Presión Osmótica y Osmolaridad

• The presentation discusses osmotic pressure and osmolarity
• Jackeline Burgos is credited as the presenter

Specific Objectives

• Understand diffusion, semipermeable membranes, osmosis, and osmotic pressure
• Relate these concepts to cellular exchange processes in the human body
• Understand how different solutes interact with the cell membrane based on molecule polarity
• Understand and apply the ionization process of electrolytes in aqueous solutions
• Calculate and convert between moles and osmoles
• Use Van't Hoff factor correctly
• Calculate osmotic parameters: osmotic pressure, osmolarity, and osmolality
• Distinguish between solution types based on osmotic pressure and understand their effects on cells

Body Fluids

• Total Body Water (TBW) is 60%
• Solids constitute 40% of the body composition
• Intracellular fluid represents 60% of TBW
• Extracellular fluid represents 40% of TBW
• Plasma is a type of extracellular fluid
• Interstitial fluid is another type of extracellular fluid
• Transcellular compartment is also present in the body

Semipermeable Membrane

• A semipermeable membrane allows solvent molecules to pass through
• A semipermeable membrane prevents solute molecules from passing through
• Pore size in the membrane influences permeability
• Solvent solubility affects permeability
• Membrane charge affects permeability

Diffusion

• Diffusion is the process by which molecules/ions move from an area of higher to lower concentration
• Diffusion speed factors include molecule size and temperature
• Diffusion happens because of the random thermal motion of solutes

Diffusion Example

• Oxygen moves from the alveoli into the blood
• Carbon dioxide moves from the blood into the alveoli

Intracellular and Extracellular fluid composition

• Sodium is higher in extracellular fluid (140 mEq/l)
• Potassium is higher in intracellular fluid (120 mEq/l)
• Chloride is higher in extracellular fluid (105 mEq/l)
• Bicarbonate is higher in extracellular fluid (24 mEq/l)
• Proteins are higher in intracellular fluid (60)
• Phosphates are higher in intracellular fluid (140)
• Osmolarity of both intracellular and extracellular fluid is about 290 mOsm/l

Electrolyte concentrations

• Sodium level is 138 mEq/L in plasma
• Potassium level is 5 mEq/L in plasma
• Magnesium level is 3 mEq/L in plasma
• Calcium level is 4 mEq/L in plasma
• Chloride level is 110 mEq/L in plasma
• Bicarbonate level is 30 mEq/L in plasma
• Phosphate is 4 mEq/L in plasma
• Proteins are 6 mEq/L in plasma

Cell Exchange with External Environment

• Passive transport includes simple and facilitated diffusion
• Simple diffusion involves lipophilic substances like O2, N2, CO2, and vitamin A
• Facilitated diffusion requires channels or transport proteins for hydrophilic substances like H2O, glucose, and electrolytes

Cell Exchange with External Environment - Primary Active Transport

• Primary active transport uses ATP
• Examples include sodium-potassium pump

Osmosis

• Osmosis is the selective passage of solvent molecules (usually water) through a porous membrane
• Osmosis goes from a dilute solution to a more concentrated one
• Osmosis occurs through a semipermeable membrane due to differences in solute concentration
• Aquaporins are involved in water transport

Osmolarity

• Osmolarity represents the concentration of osmotically active particles
• Osmolarity = Osmoles/L
• Osmotically active particles are solutes that promote solvent movement across a semipermeable or cell membrane
• The defining equation is: Osmolarity = g x C, where g = number of particles per mole in solution and C = concentration

Van't Hoff factor

• NaCl dissociates into Na+ and Cl- (i=2)
• One mole of NaCl yields 2 osmotically active particles
• Na2SO4 dissociates into 2Na+ and SO4^2- (i=3)
• One mole of Na2SO4 yields 3 osmotically active particles
• Sucrose is a nonelectrolyte (i=1)

Osmolarity Example Calculation

• 1.4 g of NaCl is dissolved in 100 ml of solution (MW of NaCl = 58.44 g/mol)
• Molarity = 0.2395 mol/L, and i=2
• Osmolarity = g x C = (2 osmoles NaCl / mol NaCl) x 0.2395 mol NaCl / L = 0.479 osmoles NaCl / L = 479 milliosmoles NaCl / L

Osmolality

• Osmolality is the number of osmoles per kilogram of solvent
• Osmolality = g x C
• C = 0.02395 moles of NaCl / 0.1 kg of solvent = 0.2395 moles of NaCl / kg of solvent
• Osmolality calculation for 1.4g NaCl in 100mL water is approximately 0.479 osmoles of NaCl per kg of H2O, assuming 100mL equals 100g and density is 1

Osmotic Pressure

• Osmotic pressure is the pressure generated by a difference in the concentration of dissolved substances separated by a semipermeable membrane
• The defining equation is π = g x C x σ x R x T
• π = Osmotic Pressure (atm or mmHg)
• g = # of particles per mole in solution (Osm/mol)
• C = Concentration (mol/l)
• σ = Reflection coefficient (ranges from 0 to 1)
• R = Gas constant (0.0821 L atm / mol K) or 62.364 mmHg L / mol K
• T = Absolute temperature (K)
• Can also use the formula π = iMRT

Osmotic Pressure Calculation Example

• 1.4 g NaCl dissolved in 100 ml solution
• π = g x C x σ x R x T
• C (Molarity) = 0.2395 mol NaCl / L and g = 2
• The result of the variables and equation becomes Π = 3.513 atm

Tonicity

• A 15% glucose solution and a 7% glucose solution are separated by a semipermeable membrane
• The 15% glucose solution has a higher osmotic pressure

Solution Classifications

• Isotonic solutions: Two solutions having the same concentration and osmotic pressure
• Hypertonic solutions: Higher concentration and therefore different osmotic pressure
• Crystalloids solutions are electrolytic and/or sugar solutions. They maintain hydroelectrolytic balance and can be hypo, isotonic, or hypertonic
  • Isotonic/Isoosmotic: 0.9% physiological solution, Ringer's Solution, Ringer lactate solution, 5% Glucosated(Dextrose) Solution, glucosalina solution
  • Hypotonic: 0.45 hyposaline
  • Hypertonic: 10%, 20%, and 40% glucosated solutions, 7.5% saline solution

Electrolyte solutions

• The osmolarity of blood is 290-300 mOsm/L
• Hypotonic solutions are <290 mOsm/L
• Isotonic solutions are 290-300 mOsm/L
• Hypertonic solutions are >300 mOsm/L

Pressure determining water flow in a capillary

• Hydrostatic pressure: The pressure exerted by the blood within blood vessels
• Osmotic pressure: Force generated by the difference in concentration in osmotically active particles
• Oncotic pressure: Force generated by the difference in concentration of colloidal particles in the blood plasma