Organization of Mammalian Body: Integumentary System

Comprehensive vocabulary flashcards covering the structure, cellular composition, derivatives, glands, and comparative biology of the mammalian integumentary system based on lecture notes.

Integumentary system

The organ system comprising the skin and its associated structures, including hair, nails, and cutaneous glands; it is a mammal's largest and most vulnerable organ.

Thick skin

Skin covering the palms of the hands and soles of the feet that contains sweat glands but lacks hair follicles and sebaceous (oil) glands.

Thin skin

Skin covering the majority of the body that possesses hair follicles, sebaceous glands, and sweat glands.

Epidermis

The outer layer of the skin, ectodermal in origin, composed of keratinized stratified squamous epithelium that lacks blood vessels.

Dermis

The inner layer of connective tissue beneath the epidermis, mesodermal in origin, ranging from $0.2\,\text{mm}$ to $4\,\text{mm}$ in thickness and richly supplied with blood vessels, nerves, and collagen fibers.

Hypodermis

A variably thick layer of subcutaneous adipose (fatty) tissue beneath the dermis that provides insulation and energy storage.

Stem cells (Epidermal)

Undifferentiated cells located in the deepest layer of the epidermis (stratum basale) that divide and give rise to keratinocytes.

Keratinocytes

The predominant cell type of the epidermis that synthesizes keratin; they are produced by mitosis of stem cells in the stratum basale or deep stratum spinosum.

Melanocytes

Cells occurring strictly in the stratum basale with branching processes that synthesize melanin pigment to shield DNA from ultraviolet radiation.

Tactile cells

Touch receptor cells situated in the basal layer of the epidermis that are associated with dermal nerve fibers.

Dendritic cells

Bone marrow-derived macrophages found in the stratum spinosum and stratum granulosum that guard against invading pathogens.

Stratum basale

The deepest epidermal layer resting on the basement membrane, consisting of a single layer of cuboidal to columnar stem cells, keratinocytes, melanocytes, and tactile cells.

Stratum spinosum

An epidermal layer composed of several layers of keratinocytes linked together by desmosomes and tight junctions, containing dendritic cells.

Stratum granulosum

An epidermal layer consisting of $3$ to $5$ layers of flat keratinocytes containing dark-staining keratohyalin granules.

Stratum lucidum

A thin, translucent epidermal layer present only in thick skin, where keratinocytes are densely packed with the clear protein eleidin.

Stratum corneum

The outermost surface layer of the epidermis, formed by up to $30$ layers of dead, scaly, keratinized cells; it is thickest on the palms and soles and thinnest on the lips.

Papillary layer

The superficial zone of the dermis composed of areolar tissue in and near the dermal papillae, rich in small blood vessels and leukocytes.

Reticular layer

The deeper, thicker layer of the dermis composed of dense irregular connective tissue providing strength and elasticity.

Hair (Pilus)

A uniquely mammalian slender filament of keratinized cells growing from a tubular epidermal invagination called a hair follicle.

Hair bulb

A swelling at the base of the hair originating in the dermis or hypodermis; it is the only site containing living cells within the hair.

Hair root

The portion of the hair contained beneath the surface inside the follicle, extending from the bulb to the skin surface.

Hair shaft

The portion of the hair extending above the surface of the skin.

Pelage

The hairy coat of a mammal, typically composed of guard hairs providing protection, camouflage, and insulation.

Bristles

Long, stiff guard hairs that serve protective functions, such as the manes of lions and horses.

Spines (Hair derivatives)

Stout, rigid modified hairs specialized for defense, found in mammals like hedgehogs and porcupines (such as Erethizon dorsatum).

Awns

The most common and widespread morphological type of guard hair in mammals.

Vibrissae

Specialized tactile hairs (whiskers) located on the face, legs, or body of mammals that communicate sensory responses via nerves at their base.

Nails

Clear, hard derivatives of the stratum corneum composed of densely packed, thin, dead cells filled with hard keratin.

Sweat glands (Sudoriferous glands)

Coiled tubular dermal glands found exclusively in mammals that connect to the skin surface via narrow ducts to secrete water and salts for thermoregulation.

Eccrine sweat glands

Glands that secrete a watery solution directly onto the skin surface through pores for evaporative cooling; they also secrete the antibacterial enzyme lysozyme.

Apocrine sweat glands

Cutaneous glands that open into hair follicles to secrete a fatty, milky fluid; they produce pheromones in many mammals and are concentrated in human axillary and genital regions.

Sebaceous glands

Cutaneous oil glands that discharge sebum into hair follicles to lubricate skin and hair; they are absent from the palms and soles and most concentrated on the face and forehead.

Sebum

An oily substance consisting of a mixture of lipids and cellular debris produced by sebaceous glands to keep pelage and skin lubricated, conditioned, and waterproofed.

Mammary glands

Modified apocrine sweat glands that develop during pregnancy and lactation to produce and secrete milk through ducts opening at the nipple.

Ceruminous glands

Simple coiled tubular modified sweat glands situated in the external auditory canal that produce secretions contributing to earwax.

Cerumen

Earwax produced by combining ceruminous gland secretions with sebum and dead epithelial cells; it lubricates the eardrum, water-repels the canal, and traps foreign particles.

True horns

Permanent, unbranched cranial structures found only in the family Bovidae (order Artiodactyla), consisting of an inner bony horncore covered by an outer keratin sheath.

Antlers

Branched, deciduous bone structures found only in the family Cervidae (order Artiodactyla); they occur only in males, except in the caribou (Rangifer) where females also bear them.