5.3C: Nails
Fingernails are made of keratin and they perform two major functions: protection and sensation.
LEARNING OBJECTIVE
Describe the structure of fingernails
Key Takeaways
Key Points
- The nail bed contains the blood vessels, nerves, and melanocytes or melanin-producing cells. As the nail is produced by the root, it streams down along the nail bed, which adds material to the undersurface of the nail and makes it thicker.
- The nail plate is the actual fingernail, composed of translucent keratin. The pink appearance of the nail comes from the blood vessels underneath the nail.
- The eponychium, or cuticle, is situated between the skin of the finger and the nail plate. It fuses these structures together and provides a waterproof barrier.
- Deformity or disease of the nails is referred to as onychosis. There are many diseases that can occur with the fingernails and toenails. The most common of these diseases are ingrown nails and fungal infections.
- Ingrown nails, also known as onychocryptosis, can affect either the fingers or the toes. In this condition, the nail cuts into one or both sides of the nail bed, resulting in inflammation and possibly infection.
Key Term
- keratin : A protein that makes up hair and nails.
Function of the Fingernail
The fingernail is an important structure made of keratin. The fingernail generally serves two purposes: it acts as a protective plate and enhances sensation of the fingertip. Nails can also help grasp small things.
The protection function of the fingernail is commonly known, but the sensation function is equally important. The fingertip has many nerve endings in it that allow it to receive volumes of information about the objects we touch. The nail acts as a counterforce to the fingertip, providing even more sensory input when an object is touched.
Nails grow from the nail bed continuously but they slow down their growth rate with age, poor nutrition, or poor circulation.
Anatomy of the Fingernail
The structure of the fingernail is divided into six specific parts:
- root
- nail bed
- nail plate
- eponychium (cuticle)
- perionychium
- hyponychium
Root and Nail Sinus
The nail sinus (sinus unguis) is where the nail root is—at the base of the nail underneath the skin. It originates from the actively growing tissue below, the matrix. The root of the fingernail is also known as the germinal matrix.
This portion of the nail is actually beneath the skin, behind the fingernail, and extends several millimeters into the finger. The fingernail root produces most of the volume of the nail and the nail bed. This portion of the nail does not have any melanocytes, or melanin-producing cells. The edge of the germinal matrix is seen as a white, crescent shaped structure called the lunula.
Nail Bed
The nail bed is a part of the nail matrix called the sterile matrix. It extends from the edge of the germinal matrix, or lunula, to the hyponychium. The nail bed contains the blood vessels, nerves, and melanocytes, or melanin-producing cells. As the nail is produced by the root, it streams down along the nail bed, which adds material to the undersurface of the nail and makes it thicker.
Nail Plate
The nail plate is the actual fingernail, composed of translucent keratin. The pink appearance of the nail comes from the blood vessels underneath the nail. The underneath surface of the nail plate has grooves along the length of the nail that help anchor it to the nail bed. The free margin or distal edge is the anterior margin of the nail plate corresponding to the abrasive or cutting edge of the nail.
Eponychium
The eponychium, or cuticle, is situated between the skin of the finger; the nail plate fuses these structures together and provides a waterproof barrier.
Perionychium
The perioncyhium is the skin that overlies the nail plate on its sides; it is also known as the paronychial edge. The perionychium is the site of hangnails, ingrown nails, and an infection of the skin called paronychia.
Hyponychium
The hyponychium is the area between the nail plate and the fingertip. It is the junction between the free edge of the nail and the skin of the fingertip, also providing a waterproof barrier.