Integumentary System: Skin Layers, Functions, and Associated Organs

Vocabulary flashcards covering primary and secondary organs, specific epidermal layers, integumentary hormones, and general structural layers of the skin.

Primary Organs

The main organs in a body system responsible for carrying out that system's primary function.

Secondary Organs (Accessory Organs)

Organs that assist and support the primary organ in carrying out its physiological function.

Skin (Primary Organ)

The largest solid organ of the human body, whose functional parenchyma consists of stratified squamous epithelial tissue ($\text{ET}$).

Skin Surface Area & Weight Trivia

Skin covers approximately $1\text{ to }2\,\text{m}^2$, constitutes about $7\%$ of overall body weight, and sheds around $40\,\text{pounds}$ of cells over a lifetime.

Thin Skin

Skin containing four specific epidermal layers found essentially everywhere on the body except the palms and soles, with the thinnest regions located on the eyelids and scrotal sac.

Thick Skin

Skin containing five specific epidermal layers found exclusively on the palms of the hands and soles of the feet.

Stratum

The anatomical designation for a specific layer within the skin (abbreviated as $\text{ST}$).

Stratum Basale

The deepest epidermal layer, which is one cell layer thick and serves as the site where mitosis begins and the production of keratin and melanin starts.

Stratum Spinosum

The specific epidermal layer located directly above the stratum basale and beneath the stratum granulosum.

Stratum Granulosum

The specific epidermal layer situated above the stratum spinosum where skin cells begin to die.

Stratum Corneum

The outermost specific layer of the epidermis, composed of dead, flaking, keratinized cells.

Stratum Lucidum

The clear additional epidermal layer present only in thick skin (palms and soles), located between the stratum corneum and stratum granulosum.

Skeletal Muscles (Integumentary Role)

Secondary organs that support the skin by attaching to the hypodermis to anchor it in place.

Endocrine Organs vs. Hormone-Producing Organs

Endocrine organs function solely to make hormones, whereas hormone-producing organs have a separate primary function while additionally synthesizing hormones.

Epidermal Growth Factor (EGF)

A hormone produced by the skin that targets the stratum basale to speed up the rate of mitosis.

Melanocyte Stimulating Hormone (MSH)

A hormone produced by the pituitary gland that signals the epidermis and melanocytes to produce more melanin.

Growth Hormone (GH)

A hormone secreted by the pituitary gland that instructs the epidermis to maintain an even rate of mitosis.

$T_3$ and $T_4$

Hormones produced by the thyroid gland that help maintain an even rate of mitosis within the skin.

Adrenocorticotropic Hormone (ACTH)

A hormone secreted by the adrenal gland that increases the production of melanin and chromatin granules.

Sex Hormones (Estrogen and Testosterone)

Hormones produced by the ovaries and testes that regulate the maintenance of hair, nails, and cutaneous glands.

Epidermis

The general outermost layer of skin composed of stratified squamous epithelial tissue, housing four or five specific strata.

Dermis

The general middle layer of skin where blood vessels, hair follicles, and glands are located, subdivided into the papillary and reticular layers.

Papillary Layer

The superficial sublayer of the dermis, composed of loose connective tissue and making up approximately $10\%$ of the dermis.

Reticular Layer

The deeper sublayer of the dermis, composed of dense irregular connective tissue and making up roughly $90\%$ of the dermis, where hair follicles and glands anchor.

Hypodermis (Superficial Fascia / Subcutaneous)

The insulating general skin layer beneath the dermis, consisting of adipose connective tissue fat pads encased in dense regular connective tissue wrappers.