Functions 1.Protection –Abrasion –Microorganisms –UV light –Hair protects –Nails protect digits from damage

Functions 2.Sensations –Free nerve endings –Merkel’s disk –Hair follicle receptor –Pacinian corpuscle –Meissner’s corpuscles –Ruffini’s end organ

Functions 3.Temperature regulation –Radiation –Conduction –Evaporation –Conduction

Functions 4.Vitamin D Production –Exposure of skin to UV radiation –Precursor molecule produced in skin –Modified in liver and kidney.

Functions 5.Excretion Water Salt Urea Uric Acid Ammonia

Hypodermis Skin rests on this, but not a part Consists of loose connective tissue Types of cells Fibroblasts Adipose cells Macrophages Also called Subcutaneous tissue Superficial fascia

Layers of the Skin Dermis Structural strength Cleavage lines Two layers Epidermis Avascular Cells Layers or strata

Dermal Layer

Epidermal Layer

Epidermal Layers Stratum Basale Deepest portion of epidermis and single layer High mitotic activity and cells become keratinized Stratum Spinosum Limited cell division Stratum Granulosum In superficial layers nucleus and other organelles degenerate and cell dies

Epidermal Layers Stratum Lucidum Thin, clear zone Stratum Corneum Most superficial and consists of cornified cells

Epidermal Cells Cell types Keratinocytes: 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