Crenation is a phenomenon which occurs when cells of animal origin are exposed to a hypertonic solution, meaning that the solution which bathes the cells has a high concentration of solutes. In crenation, the cells shrink and their shapes become distorted, often with a ruffled or scalloped edge. The change in cell shape can be seen in microscopy of the cells, and can be a sign that someone is experiencing a medical problem. Crenated cells may die as a result of impairments in cell function.

When animal cells are bathed in a hypertonic solution, it draws water out of the cells through a process known as osmosis. Water flows from areas of low solute concentration to areas of high solute concentration in an effort to stabilize the difference between the two solutions. Sometimes, particles small enough to pass through the cell walls may be drawn out along with the water, and in other cases, they remain behind because they are too big to move through the cell membrane.

As the water leaves the cell, it starts to shrivel, since much of its shape is due to the water inside which keeps it plump. Red blood cells display the results of crenation more markedly, transitioning from a round to a spiky shape. The term “crenation” is a reference to the scalloped shape of a crenated cell. Without water, the cell will have trouble functioning.

One reason for crenation to occur is dehydration. When the body is not ingesting more water, the fluid which bathes cells can become hypertonic, rather than isotonic, in which the extracellular fluid and fluid inside the cells has the same concentration of solutes. Crenation can also be associated with some disease processes. The same process is known as plasmolysis in plant cells because the rigid cell wall prevents the cell from changing shape as water is lost.

If the solution is hypotonic, with the fluid inside the cells having a higher concentration of solutes than the fluid which surrounds the cells, water will pass through the cell wall and into the cell as a result of osmosis. If enough water is absorbed, the cell will burst and release its contents. This can be a very serious consequence of drinking large amounts of water without urinating, as the kidneys cannot keep the balance of fluids in the body stable when they cannot eliminate urine.