chemical compounds that dissociate in H2O to form ions – salts, acids, bases
      • anything with a charge
    • Nonelectrolytes: do not dissociate in H2O (glucose, lipids, creatinine, urea, etc.)
body fluids1
Body Fluids
  • Osmosis: the diffusion of a solvent (such as water) across a semipermeable membrane
    • From a less concentrated solution (H2O moves out).
    • Toward a more concentrated solution (H2O moves in).
    • The solvent (H2O) moves down its concentration gradient.
  • Osmotic activity is based on the number of particles in solution.
osmotic activity
Osmotic Activity
  • Electrolytes have a greater potential for osmotic activity than nonelectrolytes
    • NaCl  Na+ + Cl- 2 particles
    • MgCl2 Mg2+ + 2 Cl- 3 particles
    • Glucose  Glucose 1 particle
  • Electrolytes have the greatest ability to cause fluid shifts.
electrolyte concentration
Electrolyte Concentration
  • Electrolyte concentration is an expression of the number of electrical charges in 1 liter [expressed as milliequivalents per liter (mEq/L)]
    • mEq/L = ion concentration (mg/L) x charge atomic weight
  • Normal plasma levels:
    • Na+ : 3300 mg/L x 1 = 143 mEq/L 23
    • Ca2+ : 100 mg/L x 2 = 5 mEq/L 40
body fluids2
Body Fluids
  • Comparison of extracellular fluid (ECF) and intracellular fluid (ICF)
    • ECF: increased Na+ and increased Cl-
    • ICF: increased K+ and increased HPO42-

Figure 26.2

fluid movement

Figure 26.1

Fluid movement



  • Movement between plasma and interstitial fluid (IF) across capillary membranes
    • Hydrostatic pressure in the capillaries pushes fluid into the IF
    • Oncotic pressure returns fluid to plasma
    • Lymphatic system returns the small remainder to the blood
  • Exchanges between IF and ICF occur across the selectively permeable cell membranes
    • H2O flow is conducted both ways
    • Ion movement is controlled and restricted
    • Ion transport is selective by active transport
water balance and ecf osmolality
Water Balance and ECF Osmolality

Figure 26.4

  • H2O sources / losses
  • Sources:
    • Intake (~2500 ml/day)
    • Metabolic H2O : H2O produced by cell metabolism
  • Losses:
    • Insensible loss: vaporizes from lungs and skin
    • Losses in perspiration and feces
    • Urinary losses (~60%)
regulation of intake output
Regulation of intake / output

Figure 26.5

  • Intake: Thirst is regulated by the hypothalamic thirst center
    • Sensory feedback from dry mouth stimulates the thirst center
    • Hypothalamic osmoreceptors lose H2O into hypertonic ECF and stimulate the thirst center
    • Angiotensin II stimulates the thirst center
  • Output:
    • Kidneys: make short term adjustments to compensate for low intake
    • Obligatory H2O loss
      • Insensible loss + Sensible loss in urine yields a daily minimum of 500ml
      • With a normal diet the kidneys must excrete 900-1200 mOsm of solute daily
water balance conservation
Water Balance: Conservation
  • ADH
    • H2O reabsorption in collecting duct
    • Hypothalamic osmoreceptors sense ECF osmolality and regulate ADH release
    • Large decreases in BP trigger ADH release via signals from baroreceptors
    • ADH acts directly and via stimulation of Renin-Angiotensin system
disorders of h 2 o balance
Disorders of H2O Balance
  • Dehydration: H2O loss and/or electrolyte imbalance
  • Hypotonic hydration: H2O intake with inadequate electrolytes; marked by hyponatremia
  • Edema: accumulation of fluid in the interstitial space
    • Hypoproteinemia: loss of colloid osmotic pressure H2O leaves plasma, enters IF
    • Any event that increases plasma  IF movement or hinders IF  plasma return
electrolyte balance role of na
Electrolyte Balance: Role of Na+
  • Na+ is the most abundant cation in the ECF
  • Na+ is the only ECF ion with significant osmotic effect
  • Cell membranes are relatively impermeable to Na+
  • [Na+] across the cell membrane may be altered
  • Na+ has the primary role in control of ECF volume and H2O distribution
electrolyte balance role of na1
Electrolyte Balance: Role of Na+
  • ECF total Na+ content may change but [Na+] remains stable because of shifts in water content
    • A change in the [Na+] in plasma will effect; plasma volume, BP, intracellular fluid volume and interstitial fluid volume.
regulation of na balance
Regulation of Na+ balance
  • Regulation of Na+ balance is linked to BP and blood volume
  • 65% of Na+ is reabsorbed in the PCT
  • 25% of Na+ is reabsorbed in the ascending limb of the loop of Henle
  • 10% remains in DCT and collecting duct filtrate
  •  aldosterone :
    • Virtually all Na+ is actively reabsorbed in DCT & collecting duct (H2O follows Na+ if ADH is present)
  • Renin-Angiotensin system is the most important trigger of aldosterone release
  • Aldosterone effect occurs slowly (hours to days)
  • Changes in blood will feedback to modulate the effect of aldosterone.
cardiovascular baroreceptors blood pressure homeostasis
Cardiovascular Baroreceptors: Blood Pressure Homeostasis
  • Decreased BP leads to:
    • Constriction of afferent arterioles
    • Activation of the renin angiotensin system
    • Release of aldosterone
    • Release of ADH
    • Conservation of Na+
    • Conservation of blood volume
    • Increased thirst