Integumentary Growth

Fingernails and toenails are clear, hard derivatives of the stratum corneum. They are composed of very thin, dead, scalelike cells, densely packed together and filled with parallel fibers of hard keratin. Most mammals have claws, whereas flat nails are one of the distinguishing characteristics of primates. Flat nails allow for more fleshy and sensitive fingertips, while they also serve as strong keratinized "tools" that can be used for digging, grooming, picking apart food, and other manipulations. Fingernails grow at a rate of about 1 mm per week and toenails somewhat more slowly. New cells are added to the nail plate by mitosis in the nail matrix at its proximal end. Contrary to some advertising claims, adding gelatin to the diet has no effect on the growth or hardness of the nails.

Saladin: Anatomy & I 6. The Integumentary I Text I I © The McGraw-Hill

Physiology: The Unity of System Companies, 2003 Form and Function, Third Edition

Chapter 6 The Integumentary System 205

Physiology For Integumentary System

Figure 6.10 Anatomy of a Fingernail.

Chapter 6 The Integumentary System 205

Nail Bed

The skin on which the nail plate rests

Nail Plate

The clear, keratinized portion of a nail

Root

The proximal end of a nail, underlying the nail fold

Body

The major portion of the nail plate, overlying the nail bed

Free Edge

The portion of the nail plate that extends beyond the end of the digit

Hyponychium3

The epithelium of the nail bed

Nail Fold

The fold of skin around the margins of the nail plate

Nail Groove

The groove where the nail fold meets the nail plate

Eponychiumb

Dead epidermis that covers the proximal end of the nail; commonly called the cuticle

Nail Matrix

The growth zone (mitotic tissue) at the proximal end of the nail, corresponding to the stratum basale of the epidermis

Lunulec

The region at the base of the nail that appears as a small white crescent because it overlies a thick stratum basale that obscures dermal blood vessels from view

ahypo = under + onych = nail bep = above + onych = nail clun = moon + ule = little ahypo = under + onych = nail bep = above + onych = nail clun = moon + ule = little

Figure 6.10 Anatomy of a Fingernail.

The anatomical features of a nail are shown in figure 6.10. The most important of these are the aforementioned nail matrix, a growth zone concealed beneath the skin at the proximal edge of the nail, and the nail plate, which is the visible portion covering the fingertip. The nail groove and the space beneath the free edge accumulate dirt and bacteria and require special attention when scrubbing for duty in an operating room or nursery. The appearance of the nails can be valuable to medical diagnosis. An iron deficiency, for example, may cause the nails to become flat or concave (spoonlike) rather than convex. The nails and fingertips become clubbed in conditions of long-term hypoxemia—deficiency of oxygen in the blood—resulting from congenital heart defects and other causes.

Before You Go On

Answer the following questions to test your understanding of the preceding section:

8. What is the difference between vellus and terminal hair?

9. State the function of the hair papilla, hair receptors, and piloerector.

10. Describe what happens in the anagen, catagen, and telogen phases of the hair cycle.

11. State a reasonable theory for the different functions of hair of the eyebrows, eyelashes, scalp, nostrils, and axilla.

12. Define or describe the nail plate, nail fold, eponychium, hyponychium, and nail matrix.

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Essentials of Human Physiology

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Responses

  • hildifons brown
    What is the integumentary system?
    6 years ago
  • fraser
    Is the nail bed the growth zone of the nail that corresponds to the stratum basal of the epidermis?
    4 years ago

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