Osmosis and Tonicity Flashcards

Aquaporin

• Facilitates water movement across cell membranes by creating specific water channels.

Factors Influencing Body Water Content

• Body water content varies by gender: males generally have higher water content than females.
• Age affects water content, with infants having more body water than adults.

Distribution of Water Among Body Compartments

• Intracellular fluid makes up 67% of total body water.
• Extracellular fluid accounts for 33%, divided into:
  • 75% interstitial fluid
  • 25% plasma

Osmosis

• Defined as the movement of water through a membrane driven by differences in solute concentration.

Osmotic Pressure

• Refers to the pressure required to prevent osmosis, measured in atmospheres (atm) or millimeters of mercury (mm Hg).

Osmolarity

• Measures the concentration of osmotically active particles in a solution, usually expressed in osmoles per liter (osmol/L or OsM), distinct from molarity.

Calculation of Osmolarity

• Osmolarity can be calculated using the formula: osmolarity (osmol/L) = molarity (mol/L) x #particles/molecule (osmol/mol).

Dissociation Factor

• Indicates the extent of molecular dissociation in a solution, with sodium chloride (NaCl) having a dissociation factor of 1.8 at body temperature.

Normal Osmolarity of the Human Body

• Typical osmolarity is around 300 mOsM, slightly less than this value.

Osmolality

• Refers to the concentration of solute in osmoles per kilogram of water; the terms osmolarity and osmolality are often used interchangeably in biological contexts.

Isosmotic Solutions

• Two solutions are isosmotic if they have the same concentration of solute particles per unit volume.

Hyperosmotic Solutions

• Solutions with a higher number of solute particles per unit volume compared to another solution.

Hyposmotic Solutions

• Solutions that contain fewer solute particles per unit volume than another solution.

Tonicity

• Hypotonic solutions cause a cell to gain water, leading to cell swelling.
• Hypertonic solutions lead to water loss from a cell, causing it to shrink.
• Isotonic solutions maintain the cell's size, with no net water movement.

Differences Between Tonicity and Osmolarity

• Osmolarity quantifies solute particles in a solution, while tonicity is a comparative term that does not have units and specifically pertains to the effect on cell volume.
• Tonicity always relates a solution's effect on a cell, while osmolarity can compare any two solutions.

Solute Penetration

• Penetrating solutes can freely enter cells, while nonpenetrating solutes cannot.

Tonicity Dependence

• Tonicity is determined by the concentration of nonpenetrating solutes within the solution.

Most Important Nonpenetrating Solute

• Sodium chloride (NaCl) is the key nonpenetrating solute in physiological contexts.

Tonicity Assessment Without Cell Exposure

• Tonicity can be inferred by comparing the concentrations of nonpenetrating solutes in the cell versus those in the solution.

Isosmotic Solution Characteristics

• An isosmotic solution cannot be hypertonic as it can't have a higher concentration of nonpenetrating solutes than the cell.
• If all solutes are nonpenetrating, the isosmotic solution is isotonic; if penetrating solutes are present, it becomes hypotonic.

Rules for Analyzing Osmolarity and Tonicity

• Assume all intracellular solutes are nonpenetrating when evaluating tonicity.
• Assess osmolarities before exposing a cell to any solution, noting that equilibrium results in isosmotic conditions.
• Tonicity specifies how cell volume will change at equilibrium.
• Determine tonicity by comparing concentrations of nonpenetrating solutes, as water moves toward higher solute concentrations.
• Always remember that hyposmotic solutions are equivalently hypotonic.