MCAT® ExamBiological and Biochemical Foundations of Living SystemsEasy
A patient is admitted to the emergency room with severe dehydration. To rapidly restore blood volume and electrolyte balance, medical personnel administer an intravenous (IV) solution that has a solute concentration equal to that of the patient's blood plasma. This type of solution is best described as:
- AColloidal
- BHypotonic
- CHypertonic
- DIsotonic
Show answer & explanationAnswer & explanation
Correct answer: D. Isotonic
An isotonic solution has the same solute concentration (osmolarity) as the body's fluids, such as blood plasma. When administered intravenously, it helps to expand blood volume without causing fluid shifts into or out of cells, which is crucial for rehydration.
Why the other options are wrong
- A. A colloidal solution contains large molecules that do not readily pass through capillary membranes but it refers to the composition, not the tonicity relative to cells.
- B. A hypotonic solution has a lower solute concentration and would cause water to move into cells, potentially causing hemolysis.
- C. A hypertonic solution has a higher solute concentration and would cause water to move out of cells, leading to crenation and further dehydration of cells.
Isotonic Solution
An isotonic solution is one that has the same solute concentration (osmolarity) as another solution, typically the intracellular fluid or blood plasma. In an isotonic environment, cells neither gain nor lose water.
- Same solute concentration as bodily fluids.
- No net movement of water across cell membranes.
- Used to expand blood volume without causing cell lysis or crenation.
- Examples include 0.9% NaCl (normal saline) and Lactated Ringer's solution.
Memory trick: Isotonic: 'Is' the 'Same' concentration, 'Stay' in shape.