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