What happens when tissue is cooled below -40°C?

When tissue is cooled below -40°C, ice formation occurs both inside and outside the cell. This phenomenon is known as intracellular and extracellular freezing. At such low temperatures, the tissue's water content begins to freeze rapidly, leading to the formation of ice crystals.

Ice formation occurs in the extracellular space initially, as this space tends to cool faster due to the direct exposure to the cooling environment. However, as the temperature continues to drop, the intracellular fluid also begins to freeze. The formation of ice crystals inside the cell can cause considerable damage to cellular structures, including membranes, organelles, and overall cellular integrity.

This dual formation of ice can lead to a range of cellular injuries, including osmotic imbalances, mechanical disruption from ice crystal growth, and potential necrosis. Understanding this process is critical in fields like cryobiology and medical treatments involving extreme cooling, such as cryotherapy, where both the formation of ice and the effects on surrounding tissues need careful management.