Skin Layers
This outermost, avascular layer of the skin serves as the body’s primary waterproof barrier and continuously sheds dead cells.
Epidermis
Making up roughly 90% of the epidermis, these abundant cells produce a tough, fibrous protein that provides structural strength and water resistance.
Keratinocytes
Produced by melanocytes, this primary biological pigment determines human skin tone and absorbs incoming ultraviolet radiation.
Melanin
The visible portion of a hair strand that projects above the surface of the skin, composed entirely of dead, keratinized cells.
Hair shaft
Distributed across nearly the entire body, these coiled sweat glands secrete a dilute, watery solution directly onto the skin surface to cool the body through evaporation.
Eccrine (or merocrine) sweat glands
Lying directly beneath the epidermis, this middle structural layer contains blood vessels, hair follicles, sebaceous glands, and collagen fibers.
Dermis
Located in the stratum basale, these spider-shaped cells produce the pigment granules that form a protective shield over cell nuclei against UV radiation.
Melanocytes
Moderate sunlight exposure is beneficial because UV rays trigger epidermal cells to convert a cholesterol precursor into this essential nutrient, which is vital for calcium absorption and healthy bones.
Vitamin D (D3)
This tiny smooth muscle attached to the hair follicle contracts when you are cold or frightened, pulling the hair upright and causing "goosebumps."
Arrector pili muscle
Becoming active during puberty in the armpits and groin, these glands produce a milky, protein- and lipid-rich sweat that creates body odor when broken down by skin bacteria.
Apocrine glands
Composed primarily of adipose (fat) tissue, this deepest layer insulates the body and anchors the skin to underlying muscle and bone.
Hypodermis (Subcutaneous)
Originating in bone marrow and found mainly in the stratum spinosum, these star-shaped immune cells engulf foreign microbes and present them to the immune system.
Langerhans cells
Excessive ultraviolet radiation is harmful because it destroys dermal collagen and damages this genetic molecule inside skin cells, forming thymine dimers that can lead to skin cancer. What does it destroy/alter that causes skin cancer?
DNA
These oil-secreting glands open into the hair follicle, releasing sebum to lubricate and waterproof the hair and surrounding skin.
Sebaceous glands
The white, crescent-shaped region visible at the proximal base of the nail plate, named for its resemblance to a "little moon."
Lunula (little moon)
Found exclusively in the "thick skin" of the palms and soles, this translucent epidermal layer rests between the stratum corneum and stratum granulosum.
Stratum lucidem
Situated at the epidermal-dermal junction, these cells pair with sensory nerve endings to act as sensitive receptors for light touch.
Merkel cells
When the skin turns blue, this is a sign of what condition?
Cyanosis
Found at the base of the hair follicle, this enlarged structure contains actively dividing cells and receives blood vessels from the dermal papilla to nourish new hair growth.
Hair bulb
This severe type of burn destroys the entire thickness of both the epidermis and the dermis, often appearing leathery, charred, or white, and is initially painless because sensory nerve endings have been destroyed.
Third degree burns
Also known as the stratum germinativum, this single-cell deepest sublayer of the epidermis is where rapid mitosis occurs and melanocytes reside.
Stratum basale
The predominant cellular residents of the dermis, these spindle-shaped cells synthesize collagen fibers, elastin, and the extracellular matrix necessary for wound healing.
Fibroblasts
Beyond melanin, human skin tone is influenced by dietary carotene and this iron-rich, oxygen-carrying protein found in dermal capillaries, which gives fair skin its pinkish hue.
Hemoglobin
Sandwiched between the inner core (medulla) and the protective outer cuticle, this thick middle layer of the hair shaft contains the melanin pigment that gives hair its natural color.
Cortex
Arising from cells in the stratum basale, this is the most common and least dangerous type of skin cancer because it rarely metastasizes.
Basal cell carcinoma