5. Integumentary (Functions)

Function of the epidermis

Forms the outermost protective barrier of the body; produces keratin for water retention; avascular and relies on dermis for nourishment via diffusion

Function of the dermis

Provides structural support to the epidermis; supplies it with nutrients via vascular diffusion; houses sensory receptors; nerve supply; and accessory structures

Function of the hypodermis

Insulation against heat loss; energy storage in the form of adipose; cushioning of underlying structures against mechanical impact

Function of the stratum basale

Primary site of mitotic cell division; replenishes all cells of the epidermis as surface cells are shed through desquamation

Function of the stratum spinosum

Houses living keratinocytes migrating superficially; contributes to the structural cohesion of the epidermis

Function of the stratum granulosum

Site where keratohyalin granules produced by keratinocytes; initiates the keratinization process that will ultimately produce the keratin barrier at the surface

Function of the stratum lucidum

Contains eleidin as an intermediate step in the keratinization pathway (keratohyalin → eleidin → keratin); present only in thick skin

Function of the stratum corneum

Provides the primary physical and waterproof barrier of the skin through fully keratinized; dead; enucleated cells; most superficial layer of protection

Function of keratohyalin

Precursor molecule produced in the stratum granulosum; converts to eleidin as part of the keratinization pathway

Function of eleidin

Precursor molecule found in the stratum lucidum; intermediate between keratohyalin and fully formed keratin

Function of keratin

Acts as the water-retention barrier on the skin surface; accumulates in dead cells of the stratum corneum

Function of keratinocytes

Produce keratin to form the epidermis's protective water-retention barrier; the majority cell type of the epidermis

Function of melanocytes

Produce melanin to protect epidermal cells from UV radiation damage; located in the stratum basale

Function of Langerhans cells

Serve as immune defense within the epidermis; part of the body's first-line immunological response

Function of Merkel cells

Act as tactile receptors for light touch by connecting to Merkel's disks in the epidermis

Function of dermal papillae

Increase the surface area of the stratum basale to support more cells in thick skin; anchor the epidermis firmly to the dermis in high-friction areas (palms; soles)

Function of collagen fibers in the reticular dermis

Provide tensile strength to the dermis; run in multiple directions to resist forces from all angles; directional orientation forms the basis of Langer's lines

Function of merocrine (eccrine) sweat glands

Thermoregulation — secrete sweat onto the skin surface; evaporation of sweat removes heat from the body

Function of apocrine sweat glands

Secrete oil and pheromones in axillary and inguinal regions; bacteria metabolize the secretion producing body odor

Function of sebaceous glands

Secrete sebum (nonpolar oil) into hair follicles to help retain moisture on the skin surface; sebum also serves as a nutrient source for surface bacteria

Function of sebum

Retains moisture on the skin surface (nonpolar; resists water loss); provides nutrients for surface bacteria

Function of hair follicles

Produce the hair shaft (dead keratinized cells); house a high concentration of melanocytes that give hair its pigmentation

Function of the arrector pili muscle

Contracts to pull the hair shaft erect in response to cold; fear; or attraction; causes cutis anserina (goosebumps) by pulling on the stratum corneum

Function of Merkel's disks

Detect light touch; located in the epidermis connected to Merkel cells

Function of Meissner's corpuscles

Detect light touch; especially concentrated in thick skin at the fingertips; located within dermal papillae of the papillary dermis

Function of Pacinian (laminated) corpuscles

Detect deep pressure; located at the border of the deep reticular dermis and hypodermis