Exam I | Osmosis and Tonicity

Question 1

What is osmosis?

Answer 1

movement of water across a semi-permiable membrane toward a higher particle concentration

Question 2

Molecules may pass through a membrane according to what 4 things?

Answer 2

• size
• solubility
• polarity
• hydrophobicity

Question 3

What is the difference between osmolality and osmolarity?

Answer 3

• osmolality is total number of molecules by volume

- osmolarity is total number of molecules by mass

Question 4

The ability of water to pass through a membrane depends on what 2 factors?

Answer 4

1) concentration gradient

2) density of aquaporins (regulated by aquaporin removal or insertion into membrane)

Question 5

osmolarity of a simple solution is the product of what?

Answer 5

• molarity

- number of particles per molecule

Question 6

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?

Answer 6

• glucose (1 particle, 300 mM)
• NaCl (2 particles, 150 mM)
• MgCl2 (3 particles, 100 mM)
• urea (1 particle, 300 mM)

Question 7

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?

Answer 7

• to the ICF

- water goes from areas of lower to higher particle concentration; NaCl dissociates into two particles

Question 8

What is osmotic pressure?

Answer 8

• pressure difference necessary to oppose movement of H20 across membrane
• created by imbalance of total particle concentration across a membrane

Question 9

what are the units for molarity?

Answer 9

mM

Question 10

what are the units for osmolarity?

Answer 10

• mOsM

- milosmoles per L(osmolality) or Kg (osmolarity)

Question 11

What is the value of physiological osmolarity?

Answer 11

• approx. 280-296 mOsM

- usually rounded to 300 for calculations

Question 12

how does the loss of fluid volume affect the movement of water across the membrane?

Answer 12

does not affect

Question 13

What is the difference between osmosis and tonicity?

Answer 13

• 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)

Question 14

What should you assume is being talked about in terms of tonicity and osmolality/osmolarity?

Answer 14

that they are talking about the ECF particle concentration in relation to the ICF

Question 15

A solution in which an RBC swells is ___ and can lead to hemolysis

Answer 15

hypotonic

Question 16

A solution in which an RBC shrinks is called ___ and can lead to crenation

Answer 16

hypertonic

Question 17

How is tonicity affected by penetrating and non-penetrating molecules?

Answer 17

• 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

Question 18

what is the difference between hyperosmotic and hypertonic?

Answer 18

• hyperosmotic means higher molarity and particle concentration
• hypertonic means water is moving out of the cell in a solution

Question 19

What information do you need to know in order to determine whether a solution will be hypertonic or hypotonic to a cell?

Answer 19

if the particles are penetrating and non-penetrating

Question 20

can a solution be both hyperosmotic and isotonic? can a solution be both hyposmotic and isotonic?

Answer 20

• yes, in the case of glucose, because cells will consume it
• no, hyposmotic solutions are always hypotonic

Question 21

What is the isotonic concentration of a saline solution (NSS) and of a dextrose-water (D5W) solution?

Answer 21

• 0.9%

- 5%

Question 22

3 reasons IV fluids are used

Answer 22

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

Question 23

what is an isotonic IV solution used for?

Answer 23

rehydration

Question 24

What requires a hypotonic IV solution?

Answer 24

• severe dehydration

- can cause vascular collapse and cellular damage

Question 25

What requires a hypertonic IV solution?

Answer 25

• hyponatremia with edema

- can cause DKA