your lanula is showing

This one time, my toenails fell off.

My dad and I had gone on a backpacking trip and I committed the rookie mistake of not breaking in my new hiking shoes first. Also, I wore tissue-thin socks like a jerk and didn’t cut my toenails short enough. The entire first day of the hike was downhill into a valley, and by the time we set up camp, both of my big toenails were barking. By the end of the week, they began to turn blue. Flash forward a few months, and they fell off. Klink klink, right onto the floor.

Now, I’m sure you’re wondering why I shared that all-too-personal story with you. I shared it with you as an opener to today’s topic: the exciting world of keratinized structures.

Keratin is a fibrous protein, one of the three major classes of proteins. Keratin is the major protein component in hair, nails, feathers, scales, horns, and a variety of other epidermal structures found in vertebrates. Within the field of anatomy, you hear these types of structures referred to as “epidermal outgrowths.” As you can surmise, this means that they originate from the epidermal tissues and can be heavily modified for different species.

Sometimes these structures arise as a means of sexual display, like big horned sheep that butt their gigantic horns for sexual rights to females. Feathers have many functions, some of which include thermoregulation, sexual display, and flight. Hair in mammals is primarily for thermoregulation. Claws are generally for foraging and defense. Scales help to protect reptiles’ bodies like armor. How do our weird little fingernails fit in to all this?

Our nails evolved from claws. Our mammal ancestors walked on all fours and foraged with claws. As the primates began to branch off and perform dexterous tasks with their hands, claws became cumbersome. Fingernails were the evolutionary solution to this problem; they protect the supple fingertips and help to perform very tiny tasks, like removing splinters.

The nail plate is made up of several layers of dead cells, the remainders of which are almost entirely keratin. It is curved so that it covers the terminal segment of your finger in a way that protects the soft nail bed underneath from damage and impact. The lanula (the half-moon shaped thing at the base of your nail) is where live cells are that produce the nail plate.

Sometimes, as a result of traumatic impact, the nail bed is damaged so badly that it separates from the nail plate, which will eventually fall off. Luckily, that little lanula will keep on working and grow a new nail plate over the course of a few months. Trust me, I know.