Integumentary Accessory Structures: Nails

Within the integumentary system, four main accessory structures aid in thermoregulation, sense of touch, protection, and much more. These four main accessory structures are:

  1. Hair Follicles
  2. Nails
  3. Sebaceous Glands
  4. Sweat Glands

The nails can be found on the tips of your toes and fingers. The main function of these structures is to protect these areas from damage and the surrounding environment. They also function as a tool and aid in gripping things for picking them up, climbing, and most other things you do with your fingers.

The structure of your nail has two major parts, the area that is below the skin and the area above (visible). On the most distal portion of the finger, you have the free edge. This is the white area of the nail that is usually cut. This is the weakest part of the nail and can be broken or damaged very easily. Where the free edge meets the finger you have the hyponychium. The hyponychium is an area of skin that connects to the bottom of the free edge. The purpose of this structure is to prevent harmful things from entering the nail bed (germs, debris, etc.)

The major part of the external surface of your nail is called the nail body. It is sometimes referred to as corpus unguis and the nail plate. The nail body is the part of the nail that ranges from the free edge to the skin where your nail begins. This nail body is made of a specific type of keratin that makes it translucent as well as layers of dead cells that makes it strong and flexible.

Below the nail body is the nail bed. The nail bed functions to support the nail body during growth. The nail bed is made of tissues such as the hyponychium and the onychondermal. The onychondermal is the strongest attachment point between your nail and the underlying tissue. Both the onychondermal and hyponychium function for attachment and protection against pathogens and the surrounding environment.

The area that is at the base of the nail body is called the lunula. This structure is usually lighter and more white in color. It is also described as a half-crescent moon. The function of the lunula is to provide a defining change in structure between the nail edge and the root. Having a lunula usually means that your root matrix is working properly and well.

At the lateral edges of the nail body, where the nail meets your skin, the lateral nail fold begins. The lateral nail fold functions to aid in the protection of the finger on the lateral edges as well as aid in guiding the proper growth of the nail.

The area where the lunula meets the proximal nail fold is called the eponychium. This structure functions similarly to the hyponychium. It seals the passageway that would be present into the proximal nail fold and into the nail plate. This functions to prevent diseases, pathogens, and other harmful debris from entering parts of the nail that can become infected.

The proximal nail fold works in combination with the eponychium to prevent debris from entering the nail plate. It also functions similar to the lateral nail folds to guide and support nail growth. Finally, the nail fold protects the nail root and matrix that is present below this area.

The nail root is located within the epidermis several millimeters below the surface. The nail root place at which most of the nail is produced and where growth begins.