6.2 Osmotic Equilibrium is maintained in ICF and ECF

• What is maintained between intracellular and extracellular fluids?

  Osmotic equilibrium
• What can develop across the cell membrane with small changes in solute concentrations?

  Large osmotic pressures
• How much osmotic pressure is exerted for each milliosmole concentration gradient of an impermeant solute?

  About 19.3 mm Hg
• What is the potential osmotic pressure across the cell membrane if intracellular fluid osmolarity is 282 mOsm/L?

  More than 5400 mm Hg
• What happens when intracellular and extracellular fluids are not in osmotic equilibrium?

  Water moves across the cell membrane
• What can cause large changes in cell volume?

  Small changes in impermeant solute concentration
• What are isotonic, hypotonic, and hypertonic fluids?

  • Isotonic: No change in cell volume (282 mOsm/L)
  • Hypotonic: Causes cells to swell (<282 mOsm/L)
  • Hypertonic: Causes cells to shrink (>282 mOsm/L)
• Why are isotonic solutions important in clinical medicine?

  They maintain osmotic equilibrium during infusion
• What happens when a cell is placed in a hypotonic solution?

  Water diffuses into the cell, causing swelling
• What concentration of sodium chloride is considered hypotonic?

  Less than 0.9 percent
• What occurs when a cell is placed in a hypertonic solution?

  Water flows out of the cell, causing shrinking
• What concentration of sodium chloride is considered hypertonic?

  Greater than 0.9 percent
• What do the terms isosmotic, hyperosmotic, and hypo-osmotic refer to?

  • Isosmotic: Same osmolarity as the cell
  • Hyperosmotic: Higher osmolarity than normal extracellular fluid
  • Hypo-osmotic: Lower osmolarity than normal extracellular fluid
• What can cause transient shifts in fluid volume between compartments?

  Highly permeating substances like urea
• What happens to concentrations of permeating substances over time?

  They become equal in both compartments
• How quickly is osmotic equilibrium usually attained?

  • Rapid transfer of fluid across the membrane
  • Usually corrected within seconds to minutes
  • Complete equilibrium takes about 30 minutes after drinking water
• Why might complete osmotic equilibrium take longer in the body?

  Fluid must be transported by blood to tissues
• How long does it usually take to achieve osmotic equilibrium after drinking water?

  About 30 minutes