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