Accessory structures of the skin include hair, nails, sweat glands, and sebaceous glands. Hair is made of dead keratinized cells, and gets its color from melanin pigments. Nails, also made of dead keratinized cells, protect the extremities of our fingers and toes from mechanical damage. Sweat glands and sebaceous glands produce sweat and sebum, respectively. Each of these fluids has a role to play in maintaining homeostasis. Sweat cools the body surface when it gets overheated and helps excrete small amounts of metabolic waste. Sebum acts as a natural moisturizer and keeps the dead, flaky, outer keratin layer healthy.
1. The appendages of the skin include hair, nails, sebaceous glands, ceruminous or wax glands, and sweat glands.
Covers the entire body except the palms of the hands, the soles of the feet, and parts of the external genitalia.
Each individual hair is made of three parts: the outer cuticle, the cortex, which is the principal portion with pigment granules, and the inner medulla with air spaces.
The visible portion of a hair is called the shaft. The root of a hair is in a hair follicle.
When the arrector pili smooth muscle contracts, it causes a hair to stand on end and causes “goose flesh.”
Begins deep in the hair follicle at the hair bulb growing by mitosis and nourished by blood vessels.
Grows and rests in cycles.
Classified as straight, curly, or tightly curly, and is due to genetic factors.
Hair in the alpha keratin chain is elastic; when stretched, it is in the beta keratin chain.
determined by complex genetic factors; heredity and other unknown factors cause graying
Gray hair - pigment is absent in the cortex
White hair - both pigment and air bubbles in the shaft absent
Modification of epidermal cells made of very hard keratin.
Lunula is the white crescent at the proximal end of a nail caused by air mixed with the keratin.
Nail body is the visible portion of a nail. The nail root is the part covered by skin.
The nail grows from the nail bed.
The cuticle is stratum corneum that extends over the nail body.
Produce sebum, found along the walls of hair follicles
Sebum, an oil, gives a cosmetic gloss to skin and moisturizes it
Secretion controlled by the endocrine system; increases in puberty and late pregnancy; decreases with age
Most numerous in the palms of our hands and in the soles of our feet
Secretory, blind tube portion is in the subcutaneous tissue
Excretory portion goes through the dermis to the surface.
Odor of sweat is produced by the action of bacteria feeding on the sweat.
Sweating is an important physiologic process that helps cool the body.
anagen
active phase of the hair growth cycle
apocrine sweat gland
type of sweat gland that is associated with hair follicles in the armpits and genital regions
arrector pili
smooth muscle that is activated in response to external stimuli that pull on hair follicles and make the hair “stand up”
catagen
transitional phase marking the end of the anagen phase of the hair growth cycle
cortex
in hair, the second or middle layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb
cuticle
in hair, the outermost layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb
eccrine sweat gland
type of sweat gland that is common throughout the skin surface; it produces a hypotonic sweat for thermoregulation
eponychium
nail fold that meets the proximal end of the nail body, also called the cuticle
external root sheath
outer layer of the hair follicle that is an extension of the epidermis, which encloses the hair root
glassy membrane
layer of connective tissue that surrounds the base of the hair follicle, connecting it to the dermis
hair
keratinous filament growing out of the epidermis
hair bulb
structure at the base of the hair root that surrounds the dermal papilla
hair follicle
cavity or sac from which hair originates
hair matrix
layer of basal cells from which a strand of hair grows
hair papilla
mass of connective tissue, blood capillaries, and nerve endings at the base of the hair follicle
hair root
part of hair that is below the epidermis anchored to the follicle
hair shaft
part of hair that is above the epidermis but is not anchored to the follicle
hyponychium
thickened layer of stratum corneum that lies below the free edge of the nail
internal root sheath
innermost layer of keratinocytes in the hair follicle that surround the hair root up to the hair shaft
lunula
basal part of the nail body that consists of a crescent-shaped layer of thick epithelium
medulla
in hair, the innermost layer of keratinocytes originating from the hair matrix
nail bed
layer of epidermis upon which the nail body forms
nail body
main keratinous plate that forms the nail
nail cuticle
fold of epithelium that extends over the nail bed, also called the eponychium
nail fold
fold of epithelium at that extend over the sides of the nail body, holding it in place
nail root
part of the nail that is lodged deep in the epidermis from which the nail grows
sebaceous gland
type of oil gland found in the dermis all over the body and helps to lubricate and waterproof the skin and hair by secreting sebum
sebum
oily substance that is composed of a mixture of lipids that lubricates the skin and hair
sudoriferous gland
sweat gland
telogen
resting phase of the hair growth cycle initiated with catagen and terminated by the beginning of a new anagen phase of hair growth
1. In response to stimuli from the sympathetic nervous system, the arrector pili ________.
A) are glands on the skin surface
B) can lead to excessive sweating
C) are responsible for goose bumps
D) secrete sebum
C
2. The hair matrix contains ________.
A) the hair follicle
B) the hair shaft
C) the glassy membrane
D) a layer of basal cells
D
3. Eccrine sweat glands ________.
A) are present on hair
B) are present in the skin throughout the body and produce watery sweat
C) produce sebum
D) act as a moisturizer
B
4. Sebaceous glands ________.
A) are a type of sweat gland
B) are associated with hair follicles
C) may function in response to touch
D) release a watery solution of salt and metabolic waste
B
5. Similar to the hair, nails grow continuously throughout our lives. Which of the following is furthest from the nail growth center?
A) nail bed
B) hyponychium
C) nail root
D) eponychium
B
1. Explain the differences between eccrine and apocrine sweat glands.
Eccrine sweat glands are all over the body, especially the forehead and palms of the hand. They release a watery sweat, mixed with some metabolic waste and antibodies. Apocrine glands are associated with hair follicles. They are larger than eccrine sweat glands and lie deeper in the dermis, sometimes even reaching the hypodermis. They release a thicker sweat that is often decomposed by bacteria on the skin, resulting in an unpleasant odor.
2. Describe the structure and composition of nails.
Nails are composed of densely packed dead keratinocytes. They protect the fingers and toes from mechanical stress. The nail body is formed on the nail bed, which is at the nail root. Nail folds, folds of skin that overlap the nail on its side, secure the nail to the body. The crescent-shaped region at the base of the nail is the lunula.