Functions1. Protection

– Abrasion– Microorganisms– UV light– Hair protects– Nails protect digits from damage

Functions2. Sensations

– Free nerve endings– Merkel’s disk– Hair follicle receptor– Pacinian corpuscle– Meissner’s corpuscles– Ruffini’s end organ

Functions3. Temperature regulation

– Radiation– Conduction– Evaporation– Conduction

Functions4. Vitamin D Production

– Exposure of skin to UV radiation– Precursor molecule produced in skin– Modified in liver and kidney.

Functions5. Excretion

• Water• Salt• Urea• Uric Acid• Ammonia

HypodermisSkin rests on this, but not a part

Consists of loose connective tissue

Types of cellsFibroblasts

Adipose cells

Macrophages

Also calledSubcutaneous tissue

Superficial fascia

Layers of the SkinDermis

Structural strength

Cleavage lines

Two layers

EpidermisAvascular

Cells

Layers or strata

Dermal Layer

Epidermal Layer

Epidermal Layers

Stratum BasaleDeepest portion of epidermis and single layer

High mitotic activity and cells become keratinized

Stratum SpinosumLimited cell division

Stratum GranulosumIn superficial layers nucleus and other organelles degenerate and cell dies

Epidermal Layers

Stratum LucidumThin, clear zone

Stratum CorneumMost superficial and consists of cornified cells

Epidermal Cells

Cell typesKeratinocytes: Produce keratin for strength

Melanocytes: Contribute to skin color

Langerhans’ cells: Part of the immune system

Merkel’s cells: Detect light touch and pressure

Desquamate: Older cells slough off

Keratinization: Cells die and produce outer layer that resists abrasion and forms permeability layer

Epidermal Cells

Coloration

•Determined by 3 factors–Pigments

•Melanin: Provides for protection against UV light•Albinism: Deficiency or absence of pigment•Carotene: Yellow pigment

–Blood circulating through the skin•Imparts reddish hue and increases during blushing, anger, inflammation•Cyanosis: Blue color caused by decrease in blood oxygen content

–Thickness of stratum corneum

Epidermal Derivatives or Accessory Sturctures

•Hair–Found everywhere on human body except palms, soles, lips, nipples, parts of external genitalia, and distal segments of fingers and toes

•Glands–Sebaceous or oil glands

–Sudoriferous or sweat glands

–Ceruminous glands

–Mammary glands

•Nails

Hair

•Composed of shaft and root

–Shaft protrudes above skin surface–Root located below surface and base forms the hair bulb

•Has 3 concentric layers

–Medulla: Central axis–Cortex: Forms bulk of hair–Cuticle: Forms hair surface

Hair

•Types of hair•Lanugo•Vellus hair•Terminal hair

•Determinant Hair•Indeterminant Hair

Hair

•Hair Growth•Growth stage

•Cells of matrix differentiate•Cells become keratinized and die•Hair follicle shortens and holds hair in place

•Resting stage•Followed by new growth phase•Hair falls out of the follicle•New hair replaces the old.

Sebaceous Glands

•Sebaceous glands–Produce sebum

–Oils hair and skin surface

Sweat Glands

•Sudoriferous glands–Merocrine or eccrine

•Most common

•Numerous in palms and soles

–Apocrine•Found in axillae, genitalia, around anus

Other Glands

•Ceruminous glands•Modified merocrine glands•Produce cerumen, earwax

•Mammary glands•Modified apocrine glands•Produce milk

Nails

•Anatomy–Nail root proximally

–Nail body distally: Eponychium or cuticle

•Growth–Grow continuously unlike hair

Nails