Which type of solution pulls fluid into the vascular space by osmosis?

The correct answer is that hypertonic solutions pull fluid into the vascular space by osmosis. Hypertonic solutions contain a higher concentration of solutes compared to the fluid within the vascular system. When hypertonic solutions are administered, the increased solute concentration in the vascular space creates an osmotic gradient that draws water from surrounding tissues and cells into the bloodstream. This process helps to expand the intravascular volume and can be particularly useful in clinical scenarios such as treating hyponatremia or managing fluid resuscitation.

In contrast, isotonic solutions maintain a balance with the body's plasma and do not create a significant osmotic gradient that would draw fluid in or out of the vascular space. Hypotonic solutions have a lower concentration of solutes than body fluids, which can lead to fluid movement from the vascular compartment into the cells, potentially causing cellular swelling. Colloidal solutions contain larger molecules, like proteins, that can also help maintain blood volume but function differently than hypertonic solutions in terms of fluid movement and osmosis.