Question
Describes what happens when an RBC of 300 mOsM internal concentration is placed in the following solutions:
a)
300
mOsM
Np
solutes
200 mOsM urea
Solution is _____osmotic and _____tonic
Does the cell gain or lose volume?
b)
300
mOsM
Np
solutes
200 mOsM urea +
100mOsM NaCl
Solution is ___osmotic and _____tonic
Does the cell gain or lose volume?
c)
300
mOsM
NP
solutes
300 mOsM NaCl +
300 mOsM urea
Solution is ___osmotic and ____
d)
300
mOsM
NP
solutes
100 mOsM urea +
350 mOsM NaCl
Solution is _____osmotic and _____tonic
Does the cell gain or lose volume?
*Notice that to "distribute the urea evenly" you did not put half into each compartment. The amount that goes into each compartment is based on the VOLUME of the compartment.*
Explanation / Answer
a) If an RBC of 300 mOsM internal concentration is placed in solutes with 200 mOsM urea, the solution is isoosmotic and isotonic. The cell gain volume and swells because the effective osmolarity is less than 300 mOsM of RBC. ----------------------------------------------------------------------------------------------------- b) If an RBC of 300 mOsM internal concentration is placed in solutes with 200 mOsM urea + 100 NaCl, the solution is hypoosmotic and hypotonic. The cell gain volume and swells because the effective osmolarity is less than 300. Here urea will diffuse across the membrane and equalize its concentration in the two compartments. Therefore, it will not contribute to effective osmolarity. ----------------------------------------------------------------------------------------------------- c) If an RBC of 300 mOsM internal concentration is placed in solutes with 300 mOsM NaCl + 300 mOsM Urea, the solution will be isosomotic and isotonic saline. The cell gain volume and swells. ------------------------------------------------------------------------------------------------------- d) If an RBC of 300 mOsM internal concentration is placed in solutes with 100 mOsM Urea + 350 NaCl, the solution is hyperosmotic and hypertonic. The cell shrinks in hypertonic saline solution. The effective osmolarity is more than 300 mOsM of the cell. So, the cell shrinks.