Key Terms
acne
skin condition due to infected sebaceous glands
albinism
genetic disorder that affects the skin, in which there is no melanin production
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”
basal cell
type of stem cell found in the stratum basale and in the hair matrix that continually undergoes cell division, producing the keratinocytes of the epidermis
basal cell carcinoma
cancer that originates from basal cells in the epidermis of the skin
bedsore
sore on the skin that develops when regions of the body start necrotizing due to constant pressure and lack of blood supply; also called decubitis ulcers
callus
thickened area of skin that arises due to constant abrasion
catagen
transitional phase marking the end of the anagen phase of the hair growth cycle
corn
type of callus that is named for its shape and the elliptical motion of the abrasive force
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
dermal papilla
(plural = dermal papillae) extension of the papillary layer of the dermis that increases surface contact between the epidermis and dermis
dermis
layer of skin between the epidermis and hypodermis, composed mainly of connective tissue and containing blood vessels, hair follicles, sweat glands, and other structures
desmosome
structure that forms an impermeable junction between cells
eccrine sweat gland
type of sweat gland that is common throughout the skin surface; it produces a hypotonic sweat for thermoregulation
eczema
skin condition due to an allergic reaction, which resembles a rash
elastin fibers
fibers made of the protein elastin that increase the elasticity of the dermis
eleiden
clear protein-bound lipid found in the stratum lucidum that is derived from keratohyalin and helps to prevent water loss
epidermis
outermost tissue layer of the skin
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
first-degree burn
superficial burn that injures only the epidermis
fourth-degree burn
burn in which full thickness of the skin and underlying muscle and bone is damaged
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
hypodermis
connective tissue connecting the integument to the underlying bone and muscle
hyponychium
thickened layer of stratum corneum that lies below the free edge of the nail
integumentary system
skin and its accessory structures
internal root sheath
innermost layer of keratinocytes in the hair follicle that surround the hair root up to the hair shaft
keloid
type of scar that has layers raised above the skin surface
keratin
type of structural protein that gives skin, hair, and nails its hard, water-resistant properties
keratinocyte
cell that produces keratin and is the most predominant type of cell found in the epidermis
keratohyalin
granulated protein found in the stratum granulosum
Langerhans cell
specialized dendritic cell found in the stratum spinosum that functions as a macrophage
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
Meissner corpuscle
(also, tactile corpuscle) receptor in the skin that responds to light touch
melanin
pigment that determines the color of hair and skin
melanocyte
cell found in the stratum basale of the epidermis that produces the pigment melanin
melanoma
type of skin cancer that originates from the melanocytes of the skin
melanosome
intercellular vesicle that transfers melanin from melanocytes into keratinocytes of the epidermis
Merkel cell
receptor cell in the stratum basale of the epidermis that responds to the sense of touch
metastasis
spread of cancer cells from a source to other parts of the body
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
Pacinian corpuscle
(also, lamellated corpuscle) receptor in the skin that responds to vibration
papillary layer
superficial layer of the dermis, made of loose, areolar connective tissue
reticular layer
deeper layer of the dermis; it has a reticulated appearance due to the presence of abundant collagen and elastin fibers
rickets
disease in children caused by vitamin D deficiency, which leads to the weakening of bones
scar
collagen-rich skin formed after the process of wound healing that is different from normal skin
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
second-degree burn
partial-thickness burn that injures the epidermis and a portion of the dermis
squamous cell carcinoma
type of skin cancer that originates from the stratum spinosum of the epidermis
stratum basale
deepest layer of the epidermis, made of epidermal stem cells
stratum corneum
most superficial layer of the epidermis
stratum granulosum
layer of the epidermis superficial to the stratum spinosum
stratum lucidum
layer of the epidermis between the stratum granulosum and stratum corneum, found only in thick skin covering the palms, soles of the feet, and digits
stratum spinosum
layer of the epidermis superficial to the stratum basale, characterized by the presence of desmosomes
stretch mark
mark formed on the skin due to a sudden growth spurt and expansion of the dermis beyond its elastic limits
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
third-degree burn
burn that penetrates and destroys the full thickness of the skin (epidermis and dermis)
vitamin D
compound that aids absorption of calcium and phosphates in the intestine to improve bone health
vitiligo
skin condition in which melanocytes in certain areas lose the ability to produce melanin, possibly due an autoimmune reaction that leads to loss of color in patches