What does it mean when we say that a 0.15 M NaCl solution is isotonic with blood, whereas distilled water is hypotonic?

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Welcome back everyone. A lactated ringer solution is isotonic with red blood cells. While a 3% sodium chloride solution is hypertonic, which of the following statements is true. We have choices A through D which compare the osmolarity of the lactated ringer solution to the 3% sodium chloride solution is either being greater or lower or equal in osmolarity. So we're going to begin by first recalling what osmolarity is defining or defined as recall that osmolarity describes the concentration of a solution expressed as total solute particles per liter or in units of osmoles per liter where the o in osmos is a capital O. And this is important because it's in the biological and medical context used to define osmotic pressure that is exerted by a solution on either side of a semi permeable membrane. So if we visualize a cell and I'll just represent a cell by a circle, we're going to recall that for optimal cell function, A K A homeostasis, it's important to attain a balance between the external osmolarity and then a balance with the internal osmolarity of a cell. And this is important to prevent the cell from shrinking or swelling which we should recall can disrupt cellular processes and can ultimately lead to cell death. Let's recall that when we observe the cell, which is going to be shrinking, this corresponds to a hypertonic environment or solution which correspond to the solution having a higher osmolarity versus other solute particles. We can also next recall that when we observe the cell swelling and this should, should say swelling that will correspond to a hypotonic solution. So, hypotonic solution which correlates to the solution having a lower osmolarity versus the other cell U particles. And third, what we want to recall is to prevent the cell shrinkage and swelling A K a excessive water movement so that we can have cell homeostasis that would correlate to having an isotonic solution where and just to make room for what we're writing an isotonic solution would correlate to our solution and solute particles having an equal osmolarity. So based on what we've outlined and going back to the prompt, we are told that the lactated Ringer solution, we use LRS for shorthand is isotonic. And so therefore, that tells us that it has equal osmolarity as the solute being red blood cells, we're also given from the prompt that the sodium chloride solution is hypertonic. And so thus, the sodium chloride solution therefore has a greater osmolarity than the red blood cells. So based on what we've outlined, we would rule out choice a which states that the lactated ringer solution has a lower osmolarity, we know that it should be equal with the red blood cells. We can also rule out choice B which states that the lactated ringer solution has a greater osmolarity as the red blood cells, we know that it should be equal. And we can also rule out choice D which states that the lactated ringer solution has the same osmolarity has red blood cells, which is correct. But then it continues to say that the 3% sodium chloride solution has a lower osmolarity than the red blood cells. And based on the prompt, the sodium chloride solution is hypertonic. So it has a greater osmolarity than the intracellular fluid of the red blood cells. So choice D is also incorrect and that leaves us with choice C as the only true and correct statement where our final answer will be choice C which states that the lactated ringer solution has the same osmolarity as red blood cells. While the 3% sodium chloride solution has greater osmolarity and this is our final answer. So I hope this made sense and let us know if you have any questions.

What does it mean when we say that a 0.15 M NaCl solution is isotonic with blood, whereas distilled water is hypotonic?

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Key Concepts

Isotonic Solutions

Hypotonic Solutions

Osmosis