What is the Difference between Isotonic, Hypertonic and Hypotonic Solutions?

Nursing BFFSeptember 17, 20232 Mins read

Hey BFF! Today, I’m going to talk about one of my favorite topics: Tonicity. Tonicity is the ability of a solution to cause water movement across a membrane. Sounds exciting, right? Well, it is, especially if you’re a cell. Depending on the tonicity of the solution you’re in, you could either swell up like a balloon, shrivel like a raisin, or stay just the same. Let me explain.

There are three types of solutions based on their tonicity: isotonic, hypotonic, and hypertonic. Isotonic solutions have the same solute concentration as the inside of the cell. This means that water molecules move in and out of the cell at the same rate, and there is no net change in cell volume or shape. This is the ideal situation for most cells, because they like to maintain a constant internal environment. Think of isotonic solutions as the Goldilocks of tonicity: not too much, not too little, just right.

Hypotonic solutions have a lower solute concentration than the inside of the cell. This means that water molecules move into the cell faster than they move out, and there is a net gain of water in the cell. This causes the cell to swell up and possibly burst. This is bad news for animal cells, which don’t have a cell wall to protect them from bursting. Think of hypotonic solutions as the soda of tonicity: too much sugar, too much water, too much pressure.

Hypertonic solutions have a higher solute concentration than the inside of the cell. This means that water molecules move out of the cell faster than they move in, and there is a net loss of water from the cell. This causes the cell to shrink and shrivel. This is also bad news for animal cells, which need water to function properly. Think of hypertonic solutions as the saltwater of tonicity: too much salt, too little water, too dry.

A solution is hypertonic when it has a higher concentration of solutes than the fluid inside the cells. A solution is hypotonic when it has a lower concentration of solutes than the fluid inside the cells. Solutes are substances that are dissolved in a liquid, such as salt or sugar. When an IV hypertonic solution is administered to a patient, water will move out of the cells and into the blood vessels to balance the solute concentration. This means that the fluid will shift from intracellular to extracellular, which is option a. Option b is incorrect because water will not move into the cells. Option c is incorrect because water will not move from the blood vessels to the cells. Option d is incorrect because water will not move from the blood vessels to the spaces between the cells.

So, how do cells cope with different tonicity? Well, some cells have special adaptations that allow them to survive in extreme environments. For example, some bacteria have pumps that can expel excess water or solutes from their cytoplasm. Some plants have vacuoles that can store or release water depending on the external conditions. Some animals have kidneys that can regulate the osmolarity of their blood and urine.

But for most cells, the best way to deal with tonicity is to avoid it altogether. That’s why cells try to stay in isotonic solutions as much as possible, or create isotonic environments around themselves by secreting or absorbing solutes. That way, they can keep their water balance and shape intact.

I hope you enjoyed this blog post about tonicity. If you want to learn more about this topic, you can check out these links:

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/a/osmosis
https://biologydictionary.net/isotonic-vs-hypotonic-vs-hypertonic-solution/
https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/hypotonic-isotonic-and-hypertonic-solutions-tonicity
https://nurseslabs.com/iv-fluids/