Chapter 5: The Integumentary System

**keratinocyte**

is a cell that manufactures and stores the protein keratin.

**Keratin**

is an intracellular fibrous protein that gives hair, nails, and skin their hardness and water-resistant properties.

**stratum basale**

(also called the stratum germinativum) is the deepest epidermal layer and attaches the epidermis to the basal lamina, below which lie the layers of the dermis.

**dermal papilla**

(plural = dermal papillae) is found in the superficial portion of the dermis.

**basal cell**

is a cuboidal-shaped stem cell that is a precursor of the keratinocytes of the epidermis.

**melanocyte**

a cell that produces the pigment melanin. 

**Melanin**

gives hair and skin its color, and also helps protect the living cells of the epidermis from ultraviolet (UV) radiation damage.

**stratum spinosum**

**i**s spiny in appearance due to the protruding cell processes that join the cells via a structure called a *desmosome*.

**Langerhans cell**

Interspersed among the keratinocytes of this layer is a type of dendritic cell called the

**stratum granulosum**

has a grainy appearance due to further changes to the keratinocytes as they are pushed from the stratum spinosum.

**keratohyalin**

which accumulates as lamellar granules within the cells.

**stratum lucidum**

is a smooth, seemingly translucent layer of the epidermis located just above the stratum granulosum and below the stratum corneum.

**eleiden**

a clear protein rich in lipids, derived from keratohyalin, which gives these cells their transparent (i.e., lucid) appearance and provides a barrier to water.

**stratum corneum**

is the most superficial layer of the epidermis and is the layer exposed to the outside environment.

**dermis**

might be considered the “core” of the integumentary system (derma- = “skin”), as distinct from the epidermis (epi- = “upon” or “over”) and hypodermis (hypo- = “below”).

**papillary layer**

is made of loose, areolar connective tissue, which means the collagen and elastin fibers of this layer form a loose mesh.

**Elastin fibers**

provide some elasticity to the skin, enabling movement.

**hypodermis**

(also called the subcutaneous layer or superficial fascia) is a layer directly below the dermis and serves to connect the skin to the underlying fascia (fibrous tissue) of the bones and muscles.

**melanosome**

The melanin is transferred into the keratinocytes via a cellular vesicle called a

**hair follicle**

Strands of hair originate in an epidermal penetration of the dermis called the

**hair shaft**

is the part of the hair not anchored to the follicle, and much of this is exposed at the skin’s surface.

**hair root**

The rest of the hair, which is anchored in the follicle, lies below the surface of the skin and is referred to as the

**hair matrix**

The hair root ends deep in the dermis at the **hair bulb**, and includes a layer of mitotically active basal cells called the

**hair papilla**

which is made of connective tissue and contains blood capillaries and nerve endings from the dermis

**internal root sheath**

The cells of the ___ surround the root of the growing hair and extend just up to the hair shaft.

**external root sheath**

The **___**, which is an extension of the epidermis, encloses the hair root.

**glassy membrane**

is a thick, clear connective tissue sheath covering the hair root, connecting it to the tissue of the dermis.

**arrector pili**

Each hair root is connected to a smooth muscle called the

**anagen phase**

, during which cells divide rapidly at the root of the hair, pushing the hair shaft up and out.

**catagen phase**

lasts only 2 to 3 weeks, and marks a transition from the hair follicle’s active growth. 

**telogen** phase

 , the hair follicle is at rest and no new growth occurs.

**nail body**

The is formed on the **nail bed**

**eponychium**

The nail fold that meets the proximal end of the nail body forms the **nail cuticle**, also called the

**lunula**

The nail bed is rich in blood vessels, making it appear pink, except at the base, where a thick layer of epithelium over the nail matrix forms a crescent-shaped region called the___(the “little moon”).

**hyponychium**

The area beneath the free edge of the nail, furthest from the cuticle, is called the

**eccrine sweat gland**

is a type of gland that produces a hypotonic sweat for thermoregulation.

**apocrine sweat gland**

is usually associated with hair follicles in densely hairy areas, such as armpits and genital regions.

**sebaceous gland**

is a type of oil gland that is found all over the body and helps to lubricate and waterproof the skin and hair.

*cholecalciferol*

In the presence of sunlight, a form of vitamin D3 called *__*is synthesized from a derivative of the steroid cholesterol in the skin.

**rickets**

a painful condition in children where the bones are misshapen due to a lack of calcium, causing bowleggedness.

**Basal cell carcinoma**

is a form of cancer that affects the mitotically active stem cells in the stratum basale of the epidermis.

**melanoma**

is a cancer characterized by the uncontrolled growth of melanocytes, the pigment-producing cells in the epidermis.

**Eczema**

is an allergic reaction that manifests as dry, itchy patches of skin that resemble rashes.

**Acne**

is a skin disturbance that typically occurs on areas of the skin that are rich in sebaceous glands (face and back).

**first-degree**

is a superficial burn that affects only the epidermis.

**second-degree**

burn goes deeper and affects both the epidermis and a portion of the dermis.

**third-degree**

  burn fully extends into the epidermis and dermis, destroying the tissue and affecting the nerve endings and sensory function

**fourth-degree**

burn is even more severe, affecting the underlying muscle and bone.

**scar**

is collagen-rich skin formed after the process of wound healing that differs from normal skin.

**stretch mark**

results when the dermis is stretched beyond its limits of elasticity, as the skin stretches to accommodate the excess pressure.

**corn**

is a specialized form of callus.