Exam I | Osmosis and Tonicity Flashcards
What is osmosis?
movement of water across a semi-permiable membrane toward a higher particle concentration
Molecules may pass through a membrane according to what 4 things?
- size
- solubility
- polarity
- hydrophobicity
What is the difference between osmolality and osmolarity?
- osmolality is total number of molecules by volume
- osmolarity is total number of molecules by mass
The ability of water to pass through a membrane depends on what 2 factors?
1) concentration gradient
2) density of aquaporins (regulated by aquaporin removal or insertion into membrane)
osmolarity of a simple solution is the product of what?
- molarity
- number of particles per molecule
What is the particle and molarity ratio for glucose. What are the ratios of NaCl, MgCl2, and urea in a simple solution relative to glucose?
- glucose (1 particle, 300 mM)
- NaCl (2 particles, 150 mM)
- MgCl2 (3 particles, 100 mM)
- urea (1 particle, 300 mM)
If there is one molecule of glucose in the ECF, and one molecule of NaCl in the ICF, which way will water go and why?
- to the ICF
- water goes from areas of lower to higher particle concentration; NaCl dissociates into two particles
What is osmotic pressure?
- pressure difference necessary to oppose movement of H20 across membrane
- created by imbalance of total particle concentration across a membrane
what are the units for molarity?
mM
what are the units for osmolarity?
- mOsM
- milosmoles per L(osmolality) or Kg (osmolarity)
What is the value of physiological osmolarity?
- approx. 280-296 mOsM
- usually rounded to 300 for calculations
how does the loss of fluid volume affect the movement of water across the membrane?
does not affect
What is the difference between osmosis and tonicity?
- osmosis is the mechanism of the movement of water
- tonicity is the consequence (the shift in fluid) of the movement of water across the membrane (body compartment volume changes such as edema, whether cells swell or burst)
What should you assume is being talked about in terms of tonicity and osmolality/osmolarity?
that they are talking about the ECF particle concentration in relation to the ICF
A solution in which an RBC swells is ___ and can lead to hemolysis
hypotonic
A solution in which an RBC shrinks is called ___ and can lead to crenation
hypertonic
How is tonicity affected by penetrating and non-penetrating molecules?
- only non-penetrating molecules (molecules that cannot pass the membrane) determine movement of water and thereby tonicity
- movement of penetrating molecules does not alter fluid volume
what is the difference between hyperosmotic and hypertonic?
- hyperosmotic means higher molarity and particle concentration
- hypertonic means water is moving out of the cell in a solution
What information do you need to know in order to determine whether a solution will be hypertonic or hypotonic to a cell?
if the particles are penetrating and non-penetrating
can a solution be both hyperosmotic and isotonic? can a solution be both hyposmotic and isotonic?
- yes, in the case of glucose, because cells will consume it
- no, hyposmotic solutions are always hypotonic
What is the isotonic concentration of a saline solution (NSS) and of a dextrose-water (D5W) solution?
- 0.9%
- 5%
3 reasons IV fluids are used
1) supply essential fluid when oral hydration is impractical
2) maintain normal electrolyte (ion) levels in ECF and ICF
3) to provide metabolic fuel, usually glucose, nutrients, and drugs
what is an isotonic IV solution used for?
rehydration
What requires a hypotonic IV solution?
- severe dehydration
- can cause vascular collapse and cellular damage
What requires a hypertonic IV solution?
- hyponatremia with edema
- can cause DKA
