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The nail plate is the part of the finger or toenail that forms a hard, protective layer at the end of each digit. It is made of keratin and grows from its base, at the nail root, towards the end of the finger or toe. Made up of entirely dead cells, the nail is embedded onto living tissue at the sides, and grows over the living tissue of the nail bed beneath it. Humans and other primates have nail plates, while other animals often have similar structures such as claws or hooves, which grow in the same manner and are formed out of the same material.
The nail plate stretches from the nail root in the middle of the last joint of each digit towards the digit's tip. The nail root is formed by a fold in the skin, and it is from here that cells are deposited onto the nail plate. Nails can be regrown if they are pulled out as long as the nail bed is not damaged. In humans it takes about four weeks for a nail to regrow from the bed to the tip of the digit.
The cells in the nail plate are transparent in the part of the nail that stretches across the living tissue of the nail bed but whiten in the part of the nail that stretches beyond the bed. The apparent color of a nail comes from the tissue in the bed beneath it. The nail plate and bed are not attached, making it possible for the nail to grow across this surface from the nail root to the tip of the finger or toe.
Ridges on the underside of the nail hold it in place and keep it from slipping off. These ridges form a loose connection between the nail plate and the nail bed. The nail plate is also not attached to the sides or tip of the finger or toe, though there are folds of skin that form barriers around these edges to prevent microbes from entering the body through the spaces around the nails.
The primary material in the nail plate is known as keratin. This material is a type of protein that contains many fibers, making it strong and resilient. It is also the primary component of hair, fur, and the outer layer of skin in all animals. Cells that have been keratinized, or infused with long strands of keratin, stop metabolizing. Thus, any cell that has completed this process is no longer living, though it may still serve a valuable purpose in the body.