HESI A2 - Skin - Key Terms and Concepts

Epidermis

The skin's outermost layer, which acts as a barrier to keep the environment out.

Dermis

The thick layer of skin with connective tissue, blood vessels, and nerves underneath the epidermis.

Hypodermis

The fat and connective tissue that make up the skin's deepest layer, which acts as a cushion and an insulator.

Keratinocytes

The main epidermal cells that generate the skin-fortifying protein keratin.

Melanocytes

Cells located in the epidermis that produce melanin, the pigment responsible for skin color.

Langerhans cells

Immune cells in the epidermis that help detect and fight infections.

Merkel cells

Specialized cells in the epidermis that function as touch receptors.

Stratum basale

The deepest epidermal layer, containing actively dividing cells that drive skin regeneration.

Stratum corneum

Dead keratinized cells that form a protective barrier in the epidermis' outermost layer.

Stratum spinosum

A layer of the epidermis where skin cells (keratinocytes) start producing keratin and form intercellular junctions for strength and support.

Thermoregulation

The ability of the skin to regulate body temperature through sweat production and blood flow.

Sensation

The function of the skin that allows the detection of touch, pressure, pain, and temperature changes.

Vitamin D synthesis

The process by which the skin converts sunlight into vitamin D, which is essential for bone health.

Waterproof barrier

The skin's defense mechanism, which stops dangerous things from entering and excessive water loss.

Excretion

The elimination of waste products such as urea and salts through sweat glands.

Absorption

The skin's capacity to absorb specific chemicals, such as drugs and topical therapies.

Elasticity

The property of the skin that allows it to stretch and return to its original shape.

Tensile strength

The skin’s resistance to tearing due to the collagen fibers in the dermis.

Desquamation

The natural shedding of dead skin cells from the epidermis.

Skin microbiome

The community of microorganisms living on the skin that helps protect against harmful pathogens.

Sebaceous gland

Sebum, an oily fluid that lubricates and waterproofs the skin, is produced by this gland.

Sweat gland

A skin gland that secretes sweat, playing a key role in cooling the body and excreting certain waste products.

Eccrine gland

A type of sweat gland that is found all over the body and helps cool the skin through evaporation.

Apocrine gland

A sweat gland found in areas like the armpits and groin that becomes active during puberty.

Sebum

Sebaceous glands secrete this oily fluid, which keeps the skin moisturized.

Ceruminous gland

A gland in the ear canal that produces earwax to protect against infection.

Mammary gland

A specialized gland in the skin that produces milk in females after childbirth.

Pheromones

Chemical signals released by the skin that can influence social and reproductive behaviors.

Sweat pore

The opening on the skin’s surface through which sweat is released.

Acid mantle

A thin coating of oil and perspiration that coats the skin and helps keep infections at bay.

Acne

A skin disorder often caused by bacteria, clogged pores, and inflammation of the sebaceous glands.

Eczema

A long-term inflammatory skin disorder that results in dryness, redness, and itching.

Psoriasis

An autoimmune skin condition that causes thick, scaly areas due to fast cell turnover.

Dermatitis

Inflammation of the skin caused by allergies, irritants, or infections.

Melasma

A condition that causes dark patches on the skin due to increased melanin production.

Vitiligo

A skin disorder that causes pale or white patches as a result of melanocyte damage or dysfunction, which causes pigment loss.

Hives

Raised, itchy skin welts brought on by an allergic response.

Blister

A fluid-filled sac that forms on the skin due to friction, burns, or infections.

Callus

An area of thickened skin that develops over time in response to repeated friction or pressure as a protective adaptation.

Keloid

A raised scar that forms due to excessive collagen production during wound healing.

Epidermal regeneration

The process by which new skin cells are produced in the basal layer to replace damaged or dead cells.

Inflammatory phase

The immune system fights infection and clears debris during the second stage of wound healing.

Proliferative phase

The third stage of wound healing, where new tissue forms to replace damaged skin.

Remodeling phase

Collagen is rearranged during the last phase of wound healing to fortify the skin.

Fibroblast

A cell in the dermis that produces collagen and helps repair wounds.

Collagen production

The process of forming collagen fibers that provide structure and strength to the skin.

Elastin degradation

The breakdown of elastin fibers in aging skin, leading to wrinkles and sagging.

Free radicals

Molecules that are unstable and harm collagen and cells, which causes skin aging.

Photoaging

Skin damage and premature aging caused by prolonged exposure to ultraviolet radiation.

Wrinkle formation

The development of fine lines and folds in the skin due to loss of collagen, elastin, and moisture.

Melanin

A pigment produced by melanocytes that gives skin, hair, and eyes color and helps protect against UV radiation.

Come Let's Get Some Beer (Five Layers of Epidermis from superficial to deep)

Stratum Corneum

Stratum Lucidum

Stratum Granulosum

Stratum Spinosum

Stratum Basale

Stratum lucidum

It is an extra layer of epidermis that makes the palms and soles the thickest while being hairless. It is an additional barrier against moisture loss and friction, improving skin protection.

Stratum granulosum

An epidermal layer where cells start to flatten and keratinization occurs.

Melanocyte-stimulating hormone (MSH)

A peptide hormone produced by the anterior pituitary that stimulates melanin production for skin pigmentation, provides some UV protection, and plays a role in appetite regulation.

Hair

It is a threadlike outgrowth from the epidermis made up of keratin.

Hair follicle

The structure within the skin that supports hair growth and houses the hair shaft; it includes the arrector pili muscle, which helps raise the hair and trap air for temperature regulation.

Nails

Hard, keratinized structures located at the distal ends of fingers and toes.

Hair shaft

The visible part of the hair that extends above the skin or scalp.

Keratin

A tough, fibrous structural protein found in the epidermis, hair, and nails. It strengthens these tissues and helps make the skin water-resistant.

Carotene

A pigment with a yellow-orange tint found in the stratum corneum and the adipose tissue.

Arrector pili

Tiny muscles attached to hair roots contract in response to cold or strong emotions, creating the effect commonly known as "goosebumps."

Skin functions

1. Protection against harmful microorganisms

2. Sensation to touch or pain

3. Fluid balance

4. Temperature regulation