Osmosis, Tonicity, and Pressures Flashcards

A set of vocabulary flashcards covering the principles of osmosis, various types of pressure, osmolarity vs. tonicity, and their clinical relevance to cell volume and fluid exchange.

Osmosis

The movement of water across a semipermeable membrane from a lower solute concentration toward a higher solute concentration.

Osmotic pressure

A pulling force created by non-permeable solutes that is driven by differences in solute concentration across a semipermeable membrane.

Hydrostatic pressure

A pushing pressure exerted by a stationary fluid at equilibrium that causes water or fluid to move.

Oncotic pressure

Also known as colloid osmotic pressure, it is the osmotic pressure generated primarily by plasma proteins (especially albumin) which pulls water into blood vessels.

Osmolarity

The concentration of osmotically active particles per liter of solution, expressed in units of $\text{osm/L}$ or $\text{mOsm/L}$. Prints the total concentration of dissolved particles regardless of membrane permeability.

Osmolality

The concentration of osmotically active particles expressed as osmoles per kilogram ($\text{osm/kg}$) of water.

Isosmotic

Solutions that have equal osmolarity (total solute concentration) and equal osmotic pressure.

Hyperosmotic

A solution with a higher osmolarity and greater osmotic pressure than the comparison solution, causing water to tend to move toward it.

Hypo-osmotic

A solution with a lower osmolarity and lower osmotic pressure than the comparison solution, causing water to tend to leave it.

Tonicity

A property of a solution relative to a cell that describes how it affects cell volume; it depends only on solutes that cannot easily cross the cell membrane.

Isotonic

A solution in which cells neither swell nor shrink when immersed because there is no osmotic pressure difference between the cell interior and the extracellular solution.

Hypotonic

A solution that causes cells to swell because water enters the cells due to the extracellular fluid having a lower effective solute concentration.

Hypertonic

A solution that causes cells to shrink because water leaves the cells due to the extracellular fluid having a higher effective solute concentration.

Albumin

The primary plasma protein responsible for generating oncotic pressure to help maintain intravascular fluid volume.

Edema

Tissue swelling that can result from a decrease in blood oncotic pressure (e.g., due to liver failure or protein-losing enteropathy), leading to fluid leaving the vessels.

Maintenance of Osmotic Balance

Cells maintain an osmolarity of approximately $290-300\,\text{mOsm/L}$ as water continually moves between intracellular and extracellular fluid.