Chapter 4 of 5 - Integumentary System Course
The skin's appendages - hair, nails, and glands - are accessory structures that originate in the epidermis but extend into the dermis and even the hypodermis.
Hair is found on nearly every body surface except the palms, soles, lips, and parts of the external genitalia. Each hair grows from a hair follicle - a tube-like invagination of the epidermis that extends into the dermis.
| Part | Description |
|---|---|
| Hair shaft | Visible part above the skin surface (dead keratinized cells) |
| Hair root | Portion embedded in the follicle below the skin |
| Hair bulb | Expanded base containing the matrix (growth zone) and melanocytes |
| Dermal papilla | Connective tissue at the base supplying blood to the hair bulb |
| Arrector pili | Smooth muscle that contracts to produce "goosebumps" |
Anagen
Active growth (2-7 years)
Catagen
Regression (2-3 weeks)
Telogen
Resting & shedding (~3 months)
About 85-90% of scalp hairs are in the anagen phase at any time. Humans normally shed 50-100 hairs per day as follicles cycle through telogen and restart anagen.
Quick Check
What muscle causes 'goosebumps' when it contracts?
Nails are hard, keratinized plates that protect the dorsal tips of fingers and toes and help with fine manipulation (picking up small objects, scratching):
| Structure | Description |
|---|---|
| Nail plate | Visible hard keratin surface |
| Nail bed | Skin beneath the nail plate (pink due to capillaries) |
| Nail matrix | Growth zone under the proximal nail fold (produces the nail) |
| Lunula | White crescent at the nail base (visible part of the matrix) |
| Cuticle (eponychium) | Fold of skin overlapping the proximal nail edge |
Fingernails grow about 3 to 4 mm per month. Toenails grow more slowly (about 1 mm per month). A completely lost fingernail takes roughly 6 months to regrow, while a toenail takes 12 to 18 months.
Fill in the Blank
The white crescent visible at the base of the nail is called the________, which is the visible portion of the nail matrix.
The skin contains several types of exocrine glands that serve different functions:
| Gland Type | Secretion | Location | Function |
|---|---|---|---|
| Eccrine sweat | Watery sweat (99% water) | Entire body (densest on palms, soles) | Thermoregulation, excretion |
| Apocrine sweat | Thicker, lipid-rich secretion | Axillae, groin, areolae | Active at puberty; bacteria cause body odor |
| Sebaceous | Sebum (oily secretion) | Associated with hair follicles | Lubricates hair and skin; antimicrobial |
| Ceruminous | Cerumen (earwax) | External ear canal | Traps debris; antimicrobial |
Quick Check
Which type of sweat gland is primarily responsible for thermoregulation?
Fill in the Blank
Sebaceous glands secrete an oily substance called________that lubricates the skin and hair while also providing a mild antimicrobial barrier.
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