Final answer:
The nail matrix is the part of the nail that won't grow back once destroyed. It is responsible for the continuous growth of the nail by producing new cells. Severe damage to the nail matrix results in irreversible nail loss or disfigurement.
Step-by-step explanation:
Once destroyed, the part of the nail that won't grow back is the nail matrix. The nail matrix is a deep layer of living epidermal tissues located at the proximal end of the nail. It contains stem cells that divide to produce new cells for nail growth, forming the nail root and eventually the nail plate. If the nail matrix is severely damaged or destroyed, it cannot regenerate, leading to permanent nail loss or disfigurement.
The nail plate is the portion of the nail that is visible and external to the skin, and although composed of densely packed dead keratinocytes, it continues to grow outward as new cells are formed at the matrix. However, only the parts of the nail made from living cells, such as the nail matrix, possess the ability to grow back after an injury.